Transport in Plants MCQs

Analyze how a solute's physical properties affect its movement across the plasma membrane:

I. Lipid-soluble substances dissolve easily in the membrane and diffuse across it much faster than lipid-insoluble ones.
II. Solutes with a hydrophilic moiety find it extremely easy to pass directly through the hydrophobic lipid core of the membrane.
III. Specialized membrane proteins provide selective sites and channels to facilitate the crossing of hydrophilic substances.
IV. Facilitated diffusion of hydrophilic molecules can drive their net transport from lower to higher concentration using ATP.

Which of the above statements are correct?

Examine the structural adaptations of mature phloem sieve tube elements:

I. Sieve tube elements are dead at maturity, containing hollow lignified walls similar to xylem vessels.
II. End walls of sieve tube cells are perforated to form sieve plates, which facilitate cytoplasmic continuity.
III. Sieve tube elements lack a nucleus, ribosomes, and a vacuole at maturity, relying on companion cells for metabolic maintenance.
IV. Cytoplasmic strands extend directly through the perforations of sieve plates to form continuous trans-cellular filaments.

Which of the above statements are correct?

Review the energetic differences between phloem loading at the source and unloading at the sink:

I. Loading of sucrose into companion cells and sieve tube elements at the source requires the active expenditure of ATP.
II. Unloading of sucrose out of sieve tubes into sink storage or metabolic cells occurs purely via passive simple diffusion.
III. Active phloem loading at the source sets up a hypertonic condition that draws water from the adjacent xylem.
IV. Active unloading at the sink decreases the solute concentration, leading to a high water potential inside the phloem.

Which of the above statements are correct?

Consider the physical parameters that alter transpirational water loss in terrestrial plants:

I. High relative humidity in the atmosphere increases the rate of transpiration by steepening the water vapor gradient.
II. Increasing ambient temperature increases the kinetic energy of water molecules, accelerating transpiration.
III. High wind speed sweeps away the boundary layer of saturated air from the leaf surface, increasing water loss.
IV. Internal plant factors like the percentage of open stomata and canopy structure directly regulate transpiration.

Which of the above statements are correct?

Study these statements regarding the transport characteristics of the root endodermal layer:

I. The endodermis allows all solutes to cross its plasma membrane indiscriminately due to the absence of transport proteins.
II. The suberised Casparian strip blocks the apoplastic pathway, forcing water and solutes into the symplast.
III. Endodermal cell membranes contain selective transport proteins that act as critical control points for the plant.
IV. Due to the presence of the suberised Casparian strip, the endodermis can actively transport mineral ions in one direction only (into the vascular cylinder).

Which of the above statements are correct?

Three identical plant cells are placed in different external solutions:

Cell X is in a hypertonic solution and is fully plasmolysed.
Cell Y is in an isotonic solution and is flaccid.
Cell Z is in a hypotonic solution and is fully turgid.

Analyze the following statements:

I. Cell X has a negative pressure potential (Ψ_p < 0) or zero pressure potential, and its water potential is extremely low (highly negative).
II. The pressure potential (Ψ_p) of the flaccid Cell Y is equal to zero.
III. For the turgid Cell Z, the water potential (Ψ_w) reaches its maximum possible value, which can be zero if turgor pressure completely balances solute potential (Ψ_p = -Ψ_s).
IV. Water potential of Cell X is higher than the water potential of Cell Z.

Which of the above statements are correct?

Consider the physical nature of xylem vessels and tracheids in mature roots:

I. Tracheids and vessels are dead, hollow, lignified tubes that lack cytoplasm at maturity.
II. Because they lack living protoplasm, tracheids and vessels belong to the apoplastic pathway.
III. Water transport through these conduits is active and requires cellular ATP to drive the water column upward.
IV. These conduits form a continuous system of pipes spanning from the roots to the leaves.

Which of the above statements are correct?

Review the thermodynamic properties of solutions:

I. Liquid water molecules are in constant, rapid, and random motion, giving them kinetic energy.
II. Adding solutes to pure water increases the concentration of free water molecules, thereby raising the water potential.
III. Pure water has the maximum possible water potential, which is conventionally defined as zero.
IV. The magnitude of the reduction in water potential due to solute dissolution is called solute potential (Ψ_s) and is always negative.

Which of the above statements are correct?

Analyze the physiological response of stomata during water deficit:

I. Under water stress, the plant hormone abscisic acid is synthesized to promote guard cell turgidity.
II. When guard cells lose water, their turgor pressure drops, and they become flaccid.
III. As turgor is lost, the thick, elastic inner walls of the guard cells regain their original shape, closing the pore.
IV. Stomatal closure during drought is a vital adaptation that minimizes transpirational water loss to protect the plant.

Which of the above statements are correct?

Examine how nutrients are redistributed inside a perennial plant during senescence:

I. Mineral nutrients are fixed permanently within tissues and can never be remobilized once deposited.
II. Before leaf fall in deciduous plants, mobile nutrients are withdrawn from senescent leaves and exported to younger tissues.
III. Nitrogen, phosphorus, potassium, and sulfur are highly mobile elements that are readily remobilized.
IV. Structural components like calcium are highly mobile and easily withdrawn from aging leaves.

Which of the above statements are correct?