NCERT Class 11-Biology: Chapter –11 Transport in Plants Part 8

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Question 17:

If you are provided with two tubes (A and B), where one is narrow and the other is relatively wider and if both are immersed in a beaker containing water as shown in the figure given on next page.

Chapter 11 - Question 17 Image of Higher Water Rise

Chapter 11 - Question 17 Image of Higher Water Rise

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Why does B show higher water rise than A?


Tube B shows higher water rise than tube A because surface area is less in the narrow tube or tube B due to which the surface tension is more in that so the level of rise of water is more in that as well. Surface tension is inversely proportional to the surface area and surface tension arises from strong interactions between water molecules so lesser the space or area, more is the compactness and this results in more surface tension eventually leading to higher water rise in the tube.

Question 18:

What are ‘aquaporins’? How does presence of aquaporins affect osmosis?


Aquaporins are a kind of membrane proteins that form channels in the membrane and are usually facilitating transport of water between cells.

When aquaporins are present, more water molecules can travel from the more dilute solution to less dilution solution across the semi-permeable membrane so presence of aquaporins would increase the rate of osmosis thus facilitating it.

Question 19:

ABA (Abscisic acid) is called a stress hormone.

a. How does this hormone overcome stress conditions?

b. From where does this hormone get released in leaves?


(a) Stress hormone is a hormone which induces various changes/responses in a plant when subjected to stress. Abscisic acid is a stress hormone and during stress conditions it induces changes like closing of stomata to prevent further water loss during scarcity of water, aids in seed germination when conditions are favourable and dormancy when not and other changes as and when required.

(b) This hormone, abscisic acid gets released in the leaves from the mesophyll cells of the plant.

Question 20:

We know that plants are harmed by excess water. But plants survive under flooded condition. How are they able to manage excess water?


Plants are harmed by excess water because when excess water is present, there is a deprivation of oxygen in the plant roots causing an anaerobic condition. Thus aeration is affected. But at the same time there are air which are trapped in the soil due to its structure and texture. But if the water logging is permanent then there is no way plants can survive because the oxygen would be used up and the lack of it will lead to the plant eventually dying in the anaerobic condition it will be subjected to.

Question 21:

Differentiate between diffusion and translocation in plants.


Differentiate of diffusion and translocation



(i) This is a passive process

(i) This is an active process.

(ii) Energy is not required

(ii) Energy is required

(iii) Facilitates movement of water and gases

(iii) Facilitates movement of organic compounds

Question 22:

How is facilitated diffusion different from diffusion?


Differentiate of diffusion and facilitated diffusion


Facilitated Diffusion

(i) During diffusion, movement is along osmotic gradient

(i) During facilitated diffusion, movement is along osmotic gradient

(ii) It is a slow process

(ii) It is a fast process

(iii) It is not dependent on a living system.

(iii) It is dependent on a living system.