IB Bio 9.3

The photomicrograph shows a section through the top of a plant shoot.

What are the structures labelled X and Y?

• A. Developing Bud, Xylem

• B. Developing Leaf, Xylem

• C. Developing bud, meristem

• D. Developing leaf, meristem

How does auxin exert its effect on plant cells?

• A. Acts directly on the cell wall, causing expansion

• B. Binds to a receptor resulting in expression of genes

• C. Binds to a receptor resulting in expression of genes

• D. Causes the cell to undergo cell division

How does auxin contribute to phototropism?

• A. It increases production of light-sensitive proteins.

• B. It increases growth of cells on the shaded side of the stem.

• C. It inhibits growth of axillary buds.

• D. It inhibits stem elongation.

Expansin is a plant protein that loosens connections between cellulose fibres in plant cell walls, allowing growth. In what location would expression of the expansin gene be expected to be increased?

• A. On the shaded side of a shoot being exposed to light

• B. On the light side of a shoot being exposed to light

• C. On the shaded side of a leaf that is transpiring rapidly

• D. On the light side of a leaf that is transpiring rapidly

What is/are the effect(s) of auxin in plants?

I.   Increasing the rate of cell elongation in stems

II.  Changing the pattern of gene expression in shoot cells

III. Detecting the direction of light

• A. I only

• B. I and II only

• C. II and III only

• D. I, II and III

What allows most plants to continue producing more roots, leaves or stems throughout their life?

• A. Auxin

• B. Meristems

• C. Phloem

• D. Cellulose

How do auxins cause plant shoots to grow towards light?

• A. Increase cell division on the side of the stem near the light source

• B. Increase cell division on the side of the stem away from the light source

• C. Increase cell elongation on the side of the stem near the light source

• D. Increase cell elongation on the side of the stem away from the light source

A man attaches a bird box to the trunk of a dicotyledonous tree. A few years later he returns to the tree and finds that his bird box is still attached and the tree is much taller. How high will his bird box be from the ground?

• A. Unchanged as growth from the apical meristem would be above the box

• B. Unchanged as growth from the lateral meristem would be above the box.

• C. Higher as growth from the apical meristem would be below the box

• D. Higher as growth from the lateral meristem would be below the box.