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B - Biology (A-Level) > Topic 6C - Homeostasis > Flashcards

Topic 6C - Homeostasis Flashcards

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1
Q

What is homeostasis?

A

The maintenance of a stable internal environment

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2
Q

Your internal environment is kept in a state of…

A

…dynamic equilibrium

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3
Q

Why is it important to regulate core body temperature and blood pH?

A

Temperature and pH affect enzyme activity, which affects the rate of metabolic reactions

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4
Q

What are metabolic reactions?

A

Reactions in living cells

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5
Q

How does the optimum temperature affect the rate of metabolic reactions?

A

The rate increases as:
More heat means more kinetic energy so molecules move faster. This means the substrate molecules are more likely to collide with the enzymes’ active sites, creating enzyme-substrate complexes. The energy of these collisions also increases, which means each collision is more likely to result in a reaction.

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6
Q

How does too low a temperature affect the rate of metabolic reactions?

A

The rate slows as:

Enzyme activity is reduced.

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7
Q

How does too high a temperature affect the rate of metabolic reactions?

A

Enzymes denature so the reaction essentially stops as:
The rise in temperature causes the enzymes to vibrate more. This vibration breaks the hydrogen bonds holding the enzyme in its 3D shape, therefore the active site changes shape and so enzyme-substrate complexes can no longer form.

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8
Q

How does too high a pH affect the rate of metabolic reactions?

A

Enzymes denature so the reaction essentially stops as:
The alkaline conditions break ionic and hydrogen bonds that hold the 3D structure of enzymes together, thereby deforming the active site of the enzyme so no more enzyme-substrate complexes can form.

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9
Q

How does too low a pH affect the rate of metabolic reactions?

A

Enzymes denature so the reaction essentially stops as:
The acidic conditions break ionic and hydrogen bonds that hold the 3D structure of enzymes together, thereby deforming the active site of the enzyme so no more enzyme-substrate complexes can form.

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10
Q

How does optimum pH affect the rate of metabolic reactions?

A

Enzyme are at their highest rate of activity and so are able to catalyse reactions faster and with greater efficiency.

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11
Q

How is pH calculated?

A

pH = -log{H+}

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12
Q

How do enzymes speed up reactions?

A

Enzymes lower the activation energy of reaction, thereby speeding them up as less energy is required.

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13
Q

What is a substrate?

A

The molecule that is reacting (the reactant).

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14
Q

What is a logarithmic scale?

A

A scale that uses the logarithm of a number instead of the number itself.

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15
Q

Why is a logarithmic scale sometimes used to express pH?

A

It is easier to compare when they are in a logarithmic scale as sometimes H+ can vary on a linear scale.
Makes it easier to plot small and large values on the same graph e.g -log(0.1) = -1 and -log(1000) = -3

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16
Q

What would metabolic reactions be like with denatured enzymes?

A

They may still happen but at a rate too slow for the body’s needs.

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17
Q

How does too high a blood concentration of glucose affect the body?

A

Water potential of blood is reduced, therefore water diffuses by osmosis from surrounding cells into the blood, causing surrounding cells to shrivel up and die.

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18
Q

How does too low a blood concentration of glucose affect the body?

A

Cells are unable to carry out normal activities as there isn’t enough glucose for respiration to provide energy.

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19
Q

What is water potential?

A

The potential of water molecules to diffuse out of or into a solution.

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20
Q

What is the negative feedback mechanism?

A

A mechanism that restores the level to normal after a change.

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21
Q

What is the positive feedback mechanism?

A

The mechanism that amplifies a change away from the normal level.

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22
Q

What is an example of negative feedback?

A

Core temperature decreases. Receptors in hypothalamus detect decrease. Signal is sent through CNS to effector. Muscles start contracting (you start shivering). Core temperature starts increasing back to the normal level.

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23
Q

What is an example of positive feedback?

A

Skin is cut and blood platelets leaves the body. Decrease in platelets detected and platelets are activated and release a chemical which activates more platelets.

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24
Q

What is an example of a homeostatic system breaking down?

A

When you have hypothermia, heat is lost quicker than it can be produced. As body temperature falls the brain doesn’t work properly and shivering stops - making body temperature fall even more. Positive feedback takes body temperature further and from the normal.

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25
Q

What is concentration of glucose in the blood typically?

A

90mg per 100cm^3.

26
Q

Where is insulin secreted from?

A

Beta cells in clusters of pancreatic cells called the islets of Langerhans.

27
Q

Where is glucagon secreted from?

A

Alpha cells in clusters of pancreatic cells called the islets of Langerhans.

28
Q

How does insulin affect blood glucose concentration? (3)

A

Insulin lowers blood glucose concentration by:

(1) binding to specific receptors on the cell membranes of muscle cells and liver cells (hepatocytes). This increases the membranes permeability to glucose, so they take up more glucose.
(2) Insulin also activates enzymes in hepatocytes that convert glucose into glycogen. The cells then store glycogen in their cytoplasm. This is called glycogenesis.
(3) Insulin also increases the rate of respiration of glucose, particularly in muscle cells.

29
Q

How does glucagon affect blood glucose concentration? (3)

A

Glucagon raises blood glucose concentration by:

(1) binding to specific receptors on the cell membranes of hepatocytes and activating enzymes that break down glycogen into glucose. This is called glycogenolysis.
(2) Glucagon also activates enzymes involved in the formation of glucose from glycerol and amino acids. This is called gluconeogenesis.
(3) Glucagon decreases the rate of respiration of glucose in cells.

30
Q

How does insulin travel around the body.

A

In the blood as it is a hormone.

31
Q

How does glucagon travel around the body.

A

In the blood as it is a hormone.

32
Q

What are glucose transporters?

A

Channel proteins which allow glucose to be transported across a cell membrane via facilitated diffusion.

33
Q

GLUT4 is a…

A

glucose transporter.

34
Q

Where is GLUT4 found?

A

Cardiac and skeletal muscle cells.

35
Q

How does low insulin levels affect GLUT4?

A

GLUT4 is stored in vesicles in the cytoplasm of cells.

36
Q

How does high insulin levels affect GLUT4?

A

Insulin binds to the cell membranes of hepatocytes, which triggers the movement of GLUT4 to the membrane.

37
Q

How does glucose enter hepatocytes?

A

Facilitated diffusion via glucose transporters.

38
Q

Adrenaline is a…

A

hormone.

39
Q

Where is adrenaline secreted from?

A

The adrenal gland.

40
Q

Where is the adrenal gland located?

A

Just above the kidneys.

41
Q

When is adrenaline secreted? (3)

A

(1) when there’s a low concentration of glucose in your blood
(2) when you’re stressed
(3) when you’re exercising

42
Q

What does adrenaline do? (4)

A

(1) activates glycogenolysis
(2) inhibits glycogenesis
(3) activates glucagon secretion
(4) inhibits insulin secretion

43
Q

Why does adrenaline do what it does?

A

To increase glucose concentration, getting the body ready for action (which would require glucose for insulin)

44
Q

What is the second messenger model?

A

The binding of the hormone to cell receptors activates an enzyme on the inside of the cell membrane, which then produces a chemical know as a second messenger

45
Q

Give an example of a second messenger model. (5)

A

(1) Adrenaline or glucagon binds to the cell surface receptors of hepatocytes.
(2) This activates the enzyme adenylate cyclase.
(3) Activated adenylate cyclase converts ATP into cAMP (a second messenger).
(4) cAMP activates an enzyme called protein kinase A.
(5) Protein kinase A causes a cascade that breaks down glycogen into glucose.

46
Q

What is glycogenesis?

A

The conversion of glucose to glycogen.

47
Q

What is glycogenolysis?

A

The breakdown of glycogen to glucose.

48
Q

What is gluconeogenesis?

A

The synthesis of glucose from glycerol and amino acids.

49
Q

What activates glycogenesis?

A

Insulin.

50
Q

What inhibits glycogenesis?

A

Adrenaline.

51
Q

What activates glycogenolysis?

A

Glucagon and adrenaline.

52
Q

What activates gluconeogenesis?

A

Glucagon.

53
Q

What is diabetes?

A

A condition where blood glucose concentration can’t be controlled properly.

54
Q

How is Type I diabetes linked with beta cells?

A

The immune system attacks the beta cells in the islets of Langerhans so they can’t produce any insulin.

55
Q

How is Type II diabetes linked with beta cells?

A

Beta cells don’t produce enough insulin or the body’s cells don’t respond properly to insulin.

56
Q

When do you usually get Type I diabetes?

A

You can get it whenever. However some people have a genetic predisposition and they also think it may be triggered by a viral infection.

57
Q

When do you usually get type II diabetes?

A

It is usually aquifer later in life and is often linked to obesity, lack of exercise and poor diet.

58
Q

How is Type I diabetes treated?

A

Insulin therapy - they receive regular insulin injections throughout the day or use an insulin pump to have it delivered continuously.

59
Q

How is Type II diabetes treated?

A

By eating a healthy balanced diet, losing weight (if necessary) and regular exercise. Glucose-lowering medication can be taken if diet and exercise can’t control it.

60
Q

What is hypoglycaemia?

A

When you have too little glucose in your system.

61
Q

What is hyperglycaemia?

A

When you have too much glucose in your system.

B - Biology (A-Level) (10 decks)

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