A2 Biology Aqa Unit 5 Revision

Front 1

Define Homeostasis

Back 1

The maintenance of an organisms internal environment within set limits

Front 2

What is the result of the temperature being too high or too low(above optimum)?

Back 2

1) Temp too high: enzymes may denature - breaks H bonds which hold tertiary structure in place hence enzyme active site changes shape - can no longer form e-s complexes
1) Temp too low: enzyme activity becomes too slow, low efficiency of metabolic reactions

Front 3

What is the result of pH changing?

Back 3

If too high or too low, it breaks H bonds, so shape of enzyme active site changes and it not longer forms e-s complexes = less efficient metabolic reactions.
NBB// different enzymes will have different optimum pH's

Front 4

What is the result of blood glucose levels being too high or too low?

Back 4

1) too high: decreases water potential of blood hence water diffuses out of cells by osmosis - cell shrivels up
2) too low: increases water potential of blood hence water diffuses into cells by osmosis - cell lysis (burst)

Front 5

Ectotherms

Back 5

- cant solely control body temperature internally (metabolism doesnt produce enough heat to maintain constant body temp)
- control it by changing their behaviour.
- Internal temp and level of activity depends on external temperature

Front 6

Endotherms

Back 6

-Control body temperature internally (homeostasis) but also by behaviour
- high metabolic rate and generates a lot of heat this way
-internal temp and activity largely unaffected by external temp

Front 7

4 ways in which heat can be lost

Back 7

evaporation of water
conduction
convection
radiation
(bottom 3 + metabolism also cause heat gain)

Front 8

How do ectotherms control their body temperature?

Back 8

- expose themselves to sun
- take shelter/shade (burrow at night when temp is too low to reduce heat loss)
-gain heat via conduction from ground
- small amount from metabolism
- colour variations ( darker absorbs more heat/light reflects more).

Front 9

Endotherms controlling increase in temperature

Back 9

- thermoreceptors in skin detect increase in temp
- send nerve impulses along sensory neurone to heat loss centre in the hypothalamus
-detects rise in temp sends nerve impulses to effectors
- vasodialation(a)/sweating/hairs down = temp returned back to normal

Front 10

Endotherms controlling decrease in temperature

Back 10

-thermoreceptors in skin detect fall in external temp
- send nerve impulses along sensory neurone to heat gain centre in hypothalamus
-detects fall in core temp sends nerve impulses to effectors
-vasoconstriction(a)/erector muscles contract/shivering/adrenaline and thryoxine released

Front 11

Explain how vasoconstriction helps increase temperature

Back 11

Arteries supplying capillaries near skin surface vasoconstrict, shunt vessels vasodialate
more blood travelling to capillaries near surface hence= more heat loss

Front 12

Explain how shivering can help increase the temperature

Back 12

Shivering - skeletal muscles repeatedly and involuntarily contract and relax
Heat generated by friction or Respiration/metabolism

Front 13

Explain how secretion of adrenaline and thryoxine can increase the temperature?

Back 13

Increase metabolism hence more heat released via r/s

Front 14

How does Erector pilli muscle contraction help increase the temperature?

Back 14

Hairs stand up
Traps layer of air - forms insulation layer
less heat loss

Front 15

Regulation of blood glucose levels: Too high blood glucose?

Back 15

- beta cells in islets of langerhans in the pancreas detect blood glucose levels are too high
- beta cells produce and secrete hormone insulin into blood
-insulin binds to specific receptor sites on muscle and liver cells
EFFECT:insulin stimulates uptake of glucose (increases permeability)
increases rate of respiration in cells
liver cells: glucose ---> glycogen and glucose--->fats
muscles cells: glucose ---> glycogen

Front 16

Regulation of blood glucose levels: Too low blood glucose?

Back 16

- alpha cells in islets of langerhans detect fall in blood glucose level
- alpha cells produce and secrete hormone glucagon into the blood
- glucagon binds to specific receptors on liver and muscle cells
EFFECT: Liver cells: glycogen----> glucose and fats/aa/glycerol ----)glucose
muscle cells: glycogen ----> glucose
decreases rate of respiration in cells

Front 17

BLOOD GLUCOSE LEVELS TOO HIGH:
name hormone and receptor

Back 17

Receptor: beta cells in islets of langerhans
hormone: insulin

Front 18

BLOOD GLUCOSE LEVELS TOO LOW:
Name hormone and receptor

Back 18

receptor - alpha cells in the islets of langerhans
hormone: glucagon

Front 19

How does insulin increase membrane permeability to glucose?

Back 19

When insulin-receptor complexes form:
- changes tertiary structure of glucose transport proteins making more channels open
- increases number of carrier molecules on cell membrane surface
(insulin-receptor complex taken into nucleus stimulates synthesis of facilitated diffusion carrier proteins which insert into membrane)

Front 20

glycogen ---> glucose

Back 20

glycogenolysis

Front 21

glucose ----> glycogen

Back 21

glycogenesis

Front 22

fats/aa/glycerol ----> glucose

Back 22

glyconeogenesis

Front 23

The second messenger model

Back 23

Hormone is first messenger (glucagon or adrenaline) binds to specific receptors on cell-surface membrane to form hormone-receptor complex.
This complex activates an enzyme inside the cell that converts ATP ---> x100 cyclic AMP
cAMP is the second messenger and causes a series of chain reactions that activates an enzyme to catalyse the reaction that will produce the desired response eg. increase blood glucose levels

Front 24

Action of Adrenaline and glucagon

Back 24

WHEN GLUCOSE LEVELS ARE TOO LOW:
Hormone is 1st messenger binds to specific receptor on liver or muscle cell forms hormone receptor complex activates enzyme to convert ATP --> X100 cAMP, this 2nd messenger causes a series of chain eactions that activates different enzyme to convert glycogen -----> glucose

Front 25

Why do you get amplification?

Back 25

Enzymes are reuseable, once activated they will continue to do their function, hence 1 adrenaline molecule will activate one enzyme which produces hundreds of cAMP which goes on to activates hundreds of other enzymes to catalyse glycogen-->glucose = amplification

Front 26

What does adrenaline do?

Back 26

- inhibits insulin secretion and glycogenesis
-activates glycogenolysis
-activates glucagon secretion

Front 27

Diabetes type 1

Back 27

blood glucose levels cant be controlled
Beta cells cant produce any insulin
after eating blood glucose levels rise but stay high = HYPERGLYCAEMIA
solve: regular controlled injections of insulin, controlling diet/ consumption of carbohydrates

Front 28

Diabetes type 2

Back 28

acquired later in life
beta cells dont produce enough insulin or I-R dont work so cells cant uptake glucose
solve: lose weight, control carbs or use glucose-lowering tablets

Front 29

Symptoms of diabetes

Back 29

Lots of Urine due to excess water in blood
High thirst

Front 30

Basics of oestrous cycle

Back 30

pituitary gland ---> FSH ---> OVARIES produce oestrogen (low level) ---> oestrogen high level ----> FSH AND LH surge ----> progesterone =
pregnant or cycle restarts

Front 31

What happens in oestrous cycle ? detailed
1 follice contains 1 egg

Back 31

1) pituitary gland releases FSH into blood
FSH stimulates growth of follicle, oestrogen secretion.
2) As the follicle grows it secretes small amounts of oestrogen (low conc) which stimulates the uterus lining to repair and thicken and inhibits the release of FSH.
3) As follicle develops further it secretes more oestrogen (high conc) until it reaches a critical point where it stimulates release of FSH and LH
4) The sudden surge of LH causes final development of follicle, causes ovulation(egg release), stimulates corpus luteum to develop
5) corpus luteum secretes progesterone so progesterone levels rise, this maintain the uterus lining and it inhibits the release of FSH and LH
4) Corpus luteum degenerates so progesterone levels fall, thus uterus lining not maintained/breaks down and menstruation triggered/cycle repeats unless egg is fertilised

Front 32

2 key points of oestrous cycle curve

Back 32

1) LH surge higher than FSH surge
2) LH peaks earlier