Leaves, Stems and Roots

This science resource explains the function of leaves, stems and roots.

The leaf in the image below has veins running through it. The veins carry water and nutrients from the roots into the leaf.

The veins also carry ‘sugars’ out of the leaf. These ‘sugars’ are made inside the leaf and are transported to other parts of the plant to provide energy for growing and staying healthy.

Veins give support and help the leaf keep its ‘leafy’ shape…. much like our skeleton helps us keep our ‘human’ shape.

Human Skeleton demonstrating how veins support the leaf

Leaf showing veins which carry water into the leaf and sucrose out of the leaf

Click on image for slide show

How carbon dioxide enters leaves through the ‘stomata’.

Believe it or not every leaf has thousands of tiny mouths called ‘stomata’. The ‘stomata’ on leaves are too small to see with your own eyes. You can only see the stomata if you look at leaves under a powerful electron microscope.

electron microscope used to examine the stomata on leaves

This is what the ‘stomata’ of a tomato leaf looks like under an electron microscope:

stomata- seen under a microscope

Below you see what a single ‘stoma’ of a tomato leaf looks like under an electron microscope.

  • Is this ‘stoma’ open or closed?

stoma in a tomato leaf demonstrating transpirationDartmouth.edu/imagesindex.html

Carbon dioxide is an important gas that enters the ‘stomata’ in daylight. Carbon dioxide helps plants make ‘sugar’ when it is light.

Expelling oxygen through the ‘stomata’

At the same time as using carbon dioxide to make sugars, leaves make large quantities of oxygen. Leaves do not need all this oxygen and expel it into the atmosphere through their ‘stomata’ during daylight.

Times when the stomata of leaves close

At night after the sun has set the ‘stomata’ of leaves often close up. If there is no light from the sun plants cannot make any ‘food’. If plants cannot make any food when it is dark there is no point in their ‘stomata’ being open. At night plants do not need any carbon dioxide entering their leaves.

Evening on the Prairie Albert Bierstad 1870 demonstrating how photosynthesis does not occur at night

Evening on the Prairie- Albert Bierstad 1870

The green color of leaves

Leaves need to soak up (absorb) light to help them make sugars. The green color of leaves really helps them ‘absorb’ large amounts of sunlight. This green color is called ‘chlorophyll’. Plants use up a lot of energy making ‘chlorophyll’.


Parts of a plant-stems (also called ‘stalks’)

Plants need water just like humans do. Water is sucked up into the plant from its roots. In this hollyhock water is sucked up from the roots and travels to the leaves and flowers along the stem.

  • Why do you think that veins of stems are like straws?

Drinking Straws are analogous to a part of the plant called a xylem

the stem- seen in a hollyhock

  • Can you see the veins in this piece of celery?
 celery cross section shwoing veins whcih transport water

©Fir002 Flagstaffotos.com.au

This painting shows a celery plant including the roots, leaves and flowers.

celery plant showing roots, stem, flowers and leaves

Potatoes- are they part of the stem or part of the roots?

It is surprising to think that potatoes are actually part of the stem of a potato plant and not part of the roots! Potatoes are underground parts of the stem which store food for the plant. This supply of food provides energy for potato plants during long cold winters.

cross section of potato plant showing leaves, stem, roots and tubers

Parts of a Plant-Roots

Roots anchor plants to the ground and stop them being blown away. Plants also use their roots to suck up water and vital minerals from the soil into their stems.Anchor demonstrating how roots anchor plants to the ground

Parts of a plant called the 'roots'

  • Look at all these roots. What do humans do with them?!

many different varieties of carrots all laid out

 Science projects about flowers

  • Examine a collection of leaves with magnifying glasses to see patterns made by veins.
  • Make leaf rubbings
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