Survival + Response

Question 1

What is a stimulus?

Answer 1

A detectable change in the internal or external environment of an organism that elicits a response

Question 2

Give two examples of how responding to stimuli aids survival

(predation, temp. food)

Answer 2

1. Moving away from predators or extremes of temperature
2. Moving towards a source of food

Question 3

How does responding to stimuli link to natural selection?

Answer 3

Organisms with appropriate responses are more likely to survive, reproduce and pass on advantageous alleles, creating a selection pressure

Question 4

What is the correct sequence of events in response to a stimulus?

Answer 4

Stimulus -> receptor -> coordinator -> effector -> response

Question 5

What is a taxis?

Answer 5

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

Question 6

How do motile organisms respond in a taxis?

Answer 6

By moving their whole body either towards a favourable stimulus or away from an unfavourable one

Question 7

What is the movement of an organism towards a stimulus known as?
What is the movement of an organism away from a stimulus known as?

Answer 7

Movement towards a stimulus = positive taxis

Movement away from a stimulus = negative taxis

Question 8

Give an example of a positive chemotaxis (bacteria) and outline a benefit for the organism

Answer 8

Some bacteria move towards regions of higher glucose concentration because it increases survival as the glucose acts as a source of food

Question 9

Give an example of a negative phototaxis (earthworms) and outline a benefit for the organism

Answer 9

Earthworms show a negative taxis (phototaxis), and move away from light. This is so they are taken into the soil, conserve water, locate food and avoid predators

Question 10

What is a kinesis?

Answer 10

A form of response where an organism changes its speed and the rate at which it changes direction in response to a stimulus

Question 11

Is kinesis directional or non directional response?

Answer 11

Kinesis involves an animal responding to a stimulus but not directionally

Question 12

Why is kinesis important when a stimulus is less directional?

Answer 12

Because the factors like humidity and temperature do not always produce a clear gradient from one extreme to another

Question 13

How does an organism respond if it crosses a sharp boundary between favourable and unfavourable environments?

Answer 13

It’s rate of turning increases, raising the chance of a quick return to a favourable condition

Question 14

How does kinesis in woodlice increase their chances of survival?

Answer 14

Kinesis keeps woodlice in damp conditions, preventing water loss and reduces the risk of drying out

Question 15

How does an organism respond if it moves deeper into an unfavourable environment?

Answer 15

Its rate of turning decreases, moving in long straight lines with occasional sharp turns, increasing the chance of reaching a new favourable environment

Question 16

How do woodlice respond when moving from a damp area to a dry one?

Answer 16

They move more rapidly and change direction more often, increasing their chances of returning to the damp area

Question 17

How do woodlice behave once they return to a damp area?

Answer 17

They slow down and change direction less often, so they remain in the favourable damp area

Question 18

What is a tropism?

Answer 18

When part of a plant has a directional growth response to a stimulus

Question 19

What is a positive phototropism?

Answer 19

When part of a plant grows towards light, it is positive phototropism

Question 20

How do positive phototropism and negative gravitropism benefit plant shoots?

Answer 20

They place leaves in the most favourable position to capture light for photosynthesis

Question 21

What is a positive gravitropism?

Answer 21

When part of the plants grows towards gravity

Question 22

How do negative phototropism and positive gravitropism benefit plant roots?

Answer 22

They increase the chance roots will grow into the soil, where they can absorb water and mineral ions

Question 23

What is a negative phototropism?

Answer 23

When a part of the plant grows away from the light

Question 24

What type of phototropism does the shoots/roots show?

Answer 24

Shoots = positive phototropism

Roots = negative phototropism

Question 25

What is a negative gravitropism?

Answer 25

When part of a plant grows away from gravity

Question 26

What type of gravitrotropism does the shoots/roots show?

Answer 26

Shoot = negative gravitropism Roots = positive gravitropism