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On this page, you will find why Do We Fall ill Class 9 Notes Science Chapter 13 Pdf free download. CBSE NCERT Class 9 Science Notes Chapter 13 Why Do We Fall ill will seemingly help them to revise the important concepts in less time.

CBSE Class 9 Science Chapter 13 Notes Why Do We Fall ill

Why Do We Fall ill Class 9 Notes Understanding the Lesson

1. Cells are basic unit of living organisms and a lot of activities and chemical reactions are taking place in the cells, so even though they look static they are in a dynamic state as a lot of activities are continuously going inside them.

2. Growth and repair of cells is a continuous process which occurs in living organisms.

3. Activities of all the organs in our body are occurring in a coordinated and interconnected way. For example, poisonous substances would accumulate in the body if the urine is not filtered properly by the kidneys. This in turn would affect the activities of the brain and it will not be able to think properly.

4. Food and energy is needed by all the tissues of a living body in order to function properly.

5. If the functioning of cells and tissues gets adversely affected it would result in lack of proper activity of the body.

6. ‘Health’ is defined as a state of physical, emotional, mental and social well being of a person.

7. The health of an individual depends on the surroundings or the environment of an individual. The environment includes the physical environment.

8. Social environment is also an important factor for health of an individual. Even our physical environment is decided by our social environment.

9. Personal hygiene, public cleanliness, social equality, harmony and good economic conditions are necessary for individual health.

10. Disease refers to any condition that disturbs the normal functioning of the living organism. It is a condition of disturbed ease when an individual feels uncomfortable. Being disease-free is a concept which applies to individual sufferer.

11. Even a disease free person can be considered as having a poor health if the person is unfit in terms of social and mental health. So, health is a concept which applies to societies and communities.

12. The functioning or the appearance of one or more systems of the body gets adversely affected when a person is suffering from a disease. These changes result in symptoms and signs of the disease.

13. Signs and Symptoms

• Symptoms are the physical disturbances that indicate that something is wrong with the functioning of the body and that there may be a disease, but they don’t indicate what the disease is. For example, headache, cough, pus in wound, etc., are symptoms of a disease.
• On the basis of the symptoms, physicians look for the signs of a disease. Signs give a more definite indication of the presence of a particular disease.

14. Types of Disease – Acute disease and chronic disease

• The disease which lasts for only very short periods of time is called acute disease.
  For example: common cold
• The disease which can last for a long time, even as much as a lifetime is called as chronic disease. They have a long-term effect on the health of a person.
  For example: elephantiasis

15. Causes of disease – Immediate and contributory

• Immediate causes: These are the first level causes or the primary cause of the disease.
  Example: The various bacteria, virus, fungi, protozoans, etc., which cause infection in an organism.
• Contributory causes: These are the second level of causes or the internal factors which result in a disease.
  For example: Pollutants in the atmosphere, inadequate diet, poor health, improper nourishment, lack of public services, poor economic condition, genetic abnormalities, etc.
• The immediate cause of disease can be of two types: Infectious diseases and non-infectious dis¬eases.
• Infectious diseases: These diseases are caused by infectious agents. These can spread from one person to another through some medium or by direct contact.
  Example: Pneumonia, common cold, tuberculosis, etc.
• Non-infectious diseases: These do not spread from one person to another person in the community. They are caused due to internal factors.
  Example: Cancer, high blood pressure, diabetes, etc.
• Infectious agents: The organisms (unicellular or multicellular) which cause infection are called as the infective agents.
  Example: virus, bacteria, worms, fungi, etc.

Examples of diseases caused by infectious agents

• By viruses: Common cold, influenza, dengue fever and AIDS.
• By bacteria: Typhoid, cholera, tuberculosis, anthrax, etc.
• By fungi: Many common skin infections like ringworm disease.
• By Protozoans: Malaria and kala-azar.
• By worms: Intestinal worm infections, elephantiasis.

Antibiotic: Chemicals produced by certain microorganisms like bacteria and fungi which inhibit the growth of the other microorganisms are called as antibiotics.

Mode of action of antibiotic: Antibiotics usually block the important biochemical pathways of bacteria. Example: The antibiotic penicillin blocks the processes that help in synthesis of a cell wall in the bacteria. Due to this, the bacteria become unable to make cell walls to protect them and die easily. Human cells don’t make a cell wall, so penicillin does not affect them.

16. Antibiotics do not work against viruses:
Reason: Viruses do not use their own biochemical pathways for the synthesis of their cell wall. They have very few biochemical mechanisms. So, antibiotics do not work against viral infections.

17. Means of spread of diseases
Infectious diseases can spread from an infected person to a healthy person by various transmitting agents, so they are called as communicable diseases. These diseases can be spread through air, water, vectors and physical contact.

(i) By air: The little droplets thrown out by an infected person who sneezes or coughs can result in a new infection in a healthy person if the person breathes in the droplets released by the infected person. Example: common cold, pneumonia and tuberculosis.

(ii) By water: If the excreta from someone suffering from an infectious gut disease, such as cholera, get mixed with the drinking water used by people living nearby. The microbes will enter new hosts through the water they drink and cause disease in them.
Example: cholera.

(iii) By Sexual contact: Some diseases are transmitted by sexual contact from one partner to the other. Example: syphilis, AIDS, etc.
It is important to note that: AIDS does not spread by casual physical contacts like handshakes or hugs or sports, like wrestling. AIDS can spread in four ways, sexual contact, transfusion of AIDS infected blood, from an infected mother to her baby during pregnancy or through breast feeding.

(iv) By vectors: Many diseases are transmitted by animals from an infected person to a healthy person. These animals act as intermediaries and are called vectors. The most common example of vectors are mosquitoes. The females of many species of mosquitoes need highly nutritious food in the form of blood in order to be able to lay mature eggs.

18. Different species of microbes have evolved to affect different parts of the body. The selection is generally connected to their point of entry.

• They usually go to the lungs if they enter from the air via the nose.
  Example: bacteria causing tuberculosis.
• They can stay in the gut lining or go to the liver if they enter through the mouth. Example: bacteria which causes typhoid remains in the gut lining whereas the viruses that cause jaundice go to the liver.

19. Other ways are:

• The AIDS causing virus HIV comes into the body via the sexual organs and then spreads to lymph nodes all over the body.
• Malaria-causing microbes which enter through a mosquito bite go to the liver, and then to the red blood cells.
• The virus causing Japanese encephalitis or brain fever enters through a mosquito bite and goes on to infect the brain.

20. The signs and symptoms of a disease depend on the tissue or organ which the microbe targets.

• If the lungs are the targets, then symptoms will be cough and breathlessness.
• If the liver is the target, there will be jaundice.
• If the brain is the target, it will result in headache, vomiting, fits or unconsciousness.

21. Inflammation: An active immune system recruits many cells to the affected tissue to kill off the disease- causing microbes. This recruitment process is called inflammation. Local effects such as swelling and pain, and general effects such as fever are caused as a part of this process.

In AIDS, the virus called HIV goes to the immune system and damages its function. As a result, the body can no longer fight off even the minor infections. For example, a very small cold can become pneumonia or minor gut infection can produce major diarrhoea with blood loss. Ultimately, the immune system of the person becomes very weak and these and other infections kill people suffering from HIV-AIDS.

22. Principles of Treatment
There are two ways for treatment of infectious diseases:

•  to reduce the effects of the disease: The main focus is to reduce the symptoms which are usually due to inflammation. For example, rest is taken to conserve energy, medicines are taken to bring down fever or to reduce pain or loose motions, etc.
• to kill the cause of the disease: The main focus on this is to get rid of the disease causing microbe from the body. For example, medicines like antibiotics are taken to kill microbes.

23. Principles of Prevention
Prevention is better than cure because the methods which deal with getting rid of an infection have three limitations.

• During treatment, the body functions of the person get damaged and may never recover completely.
• The person suffering from a disease is likely to be dridden for some time as the treatment of a disease takes time.
• The person suffering from an infectious disease can serve as the source of spread of infection to other people.

23. Ways of Prevention of disease are
(i) General ways: These focus on preventing exposure to the disease causing organisms. Public hygiene is important for the prevention of infectious diseases.
For example,

• By providing living conditions that are not overcrowded, exposure to air-borne infections can be avoided.
• By providing safe drinking water and treating water to kill microbes in it, the water-borne infections can be prevented.
• By providing clean environment which do not allow spread of microbes/vectors, the vector-borne infections can be prevented.
• For vector-borne infections, we can provide clean environments. This would not, for example, allow mosquito breeding.

(ii) Specific ways: These methods are adopted to make the immune system of the person strong by vaccination to create immunisation and taking proper and sufficient food for keeping the body healthy.

24. Vaccine: A modified suspension of disease causing microorganisms which have been weakened so that they are not able to cause disease but help to activate the immune system of the organism to produce antibodies against the disease causing organism. Edward Jenner developed the first vaccine against the smallpox disease. The process of inoculation of a vaccine in a person to develop immunity against a disease is called vaccination.

Class 9 Science Chapter 13 Notes Important Terms

Health: The state of physical, emotional, mental and social well being of an individual.

Disease: Any condition that causes disturbed ease in a person or disturbs the normal functioning of the body.

Acute disease: The disease which lasts for a short time.

Chronic disease: The disease which persists for a long time.

Infectious disease: A disease which can spread from one person to other. E.g., common cold

Non-infectious disease: A disease which cannot spread from one person to other. E.g., diabetes

Antibiotics: The chemicals secreted by some microbes like fungi and bacteria which are used to control the growth of bacteria or kill the bacteria.

Immunity: The ability of the body to fight against the disease causing organisms.

Vaccine: A biological preparation that provides immunity to a person against a disease.

Vector: The organism or the agent which helps in the transmission of a disease.

Inflammation: It is the process by which the white blood cells of our blood protect us from the infections by disease-causing organisms.

Symptom: The physical disturbances which indicate the presence of a disease.

Syndrome: Group of symptoms

AIDS: Acquired immunodeficiency syndrome

HIV: Human immuno-deficiency virus

Immunisation: The process by which a person is made immune to an infectious disease . administering a vaccine.

On this page, you will find Wastewater Story Class 7 Notes Science Chapter 18 Pdf free download. CBSE NCERT Class 7 Science Notes Chapter 18 Wastewater Story will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Science Chapter 18 Notes Wastewater Story

Forests: Our Lifeline Class 7 Notes Understanding the Lesson

1. Rich in lather, mixed with oil, black-brown water that goes down the drains from sinks, showers, toilets, laundries is dirty. This is called wastewater.

2. The suspended impurities in water are called contaminants.

3. The waste water released by homes, industries, hospitals and other users is called sewage.

4. ‘Cleaning of water’ is a process of removing pollutants before it enters a water body or is reused. This pro­cess is generally known as ‘sewage treatment’.

5. Sewage treatment plant is constructed to make wastewater or sewage reusable.

6. A complete network of sewers underlying the surface is planned to collect and send the wastewater for treatment. This is called sewerage system.

7. Treatment of wastewater involves physical, chemical and biological processes, which removes physical, chemical and biological matter that contaminates the wastewater.

8. The treated water from sewage treatment plant has a very low-level organic material and suspended matter. This is discharged into the water bodies by sometimes disinfecting with chlorine and ozone.

9. By-products of wastewater treatment are sludge and biogas.

10. Where underground sewerage systems and refuse disposal systems are not available, the low-cost on-site sanitation system can be adopted.

11. Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases.

12. We must realise our responsibility in maintaining the water sources in a healthy state. Adopting good sanitation practices should be our way of life.

Class 7 Science Chapter 18 Notes Important Terms

Aeration: It is the process in which air is pumped into clarified water to help bacteria grow.

Aerobic bacteria: Bacteria that require oxygen to live and grow are called aerobic bacteria.

Anaerobic bacteria: Bacteria that can survive without oxygen are called anaerobic bacteria.

Biogas: It is a gaseous fuel produced by the fermentation of manure, plant, or crop waste under anaerobic conditions which is used to generate electricity from waste matter.

Contaminants: There are harmful substances dissolved and suspended as impurities in water.

Sanitation: The proper disposal of sewage and garbage from the houses or nearby areas is called sanitation.

Sewage: Wastewater generated by homes, offices, hospitals, industries and other areas is called sewage.

Sewer: A network of big and small pipes to carry wastewater to treatment plant is called sewer.

Sewerage: It is the drainage system of sewer.

Sludge: Sludge is the residual, semi-solid material that is produced as a by-product during sewage treat­ment of industrial or municipal wastewater.

Wastewater: The water that is not fit for use is called ‘wastewater’.

On this page, you will find Heat Class 7 Notes Science Chapter 4 Pdf free download. CBSE NCERT Class 7 Science Notes Chapter 4 Heat will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Science Chapter 4 Notes Heat

Heat Class 7 Notes Understanding the Lesson

1. Heat is a form of energy.

2. The hotness and coldness of a body is relative.

3. Our sense of touch is not always a reliable guide to the degree of hotness of an object.

4. The measure of degree of hotness of an object is called temperature.

5. Thermometer is a device which is used to measure temperature.

6. The thermometer that measures our body temperature is called a clinical thermometer.

7. Clinical thermometer consists of a long, narrow, uniform glass tube and a bulb at one end. It has a kink which prevents mercury level from falling on its own. The range of this thermometer is from 35°C to 42°C (Fig. 4.1).

8. The normal temperature of human body is 37°C.

9. To measure the temperature of non-living objects, a laboratory thermometer is used. The range of laboratory thermometer is from -10°C to 110°C. (Fig. 4.2).

10. Nowadays, a digital thermometer is used instead of a clinical thermometer. It has no mercury in it.

11. Heat always flows from higher temperature to lower temperature. The three ways in which heat can flow from one object to another are conduction, convection and radiation.

12. The process by which heat is transferred from the hotter end to the colder end of an solid object is known as conduction.

13. The materials which allow heat to pass through them easily are called conductors. For example, iron, copper, zinc, etc.

14. The material which do not allow heat to pass through them easily are called poor conductors or insulators. For example, plastic, rubber, wood, etc.

15. Convection is the process of transferring heat from a hotter region to cooler region by the actual movement of particles. It generally occurs in liquid and gaseous medium.

16. Convection takes place when the air near the heat source gets hot and rises. The air from sides comes in to take its place.

17. The flow of cool air from the sea towards the land to replace the hot air on land, is called sea breeze [Fig. 4.3(a)]. This phenomenon takes place during the day.

18. During the night, the currents of air flow from the cooler land towards the warmer sea. This is called land breeze. [Fig. 4.3(b)],

19. The process of transmission of heat without any contact between the source and the object is called radiation.

20. All hot bodies radiate heat.

21. Dark-coloured objects absorb radiation better than the light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.

22. Woollen clothes keep us warm during winter. This is because wool is a poor conductor of heat and it has air trapped in between the fibres.

Class 7 Science Chapter 4 Notes Important Terms

Celsius scale: Celsius scale or centigrade scale is the unit used for measurement of temperature. It is a metre scale of temperature.

Conduction: The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

Conductor: The material which allow heat to pass through them easily is called conductor.

Convection: The process of transferring heat from a hotter region to cooler region by the actual movement of particles is called convection.

Insulator: The material which do not allow heat to pass through them easily is called insulator.

Land breeze: The process of flowing of air currents from the cooler land towards the warmer sea is called land breeze.

Radiation: The process of transfer of heat in which no medium is required is called radiation.

Sea breeze: The flow of cool air from the sea towards the land to replace the hot air on land is called sea breeze.

Temperature: The reliable measure of the hotness of an object is called temperature.

Thermometer: A device used to measure the temperature is called thermometer.

On this page, you will find Forests: Our Lifeline Class 7 Notes Science Chapter 17 Pdf free download. CBSE NCERT Class 7 Science Notes Chapter 17 Forests: Our Lifeline will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Science Chapter 17 Notes Forests: Our Lifeline

Forests: Our Lifeline Class 7 Notes Understanding the Lesson

1. A large area of land covered mainly with trees and other plants is called a forest.

2. Forest is a system comprising various plants, animals and microorganisms.

3. The type of animals and kind of trees differ from forest to forest.

4. Forests are the habitat of a large number of different kinds of animals, birds, reptiles, etc.

5. There are four layers of forest named as emergent layer, canopy, understorey and forest floor.

6. In a forest, trees form the uppermost layer, followed by shrubs. The herbs form the lowest layer of vegetation.

7. Based on the life span of plants and trees, they are classified as annuals, biennials and perennials. The organisms which make their own food from carbon dioxide and water in the presence of sunlight and chlorophyll are called producers.

8. The organisms which consume the food made by the producers are called consumers.

9. The organisms which derive their food items from the dead and decaying animals or plants are called decomposers.

10. Plants and animals in a forest depend on each other for many things.

11. In the forest, there is interaction between soil, water, air and living organisms.

12. All plants and animals are linked together by the process of eating and being eaten. This is called a food chain. Many food chains are interlinked to form a food web.

13. Importance of forests are:

• It help in replenishing groundwater.
• It regulate climate, and help rainfall.
• It purify the air and control air pollution.
• It control floods.

14. Forests are also called green lungs because plants release oxygen during photosynthesis which helps in keeping the balance of carbon dioxide and oxygen in the atmosphere.

15. The forest harbours variety of plants, thus providing greater opportunities for food and habitat for the herbivores which in result increases the availability of food for carnivorous animals. That is why, forest is a dynamic living entity.

16. The cutting down of forest trees for personal as well as for commercial purpose is called

17. Deforestation can lead to soil erosion, water pollution, disruption in water cycle, drought, global warming, etc.

18. We must preserve our forest.

Class 7 Science Chapter 17 Notes Important Terms

Canopy: The branches of tall trees of the forest form overhanging covering like a roof over the other plants in a forest. This is called canopy.

Crown: The branchy part of the tree above the stem is known as the crown.

Decomposers: The organisms which derive their food from the dead and decaying animals or plants are called decomposers.

Deforestation: The cutting down of forest for personal or commercial purposes is called deforestation.

Humus: Microorganisms feed upon the dead plants and animal tissues and convert them into a dark coloured substance called humus.

Regeneration: Regeneration is the process of renewal, restoration and growth of new organisms or the existing organisms in an area.

Seed dispersal: The transportation of seeds from the place of their origin to faraway places through vari­ous agents is called seed dispersal.

Soil erosion: The phenomenon of washing away of the top fertile layer of soil by water, or wind is called soil erosion.

Understorey: Understorey is an underlying layer of vegetation, specifically, the vegetative layer an especially the trees and shrubs between the forest canopy and the ground cover.

On this page, you will find Water: A Precious Resource Class 7 Notes Science Chapter 16 Pdf free download. CBSE NCERT Class 7 Science Notes Chapter 16 Water: A Precious Resource will seemingly help them to revise the important concepts in less time.

CBSE Class 7 Science Chapter 16 Notes Water: A Precious Resource

Water: A Precious Resource Class 7 Notes Understanding the Lesson

1. Water is the most important compound for all living things. There can be no life without it.

2. 22 March is celebrated as the world water day to attract the attention of everybody towards the importance of conserving water.

3. Water is an universal solvent.

4. 71% of earth surface is covered with water.

5. Three forms of water are solid, liquid and gas.

6. The water on the earth has been maintained for millions of years by various processes which make the water cycle.

7. The solid form of water, snow and ice, is present as ice caps at the poles of the earth, snow-covered mountains and glaciers.

8. Liquid water is present in oceans, lakes, rivers and even underground.

9. The gaseous form of water is the water vapour which is present in the air around us.

10. The rainwater or the water from other sources like ponds, lakes, etc., percolates under the ground and collects over the impermeable rocks. This water is called

11. The upper limit of underground water is called water table. The water table varies from place to place, and it may even change at a given place.

12. The process of seeping of water into the ground is called The groundwater gets charged by this process.

13. Aquifer is a water trap where groundwater is trapped between the layers of hard rock below water table.

14. Following are the causes of water shortage:

• Increasing population
• Rapid growth of industries
• Growing irrigation requirements
• Increasing agricultural activities
• Mismanagement

15. The distribution of water is also quite uneven due to number of factors. There are some regions in our country may have floods while others may suffer droughts at the same time.

16. Water management should be done by following ways:

17. Unnecessary use of water and overdrawing of groundwater should be stopped.

18. Recharge of groundwater must be increased through various processes.

19. We should prevent the wastage of water during its supply through pipes, the leaking taps in buildings and other places.

20. Plants wilt and ultimately dry-up if they are not watered for few days.

Class 7 Science Chapter 16 Notes Important Terms

Aquifer: A water trap where groundwater is trapped between the layers of hard rock below water table.

Depletion: Depletion is reduction in number or quantity of something. Rapid growth of industries, increasing population, growing irrigation requirements and mismanagement are some of the causes for water depletion.

Drip irrigation: It is a technique of irrigation by using narrow tubings which deliver water drop by drop directly at the base of the plant.

Groundwater: The water that seeps into the earth, gets collected between the layers of rocks and found below the water table is called groundwater.

Infiltration: The process of seeping of water into the ground is called infiltration. The groundwater gets recharged by this process.

Water harvesting: The water harvesting simply involves collection of rainwater from surfaces that can be used to recharge the groundwater or storing it for later use.

Water table: The water present deep under the ground is known as groundwater and the upper limit of this layer is known as water table.