Transport in Plants MCQs

Study the structural details of guard cells and stomatal action:

I. Stomatal opening and closing is directly driven by changes in turgidity within the flanking guard cells.
II. The inner wall of each guard cell (towards the pore) is thin and elastic, while the outer wall is thick.
III. Cellulose microfibrils in guard cell walls are oriented radially rather than longitudinally, facilitating opening.
IV. Under water stress, guard cells lose turgor, causing the elastic inner walls to regain their original shape and close the stoma.

Which of the statements are correct?

Examine the variables influencing transpiration and stomatal distribution:

I. Transpiration is affected by external factors like temperature, light, relative humidity, and wind speed.
II. Plant factors affecting transpiration include the number of stomata, percent of open stomata, and water status.
III. A dorsiventral (dicotyledonous) leaf typically has a greater number of stomata on its upper epidermis.
IV. An isobilateral (monocotyledonous) leaf typically has a roughly equal stomatal count on both surfaces.

Which of the statements are correct?

Consider the evolutionary adaptations of plants balancing photosynthesis and transpiration:

I. Evaporative cooling from transpiration can cool leaf surfaces by 10 to 15°C.
II. C₄ photosynthetic plants are twice as efficient as C₃ plants in terms of carbon fixation (sugar synthesis).
III. C₄ plants lose twice as much water as a C₃ plant for the same amount of CO₂ fixed.
IV. Transpiration maintains cell turgidity, which supports plant shape and structure.

Which of the statements are correct?

Examine the physiological processes behind root mineral absorption:

I. Because mineral ions are dissolved in soil water, they are always passively absorbed by root hairs.
II. Most minerals enter the root by active transport into the cytoplasm of epidermal cells, requiring ATP.
III. Active accumulation of ions in roots lowers root water potential, facilitating water uptake via osmosis.
IV. Transport proteins of endodermal cells are critical control points where the plant adjusts the types and quantities of solutes reaching xylem.

Which of the statements are correct?

Study the fate of mineral nutrients within the plant vascular system:

I. The primary sinks for mineral elements are growing regions like meristems, young leaves, flowers, and fruits.
II. Structural elements like calcium are highly mobile and easily remobilized from senescent leaves to growing tips.
III. Nitrogen, phosphorus, potassium, and sulfur are readily remobilized from older dying leaves to younger regions.
IV. Xylem strictly transports inorganic minerals, whereas phloem exclusively transports organic compounds.

Which of the statements are correct?

Consider the following statements regarding source-sink relationships during phloem transport:

I. The source-sink relationship in plants is permanent and never gets reversed across seasons.
II. Sugar stored in roots can be mobilized to become a source of food in early spring when buds act as sinks.
III. Movement of organic food in the phloem is bi-directional (upwards or downwards), whereas xylem transport is always unidirectional.
IV. Phloem sap contains mainly water and sucrose, but other sugars, hormones, and amino acids are also translocated.

Which of the above statements are correct?

Analyze these statements concerning the loading of sugars at the photosynthetic source:

I. Glucose synthesized during photosynthesis is directly loaded into the sieve tubes without any modification.
II. Glucose is converted to sucrose (a disaccharide) before it is transported into the companion cells and sieve tubes.
III. Phloem loading of sucrose into sieve tubes is a purely passive process occurring via simple diffusion.
IV. The active transport of sucrose into the sieve tube cells sets up a hypertonic condition in the phloem.

Which of the above statements are correct?

Examine the physical changes that occur immediately following phloem loading:

I. Water from the adjacent xylem vessels moves into the phloem by osmosis, following the water potential gradient.
II. The osmotic entry of water into the phloem sieve tubes causes a significant decrease in turgor pressure.
III. High hydrostatic (turgor) pressure builds up inside the sieve tubes, facilitating the bulk flow of sap toward areas of lower pressure.
IV. Sieve tube elements form long continuous columns because of perforated end walls called sieve plates.

Which of the above statements are correct?

Study the following statements regarding the unloading process at the metabolic sink:

I. Sinks actively transport sucrose out of the phloem sap and into the target cells for utilization or storage.
II. As sugars are removed from the phloem at the sink, the osmotic pressure inside the sieve tubes increases.
III. The active removal of solutes produces a high water potential in the phloem at the sink.
IV. Water passes out of the phloem at the sink and eventually returns to the xylem.

Which of the above statements are correct?

Consider the cytological properties of mature sieve tube elements:

I. Sieve tube cells are dead at maturity, lacking cytoplasm, similar to xylem tracheids.
II. Sieve plates are perforated end walls that allow continuous cytoplasmic strands to link adjacent sieve cells.
III. Sieve tube elements depend on companion cells for metabolic support because mature sieve cells lack a nucleus.
IV. Sieve tube transport is purely physical and does not require living protoplasts.

Which of the above statements are correct?