What Plants Need to Live and Grow

 
In this article we learn about how plants obtain food to allow them to grow and stay healthy.

All living things need to get food from somewhere….humans cannot make food inside their own bodies but have to find food from ‘external sources’.

girl eating a salad-humans have to find food externally

Earth worms cannot make their own food inside their bodies and also have to find food from ‘external sources’ in the soil.

earth worm wriggling on moist soil

Plants, on the other hand, ARE ABLE TO MAKE THEIR OWN FOOD INSIDE THEIR BODIES.!!

  • How do they do that? Any ideas?

science for kids- alpine plants in colarado, usa

1) Living and growing- plants making their own ‘food’ in their leaves

Plants make ‘food’ in their leaves using a process called ‘photosynthesis’.

‘Photosynthesis’ makes it possible for the leaves of plants to produce a type of sugar called ‘glucose’. Glucose produced in the leaves not only keeps the leaves healthy but also feeds other parts of the plant.

For ‘photosynthesis’ to occur in the leaves three things need to happen:

1) Sunlight

Plants need to absorb sunlight into their leaves.  The green ‘pigment’ of plant leaves called ‘chlorophyll’ allows plants to absorb large amounts of light energy.

  • Why can plants only absorb light energy in daylight?

science for kids sun shining through leaves

2) Water

Plants need to absorb the water they need through their roots. Water is then sucked up into the plant’s leaves through their ‘stems’ (or ‘stalks’). Plants use this water to help them convert light energy into ‘glucose’.

key stage two plant absorbs water through roots

 3) Carbon Dioxide

A plant’s leaves need large quantities of carbon dioxide to make ‘glucose’. Carbon Dioxide enters a plant’s leaves through its many thousands of tiny ‘mouths’.

stoma in a tomato plant

Carbon dioxide enters a plant’s leaves through its ‘stomata’ which stay open during the day. The carbon dioxide reacts with the sunlight and water inside the leaves to make ‘glucose’.

At those times during the day when the stomata on a plant’s leaves are open the leaves lose valuable water vapour (that is, water in the form of gas). So plants need their roots to provide them with a constant source of water to re supply the leaves with water that they lose during ‘photosynthesis’.

Oxygen is produced as a waste product and is expelled out of the ‘stomata’ during ‘photosynthesis’ into the atmosphere.

  • Why does ‘photosynthesis’ not take place at night? Do the ‘stomata’ remain open at night?

School science diagram of process of photosynthesis

 Photosynthesis does not take place at night because there is no sunlight. The ‘stomata’ close at night because leaves do not need to collect any carbon dioxide. Closing the stomata also means that at night the leaves do not lose valuable water vapour.

The way in which leaves use sunlight, water and carbon dioxide to make glucose is quite complicated- and something you will not learn until you get to secondary school!

2) Living and growing- enough fertile soil for roots to grow in

In this picture you can see plants growing in a crack surrounded by rock.

  • How are plants able to grow in this crevice (crack) in the rocks? Why don’t they grow on the rocks?

Plants growing in rock crevices

If you look at this picture you can see that there is enough fertile soil for these plants to grow in. The roots are strong and healthy.

plant roots of eastern gamagrass plant

This video shows the roots of radish seeds growing in soil.

 3) Living and growing- enough space to grow roots

Plants need enough space in which to grow their roots. Some plants need more space than others.

plants need enough space to grow their roots

The roots of this spider plant are ‘pot bound’.

  • What does ‘pot bound’ mean? Will the plant be able to grow healthily with roots like this?

Root-bound spider plant

4) Living and growing- competing for light

In this wild meadow different species of flowers are competing for light. No flower wants to find itself in the shade of other taller flowers.

  • What happens if plants do not get enough sunlight?

wildflowers

Some plants are careful when they come into bloom. They need to flower at just the right time to maximize the amount of sunlight they receive. These bluebells flower in April and May before the trees grow big leaves. When the trees have a full canopy of leaves the forest floor will be plunged into semi- darkness.

blue bell woods in East Sussex, England

5) Living and Growing-absorbing important minerals through the roots

In addition to photosynthesis another way in which plants obtain food is through their roots.

Nitrogen is one of the most important nutrients that plants need to help them live healthily and grow properly. Plants growing in the wild get their nitrogen from decaying leaves, bacteria and animal waste which can all be found in the soil.

There is plenty of nitrogen in the Earth’s atmosphere. 78% of the Earth’s atmosphere is made up of nitrogen, with under 1% carbon dioxide. However plants have evolved to use their roots as a source of nitrogen and the atmosphere as a source of carbon dioxide.

Plants which are grown by humans often get extra nitrogen from fertilizers that are spread on fields and gardens.

Look at these pictures- they show different ways in which farmers add nitrogen and other important nutrients into the soil using fertilizers.

nitrogen sprayed onto fields from an aeroplane

tractor adapted to spread fertiliser

spreading fertiliser by hand

This farm in China stores cow dung in a cement pond which is then spreads on the fields.

  • Look carefully; can you see what the farmer uses to spread fertilizer onto the fields?

natural cow dung fertiliser in cement ponds

If plants do not obtain enough nitrogen their growth can be stunted and they become unhealthy. Leaves that are not fed enough nitrogen through their roots lose the ability to produce the green pigment called ‘chlorophyll’.

  • Look at this picture of corn growing. Which leaves are unhealthy?  Why are they unhealthy?

corn leaves with insufficient chlorophyll

Look at the picture from the 1940’s showing two halves of a field- one half of the field has had fertilizer added and the other half has had none added.

  • Which plants are healthier?

fertiliser applied to fields

Plant Fun Stuff

Watch this time lapse video of a dandelion flower growing; it has plenty of water, sunlight, carbon dioxide and fertile soil.

The video stops just before the seeds blow away in the wind.

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