Question 51 – Communication and homeostasis - Questions

Plants respond to their environments and to pests in various ways.

Describe the meaning of the term positive phototropism.

State the role of auxin (indole-3-acetic acid / IAA) in positive phototropism of plant shoots.

Plants can produce chemical defenses in response to herbivory (a biotic stress). Give one example of such a chemical and state how it defends the plant.

Mycorrhizae are symbiotic associations between fungi and plant roots. The fungal hyphae can connect the root systems of neighboring plants, forming a common mycorrhizal network (CMN).

When broad bean plants are attacked by aphids, they produce volatile organic compounds (VOCs) that attract predators of aphids. They can also signal neighboring plants through the CMN, priming them to release VOCs before they are attacked.

Scientists investigated this communication using pairs of broad bean plants.

This is the method that they use:

Grow a 'donor' plant and a 'recipient' plant together in the same pot.
Repeat to create 40 pairs of plants, divided into four treatment groups (10 pairs per group).
Enclose the roots of the 'recipient' plants in a mesh bag of a specific pore size.
Infest the 'donor' plants with aphids in half of the groups.

The treatment groups are summarized in the table below:

Group	Donor plant infested with aphids	Mesh bag around recipient roots
1	No	$μm0.5\ \mu\text{m}$ mesh bag (allows passage of soluble molecules but blocks hyphae)
2	Yes	$μm0.5\ \mu\text{m}$ mesh bag (allows passage of soluble molecules but blocks hyphae)
3	No	$μm40\ \mu\text{m}$ mesh bag (allows passage of soluble molecules and hyphae)
4	Yes	$μm40\ \mu\text{m}$ mesh bag (allows passage of soluble molecules and hyphae)

The scientists measured the emission rate of a defensive VOC (in arbitrary units) in the recipient plants at the start of the experiment and after 48 hours.

Suggest how the scientists could ensure that airborne volatile chemicals did not contribute to communication between plants in this investigation.

The results are shown in the table below:

Group	Mean VOC emission rate $±\pm$ standard deviation (arbitrary units) at start	Mean VOC emission rate $±\pm$ standard deviation (arbitrary units) after 48 h
1	$15 \pm 1$	$16 \pm 2$
2	$14 \pm 2$	$42 \pm 5$
3	$12 \pm 2$	$18 \pm 3$
4	$15 \pm 2$	$125 \pm 12$

The scientists conclude:

Aphid attack on the donor plants leads to a defense response (increased VOC emission) in the recipient plants.
This signaling is mediated by the common mycorrhizal network (hyphae).

Evaluate the support given by the results to the scientists' conclusions. You should comment on the quality of the scientists' data in your answer.

Plants respond to their environments and to pests in various ways.

Describe the meaning of the term positive phototropism.

State the role of auxin (indole-3-acetic acid / IAA) in positive phototropism of plant shoots.

Plants can produce chemical defenses in response to herbivory (a biotic stress). Give one example of such a chemical and state how it defends the plant.

Mycorrhizae are symbiotic associations between fungi and plant roots. The fungal hyphae can connect the root systems of neighboring plants, forming a common mycorrhizal network (CMN).

Scientists investigated this communication using pairs of broad bean plants.

This is the method that they use:

Grow a 'donor' plant and a 'recipient' plant together in the same pot.
Repeat to create 40 pairs of plants, divided into four treatment groups (10 pairs per group).
Enclose the roots of the 'recipient' plants in a mesh bag of a specific pore size.
Infest the 'donor' plants with aphids in half of the groups.

The treatment groups are summarized in the table below:

Group	Donor plant infested with aphids	Mesh bag around recipient roots
1	No	$μm0.5\ \mu\text{m}$ mesh bag (allows passage of soluble molecules but blocks hyphae)
2	Yes	$μm0.5\ \mu\text{m}$ mesh bag (allows passage of soluble molecules but blocks hyphae)
3	No	$μm40\ \mu\text{m}$ mesh bag (allows passage of soluble molecules and hyphae)
4	Yes	$μm40\ \mu\text{m}$ mesh bag (allows passage of soluble molecules and hyphae)

The scientists measured the emission rate of a defensive VOC (in arbitrary units) in the recipient plants at the start of the experiment and after 48 hours.

Suggest how the scientists could ensure that airborne volatile chemicals did not contribute to communication between plants in this investigation.

The results are shown in the table below:

Group	Mean VOC emission rate $±\pm$ standard deviation (arbitrary units) at start	Mean VOC emission rate $±\pm$ standard deviation (arbitrary units) after 48 h
1	$15 \pm 1$	$16 \pm 2$
2	$14 \pm 2$	$42 \pm 5$
3	$12 \pm 2$	$18 \pm 3$
4	$15 \pm 2$	$125 \pm 12$

The scientists conclude:

Aphid attack on the donor plants leads to a defense response (increased VOC emission) in the recipient plants.
This signaling is mediated by the common mycorrhizal network (hyphae).

Evaluate the support given by the results to the scientists' conclusions. You should comment on the quality of the scientists' data in your answer.

Communication and homeostasis

Question 25

Communication and homeostasis

Question 25

Communication and homeostasis

Question 25

Communication and homeostasis Questions

Communication and homeostasis

Question 25

Communication and homeostasis Questions