Survival and response

Question 1

What is a stimulus? (1)

Answer 1

Detectable change in the environment which can be either external or internal and produces a response in the organism

Question 2

Why do organisms need to respond to changes in their environment? (1)

Answer 2

To increase survival and reproduction

Question 3

How do individuals increase survival and reproduction? (4)

Answer 3

Avoiding harmful environment, competition and predators
Keep in a favourable environment
Grow towards/away from stimuli
DISPERSING TO FIND NEW MATES

Question 4

Describe what is meant by the term kinesis (1)

Answer 4

Movement is random/non-directional
OR
Animal does not move towards a particular stimulus

Question 5

Describe what is meant by the term taxis (1)

Answer 5

Move towards or away from a stimulus from directional stimulus

Question 6

What is positive and negative taxis? (2)

Answer 6

Positive - towards the stimulus
Negative - away from the stimulus

Question 7

Explain the advantage of simple reflex arcs (5)

Answer 7

Rapid
Protect against damage to body tissue
Do not have to be learnt
Help escape from predators
Enable homeostatic control

Question 8

What is tropism? (1)

Answer 8

Direction of growth towards or away from a stimulus

Question 9

What is the difference between tropism and taxes? (2)

Answer 9

Both directional responses
Tropism is only part (R or S) whereas in taxes the entire organism responds

Question 10

What effect does Indoleacetic acid have in the shoots? (6)

Answer 10

(promotes cell elongation)
IAA synthesised in the shoot tips
Diffuses into elongating region
Light causes movement of IAA from light side to shaded side
Higher concentration of IAA on shaded side
Causes directional growth as there is greater cell elongation on shaded side
Shaded side grows faster and causes shoot to bend towards light

Question 11

What effect does Indoleacetic acid have in the roots? (6)

Answer 11

(inhibits cell elongation)
IAA synthesised in the root tips
IAA diffuses into the cell elongation region
Light causes movement of IAA from light side to shaded side and towards gravity
Higher concentration of IAA on the shaded side
Cell elongation inhibited on the shaded side
Results in directional growth away from light towards gravity

Question 12

Advantage of taxis and kinesis (1)

Answer 12

Can maintain a mobile organism in a favourable environment