Chapter 15// Homeostasis

Question 1

Define homeostasis

Answer 1

Maintenance of constant/stable internal environment

About a set point

Despite changes to external environment

Question 2

Define metabolism

Answer 2

all chemical reactions inside body which occur in order to maintain life

Question 3

Define stimulus

Answer 3

any change in internal or external environment

Question 4

Define receptor

Answer 4

extrinsic glycoproteins that bind chemical signals, detecting change + triggering a response by the cell

Question 5

Define effector

Answer 5

muscle or gland which carries out body’s response to a stimulus

Question 6

What is negative feedback, give an example

Answer 6

when receptors detect a stimulus + effectors work to reverse the change and restore conditions to the norm. Negative feedback stops the effectors to reverse initial stimulus as the norm has been reached.

E.g. when blood sugar levels are detected to be too high, cells in pancreas release insulin which increases uptake of glucose by the liver (glucose enters through glucose transport proteins in cell surface membrane) which converts the glucose into glycogen,the receptors in blood detect glucose levels are back to normal and NEGATIVE FEEDBACK stops the pancreas releasing insulin.

Question 7

What is positive feedback (give 2 examples)

Answer 7

a change in internal environment is detected and effectors are stimulated to reinforce the change and INCREASE THE RESPONSE

e.g. blood clotting cascade or childbirth

Question 8

Explain in detail 2 examples of positive feedback

Answer 8

✅blood clotting cascade = when blood vessel damaged, platelets stick to damaged region releasing factors that initiate clotting and attract more platelets— this continues till clot is formed

✅childbirth = head of baby pressing against cervix stimulates production of oxytocin, which stimulates uterus to contract pushing head of baby even harder against cervix (triggering more oxytocin release) continuing till baby is born

Question 9

What is the difference between positive and negative feedback?

Answer 9

Positive feedback brings about more of the effect, negative feedback reverses it

Question 10

Is positive feedback involved in homeostasis?

Answer 10

positive feedback is NOT INVOLVED IN HOMEOSTASIS— homeostasis returns the body to a preset/ stable condition whereas positive feedback takes the body further away from the norm

Question 11

Give some reasons why organisms are constantly heating up/cooling down

Answer 11

• exothermic chemical reactions
• latent heat of evaporation— objects cool down as water evaporates from a surface
• radiation (transmission of EM waves to + from the air, water or ground)
• convection (heating or cooling by currents of air or water)
• conduction (heating as a result of collision of molecules)

Question 12

Define ectotherm and give some examples

Answer 12

‘Outside heat’

animals that use their surroundings to warm their bodies so their core temperature is heavily dependent on their environment

e.g. invertebrate animals, fish, amphibians, reptiles

Question 13

Define endotherm and give some examples

Answer 13

‘Inside heat’

animals that rely on their metabolic processes to warm their bodies and maintain their core temperature

Question 14

what monitors the internal temperature of the body (in the blood)

Answer 14

thermoreceptors in hypothalamus detect internal temperature (temperature of the blood)

Question 15

what monitors external temperature of the body (temperature of the skin)

Answer 15

thermoreceptors in the skin are called PERIPHERAL TEMPERATURE RECEPTORS, they detect external temperature (temperature of the skin)

Question 16

Thermoreceptors send impulses along sensory neurones to the hypothalamus, the hypothalamus sends impulses along _________

Answer 16

motor neurones to effectors (e.g. skeletal muscles, sweat glands, erector pili muscles in the skin)

The effectors respond to restore body temperature back to normal

Question 17

Give 2 behavioural responses of ectotherms

Answer 17

• bask in the sun

* press their bodies against warm ground/ cold rocks

Question 18

Give an example of an ectotherm that has physiological responses

Answer 18

Lizards living in cold conditions are dark colours in order to absorb more heat radiation

Question 19

What type of animals are more vulnerable to fluctuations in environment ?

Answer 19

Ectotherms are more vulnerable to fluctuations in environment that endotherms

Question 20

What is an endotherms physiological response when their core body temperature rises?

Answer 20

• peripheral temperature receptors in the skin and thermoreceptors in hypothalamus detect temperature of blood= together detect core body temperature is too high 🔥

VASODILATION = arterioles near surface of skin DILATE. The arteriovenous shunt vessels constrict. This forces blood to capillaries at surface allowing heat to escape

SWEATING = sweat glands secrete more sweat. The water in the sweat evaporates taking heat from the surface of the skin

HAIRS/FEATHERS LIE FLAT= the erector pili muscles in skin RELAX. So less air is trapped, so the skin is less insulated and heat can be lost more easily

Question 21

What are the vessels between arterioles and venules called?

Answer 21

arteriovenous shunt vessels

Question 22

What are the erector pili muscles?

Answer 22

Hair erector muscles

Question 23

What is an endotherms physiological response when their core body temperature falls?

Answer 23

• peripheral temperature receptors in the skin and thermoreceptors in hypothalamus detect temperature of blood= together detect core body temperature is too low 🥶

VASOCONSTRICTION = arterioles near surface of skin CONSTRICT. The arteriovenous shunt vessels dilate. This means very little blood flows to capillaries at surface~ keeping heat in!

HAIRS/FEATHERS STAND UP= the erector pili muscles in skin CONTRACT. This traps an insulating layer of air + so reduces cooling through the skin

SHIVERING= rapid/involuntary contracting + relaxing of muscles