Value Based Questions in Science for Class 9 Chapter 6 Tissues
These Solutions are part of Value Based Questions in Science for Class 9. Here we have given Value Based Questions in Science for Class 9 Chapter 6 Tissues
Name four economically important plant fibres derived from sclerenchyma. Why they differ in their softness and durability ?
Four fibres : Flax, Hemp, Jute, Coconut. In Coconut, the fibres are obtained from husk (mesocarp) of fruit. In others they are obtained from stems, being bast or phloem fibres.
The fibres differ in their hardness and strength. Hardness is due to excessive deposition of lignin as in Coconut and Jute. Because of it, they are prone to deterioration on wetting. Coconut fibres are used in preparation of mats while Jute fibres are used in preparing sacks. Flax and Hemp yield high quality durable clothing. They have smaller amounts of lignin.
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What is bark ? Give its importance. Why are certain barks used in medicines ?
Bark is the outer protective covering of stems and roots of woody plants. It is mostly made up of cork that consists of several layers of compactly arranged dead rectangular cells. The cells are impermeable due to deposition of suberin. They contain air, tannins, resins and alkaloids.
- Protection against water loss due to impermeable nature of cell walls.
- Protection against microbes due to impervious nature.
- Insulation from extremes of temperature, mechanical injury and browsing by animals.
- Cork is used commercially in stoppers for bottles, insulation boards, shock absorbers, linoleum and sports goods.
- Tannin rich bark is used in dyes.
- Inner bark of Cinnamon is a common spice.
Bark in Medicines:
- Quinine is obtained from the bark of Cinchona,
- Taxol is got from bark of Taxus. Medicinal barks possess alkaloids.
What is cartilage ? What is its importance to bones ?
Cartilage is flexible soft supportive connective tissue having non-vascularised solid matrix of chondrin with fluid filled lacunae containing 1-4 living cells called chondrocytes.
Importance to Bones :
- Cartilage occurs over articular surfaces of bones where it protects them from frictional damage during movement against one another.
- It lies at sternal ends of ribs to give them flexibility in movement during breathing,
- It occurs as intervertebral discs to function as cushions in the vertebral column.
Why are medullated nerve fibres more efficient than non-medullated nerve fibres ?
Medullated nerve fibres are those axons which have a covering of fat rich medullary sheath below the neurilemma. They are more efficient than non-medullated nerve fibres due to two reasons.
- Being well insulated, the fibres do not meet any interference in impulse conduction from other nearby nerve fibres.
- Medullated nerve fibres have nodes of Ranvier. An impulse does not travel all along the axon but jumps from one node of Ranvier to the next. By this saltation medullated nerve fibres are some fifty times (50 X) more efficient in impulse transmission as compared to non-medullated nerve fibres.
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