Fossil fuels are running out, which means we need to find new sources of energy! But what has this got to do with algae? Algae use the sun’s energy for photosynthesis and growth. We can exploit this process, and use algae to produce electricity. But this is not all: algae can also make hydrocarbons - similar molecules to those found in fossil fuels - which can be used directly as a source of biofuel.

Algae Chromatography

The aim of the exercise is to show the diversity of algae, and to demonstrate that red algae also contain green pigments (the green chlorophyll) and photosynthesise. This experiment was developed in conjunction with the researchers at the University of Cambridge, who are part of the Meet the algae: diversity, biology and energy exhibit team.

Materials required

  • Safety glasses
  • Centrifuge
  • Green algae culture
  • Red algae culture
  • Small mortar and pestle
  • 1 cm3 plastic pipettes
  • Centrifuge tubes (or test-tubes if you don't have access to a centrifuge)
  • Whatman 3MM paper (Cut into strips for the students)
  • Ethanol (Highly flammable, Harmful; see CLEAPSS Hazcard 40A)
  • Fine paint brushes
  • 50cm3 beaker

Prepare two stocks of algae: a red algae (Porphyridium) and a green algae (Chlorella). You can get the red algae Porphyridium purpureum, other red algae, and the green Chlorella from Euglena is another green-coloured alga you can use.

By extracting the pigments, and then analysing them using chromatography, it is possible to demonstrate that the red algae also contain green pigment, which is usually masked by their red pigment.

Safety: Eye protection must be worn. A risk assessment must be done for this activity. Ethanol is highly flammable, therefore must be no naked flames and wash your hands afterwards.


The green spot moves up the paper, displaying no further colours. The red spot becomes bright red and green pigments move up the paper.

Results of chromatography experimentThe green algae contain chlorophyll a and chlorophyll b (green pigments). The red algae contain chlorophyll a and phycobilin (a red pigment). Although chlorophyll is the major pigment for photosynthesis, the other pigments help algae harvest light of different wavelengths, which is useful when they are deeper in water.

You should point out to your students that algae are simple (lower) plants. It is also worth mentioning that all land plants originated from one group of green algae.







  • 1. Some algae can swim and react to light (which is known as phototaxis), so in order to settle they need to be kept in the dark.
  • 2. Both the green and red algae contain green pigment - the students should be able to see this as the pigment moves up the blotting paper.
  • 3. This green pigment is chlorophyll which is vital for photosynthesis and allows the algae to obtain energy from sunlight.
  • 4. The other pigments help algae harvest light of different wavelengths such as when they are deeper in water, giving them a greater chance of survival.

Curriculum links

Organisms and health 5a: Organisms are interdependent and adapted to their environment.
5b: Variation within species can lead to evolutionary changes, and similarities and differences between species can be measured and classified.
Energy, electricity and radiations 7b: Electrical power is readily transferred and controlled, and can be used in a range of different situations.

Applicable examination units:

Exam Board Unit

AQA: GCSE Additional Applied Science

Biology 2


OCR Gateway Science Suite: GCSE Science

B2 Understanding our Environment


OCR Gateway Science Suite: GCSE Additional Science

B4 It's a Green World

Photosynthesis, biomass, biofuels

OCR Gateway Science Suite: GCSE Biology

B6 Beyond the Microscope


Scottish Curriculum: Standard Grade Science

Topic 4: A Study of Environments

1: Energy from the Sun for Living Things

Scottish Curriculum: Standard Grade Chemistry

Topic 15: Carbohydrates and Related Substances

Scottish Curriculum: Standard Grade Biology

Topic 2: The World of Plants

Sub topic C - Making food

Northern Ireland Curriculum: GCSE Single Award Science

Module1: Staying alive

Northern Ireland Curriculum: GCSE Double Award Science & GCSE Biology

3.1 Living organisms and life processes


Science for you to try

Algae Chromatography

Algae are a diverse range of aquatic organisms that include seaweeds and small, unicellular species that grow in ponds.

In this experiment you will be looking at the different pigments that are present in two algae - a red alga (Porphyridium, left) and a green alga (Chlorella, right).



Download a pdf of the instructions here.

Red and green algal cultures

You will need:

  • Centrifuge
  • Green algae culture
  • Red algae culture
  • Small mortar and pestle
  • 1 cm3 plastic pipettes
  • Centrifuge or test-tubes
  • Strips of blotting paper
  • Ethanol
  • 50 cm3 beaker
  • Fine paint brushes

Safety: Wear safety glasses.

1. Centrifuge 10 cm3 of culture in a centrifuge tube to form an algae pellet. If you do not have a centrifuge, put the algae mixture in a small test-tube in the dark and allow the contents to settle. This should take around one hour.

2. Carefully pour off the liquid, trying to avoid disturbing the pellet of algae cells at the bottom. Then place the tube containing the algae pellet in a freezer overnight.

3. Grind the frozen pellet in a small mortar and pestle. Re-suspend the ground pellet in a small amount of water. To do this, use a 1 cm3 plastic pipette, and start by adding 1-2 drops of water. Add more if necessary, but try to use the minimum so that the solution is as concentrated as possible.

Adding algae to chromatography paper


4. Draw a line in pencil about 2 cm from the bottom of the paper you've been given. Use a fine paintbrush to place small dots of samples of green Chlorella and red Porphyridium next to each other. Add the dots of the samples a little at a time, leaving them to dry in between.

Algae chromatography in progress



5. Place the paper in 5 cm3 of ethanol (Note: make sure the solvent level is not above the level of the pencil line) in a 50 cm3 beaker and cover with a watch glass. Leave for around 10 mins to allow the solvent to move up the paper. What do you observe?




  1. Why is it best to let the algae settle in the dark?
  2. Where can you see the green pigment?
  3. What do you think this green pigment contains?
  4. Why do you think some algae contain more than one pigment?