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38 Cards in this Set
- Front
- Back
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Why do plants have to respond to their environment? |
-To avoid predation (biotic) -To avoid stress (abiotic, e.g. light intensity) |
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What is tropism? |
A directional growth response in which the direction of the response is determined by the direction of the external stimulus |
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What are the four types of tropism? |
-phototropism -geotropism -chemotropism -thigotropism |
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What is phototropism? |
response to light |
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What is geotropism? |
response to gravity |
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What is Chemotropism? |
response to chemicals |
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What is Thigomotropism? |
response to touch |
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How do plants respond to stimuli? |
Through use of growth hormones (plant growth regulators) |
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Where does growth occur in plants? |
Meristematic tissues (Meristems) |
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Name four meristems. |
-apical meristems -lateral bud meristems -lateral meristems -intercalary meristems |
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Where are apical meristems located? |
tips of roots and shoots |
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Where are lateral bud meristems located? |
buds |
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Where are lateral meristems found? |
a cylinder near the outside of roots and shoots (responsible for plant getting wider) |
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Where are intercalary meristems found? |
between nodes |
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Name four plant hormones? |
-Auxins -Cytokinins -Gibberillins -Abscisic acid |
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What is the effect of auxins? |
-promote cell elongation -inhibits growth of side shoots |
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What is the effect of cytokinins? |
promotes cell division |
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What is the effect of gibberellins? |
promotes seed germination and growth of stems |
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What is the effect of abscisic acid? |
-causes stomata closure -works antagonistically with auxins |
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What happens in the mechanism of phototropism? |
-auxins called phototropins diffuse down to the shaded side of a plant -this promotes an increase in the rate of elongation in respect to the side in the light making the shoot bend towards the light |
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What is apical dominance? |
When the growing apical bud inhibits the growth of lateral buds further down the shoot |
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What happens if the tip of a root is removed and why? |
-no growth can occur -no auxin is available |
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What does an uneven distribution of auxins result in? |
uneven plant growth |
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What is the evidence for apical dominance? |
auxin concentrations increase in lateral buds when the shoot tip is cut off |
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What is the relation between abscisic acid and auxins? |
-abscisic acid inhibits plant growth -high concentrations of auxins may keep abscisic acid levels high -when bud is removed acid levels drop and bud starts to grow |
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What can override apical dominance? |
cytokinins |
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What is positive and negative phototropism? |
-positive= grow towards light (e.g. shoots) -negative= grow away from light (e.g. roots) |
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How do gibberellins affect dwarf varieties of plants? |
the plant will grow to the same height as the tall variety |
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What is the experimental evidence for gibberellins in stem elongation?
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-gibberellin conc. of tall pea plants compared to the conc. of dwarf pea plants -plants are genetically identical -plants with higher gibberellin conc. were taller |
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What is the technical term for 'leaf loss'?
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Abscission
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How do auxins inhibit leaf loss?
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auxin is produced by young leaves, the older the leaf gets the less auxin it produces which leads to leaf loss
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How does ethene stimulate leaf loss?
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-ethene is produced by aging leaves -leaves get older, more ethene is produced -abscission layer forms at leaf stalk -isolates leaf, leaf falls off |
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What is leaf senescence?
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aging of the leaf; leaf going brown
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What enzyme digests the cells in the abscission layer?
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cellulase
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What is the commercial use for auxins?
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-promotes flowering -prevents fruit drop (however super high conc. can promote fruit drop) -grows seedless fruits by promoting ovule growth -weed killer |
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What is the commercial use for cytokinins? |
-prevent leaf senescence -used in tissue culture to help mass produce plants |
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What is the commercial use for gibberellins?
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-delays senescence in citrus, improving shelf life -elongates grape stalks so they are less compact and grapes are bigger -speeds up germination of barley in beer production -increases sugar cane yield |
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What is the commercial use for ethene?
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-speeds fruit ripening -promotes fruit drop in cotton, cherry and walnut -promoting lateral growth in some plants. yielding compact flower stems |
