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A2 Biology Revision
Unit 1

Key Words

Communication and Homeostasis

Excretion

Photosynthesis

Respiration

Model Answers

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Key Words

Module 1 - Communication and Homeostasis

Cell - Secrete the hormone glucagon and are found in the islets of Langerhans.
Acetylcholinesterase - An enzyme in the synaptic cleft. It breaks down the transmitter substance acetylcholine.
Action Potential (An) - Is achieved when the membrane is depolarised to a…

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Carbon dioxide for example if it builds up in the tissue fluid outside the cells could disrupt the
activity of enzymes by altering the pH of the environment around the cell
Maintaining the internal environment of cells
o Composition of tissue fluid is maintained by blood
The movement of blood…

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This destabilises the system and is usually harmful
o For example when the body gets too cold
Below a core temperature enzymes become less active
If they are less active the exergonic reactions that release heat are slower and
release less heat
o The body cools further, slowing downing the…

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o Sweat glands in skin
If core body temperature is too high, they secrete more sweat onto the skin, the water in which evaporates using heat from blood to
supply latent heat of vaporisation
If core body temperature is too low, less sweat is secreted , less evaporation of water,…

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The Endocrine System

Signalling via hormones
o The endocrine system is another communication system in the body
It uses blood circulation to transport its signals
This means it can be transferred all over the body
o The signals released by the endocrine system are called hormones
Hormones are released from…

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These have a variety of roles in the body:
The mineralocorticoids
o Help to control the concentrations of sodium and potassium in the blood
Example is Aldosterone
The glucocorticoids
o Help to control the metabolism of carbohydrates and proteins in the liver
Example is Cortisol

The Regulation of blood glucose…

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o A low blood glucose concentration is detected by cells
In response the cells secrete the hormone glucagon
Its target cells are the hepatocytes
o They have the specific complementary receptor for glucagon
The effects of glucagon on the cell are
o Conversion of glycogen into glucose
Glycogenolysis
o Use…

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It usually starts in childhood
o Thought to be a result of an autoimmune response in which the body's own immune system attacks the cells and destroys them
It may also be a result from a viral attack
o The body is then no longer able to manufacture sufficient insulin…

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This has a set frequency varying from person to person, at which it initiates waves of excitation
The frequency of waves is typically 60 - 80 per minute
o However the frequency of these excitation waves can be controlled by the cardiovascular centre in the
medulla oblongata
o There are…

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