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Communication, Homeostasis & Energy
Communication and homeostasis

(a) Outline the need for communication systems within multicellular organisms, with reference to the need to
respond to changes in the internal and external environment and to coordinate the activities of different
Organisms need to respond to external stimuli, e.g. temperature,…

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Physiological (temp drops)
Peripheral skin thermoreceptors are stimulated by a decrease in external
impulses are sent to the hypothalamus
vasoconstriction of arterioles to reduce heat loss by radiation / conduction /
increased metabolic rate (respiration) to generate heat energy
release of adrenaline
shivering to generate heat energy…

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(a) Outline the roles of sensory receptors in mammals in converting different forms of energy into nerve impulses.
Light sensitive cells in the retina detect light intensity and range of wavelengths (colour).
Olfactory cells in the nasal cavity detect the presence of volatile chemicals.
Tastebuds detect the presence of…

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6. The sodium ion channels close and the potassium ion channels open.
7. Potassium ions diffuse out of the cell, bring the potential difference back to negative inside
compare to out this is called repolarisation.
8. The potential difference overshoots slightly making the cell hyperpolarised.
9. The original potential difference…

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(j) Outline the role of neurotransmitters in the transmission of action potentials.
A neurotransmitter is a chemical that diffuses across the cleft of the synapse to transmit a
signal to the postsynaptic neurone. They cause the generation of a new action potential in the
postsynaptic neurone. In cholinergic synapses the…

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(a) Define the terms endocrine gland, exocrine gland, hormone and target tissue.
Endocrine gland
a gland that secrets hormones directly into the blood. Endocrine glands have no
Exocrine gland
a gland that secrets molecules directly into a duct that carries the molecules to where
they are used.

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The exocrine cells are found in the the Islets of Langerhan and consist of and cells. The
cells manufacture and secrete glucagon, whereas the cells manufacture and secrete insulin.
They are involved in the regulation of blood glucose levels.

(e) Explain how blood glucose concentration is regulated, with reference to…

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4. The glucose is quickly metabolised to ATP.
5. The extra ATP causes the K ion channels to close.
6. The K ions can no longer diffuse out, so the cells become more positive inside.
7. This change in potential difference opens the Ca ion channels.

8. Ca2+
ions enter…

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· A drop in pH detected by chemoreceptors in the carotid arteries, the aorta and the
brain (when we exercise we produce CO 2, this dissolves in H
2O in the blood and forms

carbonic acid, reducing the pH).
o CO
2+H2O H

o H CO
2 3…

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The liver is made up of lobules, which consists of cells called hepatocytes that are
arranged in rows.
Each Lobule has a Central vein in the middle that connects to the hepatic vein.
Every single lobule has branches of the hepatic artery, hepatic portal vein and bile
Hepatic artery…


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