Mod.1-Communication and Homeostasis

Question 1

Define the term stimulus.

Answer 1

A stimulus is any change in the environment that causes a response.

Question 2

Define a response.

Answer 2

A response is a change in behaviour or physiology as a result of a change in environment.

Question 3

State three examples of a stimulus and coordinating response.

Answer 3

Insect Bite- to move away (a nervous coordination)
Large barking dog running towards you- Run away (nervous and hormonal)
Smell of appetising food- salivate (nervous)

Question 4

What are the requirements of a good communication system?

Answer 4

Must be able to send and receive messages and signals and effectively distinguish between them. It must extend over the whole body.

Question 5

Define Negative feedback.

Answer 5

Process that brings about reversal of any change in conditions. Ensures optimum can be maintained, as internal enviro. is returned to original conditions.

Question 6

Define Positive feedback.

Answer 6

Process that increases any change detected by receptors it tends to be harmful and doesn’t lead to homeostasis

Question 7

Explain the difference between positive and negative feedback.

Answer 7

Negative feedback monitors a change and initiates a process to reverse the change whereas positive feedback will increase the change.

Question 8

Define an ectotherm.

Answer 8

An ectotherm is an organism that relies on external sources of heat to regulate body temperature.

Question 9

Why is it important to maintain a constant body temperature?

Answer 9

If body temp is too low, enzyme activity falls and the rate of metabolism drops. High temp. denatures proteins such as channel proteins in the membranes.

Question 10

Explain how basking can help regulate body temperature.

Answer 10

If an ectotherm is too cool it can absorb heat from the rock and direct from the sun. This will warm up the skin and the blood flowing near the surface which will warm muscles.

Question 11

Define an endotherm.

Answer 11

An organism that use internal sources of heat such as heat generated from the metabolism in the liver to maintain body temp.

Question 12

Explain how vasoconstriction helps reduce heat loss.

Answer 12

It reduces blood flow through the skin, blood flows through vessels deeper in the body. Heat is less easily radiated out from the body.

Question 13

What is a polarised membrane?

Answer 13

One that has a potential difference across it known as the resting potential.

Question 14

What is depolarisation?

Answer 14

Loss of polaris. across membrane. Refers to when Na+ ions are entering the cell making it less negative then the outside.

Question 15

What is a generator potential

Answer 15

Small depolarisation caused by Na ions entering the cell.

Question 16

How is an action potential achieved?

Answer 16

Membrane is depolarised to value +40mV. All or nothing response- membrane depolarises and lots of sodium enter the axon as the action potential is reached.

Question 17

Suggest why neurone have to carry a large number of mitochondria.

Answer 17

Mitochondria produce ATP by aerobic respiration to maintain the resting potential and for exocytosis of neurotransmitter chemicals at synapses

Question 18

Define resting potential.

Answer 18

The potential difference across the neurone cell membrane while the neurone is at rest- it is about -60mV compared with the outside.

Question 19

What is Voltage-gated channels

Answer 19

Channels in membrane that allow passage of ions. Gates open and close the channel responding to potential difference across membrane.

Question 20

What is Threshold potential.

Answer 20

P.D across the membrane -50mV. Depolarisation must reach the threshold potential in order for action potential to be created.

Question 21

Define Action potential.

Answer 21

Depolarisation of membrane so inside is more positive (+40mV) -> Transmitted along axon/ dendron plasma membrane.

Question 22

Explain why a neurone is active while it is said to be resting.

Answer 22

While the neurone is resting the membrane its actively transporting sodium ions out and potassium in.

Question 23

What is the organic role of anions inside a neurone?

Answer 23

Organic anions help ensure that the inside of the cell remains negative compared to the outside.

Question 24

Define Local currents

Answer 24

The movements of ions along the neurone. The flow of ions is caused by an increase in conc. at one point which causes diffusion

Question 25

Define saltatory conduction.

Answer 25

This means ‘jumping conduction’. It refers to the way that action potential appears to jump from one node of Ranvier to the next.

Question 26

How are sodium ion channels opened?

Answer 26

Each channel has a voltage-sensitive gate. A change in the potential around the gate causes it to move or change shape. This opens the channel.

Question 27

Explain how the myelin sheath causes saltatory conduction.

Answer 27

Myelin sheath is a layer of fatty material tightly bound to the neurone K/Na ions cannot move through sheath neurone membrane is exposed is at Ranvier nodes.