Photosynthesis

In these lessons we will:

»Revise photosynthesis

»Use a practical activity to look at the conditions needed for photosynthesis to happen

»Investigate photosynthesis using algae

Revising photosynthesis

What is photosynthesis?

Why do plants do it?

How would a person tell if a plant is photosynthesisng?

Photosynthesis

Carbon dioxide Water Glucose Oxygen

light energy

Chlorophyll

So photosynthesis makes oxygen and glucose.

How could a plant be tested for these?

An alternative is to test for a substance thatplants make from glucose.

What do plants make from glucose?

STARCH !So the plant could be tested for starch to show it had been photosynthesising.

Now the class will carry out some practical work on Geranium plants.

Each group is trying to find out what isnecessary for photosynthesis

Starch will be present ifthe plant has been photosynthesising.

» Step» Boil leaf in water for a

few minutes» Boil leaf in alcohol for

a few minutes» Place leaf in hot water

for 30 seconds» Add Iodine to leaf

» Reason» To soften cells in leaf

» To remove green pigment (chlorophyll)

» To re-soften cells in leaf

» To stain any starch in leaf

Use a white board to collect and record the results

Leaf group 1

Leaf group 4Leaf group 3

Leaf group 2

What have you learned?

•Which leaves had starch present?•What is necessary for photosynthesis?

So for photosynthesis plants need?

Carbon dioxide Water Glucose Oxygen

light energy

Chlorophyll

Write – up your practical.

•Describe what you did•Describe your results•Explain what the results mean.

Practicals

Using algal cells to investigate photosynthesis

The class will now carry out some practicalsto investigate photosynthesis using algal cells.

Initially the algal cells will need to be immobilisedusing a simple immobilisation techniquethat your teacher will show you.

Refer to guide as necessary

Investigations into photosynthesis

The immobilised algal cells can be used to investigatethe effects of a variety of factors on photosynthesis.

When completing an investigation it would be good practice to complete it in the standard format.

The teacher will advise you on this.

You should by now have a good understanding ofthe factors that affect the rate of photosynthesis.

Write down what they are and what affect they haveon a plants rate of photosynthesis.