Class 8 Biology Questions and Answers

Q. Define the term osmosis ?
Ans. Osmosis is a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated solution.

Q. What is a semipermeable membrane ?
Ans. A semipermeable membrane is one through which only certain molecules can pass through depending on properties. For example the solvent molecules can pass through but not the solute.

Q. What is the importance of water to plants ?
Ans. Water is important to plant for the following reasons.
-> To maintain cell turgidity for structure and growth.
-> To transport nutrients and organic compounds through out the plant.
-> to buffer the plant through transpiration against wide temperature fluctuations.

Q. How are root hairs adapted for absorbing water from the soil ?
Ans. Plants absorb water from the soil by osmosis. Root hair cells are adopted for this by heaving a large surface area to speed up osmosis. The absorbed water is transported through the roots to the rest of the plants where it is used for different purposes.

Q. What is diffusion ?
Ans. Diffusion is a process of movement of molecules of solid, liquid and gasses from a place of higher concentration to a place of lower concentration.

Q. Distinguish between root pressure and Turgor pressure.
Ans. Turgor pressure (T.P) is defined as the amount of pressure inside a cell solely due to its water content. Where as root pressure is developed in the root due to continues inflow of water into it and responsible for puching the plant sap upwards.

Turgor pressure keeps leaves, flowers, fruits of plants expanded and root pressure is responsible for pushing the plant sap updards.

Q. What is protoplasm ?
Ans. The colourless material comprising the living part of a cell including the cytoplasm, nucleus and other organelles.

Q. Write the importance of turgor pressure.
Ans. On absorption of water a plant cell becomes swollen or turgid. The protoplasm of this turgid cell presses the cell wall outside with a force called turgor pressure. Turgor pressure keeps leaves, flowers, fruits, etc of the plant expanded. Decreases in turgor pressure of the cell leads to wilting.

Q. What do roots absorb from the soil ?
Ans. Roots absorb soluble minerals (those that can dissolve in water) and water through their root hair cells from the soil.

Q. How does an exmosis differ from an endosmis ?
Ans. In exosmosis the water/solvent molecules flow from a cell to an external concentrated solution where as in endosmosis water/solvent molecules flow from an external dilute solution into a cell. So it’s clear that exo means out and endo means in.

Q. What is plasmolysis ?
Ans. Contraction of the protoplasm of a plant cell as a result of loss of water is called plasmolysis.

Q. Write down the factors which control transpiration.
Ans. The factors which Control transpiration are :
1. Sunlight : In daylight stomata of the leaves are open so transpiration is more.
2. Temperature : In high temperature the capacity of air to contain water vapour increases so transpiration increases.
3. Humidity : If humidity in air is high it can accept very little water vapour so transpiration decreases.
4. Air Movement : In moving air the water vapour will be swept away from the leaf as fast as it diffuses out. So transpiration is more.

Q. What is a potometer ?
Ans. A potometer is a device used for measuring the rate of transpiration of the same leafy plant shoot under different conditions.

Q. Define wilting ?
Ans. The drying out of the leaves of a plant due to inadequate water supply, excessive water supply, excessive transpiration or vascular disease. This occurs when the turgor pressure decreases.

Q. Write one disadvantage of transpiration ?
Ans. If water availability is less in soil then transpiration causes wilting and shedding or dropping of leaves.

Q. What are hydathodes ?
Ans. A Hydathode is a type of secretory tissue in leaves, that secrets water through pores in the epidermis or leaf margin. Hydathodes are responsible for guttation.

Q. What is the importance of antitranspirants ?
Ans. Antitranspirants are applied to leaves to reduce transpiration, reducing wilting and sheddinng of leaves. These are also used to protect leaves from salt burn and fungal diseases.

Q. Describe the structure of the root.
Ans. Morphologically the root system of the plant consists of a main root. Main root gives out branches called lateral or secondary root. The lateral roots also have large number of fine outgrowths called root hairs or tertiary roots. The number of root hairs per plant is millions.

Anatomically the root have :
-Root Cap : It is cap like structure at the tip of the root to protect the young and delicate cells.
-Meristematic zone : Meristematic cells found in this region. These cells divide rapidly and give rise to root and keep root growing.
-Elongation Zone : The cells of this region contain a cluster or very fine and delicate thread like structures called root hairs.

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