homeostasis and feedback mechanisms

Question 1

Homeostasis

Answer 1

Maintaining the internal environment of an organism, within certain limits

Question 2

Name five internal conditions that need to be regulated

Answer 2

• Body temperature
• Blood glucose concentration
• Blood water concentration
• Blood salt concentrations
• Blood pH

Question 3

Give 3 reasons why Homeostasis is important + explanations

Answer 3

Enzymes - Our metabolic functions are controlled by enzymes. They work under specific conditions (e.g. temperature and pH)
Water potential - changes in water potential would cause cells to lyse or shrink.
External Environment - ability to survive in a wider range of environmental conditions

Question 4

What happens when blood glucose levels rise? [3]

Answer 4

• A rise in blood sugar is detected by the pancreas
• This causes the pancreas to release insulin
• Insulin stimulates the conversion of glucose to glycogen in the liver

Question 5

What happens when blood glucose levels fall? [3]

Answer 5

• A fall in blood sugar is detected by the pancreas
• This causes the pancreas to release glucagon
• Glucagon stimulates conversion glycogen to glucose in the liver

Question 6

What happens when body temperature rises? [3]

Answer 6

• A rise in body temperature is detected by the thermoregulatory centre in the brain
• An impulse is then sent via the nervous system to the blood vessels and sweat glands
• Stimulating dilation of blood vessels and sweating

Question 7

What happens when body temperature falls? [3]

Answer 7

• A fall in body temperature is detected by the thermoregulatory centre in the brain
• An impulse is then sent via the nervous system to the blood vessels and hair erector muscles
• Stimulating constriction of blood vessels and contraction of muscles

Question 8

Negative Feedback [3]

Answer 8

• If a increase or decrease occurs, a receptor detects this and causes the change in the opposite direction
• The factor is therefore maintained around the optimum
• Both blood glucose levels and temperature are examples of negative feedback (wavy graph)

Question 9

What is Positive Feedback?

Answer 9

• Isn’t common and can be harmful, moving the variable away from the norm

Question 10

Positive Feedback [3]

Answer 10

• There is a change away from the optimum detected by the receptor
• The communication system informs the effector
• The effector reacts to increase the change (e.g. labour)

Question 11

Labour and Positive Feedback [5]

Answer 11

• Baby’s head presses on cervix
• Stretch receptors in cervix detect change
• Oxytocin released, oxytocin increases contractions of uterus
• Cervix stretches more
• Baby’s head presses on more stretch receptors repeating cycle

Question 12

Hypothermia and Positive Feedback [5]

Answer 12

• Body starts to get cold
• Body temperature drops
• Enzymes have less kinetic energy
• Respiration rate slows
• Less heat produced - body temperature drops further
  Etc.

Question 13

Hormones [5]

Answer 13

• Wide variety of chemical substances
• Made in glands
• Travel in bloodstream
• Target cells with have specific receptors for the hormone
• Have wide-spread and long-lasting effects