Survival and response

Question 1

define receptors

Answer 1

specialised cells or proteins in cell membrane which detect stimuli usually specific to one type of stimulus

Question 2

Say where each type of neurones transmits impulses

Answer 2

sensory-receptors to CNS or relay neurones
motor-CNS/relay to effectors
relay-sensory to motor (only in reflexes)

Question 3

define a reflex

Answer 3

a rapid automatic response that doesn’t need to be learnt and can be protective/prevent damage to tissues

Question 4

explain how a reflex arc works

Answer 4

stimulus-hot object
temp/pain receptors in skin
sensory neurone sends impulse relay connects sensory to motor
motor neurone sends an impulse to the effector
effector-arm muscles contract and pull away

Question 5

define taxes

Answer 5

a response where organisms move towards (+ taxis) or away (- taxis) from a directional stimulus e.g. light

Question 6

define kinesis

Answer 6

a response where an organism’s movement is affected by a non-directional stimulus e.g. humidity and responds to an unpleasant stimulus by:
-increasing speed of movement and rapid change in direction eventually slowing downs when conditions are met.

Question 7

define a tropism

Answer 7

a response in a flowering plant to a directional stimulus by regulating their growth
+ tropism=towards stimulus e.g.positive phototropism in leaves
- tropism=away from stimulus e.g.negative phototropism in roots to grow into the soil

Question 8

What are growth factors?

Answer 8

chemicals which speed up or slow down plant growth produced in growing regions (shoot/root tips) and move to other tissues to regulate growth in response to a directional stimulus.

Question 9

What are auxins?

Answer 9

growth factors stimulating growth of shoots by cell elongation
1.stimulates proton pumps in cell membrane
2.protons pumped into cell wall activating proteins called expansins
3.this protein breaks some H bonds between cellulose
4.cell walls become ‘loose and stretchy’ and become longer
high conc. auxin in roots=inhibited growth

Question 10

What is Indoleacetic acid (IAA)

Answer 10

important auxin produced in shoots of flowering plants

• long distance=moves by phloem
• short distance=moves by active transport/diffusion
• uneven distribution IAA=uneven growth of plant
• high conc. IAA= inhibitory effect of root growth

Question 11

Explain IAA and phototropism (shaded parts)

Answer 11

increased IAA conc. in shoot=shaded side elongates and bends towards light
increased IAA conc. in root=inhibits growth(cell elongation) so root bends away from light

Question 12

Explain IAA and gravitropism (in underside of shoots/roots)

Answer 12

shoot=cells elongate and grow upwards

root=root growth inhibited and grows downward