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20 Cards in this Set
- Front
- Back
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Define 'tropism'. |
A directional growth response in plants to an external stimulus. |
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Name the two types of tropic response. |
- Positive tropic response (towards the stimulus) - Negative tropic response (away from the stimulus) |
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Name four types of tropism. |
- Phototropism (light) - Geotropism (gravity) - Chemotropism (chemicals) - Thigmotropism (touch) |
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What are two reasons plants respond to their environment? |
- To avoid herbivory. - To maximise photosynthesis. |
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What are two key differences between plant and animal hormones? |
- Plant hormones can be produced by a variety of tissues, rather than just exocrine glands. - Plant hormones can be inorganic molecules, rather than just proteins. |
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Name five plant hormones. |
- Auxins. - Cytokinins. - Gibberellins. - Abscisic acid. - Ethene. |
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What are the roles of auxins? |
- Promote cell elongation. - Inhibit growth of side-shoots. - Inhibit leaf abscission. |
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What is the role of cytokinins? |
Promote cell division. |
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What are the roles of gibberellins? |
- Promote seed germination. - Promote growth of stems. |
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What are the roles of abscisic acid? |
- Inhibit seed germination and growth. - Trigger stomatal closure (when plant is stressed by low water availability. |
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What is the role of ethene? |
Promote fruit ripening. |
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What are three commercial uses for auxins? |
- Promoting root growth in cuttings. - Promoting growth of seedless fruit. - Artificial auxins are used as herbicides to cripple weed with too much shoot growth. |
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What are three commercial uses for gibberellins?
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- Delaying senescence in citrus fruit. - Increasing production of malt in brewing by speeding up germination of barley. - Increasing sugar yield. |
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What are two commercial uses for cytokinins?
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- Preventing the yellowing of lettuce leaves. - Promoting bud and shoot growth in tissue culture. |
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What is a commercial use for ethene? |
Speeding up fruit ripening in apples, tomatoes and citrus fruits. |
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Define 'meristem'. |
Growth points in a plant where immature cells are still capable of dividing. |
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Name four types of meristem, and their location in a plant. |
- Apical meristems: the tips (apices) of roots and shoots. - Lateral bud meristems: the buds. - Lateral meristems: cylinders near the outsides of roots and shoots. - Intercalary meristems: between the nodes. |
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How do auxins trigger cell elongation? |
- Auxins promote active transport of hydrogen ions into cell wall. - Resulting low pH is optimum pH for expansins. - Expansins break bonds in the cellulose. - Cell takes in more water; becomes less rigid. |
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How does shining a light on one side of a plant affect auxin concentrations? |
Auxins become more concentrated in the shaded side, causing elongation to bend the shoot towards the light. |
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What four steps lead to leaf senescence? |
- Cytokinin production decreases. - This causes a decrease in auxin production. - This causes an increase in ethene production. - This results in an increase in cellulase, - Cellulase digests the cell wall of cells in the abscission zone. |
