AQA A2 Biology Unit 5 3.5.4 Homeostasis

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Preview of AQA A2 Biology Unit 5 3.5.4 Homeostasis

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3.5.4 Homeostasis
Principles
HOMEOSTASIS is the MAINTENANCE OF A CONSTANT INTERNAL ENVIRONMENT.
Homeostatic mechanisms in the body need to monitor both the internal and external environments and respond to
any changes in order to maintain important factors such as pH, temperature, glucose, salt and water concentrations,
within their normal range.
A simple homeostatic system involves the following components:
Feedback Systems
Positive feedback enhances the effect of the
stimulus.
Negative feedback reverses the effect of
the stimulus.
Most feedback systems are negative as they
are detecting fluctuations from the normal
level and then bringing about corrective action
to bring the condition back to normal.
Importance of Homeostasis
1. Enzymes are extremely sensitive to changes in pH and temperature. Deviations from optimum conditions could
result in them being denatured or having a reduced efficiency. Other biological proteins such as channel or carrier
proteins may also be affected by temperature and pH.
Synoptic Questions:
Explain in as much detail as possible why enzyme activity is reduced when temperature falls.
o Enzyme and substrate have less kinetic energy.
o Fewer collisions.
o Fewer enzyme-substrate complexes form.
o Therefore less product is made.
Explain in as much detail as possible why enzyme activity may stop when temperature becomes very high.
o Enzyme is denatured.
o Bonds stabilising tertiary structure are broken.
o Therefore the shape of the active site is lost.
o The enzyme is no longer complimentary to the substrate.
o Therefore no enzyme-substrate complexes form.
Explain in as much detail as possible how the activity of an enzyme or a membrane protein may be affected
by changes in pH.
o Change in pH can alter the charge on the R groups of the amino acids in the active site of an enzyme
and in the binding site of a membrane protein.
o Altering bond formation and tertiary structure.
o Altering the shape of the active site of an enzyme and the binding site of a membrane protein.
2. Cells may be affected by changes in the surrounding water potential of the blood/tissue fluid.

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Synoptic Questions:
Explain in as much detail as possible the consequences of having too much glucose or ions in the blood.
o Lowers the water potential of the blood.
o Therefore water moves by osmosis from cells into the blood.
o This causes cells to shrink and become dehydrated.
Explain in as much detail as possible the consequences of the blood becoming too dilute.
o Increases the water potential of the blood.
o Therefore water moves by osmosis out of the blood in cells.…read more

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Warm substances leaving the body such as air breathed out or the loss of urine.
In mammals temperature regulation is controlled by the HYPOTHALAMUS.
This is constantly monitoring the temperature of the blood when it flows through it and it also receives information
about the external temperature from receptors in the skin. The hypothalamus responds to this information and
makes adjustments to the heat-producing or heat-losing activities of the body.…read more

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Warming Mechanisms in Endotherms
It is essential for endotherms to be able to respond rapidly to falling external temperatures.
Peripheral cold receptors in the skin detect that the environmental temperature is lower than body temperature and
they send impulses to the heat gain centre in the hypothalamus. This co-ordinates the body's response to cold by
inhibiting the activity of the heat loss centre and by sending impulses to a range of effectors which bring about
responses to cause heat gain.…read more

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At a low body temperature, the heat gain centre in the hypothalamus sends impulses to the brown fat cells via
sympathetic nerves.
This increases their rate of respiration which generates more heat.
Hibernating animals use brown fat tissue to generate heat to prevent them from freezing to death.
Hormones:
Adrenaline acts on the liver causing glycogen to be converted to glucose.
This gives a short term increase in the rate of respiration and heat is transferred to the blood flowing through the
liver.…read more

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Diabetes
Symptoms of Diabetes;
Since insulin is not being produced, blood glucose levels may rise to dangerously high levels, HYPERGLYCAEMIA.
The kidneys which normally reabsorb all of the glucose passing into the nephrons, cannot cope and so some
glucose is excreted in the urine, GLYCOSURIA.
Extra water and salt follow the glucose and the sufferer therefore urinates a lot and feels thirsty.
Uptake of glucose by body cells is very slow so the sufferer feels very tired.…read more

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Bibi-chan

thank you

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