Homeostasis

Question 1

Homeostasis

Answer 1

The maintenance of a constant internal environment

Question 2

Importance of Homeostasis

Answer 2

Ensures that cells of the body are in an environment that meets their needs and allows them to function normally despite external changes.

Question 3

Why is homeostasis important for enzymes?

Answer 3

pH and temperature sensitive -> reactions take place at a constant and predictable rate

Question 4

Why is homeostasis important for water potential?

Answer 4

Water potential of the blood and tissue fluids may cause cells to shrink and expand due to osmosis.

Question 5

What are the benefits of homeostasis for organisms?

Answer 5

Organisms are more independent of the external environment so have a wider geographical range.

Question 6

The control of any self-regulation system involves a serious of stages that feature :

Answer 6

1. Set point at which the system operates
2. Receptor
3. Controller coordinates information
4. Effector
5. Feedback loop, informs receptor of changes

Question 7

Thermoregulation

Answer 7

Regulation of body temperature

Question 8

Methods of gaining heat

Answer 8

1. Production of heat -> metabolism of food during resp.

2. Gain of heat from environment (CCR)

Question 9

Methods of losing heat

Answer 9

1. Evaporation of water e.g. sweat

2. Loss of heat to environment (CCR)

Question 10

Conduction

Answer 10

Transfer of energy through matter from particle to particle

Question 11

Convection

Answer 11

Transfer of heat due to movement of warmed matter

Question 12

Radiation

Answer 12

Transfer of heat through electromagnetic waves

Question 13

Endotherms

Answer 13

Organisms that derive most of their heat from metabolic activities inside their body

Question 14

Ectotherms

Answer 14

Organisms which obtain a large proportion of heat from sources outside the body

Question 15

How do ectotherms control their body temperature?

Answer 15

1. Exposing themselves to the sun
2. Taking shelter
3. Gaining warmth from the ground
4. Generating metabolic heat
5. Colour variations

Question 16

Core body temperature of endotherms

Answer 16

35-44 C -> range is a compromise between having a higher temp. at which enzymes work more rapidly and the amount of energy needed to maintain that higher temperature.

Question 17

Vasoconstriction

Answer 17

Diameter of the arterioles near the surface of the skin is made smaller. This reduces the volume of blood reaching the skin surface through the capillaries. Most blood passes beneath insulating layer of fat-> little heat loss

Question 18

Response to cold environment

Answer 18

1. Vasoconstriction
2. Shivering
3. Raising of hair
4. Increased metabolic rate
5. Decrease in sweating
6. Behavioural mechanisms

Question 19

Response to warm environment

Answer 19

1. Vasodilation
2. Increased sweating
3. Lowering of body hair
4. Behavioural mechanisms

Question 20

How is hair raised?

Answer 20

Hair erector muscles in skin contract, raising hairs. This enables a thicker layer of still air, a good insulator, to be trapped next to skin, improving insulation and conserving heat in mammals with thick fur.

Question 21

Two parts of thermoregulatory centre in hypothalamus

Answer 21

1. Heat gain centre -> activated by a fall in blood temp.

2. Heat loss centre -> activated by rise in blood temp.

Question 22

Thermoreceptors

Answer 22

In the hypothalamus + skin -> send impulses along the autonomic nervous system to the hypothalamus

Question 23

Characteristics of Hormones

Answer 23

1. Produced by glands which secrete hormone directly into blood
2. Carried in the blood plasma to the cells on which they act -> target cells receptors on membrane that are complimentary
3. Effective in very small quantities

Question 24

Second Messenger Model

Answer 24

1. The hormone is the first messenger, binding onto specific receptors on csm of target cells to form h-r complex
2. H-r complex activates an enzyme inside the cell that results in prod, of a chemical that acts as a second messenger
3. Second messenger causes a series of chemical changes that produce required response e.g. adrenaline -> glycogen to glucose

Question 25

Pancreas

Answer 25

Large, pale-coloured gland that’s situated in the upper abdomen behind stomach

Question 26

Islet of Langerhans

Answer 26

Hormone-producing cells consists of :
a cells -> larger and produce glucagon
b cells -> smaller and produce insulin

Question 27

Sources of blood glucose

Answer 27

1. Directly from diet
2. From the breakdown of glycogen -> stored in the liver and muscle cells by glycogenesis
3. Glucogenesis -> prod, of new glucose e.g. liver glycerol + amino acids

Question 28

How is insulin secreted?

Answer 28

b cells of the islets of Langerhans in pancreas detect a rise in blood glucose level and respond by secreting insulin directly into blood plasma.

Question 29

Insulin

Answer 29

Globular protein made of 51 amino acids

Question 30

When insulin combines with glycoprotein receptors

Answer 30

1. A change in tertiary structure of glucose transport protein channels, causing them to change shape and open, allowing more glucose into cell
2. Increase in carrier molecules in csm
3. Activation of enzymes that convert glucose to glycogen and fat

Question 31

How is blood glucose level lowered?

Answer 31

1. Increasing rate of absorption of glucose into cells
2. Increasing respiratory rate of cells
3. Increasing rate of conversion from glucose to glycogen in liver and muscle
4. Increasing rate of conversion of glucose to fat

Question 32

Glucagon

Answer 32

Only cells of the liver have receptors that bind to glucagon . They respond to fall in blood glucose by

• > activating an enzyme that converts glycogen to glucose
• > increasing conversion of amino acids and glycerol into glucose

Question 33

Adrenaline raises the blood glucose level by:

Answer 33

1. Activating an enzyme that causes breakdown of glycogen to glucose in liver
2. inactivating an enzyme that synthesis glycogen from glucose

Question 34

Diabetes

Answer 34

Chronic disease in which a person is unable to metabolise carbohydrate esp. glucose due to inability to control blood glucose levels from lack of insulin or loss of responsiveness

Question 35

Type 1

Answer 35

Insulin dependant : may be result of autoimmune response against b cells of islets of Langerhans

Question 36

Type 2

Answer 36

Insulin independent: Glycoprotein receptors on body cells lose responsiveness to insulin. Inadequate supply of insulin from pancreas. Usually over 40 and overweight.

Question 37

Control of Type 1

Answer 37

Injections of insulin -> dosage should match glucose intake

blood glucose monitored by biosensors

Question 38

Control of Type 2

Answer 38

Regulating intake of carbs in diet and matching this to amount of exercise. May be supplemented by insulin injection or by use of drugs that stimulate insulin prod. Other drugs slow down rate at which body absorbs glucose.