Biology Definitions

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Homeostasis
Is the maintenance of the internal environment in a constant state despite external changes.
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Negative feedback
A process that brings about the reversal of any change in conditions. Ensures that the optimum steady state is maintained, as the internal environment is returned to its original set of conditions after change. Vital for homeostasis.
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Positive feedback
A process that increases the change detected by receptors. Tends to be harmful and does not lead to homeostasis.
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Hormone
Molecules that are released by endocrine glands directly into the blood. They act as messengers carrying a signal from a endocrine gland to a specific target organ or tissue.
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Endocrine gland
Gland that secretes hormones directly into the blood. Endocrine glands have no ducts.
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Exocrine gland
Gland that secretes molecules into a duct which carries the molecules to where they are used.
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Target cells (tissues)
Cells that have receptors embedded into the plasma membrane that are complementary in shape to a specific hormone molecule. Only these cells will respond to that specific hormone. Many similar cells together form a tissue.
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First messenger
Is the hormone that transmits a signal around the body.
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Second messenger
Is cAMP, which transmits a signal inside the cell.
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Excretion
Removal of metabolic waste from the body.
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Autotrophs
Organisms that use light energy or chemical energy and inorganic molecules to synthesise complex organic molecules.
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Heterotrophs
Organisms that ingest and digest complex organic molecules releasing the chemical potential energy stored in them.
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Photosynthetic pigment
Molecules that absorb light energy. Each pigment absorbs a range of wavelengths in the visible region and has its own distinct peak of adsorption. Other wavelengths are reflected.
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Respiratory substance
Is and organic substrate that can be used in respiration.
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Card 2

Front

A process that brings about the reversal of any change in conditions. Ensures that the optimum steady state is maintained, as the internal environment is returned to its original set of conditions after change. Vital for homeostasis.

Back

Negative feedback

Card 3

Front

A process that increases the change detected by receptors. Tends to be harmful and does not lead to homeostasis.

Back

Preview of the back of card 3

Card 4

Front

Molecules that are released by endocrine glands directly into the blood. They act as messengers carrying a signal from a endocrine gland to a specific target organ or tissue.

Back

Preview of the back of card 4

Card 5

Front

Gland that secretes hormones directly into the blood. Endocrine glands have no ducts.

Back

Preview of the back of card 5
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