Responses

Question 1

What is a stimulus?

Answer 1

Detectable change in external or internal environment of an organism

Question 2

What is a response?

Answer 2

Change as a result of a stimulus - molecular level or behaviour of whole organism

Question 3

State the 5 stages of the stimulus response chain

Answer 3

receptor-> sensory neuron-> coordinator (relay)-> motor neuron-> effector

Question 4

Give an example of a taxis response

Answer 4

single celled algae move towards light (+phototaxis), increases survival chance as they are photosynthetic, so need light to manufacture food

Question 5

Give an example of a kinesis response

Answer 5

woodlice move more rapidly + change direction more often in dry conditions to increase chance of moving into different area where conditions more favourable (moist)

Question 6

How does IAA affect shoots? (+phototropism)

Answer 6

produced in tips + diffuses to shaded side. causes greater elongation due to active transport of H+ ions into cell walls. this increases plasticity of cell walls in young cells -> elongate + bend towards light

Question 7

How does IAA affect roots?
(+gravitropism)

Answer 7

produced in root tips. conc builds up on lower side as IAA on upper side pulled down by gravity. at high concs IAA inhibits cell elongation. so greater elongation of cells on upper side means roots bend downwards towards gravity

Question 8

How is an action potential generated in a pacinian corpuscle?

Answer 8

• pressure deforms stretch mediated Na+ ion channels widening them so Na+ moves into neurone
• movement of Na+ depolarises the membrane causing generator potential
• if gen. potential is above threshold level then an action potential is initiated

Question 9

Features of rod cells

Answer 9

• distributed throughout retina (peripheral vision)
• high sensitivity (detect single photon) due to summation, used at night
• one type so monochromatic vision
• many rods connected to one bipolar cell so poor visual acuity

Question 10

Features of cone cells

Answer 10

• found mainly in fovea, can only detect images at centre of retina
• low sensitivity, only work in day
• 3 types (RGB) so colour vision
• each cone connected to one bipolar cell so good visual acuity

Question 11

What two types of autonomic nervous system are there?

Answer 11

Sympathetic - stimulates effectors -> increases heart rate for exercise/emotions

Parasympathetic - inhibits effectors -> decreases heart rate for normal resting conditions

Question 12

Control of heart rate

Answer 12

• wave of electrical excitation spreads from SAN across both atria, causing contraction
• layer of non-conductive tissue prevents ventricles contracting
• AVN conveys wave of excitation after a short delay down Bundle of His to purkyne fibres at base of ventricles
• wave released, ventricles contract from bottom of heart upwards

Question 13

Control by pressure receptors

Answer 13

When blood pressure higher than normal , receptors transmit more impulses to m.o that decreases heart rate

m.o sends signals to SAN via parasympathetic nervous system

Question 14

Control by chemoreceptors

Answer 14

• increased activity increases respiration producing more CO2
• blood pH lowered
• chemoreceptors in carotid arteries increase freq. of impulses to m.o
• m.o that speeds up heart rate increases impulses to SAN via sympathetic
• SAN increases heart rate, higher blood flow removes CO2 faster