survival and response

Question 1

What do organisms gain by responding to changes in their environment?

Answer 1

An increased chance of survival

Question 2

Stimulus

Answer 2

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

Question 3

Receptor

Answer 3

Detects a stimulus
(specific to one type of stimulus)

Question 4

Coordinator

Answer 4

Formulates a suitable response to a stimulus

Question 5

Effector

Answer 5

Produces a response to a stimulus

Question 6

What is the reflex arc? [7]

Answer 6

stimulus → receptor → sensory neurone → coordinator (CNS / relay neurone) → motor neurone → effector → response

Question 7

Why is a simple reflex important? [3]

Answer 7

• Rapid (short pathway) because only 3 neurones and few synapses (synaptic transmission is slow)
• Autonomic because doesn’t involve passage to brain, and doesn’t have to be learnt
• Protect from harmful stimuli e.g. escape from predator / prevents damage to body tissues

Question 8

Taxes

Answer 8

Directional responses by simple motile organisms who move towards a favourable stimulus (positive taxis) or away from an unfavourable one (negative taxis

Question 9

Give an example of taxes

Answer 9

Woodlice show a tactic response to light
Moving away from light keeps woodlice concealed under stones and away from predators improving chances of survival

Question 10

Kineses

Answer 10

Non-directional, behavioural responses by simple motile organisms who change the speed of movement or the rate of direction change, in response to a non-directional stimulus

Question 11

Give an example of Kineses

Answer 11

Woodlice show a kinetic response to humidity.
Moving faster / changing direction more often when air drier increases chances of moving to an area of higher humidity where woodlice will lose less water, improving chances of survival

Question 12

Tropism

Answer 12

Growth of a part of a plant in response to a directional stimulus
Positive tropism - growth towards stimulus
Negative tropism - growth away from stimulus

Question 13

What do plant responses to external stimuli involve?

Answer 13

growth factors (hormone-like growth substances)

Question 14

What do growth factors do?

Answer 14

Growth factors move from growing regions (e.g. shoot tips / leaves where they are produced) to other tissues, where they regulate growth in response to directional stimuli (e.g. Auxins, such as IAA)

Question 15

What is IAA?

Answer 15

An auxin (indoleacetic acid

Question 16

What effect do auxins have on plant growth in the shoots and the roots?

Answer 16

Auxins in the shoots promote cell elongation
Auxins in the roots inhibit cell elongation

Question 17

What is Phototropism?

Answer 17

Phototropism is a directional response to sunlight

Question 18

What is Gravitropism? (aka geotropism)

Answer 18

Gravitropism is a plant response to the stimulus of gravity

Question 19

Responses [4]

Answer 19

Phototropism
Shoots - Positive
Roots - Negative
Gravitropism
Shoots - Negative
Roots - Positive

Question 20

What response do plant shoots show to sunlight and why? [3]

Answer 20

• Plant shoots show positive phototropism
• Promoting cell elongation and growing towards the sun
• Maximising the amount of light they can absorb for photosynthesis

Question 21

What response do plant roots show to sunlight and why? [3]

Answer 21

• Plant roots show negative phototropism
• Inhibiting cell elongation and growing away from the sun
• Growing deeper into the soil, maximising water uptake

Question 22

How do auxins result in phototropism in the shoots? [5]

Answer 22

• Cells in tip of shoot produce IAA
• Which initially is evenly transported down the shoot
• IAA concentration increases on the shaded side
• Promoting cell elongation on shaded side
• Shoot bends towards light

Question 23

How do auxins result in gravitropism in the roots? [5]

Answer 23

• Cells in tip of root produce IAA
• Which initially is evenly transported through the root
• IAA concentration increases on the lower side of the root
• Inhibiting cell elongation on the lower side
• Root curves downwards towards gravity