Once water is absorbed by plant roots, it has to travel against gravity through xylem. Class 9

Once water is absorbed by plant roots, it has to travel against gravity through xylem. Class 9

Question 1.

Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the ‘dead’ cells of the xylem work together with the living cells of leaves at the top to keep the water moving? (Page 34) Class 9

Answer:

Xylem cells (tracheids and vessels) are dead and hollow, forming a continuous pipeline from roots to leaves. Their dead, tube-like structure offers very little resistance to water flow. The living cells of leaves carry out transpiration - they lose water vapour through stomata into the air. This creates a transpiration pull (a suction-like force), which draws water upward through the xylem tubes against gravity. So the dead xylem cells act as passive pipes and the living leaf cells create the suction force that keeps water moving upward continuously.

Question 2.

What do you think will happen if there were no stomata in the epidermis of the stem or leaves? (Page 34) Class 9

Answer:

If there were no stomata, the following problems would occur:

1. Gaseous exchange would stop - carbon dioxide needed for photosynthesis cannot enter and oxygen produced cannot exit, so photosynthesis will fail.
2. Transpiration will stop - there will be no transpiration pull in the xylem, so water and mineral transport from roots to leaves will be severely affected.
3. Waste gases produced by the plant cannot be eliminated, causing toxin build-up. Overall, the plant's growth and survival will be severely compromised.