Survival

Question 1

Define stimulus.

Answer 1

A detectable change in the internal or external environment of an organism that leads to a response in the organism.

Question 2

What is the purpose of responding to a stimuli?

Answer 2

The ability to respond to stimuli is a characteristic of life and increases the chance of survival.

Question 3

In what way is there a selection pressure favouring organisms with appropriate responses to stimuli?

Answer 3

The organisms that survive (by responding to stimuli) have a greater chance of raising offspring and passing their alleles onto the next generation. Therefore, there is a selection pressure which favours organisms with more appropriate responses.

Question 4

Stimuli are detected by ___________

Answer 4

Receptors.

Question 5

A _______________ forms a suitable response to a stimulus.

Answer 5

Coordinator.

Coordination may be at a molecular level or involved a large organ eg the brain.

Question 6

A response is produced by an _________.

Answer 6

Effector.

Question 7

What are the two means of communication throughout the body to respond to stimuli?

Answer 7

The nervous system and the hormonal system.

Question 8

Outline the sequence of events after detecting a stimulus.

Answer 8

Stimulus ->
Receptor ->
Coordinator ->
Effector ->
Response

Question 9

Define taxis.

Answer 9

A simple response whose direction is determined by the direction of the stimulus.

Question 10

How does an organism respond to a taxis?

Answer 10

Motile organisms respond directly to environmental changes by moving its whole body either towards a favourable stimulus or away from an unfavourable one.

Question 11

Define kinesis.

Answer 11

The organism doesn’t move towards or away from a stimulus. Instead, it changes the speed at which it changes direction.

The stimulus is less directional (eg humidity / temperature).

Question 12

Define tropism.

Answer 12

The growth of a plant in response to a directional stimulus.

Question 13

Give an example of why a plant might exhibit tropisms.

Answer 13

Positive phototropism - so their leaves are in the most favourable position to capture light for photosynthesis.

Positive geotropism - increases the probability that roots will grow into the soil, where they’re better able to absorb water and mineral ions.

Question 14

Name 3 things plants respond to.

Answer 14

Light, gravity and water.

Question 15

Why are shoots positively phototrophic?

Answer 15

Because light is needed for photosynthesis.

Question 16

Why are roots positively hydrotrophic?

Answer 16

In order to absorb water for use in photosynthesis and other metabolic processes, as well as for support.

Question 17

Give an example of a plant growing factor.

Answer 17

IAA (indoleacetic acid). This is an auxin.

Question 18

Outline IAA in the shoot for phototropism.

Answer 18

In the shoot, IAA concentration increases on the shaded side. Cells elongate and the shoot bends towards the light.

Question 19

Outline IAA in the root for phototropism.

Answer 19

IAA concentration increases in the shaded side.

As a result, growth is inhibited so the root bends away from the light.

Question 20

Outline IAA in the shoot for geotropism.

Answer 20

In the shoot, IAA concentration increases on the lower side - so cells elongate so the shoot grows upwards.

Question 21

Outline IAA in the roots for geotropism.

Answer 21

In the root, IAA concentration increases in the lower side - growth is inhibited so the root grows downwards.