6 Response to stimuli

Question 1

What is a stimulus?

Answer 1

A change in the environment of an organism that leads to a response.

Question 2

How does responding to a stimuli increase chances of survival?

Answer 2

1. Organism detects and moves away from harmful stimuli,e.g. predators and extreme temperatures.
2. Organism detects and moves towards a source of food, aiding survival.

Question 3

What are stimuli detected by?

Answer 3

Detected by receptors, receptors are specific to one type of stimulus.

Question 4

What are the sequence of events that produces a response?

Answer 4

1. Stimulus
2. Receptor
3. Coordinator
4. Effector
5. Response

Question 5

Definition of taxis:

Answer 5

A simple response whose direction is determined by the direction of the stimulus. Motile organisms respond by moving their body towards a favourable stimulus or away from an unfavourable one.

Question 6

Describe the two types of taxes:

Answer 6

Positive taxis - move towards stimuli,e.g.single cell algae move towards the light, require light to photosynthesise.
Negative taxis - move away from stimuli,e.g.earthworms move away from light as they live in the soil which is dark.

Question 7

Kinesis definition:

Answer 7

A response in which the organism does not move towards or away from the stimulus. It changes the speed at which it moves and the rate at which it changes direction.

Question 8

Definition of Tropism:

Answer 8

The growth of part of a plant in response to a directional stimulus.
Positive response - Plant grows towards stimuli
Negative response - Plant grows away from stimuli

Question 9

Example of a plant growth factor

Answer 9

Indoleacetic acid (IAA)
It belongs to a group of substances called auxins and controls plant elongation.