NCERT Class 11-Biology: Chapter –11 Transport in Plants Part 7

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Question 10:

How can plants be grown under limited water supply without compromising on metabolic activities?

Answer:

Plants can be grown under limited water supply without compromising on metabolic activities by a number of ways:

Plants usually shrink when the rate of transpiration exceeds the rate of absorption of water by roots. So if we use anti-transpirant like Abscisic acid then it checks the rate of transpiration. This would reduce loss of water by plants but the metabolic activities shall go on along with diffusion of gases.

Question 11:

Will the ascent of sap be possible without the cohesion and adhesion of the water molecules? Explain.

Answer:

Ascent of sap will never be possible without the cohesion and adhesion of the water molecules because these are responsible for the same.

The continuous water column in the xylem vessels for the sap ascent is maintained by the adhesive and the cohesive forces of water. Absence of which would have led to cavitation of xylem vessels or breakage of the water column or the sap movement upwards.

Question 12:

Keep some freshly cut flowers in a solution of food colour. Wait for some time for the dye to rise in the flower, when the stem of the flower is held up in light, coloured strands can be seen inside. Can this experiment demonstrate which tissue is conducting water up the stem?

Answer:

This experiment can demonstrate which tissue is conducting water up the stem. Coloured strands are indicative that the food colour has been conducted upwards through a conducting vessel which is the xylem. We know how xylem conducts water upwards. This can be confirmed under the microscope to see the structure of the xylem. Plants contain xylem vessels from the roots to the tips of the leaves.

Question 13:

When a freshly collected Spirogyra filament is kept in a 10% potassium nitrate solution, it is observed that the protoplasm shrinks in size:

a. What is this phenomenon called?

b. What will happen if the filament is replaced in distilled water?

Answer:

When a freshly prepared Spirogyra filament is kept in 10% potassium nitrate solution, then the protoplasm is observed to shrink in size because of the phenomenon of exosmosis.

(a) This phenomenon is called exosmosis: process by which when a substance is placed in hypertonic solution, the water moves out of the cell of the substance to the outside leading to the shrinkage of the protoplasm.

(b) If the filament is replaced in distilled water, then the protoplasm again becomes turgid as water flows in as the shrunken protoplasm swells up or gets deplasmolysed.

Question 14:

Sugar crystals do not dissolve easily in ice cold water. Explain.

Answer:

When sugar crystals are placed in ice cold water, the kinetic energy of the system is low so lattice structure is formed and remains. Very few water molecules are mobile in this stage. So dissolution or diffusion of the solid crystal of sugar does not occur since the number of striking water molecules is less when water is ice cold.

Question 15:

Salt is applied to tennis lawns to kill weeds. How does salting tennis lawns help in killing of weeds without affecting the grass?

Answer:

Salt solution being hypertonic, causes exo-osmosis in plants. 1 cup salt in 2 cup of water, fairly well dissolved when sprayed on weed plants, start killing them.

Question 16:

What is the chemical composition of xylem and phloem sap?

Answer:

Chemical composition of xylem and phloem sap are as follows:

Xylem sap: Water and concentration of minerals in dilute form. It is mildly acidic.

Phloem sap: traces of minerals, water, sucrose and amino acids in some species, it also transports fructane or raffinose etc. It is mildly alkaline.

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