communication and homeostasis OCR

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Communication and homeostasis

Stimulus-is a change in the environment that causes a response

Response-change in a behaviour or physiology as a result of a change in the environment

Good communication system will:

·      Cover the whole body

·      Cell communication

·      Specific communication

·      Short & long term response


Negative feedback- brings about a reversal of any change in conditions. Insures and optimum steady state can be maintained, as the internal environment is returned to it's original set of conditions after any change.

Sensory receptors- ie temp or glucose conc receptors. Detects the change

Communication system- ie nervous or hormonal system. Transmits message from receptors to effector cells. Message may or may not pass through a coordination centre ie the brain

Effector cells- ie liver cells. The cells will bring about a response that reverses the change detected

Positive feedback- increases any change detected by the receptors. It tends to be harmful and does not lead to homeostasis

Beneficial positive feedback- ie dilation of cervix. When the cervix starts to stretch in pregnany the change is detected by anterior pituitary gland, stimulating it to release the hormone oxytocin.

oxytocin- increaces ueterine contractions, which tretches the cervix more and more oxytocin is the secreted. Once the cervix is fully dilated the baby can be born

Cell signalling


Interconnected network of neurones that signal across synapse junctions. Quick and enables rapid response.


cells in endocrine organs release hormone into blood. Carried all over the body, only recognised by target cells. Long term response


An organism that relies on external sources of heat to regulate it's body temperature

Advantages- less of their food in respiration. need less food and may be able to survive for a long period without eating. Greater proportion of the energy from food can be used for growth

Disadvantages- less active in cooler temp, and may need to warm up in the morning before they can be active, this puts them at greater risk of predation. may not be able of activity during the winter as they never warm up sufficiently


·      orientate body away from the sun- exposes lower S.A so less heat is absorbed

·      hide in burrow- reduces heat absorbtion by keeping out of sun

·      alter body shape-

·      increase breathing movements- evaporates more water


·      expose body to sun-enables more heat to be absorbed

·      orientate body to sun- more heat absorbtion


An organism that can use internal source of heat, such as heat generated from metabolism in the liver, to maintain body tem

advantages- fairly constant body temp independent of external temp. activity poss even when external temp is too cold. ability to inhibit colder parts of the planet.



·      less sweat is secreted, less vaporisation, less loss of latent heat.

·      The animal does not pant so less water evaporates.

·      Hair raised to trap a layer of insulating air…


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