Plants,+photosynthesis+and+food

== = = =__**Plants, Photosynthesis and Food**__=

Carbon dioxide + water -> glucose + oxygen

__**Cross section of a generalised leaf**__





__**Limiting factors**__



__**How does a plant lose water?**__ Plants take in water through their roots, but lose water through their leaves. In this investigation you are going to find out if different leaves have different numbers of stomata on their lower surfaces. As you go through the investigation, answer the questions found at the end of each step.

Equipment list ★ Three leaves of different shapes and sizes ★ Graph paper ★ Nail Varnish

__Step 1__ ★ A microscope ★ Three microscope slides On graph paper draw the outlines of three leaves of different shapes and sizes. **Question 1** Look at the leaves you have. Are there any differences in the colour of the upper and lower leaf surface? Do the upper and lower leaf surfaces feel different? __Step 2__ Paint the LOWER surface of each leaf with coloured nail varnish (at least 1 cm 2 ). You could use a different coloured varnish for each leaf to make it easier to identify the varnish peels later. __Step 3__ While the nail varnish is drying, count the number of squares on the graph paper that fall within the area of the leaf. This will allow you to calculate the surface area of the leaf. If the edge of your leaf fills less than half of a square, ignore it. If it fills at least half a square or more then count it.



**Question 2** Do you expect leaves with a larger surface area to lose more or less water? If leaves lose water through their stomata, would you expect to find more or fewer stomata on large leaves? What other advantages are there for a leaf to have a large surface area __Step 4__ Carefully peel the varnish from the underside of the leaves and put the peels on separate microscope slides. Make sure you know which peel comes from which leaf. Put each slide on the stage in turn and carefully focus on the peel using the LOWEST power objective lens. Remember to be careful and not to break the slide by lowering the lenses too far. **Question 3** Why is it better to look at a peel from near the middle of the leaf rather than at the edge? __Step 5__ Look for the impressions of the stomata. **Question 4** Stomata have sausage-shaped cells that control how the pore opens and closes. If the ‘sausages’ are fat, is the pore open or closed? Can you draw how the stoma might look if it is open and how it might look if it is closed? __Step 6__ For each leaf peel, count how many stomata you can see through the microscope lens. Look at an area in the middle of the peel. Try to work out how big an area you are looking at. (If you put a piece of graph paper under the microscope and count the squares, you can work out the area of the part of the leaf you are studying.) **Question 5** If you had to make a table of the numbers of stomata found on different leaves, what unit of measurement should you use to compare the leaves: a) number of stomata per cm 2, b) number of stomata on the leaf, c) number of stomata per cm? __Step 7__  Can you now work out roughly how many stomata there are on the underside of the three leaves? If you have time, repeat the investigation by looking at the stomata on the upper surface of the leaf.  **Question 6** Do you think there will be as many stomata on the top as on the bottom? Carry out the investigation and then suggest a reason for the observation you make.

__**Have a go at these questions as revision for this plants and photosynthesis topic!**__ []