Biology definitions 3.0 / 5 based on 1 rating ? BiologyUnit 2A2/A-levelOCR Created by: Katie TottenhamCreated on: 29-11-13 20:16 Negative feedback A process in which any change in a parameter brings about the reversal of that change so the parameter is kept fairly constant 1 of 17 Positive feedback A process in which any change in a parameter brings about an increase in that change 2 of 17 Homeostasis The maintenance of a constant internal environment despite external changes 3 of 17 Endocrine gland A gland that secretes hormones directly into blood capillaries 4 of 17 Exocrine gland A gland that secretes substances into a duct 5 of 17 Hormone A molecule released into the blood that acts as a chemical messenger 6 of 17 Endotherms Organisms that can control production and loss of heat to maintain their body temperature 7 of 17 Ectotherms Organisms that rely on external sources of heat and behavioural activities to regulate their body temperature 8 of 17 Target tissue Cells of an organ that are affected or stimulated by specific hormones. 9 of 17 First messenger A hormone that acts as a message in the bloodstream 10 of 17 Second messenger A cheical inside the cell released in response to a hormone binding to the cell surface membrane 11 of 17 Excretion The removal of metaolic waste from the body 12 of 17 Autotrophs Organisms that use light energy or chemical and inorganic molecules to synthesize complex organic molecules 13 of 17 Heterotrophs Organisms that ingest and digest complex organic molecules,releasing the chemical potential energy stored in them 14 of 17 Photosynthesis The process in green plants by which carbohydrates are synthesized from carbon dioxide and water using light as an energy source. 15 of 17 Photosynthetic pigment Chemical that absorbs light energy.Found in thykaloid membranes,in photosystems 16 of 17 respiratory substrate Organic substance that can be used for respiration 17 of 17
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