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| Question | Answer |
| Negative feedback | Process that reverses any change in the internal environment, to ensure that an optimum steady state can be maintained. Homeostasis is negative feedback system. |
| Positive feedback | Process that increases any change detected by the receptors. Tends to be harmful and does not lead to homeostasis. |
| Homeostasis | The MAINTENANCE of the INTERNAL ENVIRONMENT in a CONSTANT state DESPITE external CHANGES. |
| Endocrine gland | Ductless gland that secretes hormones directly into the blood. |
| Exocrine gland | Gland that secretes molecules into a duct that carries the molecules to where they are used. |
| Hormone | A molecule released into the blood (by an endocrine gland) that acts as a chemical messenger. |
| Target tissue | A tissue whose cells have receptors for a particular hormone. This is the tissue where the hormone has its effects. |
| Excretion | The removal of metabolic waste from the body |
| Autotroph | Organism that uses light energy or chemical energy, and inorganic molecules to synthesise complex organic molecules (food). |
| Photosynthetic pigment | Substance that absorbs light energy. Found in thylakoid membranes, in photosystems. Each pigment absorbs energy associated with light of a specific wavelength. Examples include chlorophyll a and chlorophyll b. |
| Respiratory substrate | An organic substrate that can be used for respiration. |
| Heterotroph | Organism that ingests and digests complex organic molecules, releasing the chemical potential energy stored in them. |
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