6C : homeostasis

Question 1

Homeostasis

Answer 1

Homeostasis is the maintenance of a constant internal environment within restricted limits in organisms via physiological control systems

Question 2

what is the internal environment

Answer 2

the blood and tissue fluid that surrounds cells

Question 3

what does homeostasis ensure

Answer 3

ensures that the cells of the body are in an environment that meets their requirements + allows them to function normally despite external changes :
- doesn’t mean that there are no changes as there are continuous fluctuations
- these changes occur around an optimum point + homeostasis is the ability to return that optimum point + so maintain organisms in a balanced equilibrium

Question 4

the importance of homeostasis in maintaining a stable core temp + blood pH

Answer 4

temp + pH affect enzyme activity and enzymes control the rate or metabolic reactions:
- they also affect proteins + channel membranes
- any changes to these factors reduces the rate of rxn of enzymes or may even prevent them working altogether
- even small fluctuations in temp or pH can impair the ability of enzymes to carry out their roles effectively
- maintaining a fairly constant internal environment means that rxns take place at a suitable rate

Question 5

temperature

Answer 5

• if too high (40°c) enzymes become denatured
• the enzymes molecules vibrate too much which breaks the hydrogen bonds holding them in shape, this alters the tertiary structure of the enzymes active site so E-S complexes cannot form as no longer complementary
• enzyme cannot function as a catalyst + metabolic rxns are less efficient
• if too low, enzyme activity is reduced and the rate of metabolic rxns are too slow
• the highest rate of enzyme activity happens at optimum temperature (37°c in humans)

Question 6

pH

Answer 6

• if too high or too low, enzymes become denatured
• the hydrogen bonds holding them in shape are broken, this alters the tertiary structure of the enzymes active site so E-S complexes cannot form as no longer complementary. Enzyme cannot function as a catalyst and metabolic reactions are less efficient
• the highest rate of enzyme activity happens at an optimum pH (usually 7 neutral, pepsin 2 stomach)

Question 7

the importance of homeostasis in maintaining stable blood glucose concentrations

Answer 7

the concentration of glucose in the blood is important because cells need glucose as a respiratory substrate and to maintain a constant water potential of the blood
- cells need glucose in order to release energy through respiration
- changes to the water potential of the blood + tissue fluids may cause cells to shrink + expand (even to bursting point) as a result of water leaving or entering by osmosis

Question 8

water potential ( high blood glucose)

Answer 8

• water potential of blood is reduced
• water molecules move by osmosis out of cells into the blood
• causes them to shrivel up and die

Question 9

water potential (low blood glucose)

Answer 9

• water potential of blood is increased
• water molecules move by osmosis into cells from the blood
• causing them to swell and burst (cytolysis)

Question 10

respiratory substrate

Answer 10

if blood glucose is too low then cells are unable to carry out normal activities because there is not enough glucose for respiration to provide energy

Question 11

homeostatic control mechanisms

Answer 11

self - regulating homeostatic systems involve receptors , a communication system (coordinator) and effectors

Question 12

name the three

Answer 12

receptor
coordinator
effector

Question 13

receptor

Answer 13

detects any deviation from the optimum point by a stimulus + informs the coordinator

Question 14

coordinator

Answer 14

coordinates information from receptors + sends instructions to an appropriate effector

Question 15

effector

Answer 15

often a muscle or gland , which brings about the changes instructed by coordinator

Question 16

what is set up

Answer 16

a feedback mechanism is set up - by which a receptor responds to a stimulus created by the change to the system brought about by the effector

Question 17

the two types of feedback mechanisms

Answer 17

• positive feedback ( not involved in homeostasis as it doesn’t keep the internal environment stable )
• negative feedback ( counteracts a change to return the system to the optimum to maintain stability)

Question 18

positive feedback

Answer 18

positive feedback amplifies the effect of a change, enhancing it further away from the normal level
- this can occur also when a homeostatic system breaks down
- it is useful as it rapidly activates something

Question 19

example (2)

Answer 19

• blood clot after an injury
• hypothermia

Question 20

blood clot after an injury

Answer 20

• platelets become activated + release a chemical which triggers activation of more platelets
• they rapidly form a blood clot at the injury site
• the process ends with negative feedback when the body detects the blood clot has been formed

Question 21

hypothermia

Answer 21

• hypothermia is low body temp below 35°c when heat is lost faster than can be produced
• as body temp falls the brain doesn’t work properly + shivering stops , making it fall more
• positive feedback takes the body temp further from the normal level
• this will continue to decrease until action is taken

Question 22

ectotherms (outside heat)

Answer 22

reptiles gain heat from the environment, so their body temperature fluctuates with the environment. They therefore control their body temperature by adapting their behaviour to changes in the internal temperature

Question 23

they control their body temp by

Answer 23

• exposing themselves to the sun
• taking shelter
• gaining warmth from ground

Question 24

exposing themselves to the sun

Answer 24

in order to gain heat lizards orientate themselves so that the maximum surface area of their body is exposed to the warming rays of the sun

Question 25

taking shelter

Answer 25

lizards will shelter in the shade to prevent overheating when the suns radiation is at its peak. At night they retreat in burrows in order to reduce heat loss when the external temperature is low.

Question 26

gaining warmth from the ground

Answer 26

lizards will press their bodies against areas of hot ground to warm themselves up. When the required temperature is reached, they raise themselves off the ground on their legs

Question 27

endotherms (inside heat)

Answer 27

animals (birds and mammals) get lost of their heat from metabolic activities inside their bodies. Body temperature remains relatively constant despite fluctuations in the external temperature. Endothermic animals use behaviour to maintain a constant body temperature but also use a wide range of physiological mechanisms to regulate their temperature

Question 28

they control their body temp in cold environments by

Answer 28

-vasoconstriction= diameter of arterioles near skin narrower to reduce volume of blood reaching surface so less heat transfer
- shivering = involuntary rhythmic contractions to produce metabolic heat
- hair rising = layer of still, insulating air
- increased metabolic rate = respiration up , more heat

Question 29

they control their body temp in hot environments by

Answer 29

• vasodilation = diameter of arterioles near skin wider to increase volume of blood reaching surface so more heat transfer
• sweating = to evaporate water from the skin surface requires energy in the form of heat
• lowering of hairs - no insulating layer of air