ExamGOAL
Books
PreviousNext
45
How can plants be grown under limited water supply without compromising on metabolic activities?
Explanation
Under conditions of limited water supply, plants reduce the loss of water through transpiration by shutting down stomata. But they carry out the important life processes like photosynthesis, respiration and transport of food, etc.
46
Will the ascent of sap be possible without the cohesion and adhesion of the water molecules? Explain.
Explanation

No, the ascent of sap is not possible without the cohesive and adhesive properties of water as they play an important role in transport of water because of the following reasons

(i) Cohesion forces hold together the water molecule in the conducting channels, so vacuum is not created.

(ii) Adhesive forces between the water molecule and cellulose of cell wall make a thin film of water along the channels so, this film can be pulled up by transpiration pull drawing more and more water upwards in the conducting channels from the root.

47
Keep some freshly cut flowers in a solution of food colour. Wait for sometime for the days 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?
Explanation
Yes, it shows that xylem tissue conducts water.
48

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?

Explanation

(a) Plasmolysis is the name of the phenomenon, occurring is Spirogyra filament when placed in 10\% potassium nitrate solution (hypertonic solution). It occurs as water from the cell is drown out to extracellular fluid causing the protoplast to shrink away from cell wall.

(b) When the Spirogyra again reabsorb water, protoplast will again and will come back in its original shape. This phenomenon is known as deplasmolysis.

49
Sugar crystals do not dissolve easily in ice cold water. Explain.
Explanation
Pure water has tremendous free energy at normal room temperature. That is called water potential. When the water temperature drops down, the free energy is reduced so, sugar does not get dissolved easily in, i.e., cold water.
PreviousNext