USABO - USA Biology Olympiad Plant Anatomy and Transport Questions and Answers

Question 1

A botanist is studying a plant adapted to an arid environment. Which of the following is an anatomical or physiological adaptation she would LEAST expect to find?

Accepted Answer

Large, broad leaves with a high density of stomata.

Answer

A thick, waxy cuticle on the leaves and stems.

Answer

Stomata located in deep pits or crypts on the leaf surface.

Answer

Crassulacean acid metabolism (CAM) photosynthesis.

Question 2

The Casparian strip is a critical component of the root endodermis. What is its primary function?

Accepted Answer

To force water and solutes to pass through the plasma membrane of endodermal cells.

Answer

To increase the surface area for water absorption.

Answer

To provide structural support to the root cortex.

Answer

To store starch and other carbohydrates for the plant.

Question 3

According to the pressure-flow hypothesis, what directly generates the hydrostatic pressure that drives the movement of sap in the phloem?

Accepted Answer

The osmosis of water into sieve-tube elements at the source following active loading of sugars.

Answer

The active transport of water from xylem to phloem at the sink.

Answer

The force of gravity pulling the dense, sugary sap downwards.

Answer

The contraction of companion cells, which squeezes sap through the sieve tubes.

Question 4

A plant cell has a solute potential (Ψs) of -0.8 MPa and a pressure potential (Ψp) of +0.5 MPa. The cell is placed in a beaker of pure water (Ψ = 0 MPa). What will be the initial net direction of water movement?

Accepted Answer

Into the cell, because its water potential is -0.3 MPa.

Answer

Out of the cell, because the pressure potential is positive.

Answer

There will be no net movement, as the potentials are balanced.

Answer

Into the cell, because its solute potential is more negative than the surrounding water.

Question 5

Which of the following correctly describes the function of companion cells in the phloem?

Accepted Answer

They provide metabolic support and load/unload sugars for the sieve-tube elements.

Answer

They form the primary structural tube for translocation.

Answer

They are dead at maturity and provide a hollow conduit for sap flow.

Answer

They regulate the opening and closing of sieve plates.

Question 6

In the secondary growth of a dicot stem, the vascular cambium is responsible for producing which tissues?

Accepted Answer

Secondary xylem and secondary phloem.

Answer

Pith and cortex.

Answer

Epidermis and periderm.

Answer

Primary xylem and primary phloem.