Topic 6–A: Stimuli and Responses- 1. Survival and response

Question 1

How do organisms increase their chances of survival?

Answer 1

By responding to changes in their external event

Question 2

Examples of animal and plants responding to their environment

Answer 2

• Animals can move away from harmful environments such as places that are too hot or too cold
• Plants can’t actually move themselves, but they can change the way they grow in an attempt to find more favourable environmental conditions. E.g. seedlings growing in dark conditions can rapidly develop very long thin stems to increase their Chances of finding light

Question 3

What do organisms also respond to?

Answer 3

• Changes in their internal environment to make sure that the conditions are always optimal for their metabolism

Question 4

Definition of stimulus

Answer 4

• A change in an organisms internal or external environment
• E.g. change in temperature

Question 5

What do simple mobile organisms have?

Answer 5

• They have simple responses to keep them in a favourable environment
• E.g. woodlice

Question 6

What response can simple responses either be?

Answer 6

1. Tactic (taxis)
2. Kinetic (kinesis)

Question 7

Tactic response (taxis)

Answer 7

• Directional movement in response to a stimulus
• The direction of this stimulus affects the response

Question 8

Example of a tactic response

Answer 8

• Woodlice show a tactic response to light
• They move away from a light source
• This helps them survive as it keeps them concealed under stones during the day so they’re safe from predators
• It keeps them in damp conditions which reduces water loss

Question 9

Kinetic response (kinesis)

Answer 9

• Non-directional (random) movement in response to a stimulus.
• The intensity of the stimulus affects the response

Question 10

Example of a kinetic response

Answer 10

• Woodlice show a kinetic response to humidity
• In high humidity, they move slowly and turn less often so that they stay where they are
• As the air gets drier, they move faster and turn more often, so that they move into a new area
• This response helps woodlice move from drier air to more humid air
• This improves their chances of survival- it reduces their water loss and it helps them concealed