Speciation Definitions, Equations and Examples

Speciation

A species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring. The process by which new species develop from existing species is known as speciation.

The important factors which could lead to the rise of a new species are:

  1. The geographical isolation of a population caused by various types of barriers such as mountains, rivers etc
  2. Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
  3. Variations caused in individuals due to natural selection.

There can be a number of ways by which this can happen.

  1. If the DNA changes are severe enough, such as a change in the number of chromosomes, eventually the germ cells of the two groups cannot fuse with each other.
  2. A new variation may emerge in which green females will not mate with red males, but only with green males. This allows very strong natural selection for greenness. Now, if such a green female beetle meets a red male from the other group, her behavior will ensure that there is no reproduction between them. Effectively, new species of beetles are being generated.

Some Important Terms

Genetic drift: Changes in the frequencies of alleles in a population that occur by chance, rather than because of natural selection.

Gene flow: The movement of genes into or through a population by interbreeding or by migration and interbreeding.

Geographical isolation: Two populations or individuals of the opposite sex are considered reproductively isolated from one another if they cannot together produce fertile offspring.

Natural selection: The differential survival and reproduction of classes of organisms that differ from one another in one or more usually heritable characteristics. Through this process, the forms of organisms in a population that are best adapted to their local environment increase in frequency relative to less well-adapted forms over a number of generations. This difference in survival and reproduction is not due to chance.

Speciation Definitions, Equations and Examples

Example 1.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Answer:
No, geographical isolation will not be a major factor in the speciation of a self-pollinating plant species as these plants receive pollen grains from the same flower or another flower on the same plant due to which new gene variants will not be introduced in the population and there will be no evolution of a new species. On the other hand, in cross pollinated species, when geographical isolation is there, accumulation of variations in traits will take place.

Example 2.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, asexual reproduction involves only one parent and hence there is very little variation over generations. As asexual reproduction is carried out within the same organism, resulting organism in next generation will have identical copies of DNA, so there will be very less genetic variant to be a cause of the speciation of an organism.

Class 10 Science Notes

Evolution Definitions, Equations and Examples

Evolution

We have seen that there is an inbuilt tendency to variation during reproduction, both because of errors in DNA copying and as a result of sexual reproduction.

  1. A rare variation can become a common characteristic in a population when the frequency of an inherited trait changes over generations. Since genes control traits, we can say that the frequency of certain genes in a population changed over generations. This is the essence of the idea of evolution.
  2. A particular variation may become common if it gives a survival advantage to the population. This is known as Natural selection which can direct evolution in a population. It results in adaptations in the population to fit their environment better.
  3. Accidents in small populations can change the frequency of some genes in a population, even if they give no survival advantage. This is the notion of genetic drift, which provides diversity without any adaptations.

Example 1.
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer:
Sexual reproduction gives rise to more viable variations as compared to asexual reproduction. It is because there is an inbuilt tendency to variation during reproduction because of errors in DNA copying. In asexual reproduction, genes cannot be separated from the parent organism.

The resulting variation in traits out of sexual reproduction not only helps in the survival of species but also support diversity in long run. Drift in genetic traits gets accumulated spanning across generations, this gives rise to the formation of new species.

Evolution Definitions, Equations and Examples

Example 2.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:
A small number of surviving tigers is the cause of worry from the point of view of genetics because the size of its population plays a dominant role for its evolutionary expansion. For a small population of tigers, diversity of traits will be adversely affected as gene pool will be less and hence there will be less variations. In the event of a disease or natural disaster possibility of survival against numbers will be greatly reduced. Small number of surviving tiger will affect diversity negatively and will result in an ecological imbalance.

Acquired and Inherited Traits

Acquired Trait is a phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weight lifter).

For evolution to take place, there must be changes in the DNA of the germ cell. Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells. Therefore the experiences of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution.

Example: If we breed a group of mice, all their progeny will have tails, as expected. Now, if the tails of these mice are removed by surgery in each generation, then these tailless mice do not produce tailless progeny because removal of the tail cannot change the genes of the germ cells of the mice.

Evolution Definitions, Equations and Examples

Differences between acquired traits and inherited traits:

Acquired Traits Inherited Traits
1. These traits or characteristics are not transmitted from one generation to the next 1. These traits are transmitted from parents to their progeny.
2. These traits do not bring about any changes in the germ cells or DNA as these are changes in non-reproductive tissues. 2. Genes of inherited traits are present in the germ cells or DNA
3. These cannot direct evolution as these are experiences of an individual acquired during its lifetime. 3. These may direct evolution as these bring about changes in the germ cells or DNA.
Example: Acquiring a new hair style Example: Hair texture

Origin of Life on Earth

J.B.S. Haldane suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed. He speculated that the conditions on earth at that time, which were far from the conditions we see today, could have given rise to more complex organic molecules that were necessary for life. The first primitive organisms would arise from further chemical synthesis.

In 1953, Stanley L. Miller and Harold C. Urey assembled an atmosphere similar to that thought to exist on early earth (this had molecules like ammonia, methane, and hydrogen sulphide, but no oxygen) over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.

Class 10 Science Notes

Heredity Definitions, Equations and Examples

Heredity

Genetics is the branch of biology which studies heredity and variation. Inheritance is the transmission
of genetically controlled traits from one generation to the next

Inherited Traits

The traits or characteristics that are transmitted from one generation to the next are controlled by genes. A gene is a segment of DNA which is responsible for the synthesis of proteins that contains a specific character of the organism. An example is the free earlobes and attached earlobes found in human population.

Mendel’s Contributions

Gregor Mendel was the first scientist to make a systematic study of patterns of inheritance which involved the transfer of characteristics from parents to progeny (offsprings). He is known as the Father of Genetics.

Heredity Definitions, Equations and Examples

Mendel’s Experiment

Mendel used a number of contrasting visible characters of garden peas – round/wrinkled seeds, tall/short plants, white/violet flowers and so on. He took pea plants with different characteristics – a tall plant and a short plant, produced progeny from them, and calculated the percentages of tall or short progeny. Mendel chose pea plants for studying inheritance because pea plants had a number of distinct differences which were easy to tell apart.

  • Availability of detectable contrasting traits of several characters.
  • Short life span of the plant.
  • Normally allows self-fertilisation but cross-fertilisation can also be carried out.
  • Large number of seeds produced.

Monohybrid inheritance:

  1. It concerns the inheritance of a single plant characteristic such as plant height or color of flowers.
  2. Mendel first crossed pure-bred tall pea plants with pure-bred dwarf pea plants and found that there were no halfway characteristics or ‘medium-height plants in this first generation, or F1 progeny. All plants were tall.
  3. Mendel then crossed the tall pea plants of the first generation by self-pollination and found that the second-generation, or F2, the progeny of the F1 tall plants are not all tall. Instead, one-quarter of them were short.
  4. Both the tallness and shortness traits were inherited in the FI plants, but only the tallness trait was expressed.
  5. Two copies of the trait are inherited in each sexually reproducing organism. These two may be identical or may be different, depending on the parentage.
  6. Out of a total of 1064 pea plants of F2 generation, Mendel found that there were 787 tall pea plants and 277 dwarf pea plants. The ratio of tall plants to dwarf plants comes to be approximately 3: 1. The ratio 3 : 1 is known as the monohybrid ratio. e.g., The genotypic ratio of F2 progeny is TT : Tt: tt = 1: 2 : 1.

Example 1.
Case Based:
Let us study further the genotype and phenotype of pea plants in the Fx and F2 generations.
Heredity Definitions, Equations and Examples 1

(A) Mendel used a number of contrasting visible characters of a garden pea for his experiments. Select the incorrect pairs of contrasting characters:
(I) Pink / white flower color
(II) Round/Wrinkled pea shape
(III) Green / White pod colour
(IV) Tall/Dwarf plant size
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) Both (III) and (IV)
Answer:
(b) Both (I) and (III)

Explanation: Mendel used the seven pairs of contrasting characters of pea plants for his experiments which are as follows:

  • Pea shape: Round or Wrinkled.
  • Pea color: Green or Yellow.
  • Pod shape: Constricted or Inflated.
  • Pod color: Green or Yellow.
  • Flower color: Purple or White.
  • Plant size: Tall or Dwarf
  • Position of flowers: Axial or Terminal.

(B) The table below gives the phenotypic ratio of Tall: Short pea plants in the F1 and F2 generation.
Select the row containing the correct information:

F1 Generation F2 Generation
(a) 3: 1 1: 3
(b) 4 : 0 1: 3
(c) 4 : 0 3: 1
(d) 3: 1 3 :1

Answer:
(c) F1 Generation: 4 : 0; F2 Generation: 3 :1

Explanation: When a pure tall pea plant (TT) is crossed with a pure short pea plant (tt), all plants in the F1 generation will be tall (Tt).

When these tall plants of F1 generation are crossed, 75 % of plants will be tall and 25 % will be short.
Heredity Definitions, Equations and Examples 2

(C) What will be the genotypic ratio of F2 genera¬tion in the above cross?
Answer:
The genotypic ratio of F2 generation in the above cross will be TT: Tt: tt = 1: 2 :1 as all pea plants obtained in the F1 generation were tall having genotype Tt, the genotype ratio in the F2 generation will be TT: Tt: tt = 1: 2 :1, as can be seen from the above diagram.

(D) What experiment can you conduct to verify that the F2 generation did in fact have a 1:2:1 ratio of TT, Tt and tt traits?
Answer:
Let us cross a tall pea plant (obtained in FI generation) with a short pea plant. Genotype of the tall parent will be Tt and that of the short parent tt. We will observe that 50 % of progenies were tall and 50 % were short, which means that the genotype of the tall plant was Tt (and not TT). Its gametes would be T and t, which when crossed with a short plant (tt) would result in 50 % plants with genotype Tt and 50 % with genotype tt.

This type of cross can be used to confirm that the F2 generation did in fact have a 1:2:1 ratio of TT, Tt, and tt trait combinations.

(E) Assertion (A): When pure tall pea plants are crossed with pure short pea plants, the percentage of short pea plants in the first filial generation is 50%.
Reason (R): All plants in the first filial generation will be tall as tallness is dominant.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(d) (A) is false, but (R) is true.

Explanation: When pure tall pea plants are crossed with pure short pea plants, all plants in the first filial generation will be tall. Therefore, the percentage of short pea plants in the Fi generation will be 0%.

Heredity Definitions, Equations and Examples

Example 2.
Outline a project which aims to find the dominant coat color in dogs.
Answer:
Select a homozygous black (BB) male dog and a homozygous white (bb) female dog. Allow them to mate and produce offspring (F1 generation). If all of the FI offspring are black, we can conclude that black coat cover is dominant than a white coat in the dog.
Heredity Definitions, Equations and Examples 3

Dihybrid inheritance:

1. It concerns the inheritance of characteristics when pea plants showing two different characteristics, rather than just one, are bred with each other.

2. The progeny of a tall plant with round seeds and a short plant with wrinkled seeds are all tall and have round seeds. Tallness and round seeds are thus dominant traits.

3. When these F1 progenies are used to generate F2 progeny by self-pollination, some F2 progeny are tall plants with round seeds, and some were short plants with wrinkled seeds.

(4) There would also be some F2 progeny that showed new mixtures. Some of them would be tall, but have wrinkled seeds, while others would be short, but have round seeds.

(5) The tall/short trait and the round seed/wrinkled seed trait are independently inherited.

Independent Inheritance of two separate traits: In the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair of traits are distributed independently to the gametes. The dihybrid cross can be shown by drawing a chart as shown:
Heredity Definitions, Equations and Examples 4

Example 3.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as:
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Answer:
(c) TtWW

Explanation: This is a dihybrid cross of a plant involving two characters in the same plant. As the progeny had violet flowers, therefore, the tall plants have genotype WW as violet is dominant. Also, almost half of the plants were short which means that the genotype is Tt.

Important Terms used in Heredity

Chromosome: Chromosomes are the carriers of genes and are long thread-like structures present in the nucleus of a cell. Each gene set is present as separate independent pieces, each called a chromosome.

DNA: Cellular DNA is the information source for making proteins in the cell. DNA is the genetic material. DNA is the carrier of genetic information from generation to generation. Every chromosome contains one molecule of DNA and genes are segments of DNA.

Genes: Gene is a segment of a large molecule called deoxyribonucleic acid (DNA) which forms the most important constituent of chromosome. Genes are located on the chromosomes at fixed positions and their number is estimated to be between 30, 000 to 40, 000. Genes control characteristics or traits.

Allele: One of the different forms of a particular gene occupying the same position on a chromosome.

Factor: The carriers of hereditary information were called as factors by Mendel. He considered each and every character as a unit, which was controlled by a ‘factor’ based on his experiments with garden pea.

F1 generation: When two parents cross or breed to produce progeny, then their progeny is called first filial generation.

F2 generation: When the first generation progeny cross among themselves to produce second progeny, then this progeny is calLed second filial generation.

Diploid: The paired condition of chromosomes is called diploid. The diploid number of chromosomes is specific for a species and every cell has diploid number of chromosomes.

Haploid: It is the set of unpaired chromosomes. Gametes have haploid set of chromosomes.

Homologous chromosome: Members of a pair of chromosomes are exactly identical as far as shape and size are concerned and hence called homologous chromosomes.

Genotype: It is the description of genes present in an organism. It is always a pair of letters such as TT, Tt or tt (where T and t are the different forms of the same gene).

Phenotype: The characteristic or trait which is visible in an organism is called its phenotype. Being tall or dwarf are phenotypes of a plant as these traits are visible.

Dominant and recessive traits: In this explanation, both TT and Tt are tall plants, while only tt is a short plant, in other words, a single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short. So, a tall plant will have genotype TT or Tt, whereas a short plant will have genotype tt. Traits like T are called dominant traits or expressed traits, while those that behave like ‘t’ are called recessive traits or repressed traits.

Heredity Definitions, Equations and Examples

Mendel’s Laws of Inheritance

Law Definition
Law of Segregation During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
Law of Independent Assortment Genes for different traits can segregate independently during the formation of gametes.
Law of Dominance Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

Expression of Traits

Genes control characteristics or traits in all organisms. Cellular DNA is the information source for making proteins in the cell. Each trait is governed by a particular hormone and the amount of the hormone made depends on the efficiency of the process for making it which in turn depends on a particular enzyme that is important for this process. If this enzyme works efficiently, a lot of hormones will be made and if the gene for that enzyme has an alteration that makes the enzyme less efficient, the amount of hormone will be less.

Example 4.
A study found that children with light-colored eyes are likely to have parents with light-colored eyes. On this basis, can we say anything about whether the light eye color trait is dominant or recessive? Why or why not?
Answer:
No, we cannot say with certainty about whether the light eye color trait is dominant or recessive without knowing the genotype of the variants. Moreover, at least three generations are required for determining whether trait is dominant or recessive.

Heredity Definitions, Equations and Examples

Example 5.
A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
Answer:
The given information is not enough to tell us which of the traits – blood group A or O – is dominant, in blood heredity, blood Type A is always dominant and blood Type 0 is always recessive.

Father’s Blood group can be AA (homozygous) or AO (heterozygous), and that of mother can be OA or 00. For daughter to be born with blood group O, she must receive O type gene one each from father and mother. For this father must have a heterozygous AO blood group and mother must have a homozygous blood group 00.

Related Theory:
Research carried out in Heidelberg, Germany by Ludwik Hirszfeld and Emil von Dungern in 1910 and 1911 showed that the ABO blood types are inherited. An individual’s ABO type results from the inheritance of 1 of 3 alleles (A, B, or C) from each parent. The possible outcomes are shown below:
Heredity Definitions, Equations and Examples 5

Both A and B alleles are dominant over O. As a result, individuals who have an AO genotype will have an A phenotype. People who are type O have 00 genotypes. In other words, they inherited a recessive O allele from both parents. The A and B alleles are codominant. Therefore, if an A is inherited from one parent and a B from the other, the phenotype will be AB. Agglutination tests will show that these individuals have the characteristics of both type A and type B blood.

Mechanism of Inheritance

The rules for the inheritance of traits in sexually reproducing organisms are related to the fact that both the parents contribute practically equal amounts of genetic material to the offspring. This means that each trait can be influenced by both paternal and maternal DNA. Thus, for each trait there w: T be two versions in each offspring.

Every germ cell takes one chromosome from each pair and these may be of maternal or parental origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny and in this way the DNA of the species becomes stable.

Example 6.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. The chromosome number is halved during gamete formation.

During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete(haploid) resulting in formation of the diploid zygote. The zygote in the progeny receives an equal contribution of genetic material from the parents.

Heredity Definitions, Equations and Examples

Sex Determination

In human beings, the sex of the offspring in the zygote after fertilization of the male and female gamete is determined by the sex chromosome. The rest of the chromosomes are called autosomes. Human beings have 22 pairs of autosomes and one pair of sex chromosomes. The females carry two X- chromosomes but the males carry a single X and a Y chromosome. Among the male gametes, half of the sperms carry X-chromosome and half carry Y-chromosome. In human beings, the sex of the individual is largely genetically determined.

  • When a sperm carrying X-chromosome fertilizes an egg, the zygote develops into female (XX).
  • When a sperm carrying Y-chromosome fertilizes an egg, the zygote develops into male (XY).

Heredity Definitions, Equations and Examples 6

Effect of environmental factors on sex determination:

In some reptiles, the temperature at which the fertilized egg is incubated before hatching is important for sex determination.

  1. In a turtle high incubation temperature results in the development of female progeny.
  2. In the case of lizard, high incubation temperature results in the development of male progeny.

Class 10 Science Notes

Accumulation of Variation During Reproduction Definitions, Equations and Examples

Accumulation of Variation During Reproduction

Heredity can be defined as resemblances among individuals related by descent or the transmission of traits from parents to the offspring. It means continuity of features from one generation to the next. Variation is defined as the occurrence of differences in the characters (or traits) among the individuals. In a number of sexually reproducing animals, including human beings, quite distinct variations are visible among different individuals. The long term accumulation of variations may lead to gradual changes in the form or functions of organisms and may even lead to the formation of a new species over time. This process is known as evolution.

In case an organism reproduces by asexual reproduction, one organism gives rise to two individuals which are similar in body design, but having subtle differences. These will in turn give rise to two individuals in the next generation. In this way, the four individuals formed will be different from each other.

If sexual reproduction is involved, greater diversity will be generated in the offspring as compared to asexual reproduction where only minor differences would be generated due to small inaccuracies in DNA copying. Depending on the nature of variations, different individuals would have different kinds of advantages. The Selection of variants by environmental factors forms the basis for evolutionary processes.

Accumulation of Variation During Reproduction Definitions, Equations and Examples

Example 1.
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer:
Trait B is likely to have arisen earlier as trait B exists in 60 % of the population as compared to trait A which exists in 10% of the population. Organisms with trait B reproduced and replicated the trait for a longer period as compared to trait A.

Class 10 Science Notes

Sexual Reproduction Definitions, Equations and Examples

Sexual Reproduction

Sexual reproduction is a type of reproduction in which the two sexes, namely, male and female are involved. It incorporates a process of combining DNA from two different individuals during reproduction.

DNA Content Re-establishment in New Generation

  1. The gametes (or reproductive cells) contain only half the number of DNA (or half the number of chromosomes) as compared to the normal body cells.
  2. The germ cell that is large and contains the food stores is called the female gamete.
  3. The gamete that is smaller and motile is called the male gamete.
  4. When a male gamete combines with a female gamete during sexual reproduction, the zygote formed will have the same number of DNA as present in the organism.

Significance of Sexual Reproduction

  1. It promotes the diversity of characters in the offspring.
  2. It Leads to variations which is necessary for evolution.
  3. It plays an important role in the origin of new species.

Sexual Reproduction Definitions, Equations and Examples

Example 1.
What are the advantages of sexual reproduction over asexual reproduction?
Answer:
As sexual reproduction involves two parents, the newly formed individual has characteristics of both the parents. More variations are produced in sexual reproduction as it involves two parents. Thus, it ensures the survival of species in a population.

Sexual Reproduction in Plants

  1. The reproductive ports of angiosperms are located in the flower.
  2. Stamens and carpeLs are the reproductive parts of a flower which contain the germ ceLLs.
  3. Stamen is the male reproductive port and produces pollen grains.
  4. Carpet is the female reproductive part and contains the ovary, style and stigma.
  5. Some flowers are unisexuaL such os papaya and watermelon whiLe some are bisexual such ashibiscus and mustard.
  6. Unisexual flowers contain either stamens or carpels.
  7. Bisexual flowers contain both stamens and carpels. Majority of the flowers are bisexual.
  8. The various parts of a flower are:
    Sepals: These are usually green in colour.
    Petals: These are coloured.
    Stamen: It is the male reproductive part of a flower and consists of a stalk called filament and a flattened top called the anther. The anthers produce the pollen grains. Each pollen grain produces two male gametes.
    Carpel: It is the female reproductive part of a flower and consists of a swollen ovary at the base, an elongated middle style and a terminal stigma. The ovary contains ovules and each ovule has an egg.

Pollination

The transfer of pollen grains from another to stigma is called pollination. The transfer of pollen grains is carried out by several agents such as water, wind, insects and other agencies.

Pollination is of two types-self pollination and cross-pollination.

Self-Pollination Cross Pollination
1. The transfer of pollen grains from the anther of a flower to the stigma of the same flower or another flower of the same plant. 1. The transfer of pollen grains from the anther of a flower to the stigma of another flower of a different plant of the same species.
2. It occurs in flowers which are genetically same. 2. It occurs between flowers which may be genetically different.
3. Self-pollination increases genetic uniformity and decreases variations. 3. Cross-pollination decreases genetic uniformity and increases variations.
4. Does not require pollinators for transfer of pollen grains. 4. Requires pollinators for transfer of pollen grains.

Sexual Reproduction Definitions, Equations and Examples

Fertilization in Plants

  1. Pollination, i.e., transfer of pollen grains from anther of a flower to stigma takes place.
  2. Pollen grains which are deposited on the stigma form tubes called pollen tubes.
  3. One pollen tube grows through the style and reaches the ovary where the ovules are located.
  4. The pollen tube normally enters the ovule through a small opening called micropyle.
  5.  Inside the ovule, the pollen tube releases two male gametes into the embryo sac which contains the egg.
Pollination Fertilization
1. Pollination is the process of transferring of pollen from stamen to the stigma of a flower. 1. Fertilization is the fusion of male gametes and female gametes of plants
2. It precedes fertilization 2. It takes place only after pollination has taken place.

Double fertilization: Inside each embryoac, two fusions, syngamy and triple fusion take place and this mechanism of two fusions occurring in an embryo sacis called double fertilization.

Syngamy: The fusion of one male gamete with the female gamete (egg) inside the embryoac is called syngamy and it results in zygote,

  1. After fertilization, the zygote divides several times to form an embryo within the ovule.
  2. The ovule develops a tough coat and is gradually converted into a seed.

Germination

The process by which the seed, which contains the future plant or embryo, develops into a seedling under appropriate conditions.

  1. The ovary grows rapidly and ripens to form a fruit.
  2. The petals, sepals, stamens, style and stigma shrivel and fall off.

Example 2.
Case Based:
Soak a few seeds of Bengal gram (chana) and keep them overnight. Drain the excess water and cover the seeds with a wet cloth and leave them for a day. Make sure that the seeds do not become dry. Cut open the seeds carefully and observe the different parts.
(A) Select the correct observations:
(I) One massive and fleshy cotyledon can be seen.
(II) It has a small pore called the micropyle at the pointed end.
(III) The plumule is the future root.
(IV) The radicle is the future root.
(a) Both (I) and (II)
(b) Both (I) and (III)
(c) Both (II) and (III)
(d) Both (II) and (IV)
Answer:
(A) (d) Both (II) and (IV)

Explanation: Gram seed has two cotyledons. Just below the hilum lies the micropyle in the form of a small pore. Water is absorbed through the micropyle during the germination of seed. The plumule is the future shoot and radicle is the future root.
Sexual Reproduction Definitions, Equations and Examples 1

(B) During the germination of seeds, the seed coat ruptures due to
(a) massive imbibition of water
(b) differentiation of cotyledons
(c) a sudden increase in cell division
(d) massive glycolysis in cotyledons and endosperm
Answer:
(a) massive imbibition of water
Explanation: During the germination of seeds, the seed coat ruptures due to massive imbibition of water through the micropyle.

(C) Name the part of the seed through which water enters the seed.
Answer:
The part of seed through which water enters the seed is the micropyle.

(D) Name the part of the flower which develops into seed and fruit respectively.
Answer:
The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit.

(E) Assertion (A): The seed of a plant contains the future plant or embryo.
Reason (R): The ovary of the flower grows rapidly and ripens to form a fruit.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.

Explanation: After fertilization, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed.

Human Reproductive System
The structures associated with reproduction are different in males and females.

Sexual Reproduction Definitions, Equations and Examples

Puberty

Puberty is the age in the life of human beings when the reproductive tissues begin to mature and the reproductive system becomes functional. It is 13 to 14 years for males and 10 to 12 years for females. Some changes begin to take place in both girls and boys during this period.

  1. Changes such as thicker hair in armpits and genital area between the thighs, thinner hair on legs and arms, oily skin and development of pimples are common to both girls and boys.
  2. However, there are also changes that are different between boys and girls. For example, increase in breast size, darkening of the skin of the nipples and beginning of menstruation are some of the changes observed in girls. Thick hair growth on the face, cracking of voice, and penis occasionally getting erect and enlarged are some of the changes observed in boys.

Role of Hormones: The testes and ovaries produce viable gametes and also secrete hormones.

  1. The testis secretes the male hormone testosterone and the ovary secretes the female hormone estrogen.
  2. Hormones regulate the process of gametogenesis (formation of gametes).
  3. Hormones maintain the structure and function of accessory sex organs
  4. Hormones develop secondary sex characters like facial, axial and pubic hair, pitch of the voice and development of mammary glands.

Male Reproductive System

Sexual Reproduction Definitions, Equations and Examples 2

The human male reproductive system consists of the following organs:

  1. Testes: The primary male reproductive organ is a pair of testis which lies in a sac-like muscular structure outside the abdominal cavity called scrotum. The formation of germ-cells or sperms takes place in the testes. It secretes the male hormone testosterone, which regulates the formation of sperms and brings about changes in appearance in boys.
  2. Scrotum: It provides an optimal temperature for formation of sperms which is 1- 3° C lower than the body temperature.
  3. Vas deferens: It is a long tube which arises from each testes and which carries sperms into organs called seminal vesicles, where the sperms get nourished and stored.
  4. Urethra: It is a common passage for the passage of both urine and spermatic fluid. The vas deferens unites with a duct coming from the urinary bladder to form urethra.
  5. Penis: It forms the external male genital organ and is a thick muscular organ which encloses the urethra. There is only one opening for the urine and sperms.

Sexual Reproduction Definitions, Equations and Examples

Example 3.
What is the role of the seminal vesicles and the prostate gland?
Answer:
Seminal vesicles and the prostate gland form the part of the accessory glands, which are associated with the male reproductive system. Seminal vesicles and prostate gland secrete a fluid which makes the transport of sperms eas-ier along the path of urethra and at the same time provides nutrition to the sperms.

Female Reproductive System

Sexual Reproduction Definitions, Equations and Examples 3
The human female reproductive consists of the following organs:
1. Ovaries: There is a pair of small and oval-shaped organs, located in the abdominal cavity near the kidney. Ovaries are the female primary reproductive organs which perform dual functions of production of female gamete or ovum and the secretion of female sex hormones, estrogen and progesterone. Each ovary is composed of ovarian follicles and these follicles undergo maturation at puberty to produce ova.

2. Fallopian tube or Oviduct: These are a pair of long convoluted tubes that carry ova or eggs from the ovary to the uterus. The fallopian tube has a funnel-shaped opening near the ovary. These tubes from both the sides open into a muscular structure, the uterus.

3. Uterus or womb: It is a hollow, pear-shaped organ within which the embryo develops. Its upper portion is broader, while its lower portion is narrower, called cervix.

4. Vagina: The cervix opens into the vagina which is a tubular structure and also called “birth canal’’. Vagina receives sperms from the male and also serves as the passage through which the fully developed foetus is born.

Sexual cycle in females: When the human females attain the age of puberty, the ovaries exhibit a cycle of events at definite intervals which are described below:

  1. The ovarian follicle grows into mature follicle.
  2. One mature follicle develops to surround one ovum.
  3. The maturing ovum is from one of the two ovaries.
  4. Ovulation: The ovum is then released from the respective ovary by the process called ovulation.
  5. As the ovarian follicles mature, the inner wall of uterus thickens to get prepared for receiving the developing zygote in case fertilization occurs.
  6. In case fertilization does not take place, the thick-ened inner wall of the uterus breaks down along with its blood vessels and moves out of the vagina in the form of bleeding, called menstrual flow which lasts for 4 – 7 days.
  7. Menstrual Cycle: The cycle of events taking place in the ovaries and uterus every twenty-eight days and marked by the menstrual flow is called the menstrual cycle or sexual cycle in the human female.
  8. Menstruation occurs every 28 to 30 days and ovulation takes place in the mid of the menstrual cycle around 14th day.
  9. Both ovulation and menstruation stops temporarily when the women gets pregnant till birth of the offspring.
  10. Menarche: The commencement of menstruation at puberty is called menarche and marks the beginning of the reproductive life of a woman.
  11. Menopause: The stoppage of menstrual flow and other events around the age of 50 years in human females is called menopause.

Fertilization

  1. The fertilization in human beings is internal.
  2. It takes place if copulation has taken place during ovulatory period, i.e., the middle of the menstrual cycle.
  3. It takes place in the fallopian tube where only one sperm out of the millions of sperms released in the vagina fertilizes the ovum.
  4. Fertilization is marked by the absence of menstrual flow.
  5. Zygote is formed after the union of the sperm and the ovum.
  6. This marks the beginning of pregnancy, i.e., the embryonic development of zygote starts in the fallopian tube.
  7. Implantation: After fertilization has taken place, the embryo moves down to reach the uterus and gets attached to its thickened wall and this close attachment of the embryo with the uterus is called implantation.
  8. Placenta: It is a special tissue that develops between uterine wall and the embryo after implantation and through which the development needs of the foetus are met from the mother’s body. This is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue and blood spaces surrounding the villi on the mother’s side. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. The waste substances generated by the developing embryo is also removed through the placenta.

Example 4.
Why does menstruation occur?
Answer:
In female reproductive system, the ovary releases one egg every month, during the same period, the uterus also prepares itself to receive a fertilised egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if fertilisation had taken place.

If the egg is not fertilised, it lives for about one day and then it is lost. The lining earlier formed to receive the fertilised egg, is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

Reproductive Health

Reproductive health is important as the process of sexual maturation is gradual and making choices can become very diffcultdue to pressures from friends, family or government agencies. Also, many diseases can be transmitted sexually as the sexual act is a very intimate connection of bodies.

Sexually Transmitted Diseases (STDs): These are the diseases that are spread from an infected person to a healthy person by sexual contact. These include bacterial infections such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS.

Sexual Reproduction Definitions, Equations and Examples

Population Control

A number of techniques have been developed to prevent and manage pregnancy as frequent pregnancies have an adverse effect on the health of a woman. These methods are described below:
Sexual Reproduction Definitions, Equations and Examples 4
Sexual Reproduction Definitions, Equations and Examples 5

Effects of contraceptives:

  1. Since oral pilLs change the hormonaL balance of the body so that eggs are not released and fertilization does not occur and hence can cause side-effects.
  2. Loop or copper-T are placed in the uterus to prevent pregnancy and can cause irritation of the uterus.
  3. Surgical methods are safe in the long run but they can cause infections and other problems if not performed properly.

Advantages of adopting contraceptive methods :

  1. Avoiding frequent and unwanted pregnancy
  2. Keeping population and hence birth rate under control
  3. Helps in keeping proper gap between two preg-nancies.
  4. Helps in preventing the spread of sexually transmitted diseases.
  5. Helps in improving the reproductive health of women.

Female Foeticide: Surgical methods can be used for removal of unwanted pregnancies and hence can be misused by people who do not want a particular child. Female foeticide is the illegal sex-selective abortion of female foetuses due to which child sex ratio is declining at an alarming rate.

Class 10 Science Notes

Types of Reproduction Definitions, Equations and Examples

Types of Reproduction

Living beings mainly reproduce by two methods – asexual reproduction and sexual reproduction. The modes by which different organisms reproduce depends on the body design of the organisms.
Types of Reproduction Definitions, Equations and Examples 1

Asexual Reproduction

Characteristics

  1. Certain body cells of an organism undergo re-peated mitotic divisions and form two or more new individuals of the same kind.
  2. The new individuals produced are genetically identical to their parents.

Advantages

  • Asexual reproduction is simple and fast.
  • Takes place in those organisms having simple body structures.

Disadvantages

  • Evolutionary change is not possible as no variation is produced. A species consequently cannot adapt to changes in its environment.
  • Asexual reproduction produces identical organisms generation after generation. In case of any defect in the parent organism, the offspring also inherits it.

Types of Reproduction Definitions, Equations and Examples

Methods of Asexual Reproduction

Asexual reproduction occurs in various ways which are described below:

Fission

It is the simplest method of asexual reproduction in unicellular organisms, such as amoeba, paramecium and other protozoa.

Different patterns of fission have been observed:
(A) In some organisms such as Amoeba, the splitting of the two cells during division takes place in any plane.
Types of Reproduction Definitions, Equations and Examples 2
(B) In Leishmania, the binary fission occurs in a definite orientation in relation to the whip-like structure called flagellum present at one end of the cell.

(C) In Plasmodium, the cell divides into many daughter cells simultaneously by multiple fission. Sometimes, during unfavorable conditions, a cyst or protective wall is formed around the cell and inside the cyst, the nucleus splits several times to form many daughter nuclei. This increases chances of their survival in favourable conditions.
Types of Reproduction Definitions, Equations and Examples 3
Multiple fission in plasmodium

Example 1.
How does binary fission differ from multiple fission?
Answer:
Binary fission: Some unicellular organisms under favorable conditions simply split into two equal halves during cell division. This is called binary fission. Examples are different bacteria and protozoa such as Amoeba.

Multiple Fission : Some organisms like the ma-larial parasite, Plasmodium, divide into many daughter cells simultaneously. This division process is called multiple fission.

Fragmentation

Fragmentation is the process of breaking off a piece of organism followed by mitotic cell division. Meiosis is not involved in this process as it is a mode of asexual reproduction. The broken part can develop into an independent adult.

Fragmentation process is limited to invertebrates, and it is absent in vertebrates. The ability of fragmentation depends on the complexity of the organism.

Budding

It takes place in multicellular organisms like hydra and yeast. A bulging or bud appears on the body as a result of repeated mitotic division.

Budding in Yeast: During budding in yeast, a small daughter bud is formed on parent and continues to grow until it gets separated. The daughter cell is generally smaller in size as compared to parent.
Types of Reproduction Definitions, Equations and Examples 4
Budding in Hydra: In hydra, the cell divides rapidly at a specific site and develops as an outgrowth called bud. These buds while attached to the parent part develop into small individual. When the small individual becomes Large enough, it detaches itself from the parent body to exist as an independent individual.
Types of Reproduction Definitions, Equations and Examples 5

Types of Reproduction Definitions, Equations and Examples

Differences between Budding and Fission

Budding Fission
1. The parent individual persists after the daughter cells daughter individual has budded off. 1. The parent individual loses its identity after splitting into two or more
2. Bud starts as a trace and slowly grows to an appropriate size before it pinches off but it is still smaller than the parent 2. The daughter individuals are identical in structure but all are smaller in size than the parent. Later they grow to attain their normal dimensions
3. Budding is rather slow and gradual 3. Fission is rapid and instantaneous

Spore Formation
Spore formation is the most common method of asexual reprod uction in majority of fungi and bacteria like rhizopus, mucor, penicillium.
During spore formation, a structure called sporangium develops from the fungal hypha.
The nucleus divides several times within the spo-rangium, and each nucleus, with a bit of cytoplasm, develops into a spore.
The spores are liberated and they develop into new hypha after reaching the ground or substratum.
The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.
Types of Reproduction Definitions, Equations and Examples 6

Example 2.
How will an organism be benefited if it reproduces through spores?
Answer:
The spores are covered by thick walls of tiny blob-on-a-stick Like structures, which are not reproductive parts, but protect the spores from unfavorable conditions, until they come into contact with moist surface and begin to grow. Such spores are produced in Large numbers and can spread through air, water or animals in contact. They germinate when conditions are favorable. Thus, organism like rhizopus is benefited greatly when it is produced through spores.

Regeneration

Regeneration is a modified form of fragmentation. It is known as a process that makes genomes, cells organs, organisms, and ecosystems resilient after disturbances or damage. Regeneration is carried out by specialized cells. From this mass of cells, different cells undergo changes in an organised sequence referred to as development to become various cell types and tissues.

Planarian flatworms are highly adapted with regeneration capabilities because of their asexual reproduction method. Star fishes also have the same ability to regenerate their arm, but unlike tailed amphibians and lizards, lost arms of star fishes could regenerate a complete new organism.

Types of Reproduction Definitions, Equations and Examples

Example 3.
Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration?
Answer:
More complex organisms cannot give rise to new individuals through regeneration because complex organism are multi-cellular organisms. In complex organisms, specialised cells are or-ganised as tissues, and tissues are organised into organs, which are strategically placed to perform different specialized functions. The tis-sues in complex organisms cannot regenerate a new individual as cell-by-cell division would be impractical.

Difference between Fission and Fragmentation:
In fission, a unicellular organism breaks up to form two or more daughter organisms, whereas in fragmentation, a multicellular organism breaks up to form two or more daughter organisms.

Difference between Fragmentation and Re-generation

Fragmentation Regeneration
1. Occurs in multi-cellular organisms with relatively simple body organization. 1. Occurs ¡n several fully differentiated organisms.
2. Organisms simply break up into smaller pieces upon maturation. These pieces or fragments grow into new individuals. 2. If the individual is accidentally cut or broken up into man pieces, many of these pieces grow into separate individuals.
3. Fragmentation results in the production of identical offprings. 3. In regeneration, the entire organism can regenerate as in certain animals ke Planaria, but mostly the organism regenerates only a part of the body.
4. No specialized cells ore involved in fragmentation. 4. Regeneration is carried out by specialised cells. These cells proliferate and make a Large number of cells. From this moss of cells, different cells undergo changes to become various cell types and tissues.
5. Example: Spirogyra 5. Example: Crabs can regenerate legs. Mammals can regenerate liver cetts and blood cells. Lizards con regenerate their toil

Vegetative Propagation

Vegetative propagation is a method of reproduction in some higher plants in which a new plant develops from the vegetative parts of a plant such as root (as in dahlia, sweet potato), stem (as in ginger, potato, onion) or leaf (as in bryophyllum).

Advantages of vegetative propagation

  1. Plants raised by this method can bear flowers and fruits earlier than those produced from seeds.
  2. It is a cheaper, easier and more rapid method of propagation in plants as compared to growing plants from their seeds.
  3. The traits or characters of the parent plant are preserved. That is, all plants produced are genet-ically similar enough to the parent plant to have all its characteristics.
  4. Better quality of the plants can be maintained.
  5. Those plants which do not produce viable seeds or seeds with a prolonged period of dormancy, such as banana, orange, rose, jasmine, etc., can be propagated by this method.

Types of Reproduction Definitions, Equations and Examples

Example 4.
Case Based:
Take a potato and observe its surface. Cut the potato into small pieces such that some pieces contain a notch or bud and some do not. Spread some cotton on a tray and wet it. Place the potato pieces on this cotton. Note where the pieces with the buds are placed. Observe changes taking place in these potato pieces over the next few days. Make sure that the cotton is kept moistened.
Select a money plant. Cut some pieces such that they contain at least one leaf. Cut out some other portions between two leaves. Dip one end of all the pieces in water and observe over the next few days.
(A) Select the incorrect observation regarding the first activity.
Notches can be seen on the surface of the potato.
All potato pieces showed growth of young shoot and roots.
The potato pieces which were having buds in notches did not show growth of young shoot and roots.
The pieces which were not having eye buds did not show any growth of shoot or root.
Both (I) and (II)
Both (II) and (III)
(I), (II) and (III)
(II), (III) and (IV)
Answer:
(b) Both (II) and (III)

Explanation: All potato pieces did not show growth of young shoot and roots. Growth of shoot and roots was shown by those potato pieces only which were having buds.

(B) In the second activity, the portions of money plant which grow and give rise to fresh leaves are:
(a) Those which have buds
(b) Those which have spores
(c) Those which have flowers
(d) Those which have nodes
Answer:
(d) Those which have nodes

Explanation: The portion of money-plant having left at the node show formation of fresh leaves. There are buds in the axil (point of attachment of the leaf at the node) of leaves that develop into shoots. These buds are called vegetative buds. A bud consists of a short stem around which immature overlapping leaves are folded. The vegetative buds can also give rise to new plants.

(C) What conclusions can be drawn from the second activity?
Answer:
It can be concluded from the second activity that green leaves can synthesize food and have the ability to grow into a plant through vegetative propagation.

(D) Which parts of a plant develop into new plants by vegetative propagation?
Answer:
Plant parts like roots, stem and leaves develop into new plants under appropriate conditions by vegetative propagation.

Explanation: All new Bryophyllum plants are genetically similar to their parent plant as they are produced when the buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and these develop into new plants.

(E) Assertion (A): All new Bryophyllum plants are genetically similar to their parent plant.
Reason (R): New Bryophyllum plants develop from the stems of their parent plant.
(a) Both (A) and (R) are true and (R) is the correct explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(c) (A) is true but (R) is false.

Explanation: All new Bryophyllum plants are genetically similar to their parent plant as they are produced when the buds produced in the notches along the leaf margin of Bryophyllum fall on the soil and these develop into new plants.

Types of Reproduction Definitions, Equations and Examples

Tissue Culture

New plants are grown by removing tissue or separating cells from the growing tip of a plant. The cells are then placed in an artificial medium where they divide rapidly to form a single group of cells or callus. The callus is transferred to another medium containing hormones for growth and differentiation. The plantlets are then placed in the soil so that they can grow into mature plants. It is commonly used for ornamental plants.

Advantages of tissue culture:

  1. It is a very fast technique. Thousands of plantlets can be produced in a few week’s time from a small amount of plant tissue.
  2. Many plants can be grown from one parent in disease-free conditions.
  3. It can grow plants round the year, irrespective of weather or season.

Class 10 Science Notes

Basic Events in Reproduction Definitions, Equations and Examples

Basic Events in Reproduction

Reproduction is a biological process by which new individuals of the same species are produced by existing organisms. Reproduction is essential for the survival of a species on the earth. The process of reproduction ensures continuity of life on earth. Reproduction gives rise to more organisms with the same basic characteristics as their parents.

A basic event in reproduction is the creation of a DNA copy as the DNA in the cell nucleus is the information source for making proteins. If the information changes, different proteins will be made leading to altered body designs. Also, during cell division, an additional cellular apparatus is created so that the DNA copies separate, each with its own cellular apparatus.

Basic Events in Reproduction Definitions, Equations and Examples

Example 1.
What is the importance of DNA copying in reproduction?
Answer:
The creation of a DNA copy is a basic and important event in reproduction. DNA in the cell nucleus contains the blueprint of body design and information for the inheritance of characteristic features from parents to next generation. During Reproduction, as the cell divides, a copy of DNA along with additional cellular apparatus, is transferred from the parent cell to its offspring.

Variation

Cells use chemical reactions to build copies of their DNA but this process of copying the DNA will have some variations due to which the DNA copies will be similar but not identical to the original. If the variations are so drastic that the new DNA copy cannot work with the cellular apparatus it inherits, then the newborn cell dies.
This tendency for variation during reproduction is the basis for evolution.

The Importance of Variation
Genetic variation is when the genes carried by the members of a population differ from one another (like hair or eye color). Genetic variation is important. If there are sudden changes in the environment, the individuals of the population will vary enough that some will be able to adapt and survive.

  1. It helps the species of various organisms to survive and flourish even in adverse environments due to the presence of some variations in some individual organisms to tolerate extreme changes in environmental conditions.
  2. It provides stability to the population of various species by preventing them from getting wiped out during adverse conditions.

Basic Events in Reproduction Definitions, Equations and Examples

Example 2.
Why is variation beneficial to the species but not necessarily for the individual?
Answer:
If a population of reproducing organisms were suited to a particular niche and if the niche were drastically altered, the population could be wiped out However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. Thus, variation is beneficial to the species but not necessarily for the individual as it helps in the survival of the species.

Class 10 Science Notes

Hormones in Animals Definitions, Equations and Examples

Hormones in Animals

Hormones are chemical substances secreted in trace amounts by specialized tissues called endocrine glands.

Characteristics of Hormones

  1. They are specific chemical messengers.
  2. They are secreted by endocrine glands.
  3. They are poured directly into the blood and carried by blood circulation.
  4. They act on specific tissue/organs called target organs.
  5. Hormones are involved in the regulation of several functions.

Example: Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific issues on which it acts include the heart. As a result, the heart beats faster, resulting in a supply of more oxygen to our muscles.

The blood to the digestive system and skin is reduced due to the contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation.

Endocrine or Hormonal System

This is another organ system that controls and coordinates various life processes.

Endocrine glands: The endocrine glands are also called ductless glands as they do not have ducts to pass their hormones. These glands are located in dif¬ferent parts of our body. Some endocrine glands perform dual functions.

  1. The pancreas secretes digestive enzymes and produce hormones insulin and glucagons.
  2. Testes and ovary produce gametes and also hormones Testosterone and oestrogen respectively.

Hormones in Animals Definitions, Equations and Examples

A brief summary of Endocrine glands, their hormones, and their functions is given below:
Hormones in Animals Definitions, Equations and Examples 1
Hormones in Animals Definitions, Equations and Examples 2

Comparison of Nervous System and Endocrine system

Nervous System Endocrine System
1. It is made of neurons or nerve cells 1. Made of glands or secretory cells.
2. Messages are transmitted in the form of electrical impulses 2. Messages are trans-mitted in the form of chemicals called hormones
3. Messages are transmitted along nerve fibres. 3. Messages are transmitted through blood stream.
4. Messages travel very fast. 4. Messages travel more slowly
5. The effect of message usually lasts for a very short while. 5. The effect of message usually lasts longer.
6. Nerve impulses are not specific in their action. 6. Action of hormones is highly specific.

Role of Iodine

Iodine is necessary for the thyroid gland to make the thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient in our diet, there is a possibility that we might suffer from goiter.

Role of Growth Hormone

Growth hormone is one of the hormones secreted by the pituitary. As its name indicates, growth hormone regulates growth and development of the body. If there is a deficiency of this hormone in childhood, it leads to dwarfism.

Hormones in Animals Definitions, Equations and Examples

Role of Insulin

Insulin is a hormone which is produced by the pancreas and helps in regulating blood sugar levels. If it is not secreted in proper amounts, the sugar level in the blood rises causing many harmful effects.

Feedback Mechanism

If it is so important that hormones should be secreted in precise quantities, we need a mechanism through which this is done. The timing and amount of hor-mone released are regulated by feedback mecha-nisms. For example, if the sugar levels in blood rise, they are detected by the cells of the pancreas which respond by producing more insulin. As the blood sug-ar level falls, insulin secretion is reduced.

Example 1.
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
Answer:
The differences between nervous and hormonal mechanisms for control and coordination in animals are listed below:

Nervous System Hormonal System
1. Consists of nerves, brain and spinal cord 1. Consists of endocrine glands and hormones
2. Consists of impulses that travel along the nerve cells 2. Consists of chemicals secreted by endocrine glands directly into the bloodstream
3. Effect is observed immediately 3. Effect is slow and delayed
4. Does not affect growth 4. May affect growth
5. Response is short-lived 5. Response usually lasts longer

Class 10 Science Notes

Coordination in Plants Definitions, Equations and Examples

Coordination in Plants

Plants show two types of movement one dependent on growth and the other independent of growth. Some common observations are:

  1. The leaves of the touch-me-not plant begin to fold up and droop on being touched. There is no growth involved in this movement.
  2. When a seed germinates, first the root goes down and the stem comes up into the air. The directional movement of a seedling is caused by growth.

Plants respond to various stimuli like light, gravity, chemicals, water, and touch etc due to the effect of hormones. However, since pLants do not have a nervous system, they do not respond as quickly as compared to animals. It usually takes a considerable time to observe the effect of a stimuli as plants respond to various stimuli very slowly.

If we touch a plant movement happens at a point different from the point of touch. So, information that a touch has occurred must be communicated.

Immediate Response to Stimulus

Nastic Movements

Nastic movement is the movement of plant organs in response to external stimulus which is independent of the direction of stimulus. For ex, the leaves of touch-me-not plant bend and droop on touching.

  1. Plants use electrical-chemical means to convey any information from one cell to another. However, there is no specialized tissue in plants for the conduction of information, unlike the nervous tissue in animals.
  2. Plants cells change their shape in response to an external stimulus by changing the amount of water in them which results in swelling or shrinking, unlike in animals, where specialized proteins
    are found in muscle cells due to which muscle cells change their shape and movement occurs.

Coordination in Plants Definitions, Equations and Examples

Example 1.
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
Answer:
Differences between the manner in which movement takes place in a sensitive plant and the movement in our legs are given below:

Movement in a Sensitive Plant Movement in Our Legs
1. It is response to stimuli (touch) which is an in-voluntary action 1. It is a voluntary action
2. There are no specialized tissues for con-duction of information 2. There is specialized nervous tissue for conduction of information
3. Plant cells change their shape and size by changing the amount of water in their cells 3. Muscles cells have specialized proteins that help in contraction and relaxation of muscles.

Movement due to Growth (Thigmotropism):

  1. Some plants like the pea plant have tendrils, which are thin, thread-like growths on the stem or leaves of climbing plants.
  2. These tendrils are sensitive to touch.
  3. When a tendril touches an object like a bamboo stick, the part of the tendril in contact with the object does not grow as rapidly as the part of the ten¬dril which is away from the object.
  4. This causes the tendril to bend towards the ob¬ject by growing towards it and circling around the object.
  5. This type of winding movement of the tendril of a climbing plant is an example of thigmotropism.

Example 2.
Case-Based:
Shreya performed an activity to understand tropism in plants. She filled a conical flask, with water and covered the neck of the flask with a wire mesh. She kept two or three freshly germinated bean seeds on the wire mesh.
Answer:
Case I: She then took a cardboard box which is open from one side and kept the flask in the box in such a manner that the open side of the box faced light coming from a window (Figure). She noted her observations after two or three days.
Coordination in Plants Definitions, Equations and Examples 1
Case II: She then turned the flask so that the shoots were away from light and the roots towards light. She left the flask undisturbed in this condition for a few days and noted her observations again.

(A) Shreya recorded her observations as given below:

The direction of Root and Shoot at (I) The direction of Old Root and Shoot at (II)
(a) Both roots and shoot bend towards the light (a) Both root and shoot bend towards the light
(b) Roots bend to-wards light and shoot bends away from light (b) Not much change in direction of old roots and shoot
(c) Shoot bends to-wards light and roots bend away from light (c) Not much change in direction of old roots and shoot
(d) Both root and shoot bend away from light (d) Both root and shoot bend away from light

Answer:
(c) (A) is true, but (R) is false.

Explanation: We observe in Case i, that shoot bends towards light whereas roots bend away from light. However, after 2 to 3 days we observe that there is not much change in the direction of old roots and shoot.

(B) Select the correct statement:
(a) Both roots and shoot show positive phototropism.
(b) Roots show negative phototropism whereas shoot show positive phototropism.
(c) Roots show positive phototropism whereas shoot show negative phototropism.
(d) Both roots and shoot show negative phototropism.
Answer:
(b) Roots show negative phototropism whereas shoot show positive phototropism. Explanation: Roots bend away from light whereas shoot bends towards light. Roots show negative phototropism whereas shoots show positive phototropism.

(C) Do you observe change in direction of the old parts of the shoot and root when direction of flask is changed?
Answer:
The change in direction of the old parts of the shoot and root, change in direction is less and not much noticeable , however there is marked and noticeable change in case of new parts of the shoot and root

(D) Are there differences in the direction of the new growth?
Answer:
Yes, new growth of parts of the shoot and root is visibly more noticeable. Shoots are found bending towards light while roots are found bending away from it

(E) Assertion (A): Direction of old parts of the root and shoot change on changing the direction of flask.
Reason (R): Roots show negative phototropism and shoot shows positive phototropism.
(a) Both (A) and (R) are true and (R) is the cor¬rect explanation of the assertion.
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion.
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(d) (A) is false, but (R) is true.

Explanation: When the direction of flask is changed in Case II, the old parts of roots and shoot do not change direction much whereas new parts change their direction.

Coordination in Plants Definitions, Equations and Examples

Example 3.
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Answer:
The movement of leaves of the sensitive plant is independent of growth whereas the movement of a shoot towards light is dependent on growth.

Movement of Leaves of Sensitive Plants Movement of a Shoot Towards Lights
1. It is a nastic movement which does not depend on the direction of stimulus applied. 1. It is a tropic movement which depends upon the direction of applied stimulus.
2. The stimulus is ‘touch’ 2. The stimulus is light.
3. It is caused due to change in the amount of water in them resulting in swelling or shrinking. 3. It is caused due to the unequal growth on the two sides of the shoot.
4. It is not a growth movement. 4. It is a growth movement.

Tropism

The movement of a plant in the direction of an exter-nal stimulus is known as tropism. Environmental trig-gers such as light or gravity will change the directions in which plant parts grow. The growth of a plant part in response to a stimulus can be of two types:

  1. Positive tropism: If the growth or movement of a plant part is towards the stimulus, it is called positive tropism.
  2. Negative tropism: If the growth of a plant part is away from the stimulus, it is called negative tropism.

Types of Tropisms

There are five types of tropisms depending on the type of stimuli. These are:

  1. Phototropism: It is the movement of a plant part in response to light. For e.g., growth of shoot in the direction of light.
  2. Geotropism: It is the movement of a plant part in response to gravitational forces. For ex, down-ward movement of roots.
  3. Chemotropism: It is the movement of plant parts in response to a chemical stimulus. For ex, the growth of pollen tube towards a chemical produced by the ovule during fertilization.
  4. Hydrotropism: The movement of a plant part in response to water is called hydrotropism. For ex, the movement of roots of a plant towards water.
  5. Thigmotropism: The directional movement of a plant part in response to the touch of an object is called thigmotropism. For ex, coiling of tendrils around support.

Example 4.
Design an experiment to demonstrate hydrotropism.
Answer:
Take two beakers A and B. Add moist soil in beaker A and sow the seeds. In beaker, B add dry soil in one part and moist soil in another part and sow the seeds. Also, place a small porous pot filled with water just adjacent to it. Keep it for some time so that the plants can grow.
Coordination in Plants Definitions, Equations and Examples 2
It is observed the roots of the plant in beaker A grow straight whereas the roots in beaker B bend and grow towards moist soil. This activity demonstrates hydrotropism or movement of plant part towards water.

Comparison between Electrical Impulse and Chemicals
Electrical impulses reach only those cells of the body which are connected by nervous tissue, not each and every cell in the animal body. Chemical compounds are secreted by stimulated cells which diffuse all around the original cell and if other cells would have the means to detect this compound, they would be able to recognize this information.
Once an electrical impulse is generated in a cell and transmitted, the cell will take some time to reset its mechanism before it can generate a new impulse.

Coordination in Plants Definitions, Equations and Examples

Phytohormones

These are chemical substances known as plant hormones which perform the function of control and coordination in plants. The different types of plant hormones are:
Auxins, Gibberellin, Cytokinin, Abscisic Acid, and Ethylene.
Stimulated plant cells release a chemical compound that diffuses all around the cell.
The cells around have the means to detect this compound using special molecules on their surfaces and are able to recognize information and also transmit it.
This information potentially reaches all cells of the body steadily and persistently.
The plant hormones are synthesized at places away from where they act and simply diffuse to the area of action.

Functions of Phytohormones: The plant hormones regulate many functions in plants which are described below:

Plant Hormone Functions
Auxins 1. Synthesized at the shoot and root tip.
2. Help the cells to grow longer as they promote cell enlargement and cell differentiation in plants.
3. Promote fruit growth.
Gibberellins 1. Promote cell enlargement and cell differentiation in plants in the absence of Auxins.
2. Help in breaking dormancy in seeds and buds.
3. Promote growth in fruits.
Cytokinin 1. Promote cell division in plants.
2. Help in breaking dormancy of seeds and buds.
3. Delay ageing in leaves.
4. Promote the opening of stomata.
5. Promote fruit growth.
Abscisic Acid 1. Functions mainly as a growth inhibitor.
2. Promotes the dormancy in seeds and buds.
3. Promotes the closing of sto-mata.
4. Promotes the wilting and falling of leaves.

Role of auxins in phototropism:

Bending of the stem towards the light:

  1. When sunlight falls from top, the auxin hormone present in the shoot tip spreads uniformly down the stem and both the sides of the stem grow uniformly.
  2. When the light falls only on side (say, right side), then the auxin hormone collects in the left side away from light.
  3. Due to the presence of more auxin hormone on the left side, this side grows faster as compared to the right side.
  4. The stem therefore bends towards the right side.

Coordination in Plants Definitions, Equations and Examples

Bending of root away from light:

  1. The effect of auxin hormone on the growth of root is opposite to the effect of auxin on the shoot.
  2. The side of a root which is away from light will have a greater concentration of auxins.
  3. Due to this, this side will grow slowly than the side which is facing the light.
  4. The root bends away from light.

Photoperiodism: The response of plant activities to the duration of light is known as photoperiodism. Flowering and germination of seeds is regulated by duration of light.

Example 5.
What are plant hormones?
Answer:
The organic substances that are produced naturally in plants and which control growth and other physiological functions in plants are known as plant hormones. Examples are auxins, gibberellins, etc.

Class 10 Science Notes

Nervous System in Animals Definitions, Equations and Examples

Nervous System in Animals

Imagine that bright Light is focussed on our eyes or we touch a hot object We are able to detect the change and respond to it with movement in order to protect ourselves. All this movement, in response to the environment, is carefully controlled as the movement to be made depends upon the event that triggers it All living organisms must use systems providing control and coordination and they must have specialized tissues to provide these control and coordination activities.

In animals, control and coordination are provided by nervous and muscular tissues. All information from our environment is detected by the specialized tips of some nerve cells. These receptors are usually located in our sense organs, such as the inner ear, the nose, the tongue, and so on.

The nervous system includes the brain, spinal cord, and nerves. It controls and coordinates various func¬tions in the body. Its functions are:

  1. It receives information from the surroundings, processes and interprets it, and responds accordingly.
  2. It passes information from one internal system to another.

Sense organs: Sense organs or receptors are specialized structures through which animals receive a variety of external information. These are:

  1. Photoreceptors for light
  2. Photoreceptors for sound
  3. Olfactory receptors for smell
  4. Gustatory receptors for taste

Sensory neurons: These are the special type of nerve cells through which the receptors pass information to the brain.

Nervous System in Animals Definitions, Equations and Examples

Neuron

A neuron is the structural and functional unit of the nervous system and is the largest cell found in the body. A neuron has three components:
Nervous System in Animals Definitions, Equations and Examples 1
Structure of a neuron

Structure of a Neuron

  1. Cell body or Cyton: The cell body is like a typical cell containing nucleus and granular cytoplasm. Stimulus is changed into impulse in the cyton.
  2. Dendrites: Dendrites are short and branched processes connected to the cyton. They receive sensation or stimulus, which may be physical, chemical, mechanical or electrical. The stimulus is passed onto cyton.
  3. Axon: Axon is the longest part of the neuron. It is a single, elongated fibre arising from one side of cyton. It conducts impulses away from the cell body. The plasma membrane of an axon is covered by a protective sheath of lipid and protein called myelin sheath, formed by the Schwann cells.

Synapse: It is the functional junction between two adjacent neurons or nerve cells, i.e., between the axon ending of one neuron and the dendrites of the next.

Nerve Impulse

Nerve impulse is the information in the form of chemical and electrical signals passing through neurons. These impulses are carried by dendrites towards the cell body.

Nerve Impulse Travelling Through the Body

  1. The information, acquired at the end of the dendritic tip of a nerve cell, sets off a chemical reaction that creates an electrical impulse.
  2. This impulse travels from the dendrite to the cell body, and then along the axon to its end.
  3. At the end of the axon, the electrical impulse sets off the release of some chemicals.
  4. These chemicals cross the gap, or synapse, and start a similar electrical impulse in a dendrite of the next neuron.

Example 1.
What is the need for a system of control and coordination in an organism?
Answer:
All living organisms respond to changes in their environment for which they need a well organized system of control and coordination. At times we have controlled movement that must be connected to the recognition of various events in the environment, followed by only the correct movement in response to the stimulus. Specialised tissues are used to provide these control and coordination activities in multicellular organisms.

Nervous System in Animals Definitions, Equations and Examples

Example 2.
How do we detect the smell of an agarbatti (incense stick)?
Answer:
The smell of an agarbatti is detected by the olfactory receptors present in our nose which generate nerve impulses that reach the olfactory lobes present in the forebrain which produce the sensation of smell.

Example 3.
Case Based:
Put some sugar in your mouth. How does it taste? Block your nose by pressing it between your thumb and index finger. Now eat sugar again. Is there any difference in its taste? While eating lunch, block your nose in the same way and notice if you can fully appreciate the taste of the food you are eating.
(A) Identify the correct statements:
(I) Taste of sugar is sweet.
(II) Gustatory receptors in our tongue are responsible for taste.
(III) Olfactory receptors in our tongue are responsible for smell.
(IV) Receptors communicate information to the mouth so that we are able to taste things.
(a) Only (I)
(b) Both (I) and (II)
(c) (I), (II) and (III)
(d) (I), (III) and (IV)
Answer:
(b) Both (I) and (II)
Explanation: The taste of sugar is sweet. The taste is because of the combined perception of our sensory organs tongue and nose. Gustatory receptors in tongue and olfactory receptors in nose are responsible for taste and smell respectively. Both sensations are communicated to the brain, which integrates the information so that flavors can be recognized and appreciated.

(B) When we block our nose by pressing it between our thumb and index finger, then:
(a) There is no change in taste of sugar
(b) We do not get the taste of sugar
(c) There is a change in the taste of sugar
(d) Sugar tastes salty
Answer:
(c) There is a change in the taste of sugar
Explanation: Smell and taste are closely linked. The taste buds of the tongue identify taste, and the nerves in the nose identify smell. Gustatory receptors in tongue and olfactory receptors in nose are responsible for taste and smell respectively. Both sensations are communicated to the brain, which integrates the information so that flavors can be recognized and appreciated.

(C) Can you fully appreciate the taste of the food you are eating if you block your nose while eating lunch?
Answer:
No, we cannot fully appreciate the taste of the food we are eating if we block our nose while eating as the general perception of taste, which we have for any particular eatable substance, is jointly created by our sense organs tongue and nose through receptors. Gustatory receptors in tongue will detect taste while olfactory receptors in nasal cavity will detect smell.

(D) Loss of smell and taste is one of the early symptoms of COVID-19. Justify.
Answer:
Smell receptors can be temporarily damaged by the influenza (flu) virus or the Corona Virus. Some people cannot smell or taste for several days or even weeks after the virus attacks our body. Sudden loss of smell also may be an early symptom of corona virus disease 2019 (COVID-19), an acute respiratory illness that has taken so many lives in 2020-21.

(E) Assertion (A): The taste of food changes when we have blocked nose due to the common cold.
Reason (R): Gustatory receptors are responsible for taste
(a) Both (A) and (R) are true and (R) is the correct explanation of the (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the (A).
(c) (A) is true, but (R) is false.
(d) (A) is false, but (R) is true.
Answer:
(b) Both (A) and (R) are true, but (R) is not the correct explanation of the (A).

Explanation: When we have a blocked nose due to common cold, our ability to taste food changes due to the blockage of olfactory bulb which are the series of nerve endings in the nose, that not only allows to smell, but to taste at the same time. Gustatory receptors in tongue will detect taste while olfactory receptors in nasal cavity will detect smell.

The ability to smell can be affected by changes in the nose, in the nerves leading from the nose to the brain, or in the brain. For example, if nasal passages are blocked due to common cold, the ability to smell may be reduced because odors are prevented from reaching the smell receptors (specialized nerve cells in the mucous membrane lining the nose). Because the ability to smell affects taste, food often does not taste right to people with a cold.

Reflex Action

Reflex action is defined as an unconscious and involuntary response of effectors (muscles and glands) to a stimulus. For example, knee-jerk reflex, coughing, sneezing, yawning, and blinking of eyes, movement of the diaphragm, etc.

Nervous System in Animals Definitions, Equations and Examples

Reflex Arc

  1. Reflex arc is the pathway taken by the nerve impulses and responses in a reflex action, i.e., from the receptor organs to the spinal cord by sensory nerves and from the spinal cord to the effector organs via motor nerves.
    Nervous System in Animals Definitions, Equations and Examples 2
  2. Nerves from all over the body meet in a bundle in the spinal cord on their way to the brain.
  3. Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain.
  4. Reflex arcs have evolved in animals because the thinking process of the brain is not fast enough.

Example 4.
What is the role of the brain in reflex action?
Answer:
The spinal cord is the main coordinating center in reflex actions and the brain has no role to play except that the information is also conveyed to the brain for memory.

Human Brain

The brain is the highest coordinating centre of the body. The brain and spinal cord constitute the central nervous system. They receive information from all parts of the body and integrate it.
Brain is protected by the cranium, a bony box in the skull and is covered by three membranes called meninges. The space between membranes is filled by cerebrospinal fluid which protects the brain from mechanical shocks.

Coordination between Nervous and Muscular Tissue

The communication between the central nervous system and the other parts of the body is facilitated by the peripheral nervous system.
Nervous System in Animals Definitions, Equations and Examples 3
The vertebrate nervous system is highly evolved and consists of:
1. Central Nervous System includes the brain and spinal cord
Spinal cord: Spinal cord is a cylindrical structure and begins in continuation with the medulla oblongata and extends downward. A total of thirty-one pairs of spinal nerves arise from the spinal cord.

Functions of the spinal cord:

  • It is the main center of reflex action.
  • It is concerned with the conduction of nerve impulses to and from the brain.

2. Peripheral Nervous System consists of cranial and spinal nerves. The cranial nerves arise from the brain and spinal nerves arise from the spinal cord.

Nervous System in Animals Definitions, Equations and Examples

Example 5.
Which signals will get disrupted in case of a spinal cord injury?
Answer:
All the signals and responses within the Central Nervous System, which are exchanged between brain and different body parts through the spinal cord may get disturbed causing impaired functioning of different body parts like in paralysis.

Also, signals for refLex actions and involuntary actions will get disrupted in case of a spinal cord injury.

The Main Functions of Brain

  1. The brain receives information-carrying impulses from all the sensory organs of the body.
  2. The brain responds to the impulses brought in by sensory organs by sending its own instructions to the muscles and glands causing them to function accordingly.
  3. The brain correlates the various stimuli from different sense organs and produces the most appropriate and intelligent response.
  4. The brain coordinates the activities of the body so that the mechanisms and chemical reactions of the bodywork together efficiently.
  5. The brain stores ‘information’ so that behaviour can be modified according to the past experience. This function makes brain the organ of thought and intelligence.

Parts of Brain

The brain has three such major parts or regions, namely the fore-brain, mid-brain and hind-brain.
Nervous System in Animals Definitions, Equations and Examples 4
Nervous System in Animals Definitions, Equations and Examples 5
Human Brain

Forebrain

  1. The forebrain includes cerebrum and olfactory lobes.
  2. The forebrain is the main thinking part of the brain.
  3. It has regions that receive sensory impulses from various receptors.
  4. Separate areas of the fore-brain are specialized for hearing, smell, sight and so on.
  5. The sensation that we have eaten enough is because of a centre associated with hunger, which is in separate part of the fore-brain.

Nervous System in Animals Definitions, Equations and Examples

Cerebrum

  1. The cerebrum is the most complex and specialized part of the brain.
  2. It consists of two cerebral hemispheres.
  3. It has a sensory area where information is received from sense organs and a motor area from where impulses are sent to effector organs.
  4. There are specific regions for each kind of stimulus and its response.
  5. Olfactory lobes: It lies below the cerebrum and contains olfacto receptors which are the organs of smell
Region Stimulus
Olfactory Lobe Visual reception
Temporal Lobe Auditory reception
Frontal Lobe Muscular activities
Parietal Lobe Touch, smell, taste, temperature and conscious association

Example 6.
What is the function of receptors in our body? Think of situations where receptors do not work properly. What problems are likely to arise?
Answer;
The main function of receptors in our body is to detect information from our environment. These receptors are usually located in our sense organs, such as tongue, nose, inner ear, skin etc. The information collected by the receptors is transferred to brain through an organised network of nerve cells for processing.

There may be situations, where receptors do not work properly. For example, gustatory receptors in tongue detect taste while olfactory receptors in nasal cavity detect smell. In case they do not work properly, the food will have no taste or may taste differently. Also, in the absence of smell, we may end up eating spoiled food or rotten fruits.

Mid brain

Midbrain connects the forebrain to the hind brain. Its functions are:

  1. It controls reflex movements of the head, neck and trunk in response to visual and auditory stimuli.
  2. It also controls the reflex movements of the eye muscles, change in pupil size and shape of the eye lens.

Hind brain

Hindbrain consists of three centres which are Cerebellum, Pons and Medulla oblongata.

  1. Cerebellum: CerebeLlum lies at the roof of the hind brain and controls the coordination and adjustments of movement and postures of the body.
  2. Pons: Pones lies just above the medulla and takes part in regulating respiration.
  3. Medulla oblongata: Medulla oblongata lies at the floor of the hind brain and continues into the spinal cord. It is the regulating centre for swal-lowing, coughing, sneezing and vomiting. It is also the seat of involuntary activities which controls heart beat, breathing and blood pressure.

Many of the involuntary actions are controlled by the mid-brain and the hind brain.

Nervous System in Animals Definitions, Equations and Examples

Example 7.
How are involuntary actions and reflex actions different from each other?
Answer:
Involuntary action and reflex action are different in the following ways:

Involuntary Action Reflex Action
1. These are muscle movements over which we do not have any thinking control. 1. These are quick automatic responses carried out by muscles without any thought processes undertaken by the brain
2. These actions are regulated by the brain 2. These actions are regulated by the spinal cord
3. These actions are performed throughout one’s life 3. These actions produced in response to an event of an emergency
4. This action may be quick or slow 4. This action is always quick
5. Example: Beating of the heart 5. Example: Immediate withdrawal of hands upon touching a hot cup of tea

Nervous Tissue in Action

Muscle cells have special proteins that change both
their shape and their arrangement in the cell in response to nervous electrical impulses.

When a nerve impulse reaches the muscle, the muscle fiber moves due to which new arrangements of these proteins give the muscle cells a shorter form.

Class 10 Science Notes

Excretion Definitions, Equations and Examples

Excretion

The biological process of removal of excess or toxic wastes from the body is called excretion. Many unicellular organisms remove these wastes by simple diffusion from the body surface into the surrounding water.

Osmoregulation: The process of maintaining the right amount of water and proper ionic balance in the body is called osmoregulation.

Excretion in Animals

A summary of excretory organs in some animals is given as follows:
Excretion Definitions, Equations and Examples 1

Excretion in Human Beings

The excretory system of human beings includes:
1. A pair of bean-shaped kidneys: Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
Excretion Definitions, Equations and Examples 2

2. Each kidney has large numbers of these filtration units called nephrons packed close together. The structure of the nephron is described below:

3. Bowman’s capsule: It is a double-walled cup-shaped structure present at the upper end of the nephron.

4. Glomerulus: These are a bundle of blood capillaries present in the Bowman’s capsule. One end of the glomerulus is attached to the renal artery (it brings dirty blood containing wastes into the kidney) and the other end is attached to the renal vein (it carries away the clean blood from the kidney). The function of the glomerulus is to filter the blood passing through it.

5. Tubule: It consists of the proximal convoluted tubule, Henle’s loop, and distal convoluted tubule. The function of tubule is reabsorption of useful substances such as glucose and amino acids into the blood capillaries.
Excretion Definitions, Equations and Examples 3

Excretion Definitions, Equations and Examples

Formation of Urine

The purpose of making urine is to filter out waste products from the blood. Nitrogenous waste such as urea or uric acid are removed from blood in the kidneys.

  1. The waste material is brought to the kidneys by the renal arteries.
  2. Blood is filtered from the blood capillaries into Bowman’s capsule.
  3. The filtrate passes into the tubule.
  4. Re-absorption of useful substances such as glucose, amino acids, salts and a major amount of water into the blood capillaries takes place.
  5. The amount of water reabsorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted.
  6. The urine formed in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder.
  7. Urine containing water and nitrogenous substances passes into the urinary bladder where it is stored till it is thrown out of the body.
  8. We can usually control the urge to urinate as the urinary bladder is muscular and under nervous control.

The urine formation involves three steps :

  1. Glomerular filtration: Nitrogenous wastes, glucose water, amino acid filter from the blood into Bowman Capsule of the nephron.
  2. Tubular reabsorption: Now, useful substances from the filtrate are reabsorbed back by capillaries surrounding the nephron.
  3. Secretion: Urea, extra water and salts are secreted into the tubule which open up into the collecting duct and then into the ureter.

Role of Kidney

Kidneys not only function to remove toxic waste, but also control water balance and levels of mineral ions in the body. Freshwater animals take up large amount of water through their skin and mouth. They need to get rid of it by frequent excretion of lot of urine. Marine animals and terrestrial animals, including humans, need to conserve water. For this, the excretory system is able to reabsorb water. Such reabsorption or removal of excessive water is under hormonaL control.

Renal failure:

The failure of the kidney due to a kidney infection or injury to kidneys or restricted blood flow to the kidneys due to which the kidney is unable to clean the blood of metabolic wastes and to maintain normal levels of water and mineral ions in body fluids is known as renal failure.

Excretion Definitions, Equations and Examples

Dialysis:

The procedure used in the artificial kidneys in place of normal is known as dialysis which is carried out during renal failure.

Principle of dialysis:

Blood is made to flow into the dialysis machine made of long cellulose tubes coiled in a tank having a dialyzing solution. Waste substances diffuse out of bLood into the tank and the clean blood is pumped back into the patient.

Artificial kidney (Fiamodialysis):

An artificial kidney is a device to remove nitrogenous waste products from the blood through dialysis. Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended in a tank filled with dialyzing fluid. This fluid has the same osmotic pressure as blood, except that it is devoid of nitrogenous wastes. The patient’s blood is passed through these tubes. During this passage, the waste products from the blood pass into a dialyzing fluid by diffusion. The purified blood is pumped back into the patient. This is similar to the function of the kidney, but it is different since there is no reabsorption involved. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is reabsorbed in the kidney tubules.

Example 1.
Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
Answer:
Comparison between the functioning of alveoli and nephron

Alveoli Nephron
1. Alveoli are balloon-like structures with thin walls and fine surfaces. 1. Nephrons are cup-shaped structures having thin walls, attached to a thin-walled tubule
2. The walls of the alveoli contain an extensive network of blood capillaries for the exchange of gases. 2. Bowman’s capsule is supplied with a cluster of capillaries, called glomerulus for filtration. A network of blood vessels is present around the tubular part of the nephron for the reabsorption of useful products and water.
3. Alveoli increases surface area for diffusion of carbon dioxide from the blood to air and oxygen from air to blood 3. Nephrons also increase the surface area for filtration of blood and reabsorption of useful products and water from filtrate leaving behind urine.
4. Alveoli only provide a surface for the exchange of gases in the lungs. 4. Tubular part of the nephron also carries the urine to the collecting duct.
5. Alveoli are very small and a large number of them are present in each lung. 5. Nephrons, as basic filtration units,     are packed close together and are present in large numbers, in each kidney.

Excretion in Plants:

  1. Oxygen and carbon dioxide are the waste products generated in plants during photosynthesis. The plants get rid of these gaseous waste products through stomata in leaves and lenticels in stems.
  2. They can get rid of excess water by transpiration.
  3. Many pLant waste products are stored in cellular vacuoles.
  4. Plants get rid of stored solid and liquid wastes by shedding of leaves, peeling of bark and felling of fruits.
  5. Other waste products are stored as resins and gums, especially in old xylem.
  6. Plants also excrete some waste substances into the soil around them.

Class 10 Science Notes