7/27/2019 Measuring the rate of photosynthesis - CO2.doc

http://slidepdf.com/reader/full/measuring-the-rate-of-photosynthesis-co2doc 1/2

Measuring the rate of photosynthesis

Light Intensity

Skills being assessed: A&I and ORR

Apparatus and Materials: Elodea (7 cm sprig), NaHCO3 solution of variousconcentrations (0.02M, 0.04M, 0.06M, 0.08M and 1M) 100 W bench lamp, beaker

(for water bath), boiling tubes, paper clip, thermometer, forceps, scissors.

Method:

1. Fill each boiling tube with a different concentration of NaHCO3.

2. Cut a sprig of Elodea (while the plant is immersed at an angle) about 7 cm

long and place it in the boiling tube with the lowest concentration of NaHCO3.

3. Use a paper clip to weight it down so it can be submerged and set up the

apparatus as shown in the illustration below. (Elodea should be inverted

position with the cut end up)

http://www.chs.helena.k12.mt.us/faculty/hbosch/biologytopics_files/webnotes/ch%208%20and

%209/Lightintensitygraphing.htm

4. The water bath is to absorb the heat from the lamp. Use the thermometer to

monitor the temperature to ensure it is kept at approximately 22°C.

5. Place the lamp 15 cm from the Elodea specimen. Allow the specimen to

adjust for 5 minutes.

6. Count the number of bubbles evolved in three consecutive minutes.

7. Use the same piece of pondweed with the other concentrations of NaHCO3

and repeat step 6.

8. Plot a graph to show how the number of bubbles varies with Carbon dioxideconcentration.

Mark Scheme

ORR

Proper format 

- Aim, apparatus and materials etc. and all are present in the correct

sequence (1 mark)

1

7/27/2019 Measuring the rate of photosynthesis - CO2.doc

http://slidepdf.com/reader/full/measuring-the-rate-of-photosynthesis-co2doc 2/2

- Correct content under each heading (1 mark)

2 marks

 Acceptable Language and expression

- Paste tense/ passive voice (1 mark)

- Few/no grammatical errors (1 mark)

2 marks

 Appropriate descriptions, tables and/or diagrams

- Method clearly described with logical sequence of activities

- Adequate detail

- Tables/diagrams appropriate/neat

 4 marks

 Accurate observations/recordings

- Significant/relevant changes recorded

- Extent/degree of change recorded

- Original and final condition compared

- Condition of control included (if relevant)

 4 marks

Total: 12 marks

Background information/biological principles, relationship to

investigation/observations

- Must include at least four points

 4 marks

Explanation/interpretation of results

- There must be at least 5 points explaining the results.

5 marks

Conclusions based on observations/data and related to aim

- While not rewriting the observation, the conclusion must include a reason.

2 marks

Limitations

- These are factors that can affect the accuracy of the data but the

experimenter has no control over these factors.

1 mark 

Total: 12 marks

2