F214 Communication and Homeostasis (OCR)

Detailed notes on the first module, Communication and Homeostasis, of the F214 exam (OCR). Notes are taken from a combination of my textbook, past mark schemes and my own knowledge. None of the images belong to me - they were taken from various sources on the internet.

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F214 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
All living things need to maintain a certain limited set of conditions…

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An ectotherm is an organism that relies on external sources of heat to regulate its body
temperature.
Advantages:

Less food used in respiration, so a greater proportion of energy used for growth
Don't need to find as much food and can last longer without eating
Disadvantages:
They are less active…

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Involuntary spontaneous contractions of skeletal muscles (shivering) generates heat from
increased respiration.
Adrenaline/thyroxine can be released to cause an increase in metabolism in liver cells to
generate heat.
Pili erector muscles can raise hair to trap a layer of insulating air to prevent heat loss by
conduction. Conversely they could…

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Motor neurones carry an action potential from the CNS to an effector such as a muscle or gland.
Relay neurones connect sensory and motor neurones.
Both neurones have many mitochondria, ribosomes, dendrites and ion pumps/channels. Many are
very long with a myelin sheath.

Motor Neurone Sensory Neurone
Cell body in…

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ion channels are concentrated. At these points only, the Na+ ions cause voltagegated sodium ion
channels to open to set up a new action potential. This is called saltatory conduction.
In myelinated neurones the local currents are longer, which speeds up the transmission of the
action potential.
(f) interpret graphs…

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(h) compare and contrast the structure and function of myelinated and nonmyelinated neurones






Myelinated neurones are electrically insulated by a myelin sheath, which consists of Schwann cells
which produce the fatty substance myelin. They are wrapped around the neurone, so the sheath
consists of layers of membrane and cytoplasm. Every…

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There are also voltagegated calcium ion channels (Ca2+ ) in the presynaptic membrane.

(j) outline the role of neurotransmitters in the transmission of action potentials

An action potential arrives at the synaptic knob, which causes voltagegated calcium ion channels
to open. Calcium ions diffuse down their concentration gradient into the…

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One presynaptic neurone might diverge to several postsynaptic neurones. This would allow one
signal to be transmitted to several parts of the nervous system. It is useful in a reflex arc ­ a signal
goes to an effector and another informs the brain.

It ensures that signals are transmitted in…

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a shape complementary to the shape of the adrenaline molecule. The receptor is associated with
an enzyme on the inner surface of the cell surface membrane, called adenyl cyclase.
Adrenaline (the first messenger) travels in the blood and binds to its specific, complementary
shaped receptor on the cell surface membrane.…

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The pancreas is a small organ lying below the stomach. It has both exocrine and endocrine
functions. The majority of the cells secrete digestive enzymes, which is the exocrine function. The
cells are in small groups surrounding a tubule which joins to other tubules to make up the
pancreatic duct.…

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