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Communication, Homeostasis & Energy
Communication and homeostasis
Communication
(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
organs.
Organisms need to respond to external stimuli, e.g. temperature, oxygen concentration and levels of
sunlight. These may be over time, e.g. winter fur to summer fur, or quickly, e.g. changing size of pupils.
Internal environments change too the build up of carbon dioxide as a result of respiration changes the pH
of the tissue fluid, and therefore inhibits enzyme activity. Multicellular organisms need to coordinate
different organs, so this requires a good communication system which will:
· Cover the whole body
· Enable cells to communicate with each other
· Enable specific communication
· Enable rapid communication
· Enable both short and longterm responses.
(b) State that cells need to communicate with each other by a process called cell signalling .
(c) State that
neuronal and hormonal systems are examples of cell signalling.
(d) Define the terms negative feedback, positive feedback and homeostasis.
Negative feedback A process in which any change in a parameter brings about the
reversal of that change so that the parameter is kept fairly constant.
Positive feedback A process in which any change in a parameter brings about an
increase in that change
Homeostasis The maintenance of a constant internal environment despite changes in
the environment
(e) Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.
Any change is detected by receptors, the communication system transmits a message from the
receptor to the effector and, through negative feedback, the effectors reverse the change.
(f) Describe the physiological and behavioural responses that maintain a constant core body temperature in
ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and
effectors in skin and muscles .
Ectotherms
Physiological
The horned lizard expands its ribcage and the frilled lizard uses its frill to expand its
surface area to absorb more heat from the sun
Locusts increase their abdominal breathing movements to increase water loss when
hot
Behavioural
Snakes expose their body to the sun so more heat is absorbed
Locusts orientate their body towards the sun to expose a larger surface area & so
more heat is absorbed. By orientating their body away from the sun, more heat is lost.
Lizards hide in burrows to prevent heat absorption by staying out of the sun.

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Endotherms
Physiological (temp drops)
Peripheral skin thermoreceptors are stimulated by a decrease in external
temp
impulses are sent to the hypothalamus
vasoconstriction of arterioles to reduce heat loss by radiation / conduction /
convection
increased metabolic rate (respiration) to generate heat energy
release of adrenaline
shivering to generate heat energy
erector pilli muscles raise hair to trap air and therefore heat
sweating or panting is reduced
Behavioural
Hot
Move into shade or hide in burrow
Orientate body to decrease surface area exposed to sun
Remain…read more

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Nerves
(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 soluble chemicals.
Pressure receptors in the skin detect pressure on the skin.
Sound receptors in the cochlea detect vibrations in the air.
Muscle spindles detect the length of muscle fibres.…read more

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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 is restored so the cell returns to its resting state.…read more

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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 neurotransmitter is acetylcholine. It is
stored in vesicles in the synaptic knob.…read more

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Hormones
(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
ducts.
Exocrine gland
a gland that secrets molecules directly into a duct that carries the molecules to where
they are used.
Hormone
a molecule released into the blood which acts as a chemical messenger
Target tissue
a group of cells that have receptors embedded in the plasma membrane that are
complementary in shape to specific hormone molecules.…read more

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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 insulin, glucagon and the liver.…read more

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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 the cell and cause the secretion of insulin by making the vesicles containing
insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis.…read more

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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
2CO3
+
o H CO
2 3 H + HCO 3
Action potentials sent down the Vagus Nerve decreases the heart rate.…read more

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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
duct.
Hepatic artery and hepatic vein are connected to the central vein blood filled spaces
called sinusoids.
The blood flows past every hepatocytes via the sinusoid, this ensures that the toxins
are broken down quickly.…read more

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