Unit 4: Section 1 - Communication and Homeostasis

Question 1

Give one example of a receptor that is a protein, and one that is a cell.

Answer 1

Protein - glucose receptors

Cell - photoreceptors

Question 2

What is homeostasis?

Answer 2

The maintenance of a constant internal environment, despite a changing external environment.

Question 3

What is negative feedback?

Answer 3

Bringing the level of something that is too high or too low, back to it’s normal range.

Question 4

What does positive feedback do?

Answer 4

Amplify a change to further increase the level away from it’s normal range.

Question 5

When might positive feedback be useful?

Answer 5

To clot blood after an injury…

• Platelets become activated and release a chemical, this triggers more platelets to be activated, and so on
• Platelets quickly form a blood clot at the injury site
• The process ends with negative feedback, when the body detects the blood clot has been formed

Question 6

What are the 3 main types of neurones and what do they do?

Answer 6

1) Sensory neurones transmit nerve impulses from receptors to the CNS
2) Motor neurones transmit nerve impulses from the CNS to effectors
3) Relay neurones transmit nerve impulses between sensory neurones and motor neurones

Question 7

What is the general structure of a neurone?

Answer 7

All neurones have a cell body with a nucleus
The cell body has extensions that connect to other neurones, dendrons and dendrites carry nerve impulses towards the cell body, and axons carry impulses away from the cell body.

Question 8

What is the difference in the structure of a motor neurone, and the structure of a sensory neurone?

Answer 8

Sensory neurones have short dendrites, one long dendron, and one short axon. Motor neurones have many short dendrites and one long axon.

Question 9

What is the resting potential?

Answer 9

-70mV

Question 10

What does the sodium potassium pump do?

Answer 10

Uses active transport to move 3 sodium ions out of the neurone for every two potassium ions that enter

Question 11

What does the potassium ion channel do?

Answer 11

Allows facilitated diffusion of potassium ions out of the neurone, down their concentration gradient.

Question 12

Describe the sequence of events that happen in an action potential

Answer 12

1) Stimulus - This excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative
2) Depolarisation - If the potential difference reaches -55mV voltage gated sodium ion channels open, more sodium ions diffuse into the neurone
3) Re-polarisation - At a potential difference of +30mV the sodium ion channels close and voltage gated potassium ion channels open. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone, this starts to get the membrane back to its resting potential.
4) Hyperpolarisation - Potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential
5) Resting potential - The ion channels are reset, the sodium potassium pump returns the membrane to its resting potential and maintains it until the membrane is excited again

Question 13

what is summation?

Answer 13

When the effect of neurotransmitter released from many neurones is added together.

Question 14

when are hormones secreted?

Answer 14

When an endocrine gland is stimulated

Question 15

How are glands stimulated?

Answer 15

By a change in concentration of a specific substance and also by electrical impulses

Question 16

what do the first and second messengers do?

Answer 16

First - carries the chemical message the first part of the way, from the endocrine gland to the receptor
Second - carries the chemical message the second part of the way, from the receptor to other parts of the cell

Question 17

Explain the cAMP example

Answer 17

1) The hormone adrenaline is a first messenger
2) It binds to specific receptors in the cell membranes of many cells
3) When adrenaline binds it activates an enzyme called adenylate cyclase
4) This catalyses the production of the second messenger cAMP
5) cAMP activates a cascade

Question 18

What does the medulla and the cortex of adrenal gland do?

Answer 18

Cortex - secretes steroid hormones eg cortisol
Medulla - secretes catecholamine hormones (modified amino acids)
eg adrenaline

Question 19

How can mammals lower their body temperature?

Answer 19

1) Sweating
2) Hairs lie flat, erector pili muscles lie flat, trapping less air, skin is cooled
3) Vasodilation

Question 20

How can mammals increase their body temperature?

Answer 20

1) Shivering
2) Hormones - increases metabolism, so more heat produced
3) Less sweat
4) Hairs stand up - erector pili muscles contract, trapping more air, skin is warmed
5) Vasoconstriction

Question 21

What is the difference between thermoreceptors in the skin, and thermoreceptors in the hypothalamus?

Answer 21

Skin - detect external temperature

Hypothalamus - detect internal temperature

Question 22

How does insulin lower blood glucose concentration?

Answer 22

1) Insulin binds to specific receptors on the cell membranes of liver and muscle cells
2) It increases the permeability of the membranes to glucose, so the cells take up more glucose
3) Insulin also actives enzymes that convert glucose into glycogen
4) Glycogen can be stored in the cytoplasm of cells as an energy source
5) The process of forming glycogen from glucose is called glycogenesis
6) Insulin also increases the rate of respiration of glucose

Question 23

How does glucagon raise blood glucose concentration?

Answer 23

1) Glucagon binds to specific receptors on the cell membranes of liver cells
2) Glucagon activates enzymes that break down glycogen into glucose
3) This is called glycogenolyisis
4) Glucagon also promotes the formation of glucose from fatty acids and amino acids, this is called gluconeogenesis
5) Glucagon decreases the rate of respiration of glucose

Question 24

How do beta cells secrete insulin?

Answer 24

1) When blood glucose level is high, more glucose enters the beta cells by facilitated diffusion
2) This increases the rate of respiration, producing more ATP
3) The rise in ATP triggers the potassium ion channels in the beta cell membrane to close
4) This means potassium ions can’t leave the cell, making the beta cell more positive
5) This triggers calcium ion channels in the membrane to open, so calcium ions diffuse into the cell
6) This causes the vesicles to fuse with the membrane, releasing insulin (this is known as exocytosis)

Question 25

What is type 1 diabetes?

Answer 25

1) The beta cells in the islet of langerhans don’t produce any insulin
2) After eating, the blood glucose level rises and stays high, this is called hyperglycaemia, which can result in death if left untreated
3) Usually develops in children or young adults

Question 26

What is type 2 diabetes?

Answer 26

1) Type 2 diabetes is usually acquired later in life, and is often linked with obesity
2) It occurs when the beta cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin. This is because the insulin receptors on their membranes don’t work properly so the cells don’t take up enough glucose.

Question 27

What are the advantages of using GM bacteria to produce insulin?

Answer 27

1) Producing insulin using GM bacteria is cheaper than extracting it from animal pancreases
2) Larger quantities of insulin can be produced using GM bacteria
3) GM bacteria make human insulin which is more effective than using pig or cattle insulin and is less likely to trigger an allergic response
4) Some people prefer insulin from GM bacteria for ethical reasons

Question 28

How can stem cells be used to cure diabetes?

Answer 28

1) Stem cells could be grown into beta cells
2) The beta cells would then be implanted into the pancreas of a person with type 1 diabetes
3) This means the person would be able to make insulin as normal
4) The treatment is still being developed, but if it’s effective it will cure people with type 1 diabetes