TOPIC 6C

Question 1

What is homeostasis?

Answer 1

• Homeostasis is the maintenance of a stable internal environment -
• Homeostasis involves control systems that keep your internal environment roughly constant (within certain limits).
• Keeping your internal environment stable is vital for cells to function normally and to stop them being damaged.
• It’s particularly important to maintain the right core body temperature and blood pH. This is because temperature and pH affect enzyme activity, and enzymes control the rate of metabolic reactions.

Question 2

Explain briefly how body temperature can affect enzyme activity, and what is the optimum temperature?

Answer 2

(see green box on page 146 in the revision guide)

Question 3

Explain briefly how blood pH can affect enzyme activity, and what is the optimum pH?

Answer 3

(see red box on page 146 in the revision guide)

Question 4

Explain briefly how body glucose concentration can affect enzyme activity.

Answer 4

(see purple box on page 146 in the revision guide)

Question 5

Describe how a homeostatic system works inside the body.

Answer 5

(see bottom box on page 146 in the revision guide)

Question 6

How does having multiple negative feedback mechanism give more control?

Answer 6

(see top of page 147 in the revision guide)

Question 7

What does a positive feedback mechanism do?

Answer 7

Positive feedback mechanisms amplify a change from the normal level.

(see page 147 in the revision guide)

Question 8

When and how do platelets undergo positive feedback?

Answer 8

(see red box onpage 147 in the revision guide)

Question 9

When and how does body temperature undergo positive feedback?

Answer 9

(see red box on page 147 in the revision guide)

Question 10

What is the blood glucose concentration normally at?

Answer 10

90mg per 100cm3 of blood.

It’s monitored by cells in the pancreas.

Question 11

What activities cause glucose levels to rise and fall?

Answer 11

Blood glucose concentration rises after eating food containing carbohydrate.

Blood glucose concentration falls after exercise, as more glucose is used in respiration to release energy.

Question 12

What 2 hormones control blood glucose concentration?

Answer 12

• Insulin
• Glucagon

They travel in the blood to their target cells (effectors)

Question 13

Where is insulin secreted?

Answer 13

Secreted by clusters of cells in the pancreas called the islet of Langerhans.

Beta cells secrete insulin into the blood.

Question 14

Where is glucagon secreted?

Answer 14

Secreted by clusters of cells in the pancreas called the islet of Langerhans.

Alpha cells secrete glucagon into the blood.

Question 15

Describe how insulin lowers blood glucose concentration?

Answer 15

(see red box on page 148 in the revision guide)

Question 16

Describe how glucagon raises blood glucose concentration?

Answer 16

(see blue box on page 148 in the revision guide)

Question 17

Draw the negative feedback loop of how blood glucose concentration is controlled by insulin and glucagon.

Answer 17

(see bottom of page 148 in the revision guide)

Question 18

What is GLUT4?

What is its function?

Answer 18

Skeletal and cardiac muscle cells contain a channel protein called GLUT4. GLUT4 is a glucose transporter.

When insulin levels are too low. GLUT4 is stored in vesicle in the cytoplasm of cells.

When insulin binds to receptors on the cell-surface membrane, it triggers the movement of GLUT4 to the membrane.

Glucose can then be transported into the cell through the GLUT4 protein, by facilitated diffusion.

Question 19

Where is adrenaline secreted?

Answer 19

Adrenaline is a hormone that is secreted from your adrenal glands (found just above your kidneys)

Question 20

When is adrenaline secreted? (in referring to blood glucose concentrations)

And what does it do?

Answer 20

Its secreted when there’s a low concentration of glucose in your blood, when you’re stressed and when you’re exercising.

Adrenaline binds to receptors in the cell membrane of liver cells:

• It activates glycogenolysis (the breakdown of glycogen to glucose)
• It inhibits glycogenesis (the synthesis of glycogen form glucose)

It also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration.

Adrenaline gets the body ready for action by making more glucose available for muscles to respire.

Question 21

What is glycogenolysis?

Answer 21

The breakdown of glycogen to glucose.

Question 22

What is glycogenesis?

Answer 22

The synthesis of glycogen form glucose.

Question 23

How do both adrenaline and glucagon activate glycogenolysis inside the cell even though they bind to receptors on the outside of the cell?

Answer 23

(see purple box on page 149 in the revision guide)

Question 24

Describe type 1 diabetes.

Answer 24

(see green box on page 150 in the revision guide)

Question 25

Describe type 2 diabetes.

Answer 25

(see blue box on page 150 in the revision guide)

Question 26

How can you reduce the risk of developing type 2 diabetes?

Answer 26

• Eat a diet that’s low in fat, sugar and salt, with plenty of whole grains, fruit and vegetables.
• Take regular exercise.
• Lose weight if necessary.

(see page 150 in the revision guide)

Question 27

Describe how can you use colorimetry to determine the concentration of a glucose solution.

Answer 27

(see page 151 in the revision guide)

Question 28

What are the main functions of the kidneys?

Answer 28

• To excrete waste products, such as urea.

- Regulate water potential of the blood.

Question 29

Briefly describe how the kidneys produce urea from blood.

Answer 29

As the blood passes through capillaries in the cortex |(outer layer) of the kidneys, substances are filtered out of the blood and into long tubules that surround the capillaries.
This process is called ultrafiltration.

After ultrafiltration, useful substances, such as glucose and the right amount of water, are then reabsorbed back into the blood.
This process is called selective reabsorption.

The remaining unwanted substances pass along to the bladder and are excreted as urine.

Question 30

Describe ultrafiltration of the kidneys in detail.

Answer 30

(see page 152 in the revision guide)

Question 31

Describe selective reabsorption in the kidneys in detail.

Answer 31

(see page 153 in the revision guide)

Question 32

Describe briefly how the kidneys regulate water loss from the body.

Answer 32

(see top of page 154 in the revision guide)

Question 33

Where is the loop of Henle located?

Answer 33

The loop of Henle is located in the medulla (inner layer) of the kidneys. Its made up od 2 ‘limbs’ - the descending limd and the ascending limb.

The limbs control the movement of sodium ions so that water can be reabsorbed by the blood.

Question 34

How does the loop of Henle maintain a sodium ion gradient?

Answer 34

(see page 154 in the revision guide)

Question 35

What cells is water potential controlled by?

Answer 35

The water potential of the blood is monitored by cells called osmoreceptors in a part of the brain called the hypothalamus.

(see page 155 in the revision guide)

Question 36

When you’re dehydrated do blood ADH levels rise or fall?

Answer 36

Rise.

see page 155 in the revision guide

Question 37

When you’re hydrated do blood ADH levels rise or fall?

Answer 37

Fall.

see page 155 in the revision guide