OCR Biology F2144 - module 1 Communication and homeostasis

These are my summary notes for OCR Biology F2144 - module 1 Communication and homeostasis from my A2 OCR Boilogy textbook (purple with brain MRI on cover). Words in light blue are definitions and bolded words are either key words or key parts of definitions. Enjoy!

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OCR Biology F2144 - module 1 Communication and homeostasis
Stimulus ­ any change in the environment that causes a response
Respons e ­ a change in behaviour or physiology as a result of a change in the
Conditions needed to maintain life (and keep enzymes working):
Suitable temperature
Suitable pH
Aqueous environment that keeps the substrates and products in solution
Freedom from toxins and excess inhibitors
Homeostasis ­ the maintenance of the internal environment in a constant state
despite external changes
Negative feedback ­ a process that brings about a reversal of any change in
conditions. It ensures that an optimum steady state can be maintained, as the
internal environment is returned to its original set of conditions after any change.
Positive feedback ­ a process that increases any change detected by the receptors. It
tends to be harmful and does not lead to homeostasis.
Ectotherm­ an organism that relies on external sources of heat to regulate its body
Advantages Disadvantages
Use less food for respiration and can Less active in cooler temperatures and
survive longer without food have to warm up before they can be
active; which puts them at greater risk
of predation
Don't have to spend as much time Not always able to be active during
looking for food winter, so they have to hibernate and
build up food stores
Greater proportion energy obtained
from food can be used for growth
Adaptation How it helps regulate temperature
Expose body to sun Enables more heat to be absorbed
Orientate body to sun Expose larger surface area to sun for
more heat absorption
Orientate body away from sun Expose smaller surface area so that les
heat is absorbed
Shelter in burrow Reduces heat absorbed by keeping out
if the sun
Alter body Shape Exposes more/less surface area
to the sun

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Increase breathing movements Evaporates more water
Endotherms ­ an organism that can use internal sources of heat to maintain its body
Advantages Disadvantages
Body temperature is fairly constant Have to spend a lot of energy on
whatever the temperature is externally keeping themselves warm when it is
Can still function in the cold They have to consume a lot of food to
make up for the amount of energy they
Are able to live in colder parts of the Less energy is…read more

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Skeletal muscles No spontaneous Spontaneous contractions
contractions (shivering); generates heat
as muscle cells respire
Peripheral temperature receptors are located on the surface of the skin and
monitor the temperature in extremities. The information is then fed to the
thermoregulatory centre in the brain (hypothalamus), where a mechanism is then
initiated to maintain body temperature.
Sensory neuron :
Carries impulse from receptors to the
CNS and converts stimulus energy into
electrical energy
Motor neuron:
Carries impulse from CNS
to effectors.…read more

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Stimulus ­ causes sodium ion channels to open, Na+ ions flood in making the
axon more positive
2. Depolarisation ­ the change in potential difference causes voltage-gated
sodium ion channels to open and then trigger more to open along the axon
3. Repolarisation - after 0.5 ms the sodium gate, the potential difference has
now increased to +35mV. This more positive charge causes potassium ion
channels to open and K+ ions flood out, reducing the potential difference.
4.…read more

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Spatial = space
1. Action potential reaches pre-synaptic know and causes voltage-gated calcium
ion channels to open, so Ca2+ ions flood in
2. The Caions cause the synaptic vesicles to fuse to the pre-synaptic know
membrane and acetylcholine is released into the synapse by exocytosis
3. Acetylcholine binds to the receptor sites on the sodium channels and cause
them to open
4.…read more

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Target cells ­ cells that possess a specific receptor on their plasma membrane.…read more

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The islets of Langerhans ­ small patches of tissue in the pancreas that have an
endocrine function
-cells ­ cells found in the islets of Langerhans and secrete the hormone glucagon
-cells - cells found in the islets of Langerhans and secrete the hormone insulin
Insulin ­ a hormone that causes blood glucose levels to go down; detected by
receptors on liver and muscle cells
Glucagon ­ a hormone that causes blood glucose levels to rise; detected by
receptors on liver cells
How insulin is…read more

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Treatment: careful monitoring and control of diet
Stem cells could be used to cure diabetes, as they are unspecific they can be grown
into -cells and implanted into the pancreas. This treatment would mean that a
person with diabetes could produce their own insulin and wouldn't need regular
insulin injections.…read more


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