survival and response

Question 1

why do organisms respond to changes in their environment?

Answer 1

to increase their chance of survival

• finding favourable living conditions
• finding food
• avoiding predators

Question 2

how do organisms respond?

Answer 2

receptors detect stimulus
set to coordinator (brain or spinal cord)
effectors bring about response

Question 3

tropisms

Answer 3

growth response to a stimulus

phototropism - growth response to light
gravitropism - growth response to gravity

positive = towards
negative = away

Question 4

indoleaetic acid

Answer 4

synthesised in growing tips of root and shoots
(meristem, cells dividing)
- effects the plants direction of growth

causes:
in shoot = cells elongate
in roots = reduces rate

Question 5

IAA in phototropism

Answer 5

in shoots, IAA = more elongation
- IAA moves to shaded side
- causes faster rate of elongation
- cells growth
- shoot bends towards light

in roots, IAA = less elongation
- moves to shaded side
- prevents growth
- roots bends away

Question 6

IAA in gravitropism

Answer 6

in roots, IAA = less elongation
- IAA move to underside
- prevents growth
- roots bend downwards

in shoots, IAA = more elongation
- IAA moves to underside
- causes cell to elongate
- shoots growth upwards

Question 7

taxes

Answer 7

directional response to a directional stimulus
eg light (phototaxis)

organism moves towards or away from stimulus

eg woodlice move away from light, keeps hem hidden from prey

Question 8

kinesis

Answer 8

non-directional response to a non-directional stimulus
eg humidity

affects organisms movement
- move more or less

eg move less to stay in a condition, move more to find it again