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Plants at Work

• Green plants use chlorophyll to trap light energy for photosynthesis.
• During photosynthesis, green plants convert carbon dioxide and water into sugar and oxygen.
• Plants provide oxygen for animals and use up waste carbon dioxide.
• Leaves are adapted for absorbing sunlight to use in photosynthesis.
• Leaves are adapted to allow gases to pass in and out.
• Plants need carbon dioxide, light and the right temperature to grow well.
• Plants also need nutrients from the soil for healthy growth.
• Extra nutrients are sometimes added in the form of fertilisers.
• Microbes can get nitrogen out of animal wastes, like manure, and this can be used by plants for growth.
• Roots anchor a plant in the ground and the stem supports the leaves and flowers.
• Water passes up the stem in the xylem. Food passes from the leaves in the phloem.
• Flowers have sepals, petals, stamens and carpels.
• The anthers make pollen grains and the ovary makes ovules.
• Pollination is the transfer of pollen from the anthers to the stigma.
• Fertilisation occurs when a pollen nucleus joins with an ovule nucleus.
• After fertilisation the ovary changes into the fruit and the fertilised ovule grows into a seed.
• Seeds can be scattered by the wind, by animals and by being flicked out of pods.
• Plants are important because they provide food, fuel, building materials and medicines.

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. So how do root cells get the food they need? Also, the leaves need water for photosynthesis, but how do they get water from the roots? There has to be a transport system going up and down the plant…

This system is made up of lots of tubes or vessels that branch throughout the plant, like our circulatory system.

Xylem  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 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. 

Like all of us plants start life very small.  They need the right kinds of things to grow properly and to respond in the right way. 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 these to plants in either organic material or 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. Sometimes plants get ill because one particular nutrient is missing or has been lost from the soil perhaps by overuse.

What you should be able to do.

• Explain the effect of increasing light on the amount of oxygen made by pond weed.
• Test a green leaf for starch.
• Plan an investigation to see if a plant can make food without any light.
• Test a patched leaf to show that only the green parts are able to make starch.
• Observe a leaf section under the microscope and locate the important parts.
• Make an imprint of a leaf surface with nail varnish.
• Plan an investigation into the number of air-holes in leaves.
• Plan an investigation to see how the growth of duckweed depends on fertiliser.
• Cut up some celery to show the xylem.
• Measure how quickly water moves up a stem to the leaves in different conditions.
• Find the xylem and phloem on a microscope slide of a stem section.
• Plan an investigation to find out how strong a stem or a root is.
• Remove the parts of a flower and make a flower poster.
• Observe pollen grains under the microscope.
• Describe how insect pollination and wind pollination can take place.
• Make a table of differences between insect-pollinated flowers and wind-pollinated flowers.
• Plan an investigation to find out how slowly different seeds fall.