Plant Transport and Physiology

Temporary wilting occurs when plants lose turgor during the day due to high transpiration rates exceeding water uptake, but recover at night when transpiration slows and roots can catch up. Permanent wilting occurs when soil water is permanently unavailable. Guttation is water droplet excretion from leaf margins, while exudation is general oozing of fluids.

About 90% of water absorbed by herbaceous plants is lost through transpiration. This high loss is the trade-off for opening stomata for CO2 uptake during photosynthesis. The other percentages (80%, 60%, 40%) underestimate actual transpiration losses in most herbaceous plants.

Wheat and other grasses (monocots) have dumb-bell shaped guard cells, while dicots like beans, groundnut, and sunflower have kidney-shaped guard cells. This structural difference is a key anatomical feature distinguishing monocots from dicots in their leaf anatomy.

Root pressure builds up in roots when water absorption exceeds water loss. This occurs when transpiration is low (minimal water loss from leaves) and absorption is high (active water uptake by roots). Option A correctly identifies this condition. Option B (high transpiration) would reduce root pressure, and Option C (both low) would not generate significant pressure. Option D describes conditions that would deplete water pressure.

Guard cells contain chloroplasts and photosynthesize during daylight. They produce sugars like glucose, which lowers the guard cell's water potential. Water enters by osmosis, increasing turgor pressure and causing stomata to open. Option A correctly explains the mechanism. Options B and C describe structural features but not the cause of opening. Option D states the purpose, not the cause.

When CO2 concentration rises around a leaf, it triggers a feedback mechanism - stomata partially close to reduce CO2 intake and conserve water. This decreases transpiration. Option D correctly describes this response. Options A and B are incorrect because high CO2 causes closure, not opening. Option C is incorrect because transpiration is affected through stomatal behavior.

Wilting occurs when water loss exceeds water uptake, causing loss of turgor pressure. High temperature (Option A) increases transpiration rate significantly, which can lead to wilting if water absorption cannot keep up. Options B and C (high humidity, rainfall) would reduce water stress. Option D is incomplete - absorption itself is not a condition; rather, insufficient absorption causes wilting.

Water potential (Ψ) is the sum of its components. In plant physiology, Ψ = Ψs + Ψp, where Ψs (or yw) is solute potential (osmotic potential) and Ψp (or yp) is pressure potential (turgor pressure). Option D shows this relationship correctly (ys + yp, using subscripts for solute and pressure). Options A, B, and C are incorrect representations of the water potential equation.

When plant cells are placed in distilled water (pure water with no solutes), water enters the cells by osmosis since the cell has higher solute concentration. Water influx increases turgor pressure, making the cells turgid (Option A). Flaccid (B) means no turgor. Plasmolysed (C) occurs when water leaves the cell in hypertonic solution. Impermeable (D) is unrelated.

Increased CO2 concentration around leaves triggers stomatal closure as a regulatory response. However, this is typically partial closure (Option A), not complete closure. Complete closure would severely limit photosynthesis. Opening (C) would occur in low CO2 conditions. No effect (D) is incorrect because CO2 levels directly influence stomatal aperture through feedback mechanisms.

Root pressure is the positive pressure that develops in the roots due to active water absorption. It is maximum when transpiration is very low (usually at night or high humidity) because less water is being pulled up by transpiration pull, and absorption remains high due to active transport in roots. This allows water to be pushed up the xylem. When transpiration is high, the tension created by transpiration pull dominates over root pressure.

Zinc deficiency causes exanthema (also known as mottle leaf) in citrus plants. Symptoms include yellowish mottling between leaf veins, small narrow leaves, stunted growth, and reduced fruit size. Zinc is essential for several enzyme systems including carbonic anhydrase and alcohol dehydrogenase. Manganese deficiency causes different symptoms (interveinal chlorosis), boron deficiency causes corking and cracking, and copper deficiency causes wilting and dieback.

 Deficiency of molybdenum causes mottling and necrosis of leaves.

 Root hairs do not play any role in both water and mineral intake.