Homeostasis

Question 1

What is homeostasis?

Answer 1

The maintenance of a stable internal environment.

Question 2

Why is it important to maintain a stable body temperature?

Answer 2

1. If the temperature is too low the enzyme activity is reduced. This lowers the rate of metabolic reactions.
2. As the temperature increases the particles have more energy and love faster. This means there are more frequent and successful collisions between the substrates and enzymes. The increased formation of enzyme-substrate complexes increases enzyme activity and the rate of metabolic reactions.
3. If the temperature gets too high the enzymes will denature meaning they will no longer be able to catalyse metabolic reactions and the rate increases.

Question 3

Why is it important to maintain stable blood pH levels?

Answer 3

If the blood pH levels are too high or too low the ionic bonds that hold the tertiary structure of the enzymes together will break. This means the active site of the enzymes will change shape and it will no longer be able to form an enzyme-substrate complex. This decreases enzyme activity and the rate of metabolic reactions. The highest rate of enzyme activity and metabolic reactions is at optimum pH.

Question 4

Why is it important to maintain a stable blood glucose concentration?

Answer 4

1. If the blood glucose levels are too high water will diffuse out of cells via osmosis. This causes cells to shrivel up and die.
2. If the blood glucose levels are too low water will diffuse into cells which will cause them to burst. There also won’t be enough to carry out respiration, which releases energy for metabolic reactions.

Question 5

What is a negative feedback mechanism?

Answer 5

The effectors counteract the change to restore levels to normal.

Question 6

What is a positive feedback mechanism?

Answer 6

The effectors amplify the change to raise the levels away from the normal.

Question 7

How do blood glucose levels rise?

Answer 7

When we eat food that contains carbohydrates.

Question 8

How do blood glucose levels fall?

Answer 8

When the glucose is used for respiration and the release of energy.

Question 9

What is the role of the beta cells in the islet of Langerhans?

Answer 9

They release insulin

Question 10

What is the role of the alpha cells in the islet of Langerhans?

Answer 10

They release glucagon.

Question 11

Describe what happens when the blood glucose levels are too high.

Answer 11

1. The beta cells in the islet of Langerhans detect the increase in blood glucose levels and release insulin.
2. The insulin binds to receptors on the cell membrane of the liver cells.
3. This triggers the release of GLUT-4 from the vesicles in the cells. These then move to the membrane and allow the movement of glucose into the cell via facilitated diffusion.
4. The insulin activates enzymes that convert glucose into glycogen via glucogenesis.

Question 12

Describe what happens when the blood glucose levels are too high.

Answer 12

1. The alpha cells in the islet of Langerhans detect the increase in blood glucose levels and release glucagon.
2. The glucagon binds to receptors on the cell membrane of the liver cells.
3. It activates enzymes that convert glycogen into glucose via glycogenolysis.
4. It activates enzymes that make glucose from other biological molecules, like lipids, via gluconeogenesis.

Question 13

When is adrenaline released?

Answer 13

It is secreted from the adrenal glands when the blood glucose levels are low and the body needs to get ready for action.

Question 14

What is the role of adrenaline?

Answer 14

It activates glycogenolysis and inhibits glycogenesis. It activates glucagon secretion and inhibits the secretion of insulin.

Question 15

What is the second messenger model?

Answer 15

It describes how glucagon and adrenaline activate glycogenolysis.

Question 16

Describe the second messenger model.

Answer 16

1. When glucagon binds to receptors on the cell membrane of liver cells, it activates adenylate cyclase.
2. The adenylate cyclase converts ATP into cAMP.
3. The cAMP activates protein kinase A.
4. The protein kinase A triggers a cascade of reactions that turn glycogen into glucose.

Question 17

What is type 1 diabetes?

Answer 17

The immune system attacks the beat cells so they can’t produce enough insulin.

Question 18

How is type 1 diabetes dealt with?

Answer 18

Regular insulin injections.

Question 19

What is type 2 diabetes?

Answer 19

The liver cells no longer respond to insulin. This could be due to the receptors on the cell membrane being damaged.

Question 20

How is type 2 diabetes dealt with?

Answer 20

1. Regular exercise.
2. Healthy diet.

Question 21

Draw the structure of a kidney.

Question 22

How does the glomerular filtrate form in the nephrons?

Answer 22

1. The efferent arterioles are smaller than the afferent arterioles, which means that the glomerulus is under high pressure.
2. This pushes water and other small molecules out of the capillary and into the Bowman’s capsule.
3. The filtrate then passes through the capsule and enters the nephron.

Question 23

Why are proteins and other large molecules not part of the glomerular filtrate?

Question 24

What happens in the PCT?

Answer 24

1. Useful solutes like glucose are reabsorbed into the blood via active transport and facilitated diffusion.
2. Water is reabsorbed via osmosis into the blood.

Question 25

What is the control of the blood water potential called?

Answer 25

osmoregulation

Question 26

How do mammals lose water?

Answer 26

They lose it in urine and sweat.

Question 27

Where is water reabsorbed in the nephrons?

Answer 27

1. In the PCT.
2. In the DCT and collecting duct.
3. The loop of Henle.

Question 28

Describe how water is reabsorbed in the loop of Henle.

Answer 28

1. The ascending limb is permeable to sodium ions and not water.
2. Sodium ions are actively pumped out of the ascending limb, which decreases the water potential of the medulla.
3. The water potential inside the descending limb is higher than the water potential of the medulla, so water moves out of it via osmosis.
4. Water also moves out of the DCT and collecting duct via osmosis.
5. The water is reabsorbed into the blood via a capillary network.

Question 29

Describe how water is reabsorbed in the DCT and collecting duct.

Answer 29

1. ADH binds to receptors on the walls of the DCT and collecting duct.
2. This causes the cells to release aquaporins.
3. The aquaporins allow water to move from the DCT and collecting duct into the medulla.
4. The water is reabsorbed into the bloodstream via osmosis.

Question 30

How does the amount of ADH in the blood change when the blood water potential is too high? What effect does this have?

Answer 30

1. The osmoreceptors in the hypothalamus detect an increase in the blood water potential.
2. They send an impulse along the sensory neuron to the posterior pituitary gland.
3. The posterior pituitary gland releases less ADH, which makes the walls of the DCT and collecting duct less permeable to water.
4. Less water is reabsorbed into the blood. The water potential decreases.

Question 31

How does the amount of ADH in the blood change when the blood water potential is too low? What effect does this have?

Answer 31

1. The osmoreceptors in the hypothalamus detect a decrease in the blood water potential.
2. They send an impulse along the sensory neuron to the posterior pituitary gland.
3. The posterior pituitary gland releases more ADH, which makes the walls of the DCT and collecting duct more permeable.
4. More water is reabsorbed into the blood. The water potential increases.