Section 6- Response To Environment

Question 1

What is a stimulus?

Answer 1

A detectable change in the environment

Question 2

What are stimuli detected by?

Answer 2

Receptors

Question 3

What is taxis?

Answer 3

Simple directional response
Organisms move their body towards favourable environment

Question 4

What is kinesis?

Answer 4

A non directional response to stimuli
If it is in an unfavourable environment, the rate at which it changes increases

Question 5

What is a tropism?

Answer 5

Growth of part of a plant in response to directional stimuli
Plant shoots grow towards light and away from gravity

Question 6

What is photo tropism?

Answer 6

Response of the shoots to unilateral light

Question 7

What is photo tropism?

Answer 7

Response of the shoots to unilateral light

Question 8

What are the controls of tropisms by IAA?

Answer 8

• the shoot produces IAA which is then transported down the shoot
• IAA is transported evenly throughout the shoot
• light causes IAA to move from the light side to the shaded side
• greater conc of IAA to shaded side
• IAA causes elongation on shaded side, causes root to grow towards the light
• inhibits in roots

Question 9

What is gravitropism?

Answer 9

Response of a horizontally growing root to gravity

Question 10

What are the controls of gravitropism by IAA?

Answer 10

• cells in the root produce IAA which is transported along the root
• IAA is transported to all sides of the root
• gravity influences the movement of IAA from the upper to lower side of the root
• greater conc of IAA on lower side
• IAA inhibits elongation of root, cells on the upper side have a greater elongation
• root bends towards gravity

Question 11

Role of IAA in growth:

Answer 11

• transport of IAA is away from the tip of the shoots and roots
• IAA increases ability to stretch in the cell walls
• this is by the acid growth hypothesis, e.g the active transport of hydrogen from the cytoplasm into spaces of the cell wall causing it to elongate
• a stimuli (light) causes uneven distribution leading to the response

Question 12

What are the two divisions of the nervous system?

Answer 12

Central nervous system
Peripheral nervous system

Question 13

What is apart of the central nervous system?

Answer 13

Brain and spinal cord

Question 14

What is apart of the peripheral nervous system?

Answer 14

Pairs of nerves originating from brain or spinal cord

Question 15

What is the peripheral nervous system divided into?

Answer 15

Sensory nervous system- carries nerve impulses from receptors towards CNS
Motor nervous system- carries nerve impulses away from CNS to effectors

Question 16

What is the motor nervous system subdivided into?

Answer 16

Voluntary nervous system
Autonomic nervous system

Question 17

What is the voluntary nervous system?

Answer 17

Carries nerve impulses to body muscles under voluntary control

Question 18

What is autonomic nervous system?

Answer 18

Carries nerve impulses to glands, smooth muscle and cardiac muscle

Question 19

What is the spinal cord?

Answer 19

Column of nervous tissue that runs along the back, lies at the back for protection, emerging at intervals and pairs of nerves

Question 20

What is a reflex arc?

Answer 20

Where the response is rapid, short lived and involuntary

Question 21

What is the pathway of neurones?

Answer 21

Stimulus -> receptor -> sensory neurone-> coordinator -> intermediate neurone -> motor neurone -> effector -> response

Question 22

What is a pacinian corpuscle?

Answer 22

A sensory receptor which responds to changes in mechanical pressure

Question 23

What does a pacinian corpuscle produce?

Answer 23

• a generator potential

Question 24

Where can a pacinian corpuscle be found?

Answer 24

• on the fingers, feet, joints, tendons and ligaments

Question 25

What is the structure of a pacinian corpuscle?

Answer 25

- the sensory neurone at the end of the pacinian corpuscle contains sodium ion channels, they are stretch mediated

Question 26

What is the function of a pacinian corpuscle?

Answer 26

- at normal resting rate the Na+ channels are too narrow to allow Na+ to pass through - when pressure is applied it deforms and the membrane around the neurone becomes stretched - this widens the channel allowing Na+ to diffuse through - the Na+ depolarises the membrane which produces a generator potential - this creates an action potential that passes along the neurone

Question 27

What are the receptors in the eye?

Answer 27

- light receptors

Question 28

Where are light receptors found?

Answer 28

The retina

Question 29

What are the two main types of light receptors?

Answer 29

- rod cells - cone cells

Question 30

What are both their functions?

Answer 30

To act as transducers converting light energy into electrical energy of a nerve impulse

Question 31

What does the autonomic nervous system do?

Answer 31

Controls involuntary activities of internal muscles and glands

Question 32

What is the autonomic nervous system made of?

Answer 32

Sympathetic nervous system Parasympathetic nervous system

Question 33

What is the sympathetic nervous system?

Answer 33

Stimulates effectors to speed up activity used in ‘fight or flight’ Helps to respond to stressful situations by heightening awareness

Question 34

What is the parasympathetic nervous system?

Answer 34

Inhibits effectors, slows down activity, conserves energy and controls under normal resting conditions

Question 35

How do you control heart rate?

Answer 35

- muscle of the heart = cardiac muscle - contraction is initiated within itself, within the right atrium (SAN) wheee the stimulus for the contraction originates

Question 36

What is the control for the basic heart rate?

Answer 36

1) waves of electrical excitation spreads out from senatorial node across both atria causing them to contract 2) the atrioventricular septum prevents the wave crossing over to the ventricles, it enters the AVN 3) after a short delay, AVN conveys the waves over purkinje fibres which makes the bundle of His 4) the bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles 5) the wave of electrical excitation is released from purkinje fibres causing the ventricles to contract

Question 37

How do you modify the heart rate?

Answer 37

- changes in the heart rate are controlled in the brain by medulla oblongata - has a centre that increases heart rate via SAN - centres are stimulated by chemical or pressure changes

Question 38

What are chemoreceptors?

Answer 38

Found in the wall of the caretol arteries and aorta

Question 39

What do they do?

Answer 39

- sensitive to changes in the pH that result from changes in CO2 conc - they detect lower pH and increase the frequency of nerve impulses to the acceleratory centre in the medulla oblongate (to increase the heart rate) - the centre increases the frequency of impulses via the sympathetic nerve to SAN, that increases the rate of production of electrical waves from SAN, increasing heart rate - increasing blood flow causes more CO2 to be removed by lungs - blood pH returns to normal, chemoreceptors reduce their frequency to the medulla which reduces the frequency to SAN

Question 40

What are pressure receptors?

Answer 40

- found in walls of carotid arteries and aorta

Question 41

What do they do?

Answer 41

- when blood pressure is higher than normal, pressure receptors transmit more nerve impulses to the centre in the medulla oblongata that decreases heart rate, this sends impulses in the parasympathetic nervous system to the SAN which decreases heart rate - when the blood pressure is lower than normal, pressure receptors transmit more nerve impulses to the medulla, this sends more SAN and increases heart rate

Question 42

What are the three types of neurone?

Answer 42

Sensory Motor Intermediate

Question 43

Where does the sensory neurone relay the message to?

Answer 43

Brain or spinal cord