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14 Cards in this Set
- Front
- Back
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Why do Plants need to respond to the environment? |
They are more likely to survive by responding to the presence of predators and abiotic stress. |
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What is a tropism? |
A plant's reponse to a directional stimulus. Positive- towards the stimulus. Negative- away from the stimulus. |
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Where are Auxins produced? How are they transported around the plant? |
In the tips of shoots (apical buds). They are transported by diffusion and active transport over short distances, and via the phloem over longer distances. This results in different parts having different amounts of auxins, so growth is uneven. |
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Describe apical dominance. |
Auxins stimulate growth in the apical bud and inhibit growth in side shoots. This prevents side shoots from growing, saving energy and reducing competition. This allows a plant to grow very tall quickly. If the apical bud is removed, the apical bud won't produce auxins so the side shoots will start growing. |
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How can side shoots grow at the bottom of a plant? |
The further away from the apical bud, the lower the concentration of auxin, so therefore side shoots are able to grow. |
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What is the experimental evidence for auxins? |
Plant 30 similar plants and record the number of side shoots growing. For 10 plants, remove the tip and apply auxin past, for 10 remove the tip and apply a paste without auxin and for the other 10 leave as a control. Leave the plants to grow for 6 days and count the number of side shoots. |
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What is the function of giberellins? |
They stimulate seed germination, stem elongation, side shoot formation and flowering. They do not inhibit plant growth. |
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How do Auxins and Gibberellins interact? |
They are often synergistic- they make the plant grow tall. They are often antagonistic- the growth of side shoots. |
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What is the experimental evidence for Gibberellins? |
Plant 40 similar plants. Leave 20 as controls. Water the other plants with a dilute solution of Gibberellin. Let the plants grow for 28 days and measure stem length each week. |
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Describe the process of leaf abscission. |
Auxins inhibit leaf loss- they are produced by young leaves but as the leaf gets older, less auxin is produced. Ethene stimulates leaf loss. An Abscission layer develops at the bottom of the stalk. Ethene stimulates the cells in the layer to expand, breaking cell walls so the leaf falls off. |
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How is ethene used comercially? |
It stimulates ripening of fruit by stimulating enzymes that break down chlorophyll and convert starch into sugars. |
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How are auxins and gibberellins used commercially? |
They make the fruit develop without fertilisation. |
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How are auxins used comercially? |
Triggering the fruit to drop. Selective weed killers- they make weeds produce long stems rather than lots of leaves so the weed grows too fast and cannot get water. Rooting hormones- making a cutting grow roots. |
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