Survival and Response

Question 1

State what organisms do to increase their chances of survival.

Answer 1

Respond to stimuli, which are changes in the external and internal environment.

Question 2

What is the point of taxis and kinesis?

Answer 2

Enable mobile organisms to stay in a favourable environment.

Question 3

What is a taxis?

Answer 3

A directional response to a stimulus.

Question 4

Describe how organisms move in response to a taxis.

Answer 4

Towards or away from a stimulus.

Question 5

What is a phototaxis?

Answer 5

Where organisms move directly towards or away from light.

Question 6

What is a chemotaxis?

Answer 6

Organisms move directly towards or away from a chemical.

Question 7

What does positive taxis mean?

Answer 7

The organism moves towards the stimulus.

Question 8

What does negative taxis mean?

Answer 8

The organism moves away from the stimulus.

Question 9

What are kinesis?

Answer 9

Non directional responses.

Question 10

State the 2 things that kinesis measure.
What do these depend on?

Answer 10

Speed of movement.
Rate of change of direction.
These all depend on the intensity of the stimulus.

Question 11

State 3 things that organisms must be able to in order to survive.
(2 of these things the organisms must be able to find, the other the organism must avoid happening).

Answer 11

Find favourable conditions to live.
Find food.
Avoid being eaten.

Question 12

Name the type of cell that detects a change in the environment.

Answer 12

Receptor cell.

Question 13

Name 2 effectors.

Answer 13

Muscle
Glands

Question 14

Name 2 coordinators.

Answer 14

Brain and Spinal Cord

Question 15

Briefly describe the reflex arc.

Answer 15

A stimulus is detected by a receptor.
Sensory neurone.
The response is processed by coordinator in a relay neurone (Brain or spinal cord).
Motor neurone.
A response is produced by a gland or muscle (nerve).

Question 16

Why do reflex arcs need to be autonomic?

Answer 16

So we can quickly respond to danger without learning a response.
This prevents harm to body tissues.

Question 17

State 2 roles of growth factors in flowering plants. Give examples.

Answer 17

Specific growth factors (hormones, such as auxins) from growing regions (shoots).
Regulate growth of other tissues in response to directional stimuli. (Tropism)

Question 18

What is a tropism?

Answer 18

Growth towards a stimulus.

Question 19

What is IAA (indoleacetic acid) an example of?

Answer 19

An auxin, which is a growth hormone.

Question 20

In shoots, how do high concentrations of IAA affect cell elongation?

Answer 20

Stimulates cell elongation.

Question 21

In roots, how do high concentrations of IAA affect cell elongation?

Answer 21

Inhibit cell elongation.

Question 22

What is a phototropism?
What are positive/negative phototropisms?

Answer 22

Growth response to light
Positive phototropisms cause growth towards light.
Negative phototropisms cause growth away from light.

Question 23

Describe positive and negative gravitropism caused by IAA.

Answer 23

1. Cells in tip of shoot / root produce IAA
2. IAA diffuses down shoot / root (evenly initially)
3. IAA moves to lower side of shoot / root (so conc. ↑)
4. In shoots this stimulates cell elongation whereas in roots this inhibits cell elongation
5. So shoots bend away from gravity whereas roots bend towards gravity

Question 24

Describe positive and negative phototropism caused by light in shoots and roots.

Answer 24

1. Cells in tip of shoot / root produce IAA → IAA diffuses
   down shoot / root (evenly initially)
2. IAA moves to shaded side of shoot / root (so conc. ↑)
3. In shoots this stimulates cell elongation whereas in
   roots this inhibits cell elongation
4. So shoots bend towards light
   whereas roots bend away from light