Response to stimuli

Question 1

Describe taxes

Answer 1

• Simple response where organism moves it’s entire body towards favorable stimulus/ away from unfavorable
• Towards = positive taxis
• Away = negative taxis

Question 2

Describe kinesis

Answer 2

• Organism changes speed of movement and rate of changing direction
• If move from beneficial to harmful environment = increases rate of change in direction to return to favorable environment
• If surrounded by negative stimuli rate of turning decreases = moves in a straight line = increase chance of finding new favorable location

Question 3

What is tropism?

Answer 3

• Plant respond to stimuli via growth
• Positive = towards stimuli
• Negative = away from stimuli
• Stimuli of light + gravity

Question 4

What is IAA?

Answer 4

• Growth factor
• Made in tips of shoots/roots
• Controls cell elongation in shoots
• Inhibit growth in roots

Question 5

Describe positive phototropism in shoots

Answer 5

• Shoot tips produce IAA = elongation
• IAA diffuses to other cells
• Unilateral light = IAA diffuses to the shaded side = higher concentration on shaded side
• IAA causes cells on shaded side to elongate = plant bends towards light

Question 6

Describe negative phototropism in roots

Answer 6

• IAA moves to the side away from light
• High concentration inhibits elongation = elongates on the side towards the light
• Root bends away from light

Question 7

Describe negative gravitropism in shoots

Answer 7

• IAA will diffuse from the tip downwards to the lower side
• Shoot elongates = grows upwards against gravity

Question 8

Describe positive gravitropism in roots

Answer 8

• IAA moves to lower side of roots = upper side elongates
• Root bends down towards gravity

Question 9

What is a stimulus?

Answer 9

Detectable change in the environment

Question 10

What is a receptor cell?

Answer 10

• Cells that detect specific stimuli
• Stimulation = action potential = response

Question 11

What is the Pacinian corpuscle?

Answer 11

• Receptor that responds to pressure change
• Located deep in the skin of fingers and feet
• Consists of a sensory neuron + wrapped in layers of tissue with layers of gel in between each layer

Question 12

Describe how Pacinian corpuscle works

Answer 12

• Cell membrane around sensory neuron has stretch mediated Na+ channel
• Resting state Na+ channel too narrow for diffusion = resting potential maintained
• Pressure applied = deforms membrane + stretches/widens channels = Na+ diffuses in = action potential

Question 13

2 types of photoreceptors in retina

Answer 13

1) Rod: Distributed around retina but not in fovea
2) Cone: Mainly central fovea

Question 14

Describe the rod

Answer 14

• Rhodopsin pigment broken by light energy
• Low resolution visual acuity = retinal convergence = many rod cells synapse with 1 bipolar neuron
• Monochromatic vision
• Very sensitive to light intensity due to spatial summation

Question 15

Describe the cone

Answer 15

• 3 iodopsin pigments broken by light energy
• High resolution visual acuity = no retinol convergence = 1 cone synapse with with 1 bipolar neuron
• Tricolor: Red + blue + green absorbed by 3 different iodopsins
• Less sensitive to light intensity

Question 16

Path of light from photoreceptor to brain

Answer 16

Photoreceptor - Bipolar neuron - Ganglion cells of optic nerves - Brain

Question 17

2 nodes involved in heart contractions

Answer 17

1) SAN: In wall of right atrium AKA pacemaker
2) AVN: Lower border of right atrium

Question 18

Describe how heart beats are coordinated

Answer 18

• SAN initiates wave of depolarization across atria = contraction
• AVN releases another wave of depolarization
• Non-conductive layer between atria/ventricle prevents depolarization from travelling = bundle of His in septum conducts
• Depolarization travels down septum to Purkyne fibers in wall of ventricles
• Apex contracts = ventricles contract

Question 19

Why do non-conducting tissue delay impulse?

Answer 19

• Allows time for atria to pump blood into ventricle
• Cells can repolarize

Question 20

What is the autonomic nervous system?

Answer 20

• Controls involuntary actions of glands + muscles
• Consists of sympathetic + parasympathetic

Question 21

Difference between 2 autonomic nervous systems

Answer 21

• Sympathetic: Stimulates effectors to speed up activity
• Parasympathetic: Inhibits effectors to slow down

Question 22

Heart rate in response to increased pressure

Answer 22

• Increased pressure = Pressure-receptors in the aorta + carotid are stretched
• More electrical impulses sent to medulla oblongata via parasympathetic to SAN to decrease frequency of electrical impulses
• SAN = reduced heart rate

Question 23

Heart rate in response to decreased pressure

Answer 23

• Decreased pressure = Pressure-receptors in aorta + carotid are not stretched
• More electrical impulses sent to medulla oblongata via sympathetic to SAN to increase electrical impulses
• SAN = increased heart rate

Question 24

Heart rate in response to decreased pH

Answer 24

• Decreased pH = Chemoreceptors in aorta + carotid pick up change
• More electrical impulses sent to medulla oblongata via sympathetic to SAN to increase frequency of electrical impulses
• SAN = increases rate of blood delivered to lungs to remove CO2