NCERT Class 11-Biology: Chapter –11 Transport in Plants Part 5

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Question 19:

Transpiration is a necessary evil in plants. Explain.

Answer:

Transpiration is the process by which plants lose water in form of water vapour from aerial parts of the plant. When there is a huge amount of transpiration that takes place, it leads to huge amount of water loss thus causing wilting of the plant. But transpiration is needed for the pull of water and minerals from the root to the other parts of the plant and is needed for stomatal opening for the purpose of photosynthesis and respiration. So though it is a necessary evil and might also cause death of the plant if excessive water is lost, yet this process is necessary to carry out the other processes and for the need of water and minerals which is why transpiration is considered a necessary evil in plants.

Question 20:

Describe briefly the three physical properties of water which helps in ascent of water in xylem.

Answer:

The three physical properties of water which helps in ascent of water in xylem are:

(i) Adhesion: It is the attraction between water molecules and other molecules other than water molecules (here surface of the xylem vessel).

(ii) Cohesion: Cohesion is the force due to which molecules of water stay linked together due to hydrogen bonding in between them. It provides strength against the pressure by the transpiration pull.

(iii) Surface tension: It is the property of the surface of a liquid to resist an external force applied owing to the cohesive nature of the molecules of the liquid.

Question 21:

A gardener forgot to water a potted plant for a day during summer, what will happen to the plant? Do you think it is reversible? If yes, how?

Answer:

If the gardener forgets to water the plant for a day during summer, the rate of transpiration is more due to the higher temperature than the absorption of water so this will lead to wilting or losing of the plant’s turgidity.

It is reversible only if the time for which it is not watered is short. If its long then the plant eventually dies but if its small then upon getting the required amount of water, the tissues again gain turgidity.

Question 22:

Identify a type of molecular movement which is highly selective and requires special membrane proteins, but does not require energy.

Answer:

The type of molecular movement which is highly selective and requires special membrane proteins but does not require energy is passive diffusion.

Facilitated diffusion facilitates movement of molecules or ions which are larger in size, polar or charged to move across a cell membrane which is selectively permeable. It uses membrane proteins like carrier and channel proteins for facilitating the movement of the substances along the concentration gradient.

Question 23:

Correct the statements

a. Cells shrink in hypotonic solutions and swell in hypertonic solutions.

b. Imbibition is a special type of diffusion when water is absorbed by living cells.

c. Most of the water flow in the roots occurs via the Symplast.

Answer:

(a) Cells shrink in hypertonic solution and swell in hypotonic solutions.

Explanation: A hypertonic solution has more concentration of solution thus the net movement of water is from the cell to the outside causing the cell to shrink as water moves out of the cell. A hypotonic solution has less solute concentration as compared to within the cell so there is a net movement of water inside the cell from outside causing the cell to swell.

(b) Imbibition is a special type of diffusion when water is absorbed by dead or living cells.

Explanation: Imbibition is a special type of diffusion when water is absorbed by dead or living cells. Eg: absorption of water by seeds which is required for germination or absorption of water by dry wood that causes it to swell.

(c) Most of the water flow in roots occurs via the apoplast pathway.

Explanation: In the symplast pathway, water moves between cytoplasm or vacuoles of the neighbouring cells. In the apoplast pathway can only take water near the xylem, where the Casparian strip forms an impermeable barrier to water in the cell walls, so water moves into the cytoplasm.

Short Answer Type Questions

Question 1:

Minerals absorbed by the roots travel up the xylem. How do they reach the parts where they are needed most? Do all the parts of the plant get the same amount of the minerals?

Answer:

Minerals are taken by the roots from the soil and are transported to various parts of the plants wherever needed via the xylem vessels. The mineral requirement is not same for all plants and neither for all plant parts so all the parts of the plants do not get the same amount of minerals. Growing parts of the plants usually require more of the minerals. Minerals exit the xylem and by diffusion gets into the cells where they are needed. Places where concentration of minerals is already higher, these minerals are taken there by active transport.

Question 2:

If one wants to find minerals and in the form they are mobilised in the plant, how will an analysis of the exudate help?

Answer:

Exudates’ analysis would help to find minerals and in the form that they are mobilised in the plant because exudates are often plant sap which contains xylem sap as well as phloem sap. It has a composition of amino acids, sucrose, organic and inorganic acids, water, ions, sugars etc. If we perform an analysis of the plant exudates, then we can find out which mineral nutrient is transported in the plant and in which form it is transported.

For eg: Nitrogen can be carried in organic forms like amino acids or as inorganic ions.

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