B15 - Homeostasis

Question 1

What is homeostasis?

Answer 1

When the body maintains a dynamic equilibrium, small fluctuations over a narrow range of conditions
- it is essential to monitor changes in the internal environment like pH of blood, core body temperature, conc. of urea and Na+ ions in the blood

Question 2

What are receptors and effectors?

Answer 2

• help maintain a dynamic equilibrium by detecting change in the internal and external environment of an organism
• info from sensory receptors transmitted to the brain
  -impulses sent along motor neurones to trigger change and restore equilibrium

Question 3

What are feedback systems?

Answer 3

• when sensory receptors (detect change) and effectors (trigger a response to restore equilibrium) work together to maintain a constant and steady environment

Question 4

What are negative feedback systems?

Answer 4

effectors work to restore conditions to original state and reverse the initial change
- e.g. blood sugar levels of insulin and glucagon
1. ideal conditions
2. increase/ decrease detected by sensory receptors
3. responses by effectors lower/ raise levels
4. return to ideal conditions

Question 5

What is a positive feedback system?

Answer 5

• change in the internal environment detected by sensory receptors and effectors work to reinforce the change and increase the response

1. change detected
2. responses reinforce change
3. conditions change

Question 6

What are examples of positive feedback?

Answer 6

• blood clotting cascade: where a blood vessel damaged, platelets stick to damaged region and release factors that initiate clotting and attract more platelets
• childbirth: where the baby presses against the cervix, stimulating the production of oxytocin which stimulates the uterus to contract pushing the head of the baby against the cervix and releasing more oxytocin until the baby is born

Question 7

What is thermoregulation?

Answer 7

the maintenance of the core body temperature to maintain optimum enzyme activity
(at high temps, enzymes denature)

Question 8

What physical processes lead to heat loss?

Answer 8

• latent heat of evaporation - objects cool down as water evaporates from surface e.g. sweating
• radiation - transmission of electromagnetic waves to and from air, water and ground
• convection - heating and cooling of organism (hot air rises and cool sink causing convection current around organism

Question 9

What physical process lead to heat gain?

Answer 9

• exothermic chemical reactions
• conduction - heating as a result of frequent collisions of molecules

Question 10

What are ectotherms (outside heat)?

Answer 10

• organisms that use surroundings to warm their bodies
• e.g. invertebrate animals, fish, amphibians, reptiles
• ectotherms in water don’t need to thermoregulate due to high heat capacity of water
• on land, the temp varies per season so organisms have found multiple ways to adapt and cool down/ warm up

Question 11

What are endotherms (inside heat)?

Answer 11

• rely on metabolic processes to warm up and maintain a very stable core body temp
• survive in a range of environments due to multiple adaptations e.g. metabolic rate of endotherms is x5 than ectotherms (warming and cooling are metabolic processes)
• e.g. mammals and birds

Question 12

How do ectotherms warm up using behavioural response?

Answer 12

• need to be warm enough for metabolic reactions to be fast enough so might bask in the sun with maximum surface area exposed e.g. locusts and butterflies orientate themselves for maximum sun exposure and spread wings to increase s. area so warm enough to fly
• can increase temp through conduction via pressing themselves on warm ground
• exothermic metabolic reactions e.g. iguanas contract muscles and vibrate to increase metabolism to raise their body temp

Question 13

How do ectotherms cool down via behavioural responses?

Answer 13

• minimise s. area exposed to sun, hide on burrows, caves
• press bodies against cool ground/ rocks
• minimise movement to reduce metabolic heat generated

Question 14

How do ectotherms regulate temp using physiological responses?

Answer 14

• lizards in colder climates are usually darker to absorb more radiation than light colours
• some alter heart rate to increase/ decrease metabolic rate and regulate temp
• need less food than endotherms since use less energy to regulate temp so can life in very difficult environments where food is in short supply

Question 15

What is an endocrine gland?

Answer 15

• group of cells specialised to secrete hormones directly into the bloodstream
• e.g. adrenal gland and pancreas

Question 16

Endocrine Glands

Answer 16

• pituitary gland - produces growth hormone, which controls growth of bones and muscles, release ADH (increases reabsorption of water in kidneys), releases gronadotrophin (controls development of ovaries and testes)
• Thyroid gland - produces thryoxine; controlling rate of metabolism and rate of glucose is used in respiration