Safety Notes: There are no harmful chemicals in this investigation if handled appropriately
Apparatus

Beaker (100 or 250 ml) with 50-100ml calcium chloride (1.5% w/v)

Clamp and clamp stand

Small beaker/bijou bottle with lid

Green algal suspension

Sodium alginate solution

Syringe

Distilled water

Plastic sieve

Pipettes
Method
(Your teacher / technician may have already done steps 1 and 2 for you.)
1. You will be given a beaker with algae settled at the bottom. Carefully pipette off the water, taking care not to bubble air into the beaker as this may disturb the algae.
2. Pipette 3mls of the concentrated green algae at the bottom of the beaker into a bijou bottle.
3. Pipette 3mls of the sodium alginate into the bijou bottle with the algae. Place the lid onto the bottle.
4. Gently mix the algae and alginate together by tipping your bijou bottle back and forward.
Try not to be too vigorous as this may trap air bubbles in the mixture.
5. Place a syringe vertically in the clamp stand.
6. Pour approx. 50ml calcium chloride in a beaker. Place the beaker directly underneath the syringe.
7. Pour your algae and alginate mixture into the syringe. The mixture will drip slowly into the beaker of calcium chloride.
8. When all the mixture has all dripped through, leave the algal balls in the beaker of calcium chloride for 5-10 minutes. They will become solid.
9. Tip the algal balls into a tea strainer and rinse with distilled water.
10. Place the algal balls in a beaker of fresh distilled water until you need them for the investigation.
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to answer the question ‘Does photosynthesis need light to proceed?’
Method
1. Place the same number of algal balls (rinsed with distilled water) into two bijou bottles.
2. Fill each bottle full with red indicator solution using a pipette and replace lid
3. Fill a third empty bijou bottle with the indicator solution (this is a control)
4. Wrap black paper round one of the bottles containing algal balls and indicator.
5. Tape this firmly into place so that no light can get into the bottle.
6. Place all three bottles near to the light source that your teacher has asked you to use. They should be at the same distance from the light. Leave for half an hour.
7. Prepare a results table to record the colour and pH in each bottle afterwards
Results table
Bottle contents
1 1 control (indicator only)
2 2 algal balls + indicator no covering on the bottle
3 3 algal balls + indicator + black sugar paper covering
Things to consider while you wait
Indicator colour at the start
Indicator colour after 30 mins
This indicator solution goes purple when carbon dioxide is removed from it
1. What process in plants uses carbon dioxide?
2. In which of your bottles will this process be taking place?
This indicator solution goes yellow when carbon dioxide is added to it
3. What process in living things (including plants) produces carbon dioxide?
4. In which of your bottles will this process be taking place?
5. Why have we set up a bottle without the algal balls?
6. What are your predictions? Explain using the terms ‘photosynthesis’ and ‘respiration’.
What do your results show?
After you have collected your results, compare them to other groups near you and say whether they fit your predictions. Try to explain any anomalies (odd results).
Can you answer the question that you were investigating?
How will you show your results on a graph/chart?
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to answer the question ‘Does light intensity affect the rate of photosynthesis?’
Method
1. Place the same number of algal balls (rinsed with distilled water) into 5-6 bijou bottles.
2. Fill each bottle full with indicator solution using a pipette and replace the lid
3. Place the bottles equal distances apart along a 30cm ruler
4. Place a switched off lamp at one end of the ruler facing the bottles
5. Switch on the lamp and set your timer for the time you have chosen
6. When the time is up, record the colour and /or pH in each tube
Results table
Distance from the lamp (cm) Indicator colour at the start or pH value at the start
Things to consider while you wait
Indicator colour after 30 mins or pH value after 30 mins
This indicator solution goes purple when carbon dioxide is removed from it
1. What process in plants uses carbon dioxide?
2. In which of your bottles will this process be taking place most quickly? - explain
This indicator solution goes yellow when carbon dioxide is added to it
3. What process in living things (including plants) produces carbon dioxide?
4. In which of your bottles will this process be taking place?
5. What are your overall predictions?
– explain using the terms photosynthesis and respiration
What do your results show?
After you have collected your results, compare them to other groups near you and say whether they fit your predictions. Try to explain any anomalies (odd results).
Can you answer the question that you were investigating?
How will you show your results on a graph/chart?
Questions on the method
Was this a fair test?
What were your variables (dependent, independent, control)?
Can you think of a method that would have enabled you to collect more reliable data?
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to answer the question, ‘Does light intensity affect the rate of photosynthesis?’
Method
1. Wrap one of the three different neutral density filters around three different bijou bottles
2. Check there are no gaps then fix the filters into place with sticky tape
3. Leave a fourth bottle with no filter, and a fifth bottle covered in black paper
4. Place the same number of balls into each of the small bottles.
5. Fill each bottle full with hydrogen carbonate indicator solution and replace the lid
6. Place the bottles equal distances away from a switched off light source, making sure the sticky tape faces away from the light
7. Once they are all in place, switch on the light and leave for 30 mins
When the time is up, remove the filters and record the colour and /or pH in each tube
Results table
Filter on bottle
0.00 ND (no filter)
0.15 ND
0.30 ND
0.60 ND
1.00 ND (black paper)
% light transmitted into the bottle Colour / pH value of indicator after x mins
100
71
50
25
0
Note: When light hits a neutral density (ND) filter, some is absorbed and some is allowed through
(transmitted) regardless of the colour of the light. Some ND filters transmit more light than others.
Things to consider while you wait
1. Which of your algal balls will be getting the most light? Which will be getting the least?
This indicator solution goes purple when carbon dioxide is removed from it
2. What process in plants uses carbon dioxide?
3. In which of your bottles will this process be taking place most quickly? - explain
This indicator solution goes yellow when carbon dioxide is added to it
4. What process in living things (including plants) produces carbon dioxide?
5. In which of your bottles will this process be taking place?
6. What are your overall predictions?
– explain using the terms photosynthesis and respiration
What do your results show?
After you have collected your results, compare them to other groups near you and say whether they fit your predictions. Try to explain any anomalies (odd results).
Can you answer the question that you were investigating?
How will you show your results on a graph/chart?
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to investigate the question: At what light intensity will the algae reach their compensation point?
Respiration produces CO
2
and photosynthesis uses CO
2
. When the two processes are in balance there is no net production of CO
2
and we call this point the compensation point. We can use neutral density (ND) filters to find the light level at which this compensation point is reached.
Neutral density filters reduce transmittance of all wavelengths of light. As the ND rating increases, the amount of light transmitted into the bottle decreases and so the indicator solution containing the algal balls goes more yellow as photosynthesis slows down and respiration takes over.
Method
1. Wrap one of the three different ND filters around three different bijou bottles
2. Check there are no gaps and then fix the filters into place with sticky tape
3. Leave a fourth bottle with no filter, and a fifth bottle covered in black paper
4. Place the same number of balls into each of the small bottles
5. Fill each bottle full with hydrogen carbonate indicator solution and replace the lid
6. Place the bottles equal distances away from a switched off light source, making sure the sticky tape faces away from the light
7. Once they are all in place, switch on the light and leave for 30 mins
8. When the time is up switch off the lamp. Use a pipette the remove the indicator solution from one of the bottles and pipette this solution into a cuvette.
9. Place the cuvette into the colorimeter set at an absorbance of
550nm and record the reading.
10. Repeat with the solutions from the other bottles using clean cuvettes each time
11. Plot a graph of absorbance at 550nm against % light transmitted into the bottle
Find the value of light intensity at the compensation point (when absorbance is 0)
Results table
Prepare a results table similar to the one below
Filter on bottle
0.00 ND (no filter)
0.15 ND
0.30 ND
0.60 ND
1.00 ND (black paper)
% light transmitted into the bottle Absorbance at 550nm
100
71
50
25
0
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to investigate the question ‘Does light colour (wavelength) affect the rate of photosynthesis?’
Method
1. Wrap different colour (red, blue, green) acetate round each of three bottles. Take care not to leave gaps where white light could get in.
2. Leave a fourth bottle with no acetate, and a fifth bottle covered in black paper
3. Place the same number of algal balls into each of the small bottles
4. Fill each bottle full with hydrogen carbonate indicator solution and replace the lid
5. Place the bottles equal distances away from a switched off light source and with any sticky tape facing away from the lamp
6. Switch on the light and leave for 30 mins
7. When the time is up, remove the acetates, and record the colour and /or pH in each tube
Results table
Bottle covering Colour of light being transmitted into the bottle
Colour of light being blocked by the acetate so not getting into the bottle
Things to consider while you wait colour / pH value after 30 mins
Filters act by absorbing some colours of light and letting other colours through. So for instance, a red filter looks red because it is absorbing all the other colours except for red, and it is allowing red to pass through it (it transmits red light).
1. What coloured light is getting into each of your bottles?
This indicator solution goes purple when carbon dioxide is removed from it
2. What process in plants uses carbon dioxide?
3. In which of your bottles will this process be taking place? Explain.
This indicator solution goes yellow when carbon dioxide is added to it
4. What process in living things (including plants) produces carbon dioxide?
5. In which of your bottles will this process be taking place?
What do your results show?
After you have collected your results, compare them to other groups near you. Can you answer the question you were investigating and suggest under which colour light do algae have the fastest rate of photosynthesis?
How will you show your results on a graph/chart?
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012

Introduction
You will either have made or been given some algal balls. You are going to use them to answer the question ‘Does the number of algae/algal balls increase the rate of photosynthesis?’
Method
1. Place a different number of algal balls in each of your bijou tubes (make sure there is a regular interval between the different numbers) or
2. Place the same number of algal balls in each of your bijou tubes, making sure that each bottle contains algal balls of a different algal concentration to the other bottles
3. Fill each bottle full with hydrogen carbonate indicator solution & replace lid
4. Make sure each tube has equal and safe illumination by a lamp
5. Switch on the lamps and set your timer for the time you have chosen
6. When the time is up, record the colour and /or pH in each tube
Results table
Prepare a results table similar to the one below
Number of algal balls
0
10
20
Or
Colour / pH of indicator
Concentration of algae in the algal balls
0 (control)
0.25
0.50
Things to consider while you wait
Colour / pH of indicator
This indicator solution goes purple when carbon dioxide is removed from it
1. What process in plants uses carbon dioxide?
2. In which of your bottles will this process be taking place? - explain
This indicator solution goes yellow when carbon dioxide is added to it
3. What process in living things (including plants) produces carbon dioxide?
4. In which of your bottles will this process be taking place?
5. What are your overall predictions? Will the colour change in all of your bottles? Will it be faster in some bottles than others? Explain your predictions.
What do your results show?
After you have collected your results, compare them to other groups near you and say whether they fit your predictions. Try to explain any anomalies (odd results).
Can you answer the question that you were investigating?
How will you show your results on a graph/chart?
Copyright Science & Plants for Schools: www.saps.org.uk
Photosynthesis with Algal Balls: Students’ Guide. Revised 2012