Consider the following two statements:
I. The evolution of ${\mathrm{C}}_4$  photosynthesis is probably one of the strategies for maximizing the availability of ${\mathrm{CO}}_2$ while minimizing water loss.
II. Plants with ${\mathrm{C}}_4$ photosynthesis close their stomata during day and open them in night.
1. Both I and II are correct
2. I is correct and II is incorrect
3. I is incorrect and II is correct
4. Both I and II are incorrect

Which of the following will always be a “sink” in a plant?

A cell has less number of aquaporins when compared to another cell in a plant. With respect to the latter cell, the former cell will have:
1. a faster rate of osmosis.
2. a lower water potential.
3. a higher water potential.
4. a lower rate of osmosis.

Xylem in plants does not:
1. conduct material upward from the roots.
2. conduct materials within the dead cells.
3. transport large amounts of sugars and amino acids.
4. have a lower water potential than soil does.

Which of the following is not required for transpiration?
1. adhesion of water molecules to cellulose.
2. cohesion between water molecules.
3. evaporation of water molecules.
4. active transport through xylem cells.

The normal functioning of which of the following would be least dependent on active transport:

Identify the incorrect statement regarding xylem:
1. Xylem tracheids and vessels perform their vital function only after their death.
2. Tracheids have a strong cell wall deposited with cellulose fibrils forming thickened rings or spirals.
3. Water molecules are transpired from the cells of the leaves, and replaced by water molecules in the xylem pulled up from the roots due to the cohesion of water molecules.
4. Mass flow translocation between the source and the sink occurs due to a turgor pressure gradient.

Xylem transports air by:
1. the proton pump
2. active transport
3. chemiosmosis
4. air is not transported by xylem normally

All the following regarding the cohesion-tension model are true except:
1. Water movement is driven by transpiration.
2. The water potential of atmospheric air is more positive than that for xylem.
3. Cohesion represents the tendency for water molecules to stick together by hydrogen bonds.
4. The physical forces in the capillary-sized xylem cells make it easier to overcome gravity.

The most important problem faced by most plants during flooding is:
1. inability to receive sunlight
2. leaching of nutrients
3. damage to the root system
4. oxygen deprivation