In GCSE Science one topic studied is how organisms use nerves and hormones. This is the last of five quizzes on that subject and it looks in particular at how plants use hormones for both sensitivity and control.
We all recognise the main parts of a plant but have you ever wondered how the stem of a plant knows to grow upwards and how the roots know that they should grow downwards?
One of the characteristics of life on earth is sensitivity to the surroundings. In the case of animals how they react to external stimuli is easy to see, however, it is not always so obvious for plants. Plants don't have a nervous system or muscles but they do have hormones which they use to give them sensitivity to their surroundings. The sensitivity granted by the hormones enables plants to grow towards light and makes their roots push down into the soil.
[readmore]Certain plants living in areas where conditions mean that there are few nutrients have developed carnivorous habits. Not like the giant 'man-eating' plants of science fiction stories - they only eat insects. You probably know about the venus fly trap which has small hairs on its 'traps' that detect insects and close the trap, but there are others such as the sundew and pitcher plants. These plants have evolved to trap flies and other insects. They secrete digestive juices that slowly break down the insects into the nutrients that the plant needs. These are then absorbed by the plant cells and transported in the sap to where they are needed.
As well as for sensitivity, plants also use hormones to control their biological processes. Growth of plants is controlled by hormones but plants also use them to control their formation of flowers, stems and leaves, and for their shedding of leaves.
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You can find more about this topic by visiting BBC Bitesize - Plant organisation - AQA
Plants growing next to a window need to be turned round regularly otherwise their leaves will all lean towards the light
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If you plant a seed upside-down it doesn't matter. Gravitropism will ensure that the shoot and root grow the right way
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Auxins are a group of plant hormones that control phototropism and geotropism
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This ensures that they grow in the right direction and towards the light
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This ensures that they grow downwards, anchoring the plant in the soil and finding water and nutrients
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Some carnivorous plants respond to touch
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In this type of question you are looking for an advantage. Picking all of the fruit in one short period of time makes the process cheaper for big companies
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The stems are positively phototropic and negatively geotropic so they will grow towards the bright light source as well as upwards. The roots are positively geotropic which is why they grow downwards
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In the cells in plant shoots, the auxins are hormones that stimulate growth
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Auxins are made in the growing tips of plants - no tips, no growth. In the dark, auxin levels are higher so those seedlings grew taller. The control seedlings behaved normally and grew towards the light
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