Organisms Respond to Changes in their Internal and External Environments

Question 1

Effector

Answer 1

An organ or a cell that carries out a response to an electrical impulse.

Question 2

Stimulus

Answer 2

A change in the environment that can be detected and will provoke a response

Question 3

Receptor

Answer 3

A cell that will detect a change in the environment (stimulus)

Question 4

Sensory neurone

Answer 4

A nerve cell that carries an electrical impulse from a receptor to the central nervous system

Question 5

Synapse

Answer 5

A gap between two neurones

Question 6

Coordinator

Answer 6

Formulates a suitable response to a stimulus

Question 7

Relay neurone

Answer 7

A nerve cell that acts as a coordinator between sensory and motor neurone

Question 8

Motor neurone

Answer 8

Nerve cell that carries electrical impulses from the central nervous system and the effector

Question 9

Response

Answer 9

A hormone released by a gland, or a muscle contraction as a result of an electrical impulse.

Question 10

What does the sympathetic system do?

Answer 10

Increases heart rate and stroke volume

Question 11

What chemical does the sympathetic nervous system release on the SAN?

Answer 11

Noradrenaline

Question 12

What does the parasympathetic nervous system do?

Answer 12

Decreases heart rate and stroke volume

Question 13

What chemical does the parasympathetic nervous system releases on the SAN?

Answer 13

Acetylcholine

Question 14

What type of receptors detect changes in CO2 levels in the blood, and where are they found?

Answer 14

Chemoreceptors in the aortic arch (blood always passes through aorta) and carotid arteries (ones that go to the brain so constant blood flow).

Question 15

What activity would cause an increase in CO2 levels in the blood?

Answer 15

Exercise as increased respiration

Question 16

Describe the reflex arc for changing heart rate

Answer 16

Receptors detect a rise in CO2 levels in blood and send electrical impulse via sensory neurone to relay neurone and coordinator (medulla). Motor neurone then takes electrical impulse to ventricular muscle which release chemical onto SAN and increase heart rate and stroke volume to get normal concentration of CO2 in blood

Question 17

Describe how the sinoatrial node (SAN) controls heart rate

Answer 17

The SAN generates an electrical impulse that spreads over the atrium, causing them to contract, and blood to leave the atrium to the ventricles.
The impulse reaches the AVN (atrioventricular nerve where it is delayed to allow all of the blood to leave the atrium.
The impulse passes down the bundle of His to the purkinje fibres which cause the ventricles to contract.

Question 18

Saltatory conduction

Answer 18

When the electrical impulse jumps from one node of ranvier to the next.

Question 19

What are the three factors that affect rate of nerve impulse?

Answer 19

Temperature (faster diffusion)

How wide the axon is (more surface area so more protein channels on the membrane for diffusion)

Myelinated or not (if myelinated there will be saltatory conduction which is quicker as less action potentials generated)

Question 20

Resting potential

Answer 20

The potential across the plasma membrane of a cell that isn’t conducting an impulse

Question 21

What is occurring when an axon is at resting potential? (where are ions moving and what charge is generated where)

Answer 21

The potassium ion channel protein is open so potassium ions are moving out of the axon.
The sodium-potassium pump is actively transporting sodium ions out and potassium ions into the axon.
The sodium ion channel is shut, so sodium ions are trapped outside axon
There are more positively charged ions out of the axon.

Question 22

Depolarisation

Answer 22

When an action potential is created

Question 23

What happens in depolarisation?

Answer 23

The sodium channel opens, so sodium ions move into the axon.
The potassium channel is shut, so potassium ions are trapped wherever they are.
This means there is a more positive charge in the axon.

Question 24

Repolarisation

Answer 24

When a membrane is polarised again (a resting potential is re-established)

Question 25

Why is repolarisation important?

Answer 25

An impulse cannot be generated if the membrane of an axon is not at resting potential

Question 26

What happens in repolarisation?

Answer 26

Potassium ion channels open so potassium ions move out.
Sodium ion channel closes so sodium trapped wherever.
Sodium ions are actively transported out of axon.
More positively charged outside of axon

Question 27

What is the type of conduction happens in unmyelinated axons? Why is it slower?

Answer 27

Continuous. Much slower as action potential has to be generated across the axon

Question 28

What type of receptor detects pressure?

Answer 28

Mechanoreceptors

Question 29

Transducer

Answer 29

Converts energy in a stimulus (e.g. light) into an impulse

Question 30

Why will a thermoreceptor not transduce light?

Answer 30

Receptors are specific and thermoreceptors are for heat not light

Question 31

What is the name of a mechanoreceptor that detects changes in pressure in the skin?

Answer 31

Pacinian corpuscle

Question 32

What is the pacinian corpuscle made of?

Answer 32

An unmyelinated axon surrounded by layers of lamellae separated by gel. Attached to a sensory neurone with a myelinated axon

Question 33

What causes an impulse to be generated at the pacinian corpuscle?

Answer 33

Pressure distorts the naked axon, opening the stretch-mediated sodium ion channels to allow sodium ions into the axon (depolarisation/a generator potential)

Question 34

Why is an impulse not generated when constant pressure is applied? Why is this important?

Answer 34

The gel repositions itself to relieve the pressure. Prevents the brain being overloaded with information.

Question 35

What stimulus does the parasympathetic nervous system respond to?

Answer 35

Baroreceptors detect an increase in blood pressure

Question 36

What stimulus does the sympathetic system respond to?

Answer 36

Chemoreceptors detect an increase in CO2 in the blood due to respiration

Question 37

What happens to rhodopsin when light shines on it?

Answer 37

It breaks down to retinal and opsin
A series of reactions occur
An action potential is generated

Question 38

What are retinal and opsin converted back to?

Answer 38

Rhodopsin

Requires ATP

Question 39

Homeostasis

Answer 39

Regukation of the internal conditions in the blood