A2 OCR Biology Key Terms and Definitions Plant Responses

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Nastic Movement
A relatively rapid response of a plant to a stimulus – for example, petals closing as it gets dark; generally brought about by changes in turgor pressure of specialised cells.
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Tropism
A response to a stimulus, brought about by growth, in which the direction of growth is related to the direction of the stimulus.
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Negative Tropism
A tropic response in which growth is away from the direction of the stimulus.
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Positive Tropism
A tropic response in which growth is towards the direction of the stimulus.
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Geotropism
A tropic response to gravity.
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Plant Hormones
A substance produced in plant cells that coordinate growth and other activities of different parts of the plant; unlike animal hormones, plant hormones are not made in glands and often do not travel far from their point of synthesis.
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Phototropism
A tropic response to light
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Phototropin
A protein present in the plasma membranes of some plant cells, which is receptive to blue light.
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Auxin
A hormone produced by young plant tissues (in young leaves or at the apical meristem); it affects different tissues in different ways (encouraging growth in stems, inhibiting growth of lateral buds, cell membrane permeability and gene transcription).
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Apical Meristem
The region near the tip of a plant shoot where cells are constantly dividing.
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Lateral Bud
A bud on the side of a stem, generally in the angle between a petiole (leaf stalk) and the stem.
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Apical Dominance
The inhibition of the growth of lateral buds by the presence of an active apical meristem.
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Indole-3-acetic Acid (IAA)
A type of auxin.
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Gibberellin (GA)
A plant hormone that affects stem elongation and seed germination; it acts by causing certain genes to be transcribed.
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Leaf Abscission
The loss of leaves from a plant following the growth of an abscission layer at the base of the petiole.
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Ethene
A gaseous plant hormone that enhances fruit ripening and leaf abscission.
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Abscisic Acid (ABA)
A plant hormone produced in conditions of stress, which brings about responses such as stomatal closure.
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Abscission Layer
A layer of weak, thin-walled cells that grows across the base of a petiole and eventually allows the leaf to fall from the plant.
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Suberin
A waxy, waterproof substance found in tree bark, abscission layers and in some of the cells surrounding xylem vessels in roots.
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Card 2

Front

A response to a stimulus, brought about by growth, in which the direction of growth is related to the direction of the stimulus.

Back

Tropism

Card 3

Front

A tropic response in which growth is away from the direction of the stimulus.

Back

Preview of the back of card 3

Card 4

Front

A tropic response in which growth is towards the direction of the stimulus.

Back

Preview of the back of card 4

Card 5

Front

A tropic response to gravity.

Back

Preview of the back of card 5
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