3.5.4 - Homeostasis

Question 1

Importance of homeostasis

Answer 1

Enzymes are sensitive to temperature or pH changes, and don’t function properly in wrong conditions
Allows for reactions to take place at constant rate
Changes to water potential may cause cells to shrink or burst

Question 2

Ectotherm definition

Answer 2

Organisms that control body temperature by using the external environment through changing behaviour

Question 3

Example of an ectotherm

Answer 3

Lizards

Question 4

Endothermic definition

Answer 4

Organisms that control body temperature by behaviour and internal metabolic activity

Question 5

How ectothermic organisms control temperature?

Answer 5

Exposing themselves to sunlight/ taking shelter
Gaining hear from the ground
Generating metabolic heat
Colour variations (black for more heat)

Question 6

Is the body temperature is too high?

Answer 6

The thermoreceptors in the skin/ hypothalamus detect the change
They send an impulse to the heat loss centre of the hypothalamus (in the brain)
The impulse is sent to the skin (effector), and undergoes: vasodilation, sweating, lowering hair, lowering metabolic rate

Question 7

Vasoconstriction definition

Answer 7

When the body temperature is too low, the lumen of the arterioles near the skin surface gets smaller. This means that there’s a reduction in the volume of blood reaching the surface, so less heat lost

Question 8

How shivering increases body temperature?

Answer 8

Muscles of the body undergoing rhythmic contractions that produce metabolic heat

Question 9

How raising hair helps to increase body temperature?

Answer 9

Hair erector muscles in skin contract, raising the hair on body, enabling a thick layer of air which is a good insulator. Heat is conserved

Question 10

How does sweating reduce body temperature?

Answer 10

Evaporating water from the skin surface requires heat energy, so energy is lost

Question 11

Hormone characteristics?

Answer 11

Produced by glands that secrete the hormones directly into blood stream
Carried in blood plasma to target cells
Effective in small quantities, but have widespread effects

Question 12

Target cells definition

Answer 12

Cells on which hormones act, which have receptors on their membranes, which are complementary to the hormones

Question 13

Pancreas definition

Answer 13

Large gland in the abdomen, produces enzymes for digestion, and hormones for controlling blood glucose levels

Question 14

Islets of Langerhans defintion

Answer 14

Groups of hormone producing cells in the pancreas

Question 15

Types of cells in the Islets of Langerhans

Answer 15

Alpha and beta cells

Question 16

What alpha cells do?

Answer 16

Produce glucagon

Question 17

What beta cells do?

Answer 17

Produce insulin

Question 18

Why is it important to control blood glucose levels?

Answer 18

Glucose is main substrate for respiration, providing source of energy (ATP) for almost all organisms
If too low, cells would be deprived of energy and die
If too high, water potential in blood reduces, causing dehydration…

Question 19

Sources of glucose

Answer 19

Directly from the carbohydrates in the diet
From the breakdown of glycogen
From gluconeogenesis - the production of glucose from other sources (amino acids/ fats)

Question 20

If blood glucose levels are to high?

Answer 20

The beta cells in Islets of Lamgerhans detect this change, and produce insulin, which causes:
Conversion of glucose into glycogen
Conversion of glucose into fats
Absorption of glucose into cells
Increased cellular respiration

Question 21

Insulin defintion

Answer 21

Globular protein, hormone that brings a fall in the blog glucose levels of a person

Question 22

If blood glucose levels are too low?

Answer 22

The alpha cells in the Islets of Langerhans detect this change, and produce glucagon, which brings about the:
Conversion of glycogen to glucose
Conversion of amino acids to glucose

Question 23

Adrenaline definition

Answer 23

Adrenaline is another hormone that brings about a rise in the blood glucose levels, similar to glucagon
It activates an enzyme that breaks glycogen to glucose and inactivates the enzyme that synthesises glycogen from glucose

Question 24

Type 1 diabetes facts

Answer 24

Develops usually in childhood and quickly. It occurs when the body is unable to produce insulin, so has to be controlled by insulin injections 2-4 times a day

Question 25

Type 2 diabetes facts

Answer 25

Develops slowly and usually in over 40s. Occurs when the glycoproteins receptors lose their responsiveness to insulin

Question 26

Symptoms of diabetes

Answer 26

High blood glucose level
Glucose present in urine
Increased thirst
Urinating excessively
Tiredness
Weight loss
Blurred vision

Question 27

Homeostasis definition

Answer 27

Maintenance of a constant internal environment in organisms