Transport in Plants — NEET UG practice

This question tests the meaning of key terms related to the physical properties of water that are important in plant water transport.

Cohesion (A) refers to the mutual attraction between water molecules themselves, which helps water form a continuous column inside the xylem. So A matches (II).

Adhesion (B) refers to water's attraction towards polar surfaces, such as the walls of xylem vessels, which helps water stick to the vessel walls as it rises. So B matches (IV).

Surface tension (C) arises because water molecules at the surface are more attracted to each other in the liquid phase than to the air above, creating a "skin-like" effect. So C matches (I).

Guttation (D) is the process where excess water is lost in liquid form (as droplets) from the edges of leaves, typically when root pressure is high and transpiration is low. So D matches (III).

Combining these: A-II, B-IV, C-I, D-III.

Hence, the correct answer is D.

Substances can cross a cell membrane either with the concentration gradient (from high to low concentration) or against it (from low to high concentration).

Movement with the gradient, such as facilitated diffusion, passive transport, and osmosis (for water), does not require energy since it follows the natural tendency of molecules to spread out.

However, moving ions against their concentration gradient means pushing them from a region of lower concentration to a region of higher concentration — this goes against the natural direction of movement and therefore requires an input of energy.

This energy-requiring process is called active transport, which uses ATP to pump ions or molecules across the membrane against their gradient.

Hence, since only active transport can explain movement against the concentration gradient, the correct answer is C.

Let's evaluate each statement about the effects of transpiration in plants.

Statement I says the force generated by transpiration (called transpirational pull) can lift a column of water more than 130 meters high inside the narrow xylem tubes. This matches known physiological measurements, since transpirational pull is strong enough to draw water to the tops of even very tall trees. So Statement I is correct.

Statement II says transpiration can cool leaf surfaces by 10 to 15 degrees through evaporative cooling — as water evaporates from the leaf surface, it absorbs heat energy from the leaf, lowering its temperature. This is a well-documented cooling effect. So Statement II is also correct.

Since both statements accurately describe real properties of transpiration, the correct answer is D.