Homeostasis

Question 1

Define homeostasis

Answer 1

The maintenance of a constant internal environment in organisms

Question 2

Why is homeostasis important?

Answer 2

• ensures temperature is at its optimum for functioning of enzymes
• ensures changes to the water potential of blood and tissue fluid is kept constant; cells do not shrink/burst
• makes organism more independent of environment

Question 3

Define feedback loop

Answer 3

When changes that are brought about by effector are reported back to receptor

Question 4

Give some control mechanisms of ectotherms, to control body temperature

Answer 4

• change colour
• bask in sun
• take shelter
• gain warmth from ground

Question 5

Describe importance of surface area and volume in temperature control in endotherms

Answer 5

• heat is lost from surface area
• heat is gained from within volume (i.e respiration)
  Therefore, smaller SA to volume ratio, easier it is to maintain high body temp

Question 6

How does vasoconstriction contribute to raising body temperature?

Answer 6

• diameter of arterioles near skin reduce, reduces volume of blood reaching skin surface through capillaries
• most of blood passes beneath insulating layer of fat and so loses little heat to environment

Question 7

What controls body temperature?

Answer 7

Hypothalamus in brain

Question 8

How are impulses from thermoreceptors in skin sent to hypothalamus?

Answer 8

Via autonomic system

Question 9

Hormones are produced by…

Answer 9

Glands

Question 10

Describe the second messenger model

Answer 10

1. Hormone binds to specific receptor on cell surface membrane of cell to form hormone-receptor complex
2. This complex activates an enzyme to produce chemical that acts as second messenger
3. This causes a series of changes that produce required response

Question 11

Where are the islets of langerhans found?

Answer 11

In the pancreas

Question 12

What problems can be caused if the blood glucose conc raises too high?

Answer 12

• water potential of blood is lowered, water leaves cells by osmosis and causes dehydration

Question 13

What are the sources of blood glucose?

Answer 13

• directly from the diet
• glycogenolysis; breakdown of glycogen
• gluconeogenesis; conversion of non carbohydrates into glucose

Question 14

When insulin binds to glycoprotein receptors on cell surface membrane what happens?

Answer 14

• change in tertiary structure of glucose transport proteins; more glucose enters cell
• increase in no. Of carrier molecules
• activation of enzymes that convert glucose to glycogen and fat

Question 15

How does insulin lower the blood glucose concentration?

Answer 15

• increases rate of absorption of glucose into cells
• increases cellular respiration
• increasing rate of conversion of glucose into glycogen and fat

Question 16

Why do only liver cells respond when glucagon is released by alpha cells in islets of langerhans?

Answer 16

Only liver cells have receptors that bind to glucagon

Question 17

How does glucagon increase blood glucose concentration?

Answer 17

• activates enzyme that converts glycogen to glucose

- increases rate of conversion of amino acids and glycerol into glucose

Question 18

What is diabetes?

Answer 18

• disorder caused by lack of insulin or loss of responsiveness to insulin, results in blood glucose levels not being controlled

Question 19

What causes type 1 diabetes?

Answer 19

An autoimmune response that attacks beta cells, so insulin cannot be produced

Question 20

What causes type 2 diabetes?

Answer 20

Glycoprotein receptors on body cells lose responsiveness to insulin

Question 21

How is type 2 diabetes controlled?

Answer 21

By regulating the intake of carbohydrates and controlling amount of exercise done