Stimuli and Response

Question 1

Name three receptors

Answer 1

Rod cells
Cone cells
Pacinian Corpuscle

Question 2

Outline what happens during a simple reflex arc

Answer 2

S > R > SN > RN > MN > R > E

Question 3

Advantage of a simple reflex

Answer 3

Rapid response to stimuli and instinctive

Question 4

Common features of a sensory receptor

Answer 4

Acts as energy transducer which establishes a generator potential and responds to a specific stimuli

Question 5

Describe the basic structure of a Pacinian corpuscle

Answer 5

Single nerve fiber is surrounded by layers of connective tissue which are separated by viscous gel and contained by a capsule. There are stretch-mediated Na+ channels on the plasma membrane and capillary runs along the base layer of tissue.

Question 6

What stimulus does a PC respond to and what happens

Answer 6

1. Pressure deforms the membrane causing the stretch-mediated Na+ channels to open
2. If an influx of Na+ raises the membrane to threshold potential, a generator potential is produced.
3. Action potential moves along sensory neuron

Question 7

Where are rod and cone cells located

Answer 7

Rod = Periphery
Cone = Central Fovea

Question 8

Pigment of rod and cone cells

Answer 8

Rod = Rhodopsin
Cone = 3 types of Iodopsin

Question 9

Visual acuity of rod and cone cells

Answer 9

Rod = Low resolution as many rod cells to one bipolar neuron

Cone = High resolution as only one cone cell to one bipolar neuron

Question 10

Colour sensitivity of rod and cone cells

Answer 10

Rod = monochromatic

Cone = Tricolour ( red , blue + green)

Question 11

Light sensitivity of rod and cone cells

Answer 11

Rod = Very sensitive due to spatial summation of subthreshold impulses

Cone = Less sensitive not involved in night vision

Question 12

Pathway of light from a photoreceptor to the brain

Answer 12

photoreceptor -> bipolar neuron -> ganglion cell of optic nerve -> brain

Question 13

what is the autonomic nervous system

Answer 13

The system that controls involuntary actions of glands and muscles. Parasympathetic and sympathetic

Question 14

Difference between sympathetic and parasympathetic nervous system

Answer 14

Sympathetic = involved in flight or fight response, stimulates effectors to speed up activity

Parasympathetic = Inhibits effectors to slow down activity

Question 15

Receptor involved in changing heart rate and their function and location

Answer 15

Baroreceptors = change in blood pressure and is found in the carotid body

Chemoreceptors = change in pH , due to increase in CO2 conc. and is found in the carotid and aortic body

Question 16

How does the body respond to an increase in blood pressure

Answer 16

1. Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata
2. More impulses to SAN down vagus nerve via parasympathetic nervous system
3. This stimulate the release of acetylcholine which decrease heart rate

Question 17

How does the body respond to a decrease in blood pressure

Answer 17

1. Baroreceptors send more impulses to the cardioacceleratory centre in the medulla oblongata
2. More impulses to SAN via the sympathetic nervous system
3. This stimulates release of noradrenaline which increase HR and strength of contraction

Question 18

How does the body respond to an increase in CO2 conc.

Answer 18

1. Chemoreceptors detect pH decrease and send more impulse to cardioacceleratiry centre of medulla oblongata
2. More impulse to SAN via the sympathetic nevrous system
3. HR increase , so rate of blood flow to lungs increase and so rate of gas exchange and ventilation rate increases.

Question 19

Formula for cardiac output

Answer 19

SV x HR

Question 20

Describe how heartbeats are initiated

Answer 20

1. SAN initiates a wave of depolarisation
2. WOD spreads across both atria (atrial systole)
3. Layer of fibrous, non-conducting tissue delays while ventricles fill and valves close
4. AVN conveys WOD down septum via Bundle of HIs which branches into Purkinje fibres along ventricles
5. This cause ventricles to contract from apex upwards

Question 21

2 nodes involved in heart contraction + location

Answer 21

Sinoatrial node = right atrium
Atrioventricular node = lower end of right atrium

Question 22

Define taxis

Answer 22

Directional movement in response to an external stimulus

Question 23

Define kinesis

Answer 23

Undirectional response to presence and intensity of external stimulus

Question 24

What are plant growth factors and where are they produced

Answer 24

Chemicals that regulate plant growth repsonse to directional stimuli and are produced in plant growing regions and diffuse from cell to cell via phloem mass transport

Question 25

Why do shoots show postive phototropism

Answer 25

1. IAA diffuse to shade side of the shoot tip
2. As IAA diffuses down shaded down side , cells on shaded side elongate faster and shoot bends towards light

Question 26

Why do roots show positive gravitropism

Answer 26

1. Gravity causes IAA to accumulate on lower side of the root.
2. IAA inhibits elongation of root cells, cells on upper side of the root elongate faster so root tip bends downwards