Plant Transport and Physiology

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.

Lotus is a hydrophyte with floating leaves. Its upper surface naturally has a waxy cuticle that repels water. Adding additional wax coating would block stomata (if present) or interfere with gas exchange and transpiration, thereby hindering metabolic processes. Hydrilla, Pistia, and Vallisneria are also aquatic plants but their leaf structure and metabolic processes are not primarily dependent on the upper surface wax coating in the same way.

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.

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

The cell wall is the rigid outer layer made of cellulose in plant cells that provides structural support and protection. It lies outside the plasma membrane. Plasmodesmata are channels connecting cells. Lamella is the middle lamella between cells. Unit membrane refers to the membrane structure itself.

As the cells reach their maximum length, many epidermal cells develop lateral protrusions called root hairs. These serve to increase surface area for better absorption.

In open aestivation the petals or sepals do not overlap or even touch each other. Example: Corolla in Brassica.

Cuticular transpiration is minimal, not large, because the cuticle is a waxy waterproof layer. Lenticular transpiration is indeed insignificant (less than 1%) compared to stomatal transpiration (90%+). Stomata are correctly described as minute pores on leaf epidermis. Guttation occurs in high humidity/soil moisture conditions, not dry conditions - it happens when transpiration is limited but root pressure continues.

When guard cells have lower (more negative) water potential than adjacent cells, water enters them by osmosis, making them turgid. Turgid guard cells bend outward due to uneven cell wall thickening, opening the stomatal pore. Lower water potential drives water uptake, not closure.

Potassium (K+) ion movement is the primary driver of stomatal movement. K+ ions are pumped into guard cells to open stomata (lowering water potential, causing water uptake) and pumped out to close them (raising water potential, causing water loss). Mg++, Mn++, and Cl- are not involved in stomatal mechanism.

Heliotropism is the diurnal motion of plant parts (flowers or leaves) in response to the direction of the sun.

Sunlight heats the mesophyll cell walls, causing water to evaporate into the intercellular spaces. This creates a water vapour gradient between these spaces and the external atmosphere. Option A correctly describes this mechanism, while B incorrectly states water fills the spaces (it's vapour, not liquid). C describes xylem transport, not vapour creation, and D is too vague.