SAT - Biology Subject Plant Structure and Function Questions and Answers

Question 1

The upward movement of water through the xylem in a 30-meter tall oak tree is best explained by which of the following?

Accepted Answer

The cohesion of water molecules and the tension created by transpiration.

Answer

The cohesion-tension theory is the primary explanation for water transport over long distances in plants. Transpiration (evaporation of water from leaves) creates a negative pressure, or tension, that pulls the column of water up the xylem. The cohesive properties of water (molecules sticking together via hydrogen bonds) and adhesive properties (molecules sticking to xylem walls) ensure this column remains unbroken.

Question 2

A houseplant placed on a windowsill bends towards the light. This phenomenon, known as phototropism, is primarily mediated by the redistribution of which plant hormone?

Accepted Answer

Auxin

Answer

Phototropism is caused by the plant hormone auxin. When light strikes one side of the stem, auxin migrates to the shaded side. This higher concentration of auxin on the shaded side stimulates cell elongation, causing the stem to bend towards the light source.

Question 3

Which statement accurately compares the functions of xylem and phloem?

Accepted Answer

Xylem primarily transports water and minerals from the roots up, while phloem transports sugars from sources to sinks.

Answer

Xylem is responsible for the unidirectional transport of water and dissolved minerals from the roots to the rest of the plant. Phloem transports sugars (produced during photosynthesis) from a source (e.g., leaves) to a sink (e.g., roots, fruits), and this movement is bidirectional.

Question 4

The Casparian strip in the root endodermis is a critical structure for selective nutrient uptake because it:

Accepted Answer

forces water and solutes to pass through the selectively permeable membrane of endodermal cells.

Answer

The Casparian strip is a waxy, waterproof band that blocks the apoplastic pathway (movement through cell walls). This forces all water and dissolved minerals to cross the plasma membrane of an endodermal cell (the symplastic pathway) before entering the vascular cylinder (xylem). This ensures that the plant has selective control over which substances enter its transport system.

Question 5

Double fertilization, a process unique to angiosperms, involves the fusion of two sperm nuclei with which female gametophyte cells?

Accepted Answer

One sperm with the egg cell, and the other with the two polar nuclei in the central cell.

Answer

In double fertilization, one sperm nucleus fuses with the egg cell to form the diploid (2n) zygote, which develops into the embryo. The second sperm nucleus fuses with the two polar nuclei located within the large central cell, forming a triploid (3n) cell that develops into the endosperm, a nutrient-rich tissue.

SAT - Biology Subject Test Practice Test

SAT - Biology Subject Test Practice Test

SAT - Biology Subject Plant Structure and Function Questions and Answers