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Water transport in plants

Water transport in plants


We know that plants need water in order to make their own food by photosynthesis in the leaves but how does water reach the leaves?

 

First plants absorb water and nutrients from the soil through their roots The  water travels through the root cells by osmosis until it reaches the stem. In the stem there are cells adapted for carrying water called the xylem cells. These are largely hollow.

 

One of our children knew that water evaporates from leaves and this escape of water from the stomata in leaves is called transpiration. If you imagine all the water molecules sticking together in a long line up the stem of a plant, as water at the top evaporates from the leaf by transpiration, the other water molecules are pulled up from the roots. Another way of thinking about it is that it is like sucking at the top of a straw which makes the liquid move up the straw and into your mouth.

 

Watch the video to see how they demonstrate that plants take up water through the stem and up into the flower.

 

Taking a closer look

 

If you take the stem of a plant and cut it in half you can look at the inside of the stem more closely. Many plants have more than one set of xylem cells - trees have lots bundled together to help water travel the long distances from the roots to the leaves. If you have celery in the house this is easy to cut across and see the circles of xylem cells.

 

If you want to try the experiment at home make sure you have a water soluble food dye - these have changed in recent years and it is much harder to get it to work than it used to be. Try changing the amount of dye you add, the water you add and even the plant you use. We have used carnations, celery and even daffodils in the past.

 

You could also investigate how different conditions affect the colouring of the petals eg temperature.

Inside stems

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