6.1 Internal & External Stimuli

Question 1

What are plant growth factors?

Answer 1

Chemicals that regulate plant growth response to directional stimuli

Question 2

Where are plant growth factors produced?

Answer 2

Planting growing regions

Question 3

How do plant growth factors move around plant?

Answer 3

Diffuse from cell to cell
Mass transport in phloem

Question 4

Why do shoots show positive phototropism?

Answer 4

IAA diffuses to shaded side of shoot tip
Causes active transport of H+ ions into cell wall
Disruption of H bonds between cellulose molecules make cell more permeable to water
Cells on shaded side elongate faster due to higher turgor pressure
Shoot bends towards light

Question 5

Why do roots show positive gravitropism?

Answer 5

Gravity causes IAA to accumulate on lower side of root
IAA inhibits elongation of root cells
cells on upper side of root elongate faster
Root tip bends downwards

Question 6

What’s the acronym for contrasting mammalian hormones and plant growth factors?

Answer 6

CASTS
Concentration
Action
Synthesis
Transport
Speed

Question 7

Compare concentration of mammalian hormones and plant growth factors.

Answer 7

MH response not always dependent on concentration
PGF response proportional to concentration

Question 8

Compare action of mammalian hormones and plant growth factors.

Answer 8

MH bind to complementary proteins in/on target cells
PGF can affect all cells

Question 9

Compare synthesis of mammalian hormones and plant growth factors.

Answer 9

MH specialised glands
PGF various tissues in growing regions

Question 10

Compare transport of mammalian hormones and plant growth factors.

Answer 10

MH circulatory system
PGF diffusion or phloem translocation

Question 11

Compare speed of mammalian hormones and plant growth factors.

Answer 11

MH faster acting (homeostasis)
PGF slower acting (plant growth)

Question 12

Define taxis.

Answer 12

Directional movement in response to external stimulus

Question 13

Define kinesis.

Answer 13

Non directional response to presence and intensity of external stimulus

Question 14

What is the importance of taxis and kinesis?

Answer 14

Maintain mobile organism in optimum environment

Question 15

Why do many organisms respond to temperature and humidity with kinesis rather than taxis?

Answer 15

Less directional stimuli
Often no clear gradient from one extreme to other

Question 16

How could a student recognise kinesis in an organisms movement?

Answer 16

Organism crosses division between two environments and turning increases to return to favourable
Organism moves distance into unfavourable and turning slowly decreases to lead to new environment

Question 17

Outline events in a simple reflex arc.

Answer 17

Receptor detects stimulus
Sensory neuron
Relay neuron in CNS coordinated response
Motor neuron
Response by effector

Question 18

What is the importance of a simple reflex?

Answer 18

Rapid response to potentially dangerous stimuli since only 3 neurons involved

Question 19

What stats test could be used to determine whether factor has significant effect on organism movement in choice chamber or not?

Answer 19

Chi squared

Question 20

What features do all sensory receptors have?

Answer 20

Establish a generator potential
Respond to specific stimuli

Question 21

What is a Pacinian corpuscle?

Answer 21

A type of receptor found in the skin that responds to changes in pressure.

Question 22

Describe the structure of a Pacinian corpuscle.

Answer 22

Single nerve fibre surrounded by layers of connective tissue separate by viscous gel and contained by a capsule

Question 23

What do Pacinian corpuscles have on the plasma membrane?

Answer 23

Stretch-mediated Na+ channels

Question 24

What do Pacinian corpuscles have along the base layer of tissue?

Answer 24

A capillary

Question 25

How does a Pacinian corpuscle respond to pressure?

Answer 25

Pressure deforms membrane, causing stretch-mediated Na+ ion channels to open If Na+ influx raises membrane to threshold potential, a generator potential is produced Action potential moves along sensory neuron

Question 26

Name the two types of photoreceptor cell located in the retina.

Answer 26

Cone cells Rod cells

Question 27

Where are rod cells located in the retina?

Answer 27

Evenly distributed around periphery Not in central fovea

Question 28

Where are cone cells located in the retina?

Answer 28

Mainly central fovea

Question 29

What’s the acronym for contrasting rod cells and cone cells?

Answer 29

PACL Pigment Visual Acuity Colour sensitivity Light sensitivity

Question 30

Compare pigment of rod cells and cone cells.

Answer 30

ROD: Rhodopsin CONE: 3 types of iodopsin

Question 31

Compare visual acuity of rod cells and cone cells.

Answer 31

ROD: Low resolution as many rod cells synapse with 1 neuron CONE: High resolution as 1 cone cell synapses with 1 neuron (no retinal convergence)

Question 32

Compare colour sensitivity of rod cells and cone cells.

Answer 32

ROD: Monochromatic (all wavelengths of light detected) so can't detect different colours CONE: Tricolour (red/blue/green wavelengths absorbed by different types of iodopsin) so can detect different colours

Question 33

Compare light sensitivity of rod cells and cone cells.

Answer 33

ROD: Very sensitive CONE: Less sensitive

Question 34

What is retinal convergence?

Answer 34

The sharing of a single nerve fiber by several rod cells in the retina

Question 35

Outline the pathway of light from a photoreceptor to the brain.

Answer 35

Photoreceptor Bipolar neuron Ganglion cell of optic nerve Brain

Question 36

Define myogenic.

Answer 36

Contraction of heart initiated within muscle rather than by nerve impulses

Question 37

Name the two nodes involved in heart contraction.

Answer 37

Sinoatrial node (SAN) Atrioventricular node (AVN)

Question 38

Where is the Sinoatrial node (SAN) located?

Answer 38

Within the wall of the right atrium

Question 39

Where is the Atrioventricular node (AVN) located?

Answer 39

Near lower end of right atrium in the wall that separates the 2 atria

Question 40

Describe how heartbeats are initiated and coordinated.

Answer 40

SAN initiates wave of depolarisation Wave spreads across both atria (atrial systole) Layers of fibrous, non conducting tissue delays impulse while ventricles fill and valves close AVN conveys wave of depolarisation via Bundle of His Ventricles contract from apex upwards

Question 41

How can cardiac output by calculated?

Answer 41

stroke volume x heart rate

Question 42

What is the autonomic nervous system?

Answer 42

System that controls involuntary actions of glands and muscles

Question 43

What are the two subdivision of the autonomic nervous system?

Answer 43

Sympathetic Parasympathetic

Question 44

What is the sympathetic nervous system?

Answer 44

Involved in "fight or flight" response Stimulates effectors to speed up activity

Question 45

What is the parasympathetic nervous system?

Answer 45

Involved in normal resting conditions Inhibits effectors to slow down activity

Question 46

Name the receptors involved in changing heart rate.

Answer 46

Baroreceptors Chemoreceptors

Question 47

What is detected by the baroreceptors?

Answer 47

Changes in blood pressure

Question 48

Where are the baroreceptors located?

Answer 48

Carotid body

Question 49

What is detected by chemoreceptors?

Answer 49

Changes in pH

Question 50

Where are the chemoreceptors located?

Answer 50

Carotid body Aortic body

Question 51

How does the body respond to an increase in blood pressure?

Answer 51

Baroreceptors send more impulses to cardioinhibitory centre in medulla More impulses to SAN via parasympathetic nervous system Stimulates release of acetylcholine which decreases heart rate

Question 52

How does the body respond to an decrease in blood pressure?

Answer 52

Baroreceptors send more impulses to cardioacceleratory centre in medulla More impulses to SAN via sympathetic nervous system Stimulates release of noradrenaline which increases heart rate and strength of contraction

Question 53

How does the body respond to an increase in CO₂ concentration?

Answer 53

Chemoreceptors detect pH decrease and send more impulses to cardioacceleratory centre in medulla More impulses to SAN via sympathetic nervous system Stimulates release of noradrenaline which increases heart rate Blood flow to lungs increases so rate of gas exchange and ventilation increases