Plant Physiology and Biochemistry Questions and Answers

Answer: B

The key gives two.

Anaerobic respiration starts with glycolysis, which splits one glucose into two pyruvate molecules with a net gain of 2 ATP (4 made, 2 used). No further ATP is made when pyruvate is turned into lactate or ethanol, so the whole anaerobic yield per glucose is 2 ATP.

The wording "from pyruvate" is loose: strictly the conversion of pyruvate yields no ATP, and the 2 ATP are made earlier in glycolysis. The question is read as the net ATP at the end of glycolysis, which is two; one, three and five do not match any step.

Answer: D

Guttation is the loss of water as water droplets from the hydathodes of plants.

When the soil is moist and transpiration is low, for example at night, root pressure pushes xylem sap up and out through special pores, the hydathodes, at the tips and margins of leaves. The drops seen on grass blades in the early morning are guttation, not dew.

Loss of water vapour from the plant surface is transpiration. Sap oozing from a wounded or cut plant is bleeding. Option C mentions the xylem but leaves out the hydathodes, which is what defines guttation.

Answer: A

The ultimate electron donor and acceptor are \(H_{2}O\) and \(NADP^{+}\).

In the light reactions of photosynthesis, water is split at photosystem II (photolysis), releasing electrons, protons and oxygen; water is therefore the ultimate electron donor. The electrons pass through the electron transport chain and photosystem I to reduce \(NADP^{+}\) to NADPH, so \(NADP^{+}\) is the final electron acceptor.

\(CO_{2}\) is the carbon source that is later reduced in the Calvin cycle using NADPH, not the electron donor. \(NAD^{+}\) is the electron carrier of respiration, not of photosynthesis.

Answer: C

The key's answer is auxin and gibberellin.

Both auxins and gibberellins promote cell elongation, and both have been shown to stimulate the germination of pollen and the growth and elongation of the pollen tube towards the ovule.

Cytokinins mainly promote cell division rather than elongation, so the pairs built on them are weaker. 'Polynin' is not a known plant hormone, which rules out the first and last options.

Answer: C

The PAR range is 400 nm-700 nm.

Photosynthetically active radiation is the band of wavelengths that plants use for photosynthesis, from about 400 nm (blue-violet) to 700 nm (red), roughly the visible spectrum. Chlorophyll absorbs mostly in the blue and red parts of this band.

The other ranges either extend into the ultraviolet below 400 nm or stop short of the red end at 680 nm, so they do not match the standard definition.

Answer: B

The stress hormone is abscisic acid (printed 'Abscissic').

ABA builds up in plants under drought, salinity and cold. It closes stomata to reduce water loss, promotes dormancy of seeds and buds, and inhibits growth, helping the plant survive adverse conditions.

Gibberellins promote stem elongation and germination, auxins cell elongation and root formation, and cytokinins cell division and delay of senescence; all are growth promoters rather than stress hormones.

Answer: C

Kranz anatomy is found in the leaves of C₄ plants.

In C₄ plants such as maize, sugarcane and sorghum, the vascular bundles are surrounded by a ring of large, chloroplast-rich bundle sheath cells, with mesophyll cells arranged around them, a wreath-like ('Kranz') arrangement. CO₂ is first fixed in the mesophyll and then released in the bundle sheath, where the Calvin cycle runs.

C₃ and CAM plants lack this specialised bundle sheath, and 'C₂ plants' is not the standard category with Kranz anatomy.

Answer: A

The sunlight is transformed into chemical energy.

In photosynthesis, chlorophyll absorbs light energy and uses it to make glucose from carbon dioxide and water, releasing oxygen:

\[ 6CO_{2} + 6H_{2}O \rightarrow C_{6}H_{12}O_{6} + 6O_{2} \]

The energy of the light is stored in the chemical bonds of the glucose, which plants and the animals that eat them later release in respiration. So it becomes chemical energy.

'Physical energy' is not the form in which the energy is stored, so 'Both (A) and (B)' is wrong as well, and 'None of the above' is ruled out because chemical energy is correct.

Answer: A

The main ripening hormone is ethylene.

In climacteric fruits such as banana, mango, tomato and apple, ripening is triggered by a burst of ethylene production together with the respiratory climacteric. Ethylene switches on the genes for softening (cell-wall enzymes), colour change (chlorophyll breakdown, carotenoid synthesis), and sugar and aroma production, which is why it is used commercially to ripen fruit.

ABA mainly controls dormancy and stomatal closure, auxin promotes fruit set and growth, and gibberellin promotes fruit enlargement (as in grapes), but none of them is the main ripening hormone.

Answer: A

Apoplast transport takes place through non-living portion of the plant.

The apoplast is the continuous system of cell walls, intercellular spaces and xylem vessels outside the plasma membranes. Water moving by the apoplastic route travels through these non-living spaces without crossing any membrane, until the Casparian strip of the endodermis blocks it.

Movement through living cells is the symplast route, which passes from cytoplasm to cytoplasm through plasmodesmata, so the options naming living cells or plasmodesmata describe the symplast, and the 'both' option mixes the two routes.