A2 Unit F214 - Communication, Homeostasis and Energy
Institution
OCR
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A2 Unit F214 - Communication, Homeostasis and Energy
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By: jackieproctor • 7 year ago
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, Principles of homeostasis
Homeostasis- the maintenance of a stable equilibrium
in the conditions inside the body
Receptors and effectors are vital for the
maintenance of dynamic equilibrium. sensory
receptors detect a small change in the body and
effectors work to restore this change, this
mechanism is based on a feedback system.
Negative feedback systems work to reverse the
initial stimulus.
Positive feedback systems work to reinforce the
change detected and increase the response. E.g. in
the blood clotting cascade platelets stick to the
damaged region and they release a factor that
initiates clotting and attracts more platelets.
, Thermoregulation
Gain in heat Loss in heat
•Waste heat from cell •Latent heat of
respiration evaporation- evaporation
•Conduction from of water cools organism
surroundings •Conduction to surroundings
•Convection from surroundings Organism •Convection to surroundings
•Radiation from surroundings •Radiation to surroundings
Endotherms rely on their metabolic processes to warm .They usually have
a very stable core body temp regardless of the external temp so can
therefore survive in a wide range of environments. need to consume more
food than ectotherms of a similar size in order to meet their metabolic
needs since endotherms have a greater metabolic rate.
Ectotherms use their surroundings to warm their bodies as they cannot
control their body temp using their metabolism. Their core body temp is
heavily dependent on the environment. Many ectotherms living in water do
not need to thermoregulate due to the high heat capacity of water
meaning that the temp of the environment doesn’t change much. However
air temp can vary dramatically so ectotherms living on land have evolved a
range of strategies that enable them to warm up or cool down.
, Thermoregulation in ectotherms
Behavioural responses
Changes in an organisms behaviour:
Basking in the sun orientating the body to expose max surface area to
increase radiation absorbed from the sun. decrease surface area exposed to
the sun or find shelter from the sun in order to cool.
Increasing body temp through conduction by pressing bodies against warm
ground. Find cool ground to press body against to decrease body temp.
Minimise movements to reduce metabolic heat generated decreasing body
temp. increase exothermic metabolic reactions to increase body temp e.g.
moths vibrate their wings to warm muscles before flight.
Ectotherms may cool down by using evaporation of water from the skin
surface after emerging from water or mud.
Physiological responses
A metabolic or physiologic adjustment within the cell, or tissues, of an
organism in response to an environmental stimulus resulting in the improved
ability of that organism to cope with its changing environment.
E.g. lizards living in colder climates tend to be darker coloured than lizards
living in warm climates. Also ectotherms can alter their heart rate to increase
or decrease the metabolic rate and sometimes to affect the warming or
cooling across the body surfaces.
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