A2 OCR Biology Key Terms and Definitions Cell Communication and Homeostasis

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Hormone
A chemical secreted by an endocrine gland, which brings about a response in an organ elsewhere in the body.
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Nerve
A group of axons and dendrons, surrounded by a protective covering.
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Cell Signalling
Communication between one cell and another.
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Homeostasis
The maintenance of a stable internal environment. E.g. temperature, amount of water, concentration of glucose, etc.
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Negative Feedback
A mechanism by which a change in a parameter is detected and which brings about a response that moves the parameter back towards the norm.
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Receptor
A cell that detects a stimulus.
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Effector
An organ that carries out an action in response to a stimulus, such as a muscle that contracts or a gland that secretes a substance.
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Positive Feedback
A mechanism by which a change in a parameter is detected and which brings about an action that takes the parameter even further away from the norm.
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Conduction
Heat passes from one particle to another if they are next to each other. The speed of transfer depeneds on how good a conductor of heat the material is. Air is quite a poor conductor of heat. Water is a better heat conductor.
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Convection
If a fluid (e.g. a gas or liquid) such as air is warmed (e.g. by contact with warm skin) it becomes less dense and so will rise through surrounding cooler air.
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Radiation
This is infrared radiation mainly from the Sun. All objects emit infrared radiation. Black objects absorb the most (radiating the most); silvered surfaces reflect it (radiating the least).
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Endotherm
An organism that generates heat inside the body to maintain a constant body temperature no matter what the temperature of the environment.
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Hypothalamus
A small part of the brain in the very centre of the head, which contains receptors involved in temperature regulation and osmoregulation; it is closely associated with the pituitary gland and controls the secretion of hormones from that gland.
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Core Temperature
The temperature deep inside the body.
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Peripheral Receptors
Cells in the skin that detect a stimulus.
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Shivering
The rapid contraction and relaxation of muscles, generating heat.
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Vasoconstriction
The contraction of the smooth muscle in the walls of arterioles supplying blood to capillaries near the surface of the skin, constricting the lumen and reducing blood flow.
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Sweat Gland
A gland in the dermis of the skin that extracts fluid from blood plasma and secretes this into a duct that carries the fluid onto the surface of the skin.
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Erector Muscle
A muscle that raises a hair when it contracts.
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Vasodilation
The relaxation of the smooth muscle in the walls of arterioles supplying blood to capillaries near the surface of the skin, widening the lumen and increasing blood flow.
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Ectotherm
An organism that does not fully control body temperature by physiological (biological) means; its body temperature changes with the environmental temperature.
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Other cards in this set

Card 2

Front

A group of axons and dendrons, surrounded by a protective covering.

Back

Nerve

Card 3

Front

Communication between one cell and another.

Back

Preview of the back of card 3

Card 4

Front

The maintenance of a stable internal environment. E.g. temperature, amount of water, concentration of glucose, etc.

Back

Preview of the back of card 4

Card 5

Front

A mechanism by which a change in a parameter is detected and which brings about a response that moves the parameter back towards the norm.

Back

Preview of the back of card 5
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