When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released. The increase of which of the following ions in the cytosol of the guard cells is responsible for ultimately bringing about a closure of stomata?
1. Calcium
2. Magnesium
3. Potassium
4. Hydrogen

Various factors affect stomatal movement. Which of the following is not a correct relation between the factor and stomatal movement?
1. Stomata open in the presence of light and close in darkness.
2. Stomata tend to open more with an increase in temperature especially up to 30$°$C.
3. Water stress induces stomatal closure.
4. With an increase in carbon dioxide concentration inside the leaf, the stomata open.

Mass flow of liquid water from roots to the leaves is primarily driven by:
1. Root pressure
2. Capillary action
3. Water potential differences
4. Active transport

If a plant is incapable of bringing in enough water to remain in equilibrium with transpiration, it can result in:
1. Cavitation
2. Crenation
3. Immediate death of root
4. Opening of stomata

Phenylmercury acetate, aspirin and ABA in plant physiology act as:
1. Plant growth activators
2. Paracrine signals
3. Cofactors for metabolism
4. Anti transpirants

Identify the incorrect statement regarding cohesion-tension theory that explains the process of water flow upwards through the xylem of the plants:

1. Transpiration in leaves creates tension (differential pressure) in the cell walls of mesophyll cells.

2. Because of this tension, water is being pulled up from the roots into the leaves.

3. The pull is helped by cohesion (the stickiness between water molecules and the hydrophilic cell walls of plants) and adhesion (the pull between individual water molecules, due to hydrogen bonds).

4. This mechanism of water flow works because of water potential (water flows from high to low potential), and the rules of simple diffusion.

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?

Consider the following events occurring during mass flow [pressure flow] of phloem sap at the source. The initial events are given in correct chronological sequence. But some of the statements carry mistakes regarding the principles of the process. Identify them:
I. The sucrose is passively transported to the companion cells of the smallest veins in the leaves.
II. The sucrose is actively transported from the companion cells to the sieve tube elements.
III. Water moves by osmosis from the nearby xylem in the same leaf vein.
IV. Hydrostatic pressure moves the sucrose and other substances through the sieve tube cells, towards a sink.
1. I and II only
2. III and IV only
3. I, II and III only
4. I, II, III and IV

With respect to the mass flow translocation of phloem sap, the following events are given in the correct chronological sequence. Identify the statements that do not carry any mistake regarding the principles of the process:
I. In the storage sinks sucrose is removed into apoplast prior to entering the symplast of the sink.
II. Water moves out of the sieve tube cells by osmosis.
III. The phloem sugar is removed by the cortex of both stem and root, and is consumed by cellular respiration or else converted into starch.
IV. Finally relatively pure water is left in the phloem and this is thought to leave by osmosis or be drawn back into nearby xylem vessels by suction of the transpiration pull.
1. I, II and III only
2. I, II and IV only
3. II, III and IV only
4. I, II, III and IV