S-Cool Revision Summary
S-Cool Revision Summary
Typical plants main features:
Roots: helps the plant to stand up in a strong wind and obtain water
Flower: attracts insects to pollinate it
Leaf: carries out most photosynthesis
Root Hairs: draw in the most water possible
Stem: carries material up and down and keeps it upright
Plants obtain their food through photosynthesis but not all parts of the plant can do this. For example, the roots do not get any light.
This system is made up of lots of tubes or vessels that branch throughout the plant, like our circulatory system.
Xylem (pronounced "zy-lem") vessels or tubes reach up to the leaves from the roots. They carry water and mineral nutrients to all parts of the plant, especially the leaves.
Water moves from the soil into the roots by osmosis and then flows steadily up the xylem. As water is lost from the leaf by transpiration more water is drawn up through the xylem to replace it. The roots have root hairs on them, this increases their surface area and so allows more water to be absorbed.
Phloem (pronounced "flo-em") tubes carry the sugars such as glucose made in the leaves to all parts of the plant, including the roots. This sugar can then be stored for example as starch in a potato.
The xylem and phloem tubes are often grouped together as they travel through plants into veins and vascular bundles. For example as they pass through leaves and up stems.
Nutrients are chemicals that plants need in small amounts but which are essential to keep them healthy. They are similar to the vitamins that we need.
Gardeners and farmers add fertilisers to plants in either organic material or as chemicals. Either way they contain the nutrients required. The best known of these nutrients are nitrates, phosphates and potassium. The relative amounts of these are often shown on bags of fertiliser as an "NPK" ratio.
Some people talk to plants. It is harmless, legal and they believe it helps them grow - although others disagree.
But plants are sensitive things. They do respond to certain stimuli. A stimulus is anything that could cause a response.
Such a growth response shown by a plant is called a "tropism". It can involve all of the plant or just a small part of it.
Such a response involving light is phototropism.
However things are a bit more complicated than this - aren't they always! A growth response that is towards the stimulus is called a "positive" tropism, whereas one that is away from it is described as a "negative" tropism.
A hormone is a chemical messenger, it causes changes in how a plant or the body of an animal works.
Plants release chemicals which control the tropisms. The best known of these 'plant hormones' are the "auxins".
Auxins can make the shoot of a plant grow towards the sun. For example, by getting the cells on one side to grow larger and this pushes the whole shoot around. The auxins are released from the very tips of the shoots or roots.
Plant hormones work in the same way to get roots to bend down towards gravity or water in the soil.
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