3.6.1.1 Survival and response

Question 1

What is the purpose of organisms responding to changes in their environment?

Answer 1

To increase their chance of survival by avoiding harmful stimuli and moving towards beneficial conditions.

Question 2

What are specific growth factors in flowering plants?

Answer 2

Hormone-like substances that regulate growth by affecting tissues in response to directional stimuli.

Question 3

Where are specific growth factors produced in flowering plants?

Answer 3

In growing regions such as shoot and root tips.

Question 4

What is the role of indoleacetic acid (IAA) in phototropism?

Answer 4

IAA accumulates on the shaded side of a shoot causing cell elongation and bending towards the light.

Question 5

What is the role of indoleacetic acid (IAA) in gravitropism?

Answer 5

IAA accumulates on the lower side of roots inhibiting cell elongation and causing downward growth and on the lower side of shoots promoting elongation and upward growth.

Question 6

How does IAA affect cell elongation in shoots?

Answer 6

High concentrations of IAA stimulate cell elongation in shoots.

Question 7

How does IAA affect cell elongation in roots?

Answer 7

High concentrations of IAA inhibit cell elongation in roots.

Question 8

Define taxes.

Answer 8

Directional responses where an organism moves towards (positive) or away from (negative) a stimulus.

Question 9

Give an example of taxes.

Answer 9

Single-celled algae move towards light to increase the rate of photosynthesis (positive phototaxis).

Question 10

Define kineses.

Answer 10

Non-directional responses where the rate of movement or turning changes in response to stimulus intensity.

Question 11

Give an example of kineses.

Answer 11

Woodlice move more and turn less in dry conditions to increase their chance of finding a humid environment.

Question 12

What is a simple reflex?

Answer 12

A rapid involuntary response to a stimulus that protects an organism from harm.

Question 13

Describe the structure of a three-neurone simple reflex arc.

Answer 13

Involves a sensory neurone relay neurone and motor neurone.

Question 14

What is the function of a simple reflex arc?

Answer 14

To produce a rapid response without conscious thought protecting the organism from harm.

Question 15

Suggest two advantages of simple reflexes.

Answer 15

1. Rapid;
2. Protect against damage to body tissues;
3. Do not have to be learnt;
4. Help escape from predators;
5. Enable homeostatic control.

Question 16

Describe how indoleacetic acid (IAA) causes phototropism in shoots. (3)

Answer 16

1. Tip produces IAA;
2. IAA diffuses (into shoot)
3. (More) elongation of cells on one side (than other);,