Biology PAG 5: Photosynthesis

Combined Science PAG B4: Photosynthesis

Suggested Activity 3: Investigating how light intensity can affect the rate of photosynthesis

Instructions and answers for teachers & techniciansThis practical activity is composed of two parts; a teacher/technician section and the learner activity which can be found on page 11. This Practical activity supports OCR GCSE Biology.

When distributing the activity section to the learners either as a printed copy or as a Word file you will need to remove the teacher instructions section.

This is a suggested practical activity that can be used as part of teaching the GCSE (9-1) Gateway Science (A) and Twenty First Century Science (B) specifications.

These are not controlled assessment tasks, and there is no requirement to use these particular activities.

You may modify these activities to suit your learners and centre. Alternative activities are available from, for example, Royal Society of Biology, Royal Society of Chemistry, Institute of

Physics, CLEAPSS and publishing companies, or of your own devising.

Further details are available in the specifications (Practical Skills Topics), and in these videos.

OCR recommendations:

Before carrying out any experiment or demonstration based on this guidance, it is the responsibility of teachers to ensure that they have undertaken a risk assessment in accordance with their employer’s requirements, making use of up-to-date information and taking account of their own particular circumstances. Any local rules or restrictions issued by the employer must always be followed.

CLEAPSS resources are useful for carrying out risk-assessments: (http://science.cleapss.org.uk).

Centres should trial experiments in advance of giving them to learners. Centres may choose to make adaptations to this practical activity, but should be aware that this may affect the Apparatus and Techniques covered by the learner.

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IntroductionPhotosynthesis is a process used by plants, algae and some bacteria. Light energy is used transform carbon dioxide and water to glucose and oxygen.

Therefore, increasing the light available to a plant, will increase the rate of photosynthesis.

carbon dioxide + water glucose + oxygen

6CO2 + 6H2O C6H12O6 + 6O2

Other factors that will affect the rate of photosynthesis are temperature and carbon dioxide concentration.

In this experiment pupils investigate how light intensity affect the rate of oxygen production. The experiment is an ideal investigation to consider variables and the repeatability of data.

DfE Apparatus and Techniques coveredThe codes used below match the OCR Practical Activity Learner Record Sheet (Biology / Combined Science) and Trackers (Biology / Combined Science) available online. There is no requirement to use these resources.

1 [1]: Use of appropriate apparatus to make and record a range of measurements accurately, including: iv) time; vi) volume of liquids; vii) volume of gases

3 [3]: Use of appropriate apparatus and techniques for the: i) observation of biological changes and/or processes; ii) measurement of biological changes and/or processes

4 [4]: Safe and ethical use of living organisms (plants or animals) to measure: i) physiological functions; ii) responses to the environment

5 [5]: Measurement of rates of reaction by a variety of methods including: i) production of gas

AimsIdentify variables in an investigationMeasure the rate of photosynthesis by the production of oxygen in aquatic plants

Intended class timeThis activity will take 90 - 120 minutes depending on ability.

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Chlorophyll

Light

Chlorophyll

Light

Links to Specifications: GatewayB1.4c describe photosynthesis as an endothermic reaction

B1.4d describe experiments to investigate photosynthesis

B1.4e explain the effect of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis

B1.4f explain the interaction of these factors in limiting the rate of photosynthesis

Twenty First CenturyB3.1.1 describe the process of photosynthesis, including the inputs and outputs of the two mains stages and the requirement of light in the first stage, and describe photosynthesis as an endothermic process

B3.1.1b describe practical investigations into the requirements and products of photosynthesis

Mathematical Skills coveredM1a - Recognise and use expressions in decimal form

M2b - Find arithmetic meansM2f - Understand the terms mean, mode and medianM2g - Use a scatter diagram to identify a correlation between two variables

M4a - Translate information between graphical and numeric formM4c - Plot two variables from experimental or other data

Gateway Working scientifically references coveredWS1.2a use scientific theories and explanations to develop hypotheses

WS1.2b plan experiments or devise procedures to make observations, produce or characterise a substance, test hypotheses, check data or explore phenomena

WS1.2c apply a knowledge of a range of techniques, instruments, apparatus, and materials to select those appropriate to the experiment

WS1.2e evaluate methods and suggest possible improvements and further investigations

WS1.3a presenting observations and other data using appropriate methods to include: methods to include descriptive, tabular diagrammatic and graphically

WS1.3c carrying out and representing mathematical and statistical analysis to include: statistical analysis to include arithmetic means, mode, median

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WS1.3e interpreting observations and other data to include: presentations to include verbal, diagrammatic, graphical, symbolic or numerical form interpretations to include identifying patterns and trends, making inferences and drawing conclusions

WS1.3f presenting reasoned explanations relating data to hypotheses

WS1.3g being objective, evaluating data in terms of accuracy, precision, repeatability and reproducibility

WS1.3h identifying potential sources of random and systematic error

WS1.3i communicating the scientific rationale for investigations, methods used, findings and reasoned conclusions presentations through paper-based presentations using diagrammatic, graphical, numerical and symbolic forms

WS1.4a use scientific vocabulary, terminology and definitions

WS1.4b recognise the importance of scientific quantities and understand how they are determined

WS1.4f use an appropriate number of significant figures in calculation

WS2a carry out experiments to include: due regard to the correct manipulation of apparatus, the accuracy of measurements and health and safety considerations, and following written instructions

WS2b make and record observations and measurements using a range of apparatus and methods keeping appropriate records

WS2c presenting observations using appropriate methods to include: methods to include descriptive, tabular diagrammatic and graphically

WS2d communicating the scientific rationale for investigations, methods used, findings and reasoned conclusions presentations through paper-based and electronic reports and presentations using verbal, diagrammatic, graphical, numerical and symbolic forms

Twenty First Century IaS references covered IaS1.1 in given contexts use scientific theories and tentative explanations to develop and justify hypotheses and predictions

IaS. 3.recognise the importance of scientific quantities and understand how they are determined

IaS1.4 identify factors that need to be controlled, and the ways in which they could be controlled

IaS1. 6 plan experiments or devise procedures by constructing clear and logically sequenced strategies to:

- make observations

- produce or characterise a substance

- test hypotheses

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- collect and check data

- explore phenomena

IaS1. 8 use appropriate scientific vocabulary, terminology and definitions to communicate the rationale for an investigation and the methods used using diagrammatic, graphical, numerical and symbolic forms

IaS2.1 present observations and other data using appropriate formats

IaS2.6 when processing data use an appropriate number of significant figures

IaS2.7 when displaying data graphically select an appropriate graphical form, use appropriate axes and scales, plot data points correctly, draw an appropriate line of best fit, and indicate uncertainty (e.g. range bars)

IaS2.8 when analysing data identify patterns/trends, use statistics (range and mean) and obtain values from a line on a graph (including gradient, interpolation and extrapolation)

IaS2.9 in a given context evaluate data in terms of accuracy, precision, repeatability and reproducibility, identify potential sources of random and systematic error, and discuss the decision to discard or retain an outlier

IaS2.10 evaluate an experimental strategy, suggest improvements and explain why they would increase the quality (accuracy, precision, repeatability and reproducibility) of the data collected, and suggest further investigations

IaS2.12 explain the extent to which data increase or decrease confidence in a prediction or hypothesis

IaS3.1 use ideas about correlation and cause to:

a. identify a correlation in data presented as text, in a table, or as a graph

b. distinguish between a correlation and a cause-effect link

c. explain why individual cases do not provide convincing evidence for or against a correlation

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Starter activity - Quick quiz

1. Give the word equation for photosynthesis Carbon dioxide + water glucose + oxygen

2. Name three factors that can limit the rate of photosynthesisLight intensity, carbon dioxide concentration, temperature

3. Where in the plant does photosynthesis take place?Chloroplast

4. What chemical in the plant absorbs light? Chlorophyll

Equipment (all equipment in this section is per group) Lamp Metre stick 10ml measuring cylinder 200ml measuring cylinder 250ml beaker Funnel 1 strand of Hornwort pondweed 185ml pond water or 185ml of 1% sodium hydrogen carbonate Stop clock Plastic gloves (If using 1% sodium hydrogen carbonate)

NB/ depending on how much pondwater/sodium hydrogen carbonate is displaced, students may need to top up their 10ml measuring cylinder. There may also be spillage when trying to invert. Therefore, it is ideal to have some spare. This is explained in the technician’s notes.

Additionally, check with technicians on the number of lamps available to determine group sizes.

Health and SafetySodium hydrogen carbonate – Could irritate if it gets on student’s skin. Wear gloves when

inverting.

Electrical equipment near water – keep water away from sockets

Use of non-native species – Check the origin of your hornwort pondweed. If using a non-native species for this practical correct disposal is essential. Even the smallest part of the plant has the potential to become a massive problem. Even the water that the plant has been grown in can be dangerous to the environment. Ensure that the plants are destroyed before they leave your site. (sources: http://science.cleapss.org.uk/Resource/Bulletin-156-Summer-2016.pdf).

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Method Equipment should be setup as shown by the diagrams.

Here are step by step instructions on how to do that;

1. Use a 200ml measuring cylinder to measure out 175ml of pond water or 1% sodium hydrogen carbonate

2. Pour the pond water or 1% sodium hydrogen carbonate into the 250ml beaker

3. Place the strand of hornwort pondweed into the beaker

4. Place the lamp next to the beaker

5. Place the funnel into the beaker, over the hornwort pondweed, with the spout pointing up

6. Fill the 10ml measuring cylinder with pond water or 1% sodium hydrogen carbonateIf using 1% sodium hydrogen carbonate, gloves should now be put on

7. Place your thumb over the 10ml measuring cylinder

8. Invert (turn upside down) the measuring cylinder and place it over the spout of the funnel. Thumb should be kept over the measuring cylinder as close to the spout as possible to keep as much of the liquid in as you can. If this does not work first time, students may

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require a top up of liquid.

9. Record in the table (under level before) the level of pond water/1% sodium hydrogen carbonate in the 10ml measuring cylinder.

10. Start the stop clock to and time 10 minutes

11. After 10 minutes, record in the table (under level after) the level of liquid in the 10ml measuring cylinder.

12. Work out the difference between the levels of liquid after step 9 and step 11, record this in your table under Displacement (Difference in levels)

13. Move the lamp 80cm away from the beaker

14. Repeat steps 9 – 12. Repeat again with the lamp at 160cm and 240cmStep 6-8 may need to be repeated, depending on how much liquid was displaced

It is unlikely that students will have enough class time to repeat the test. However, as the rest of the class are following the same method, they can use results from peers.

Technician NotesEquipment - all equipment in this section is per group. The number of groups/sets should be discussed with the class teacher, based on the number of light sources available.

Lamp Metre stick 10ml measuring cylinder 200ml measuring cylinder 250ml beaker Funnel 1 strand of Hornwort pondweed 185ml pond water or 185ml of 1% sodium hydrogen carbonate Stop clock Plastic gloves (If using 1% sodium hydrogen carbonate)

NB/ depending on how much pondwater/sodium hydrogen carbonate is displaced, students may need to top up their 10ml measuring cylinder. There may also be spillage when trying to invert. Therefore, it is ideal to have some spare. This is explained in the technician’s notes.

Additionally, check with technicians on the number of lamps available to determine group sizes.

Version 1.1 – January 2018 8 © OCR 2018

Health and Safety Sodium hydrogen carbonate – Could irritate if it gets on student’s skin. Wear gloves

when inverting.

Electrical equipment near water – keep water away from sockets

Use of non-native species – Check the origin of your hornwort pondweed. If using a non-native species for this practical correct disposal is essential. Even the smallest part of the plant has the potential to become a massive problem. Even the water that the plant has been grown in can be dangerous to the environment. Ensure that the plants are destroyed before they leave your site. (sources: http://science.cleapss.org.uk/Resource/Bulletin-156-Summer-2016.pdf).

Student activity – answers1. Identify the variables in this experiment

Independent variable Light intensity/distance of lamp from the pond weed

Dependent variable The rate of photosynthesis This will be quantified by measuring the volume of oxygen (cm3) collected in the measuring cylinder

Control variables The volume of water/sodium hydrogen carbonate available to the plant (~185ml)The period of time the Oxygen production is measured over (10 mins) Concentration of CO2

Surrounding temperature

2. Which control variable with be difficult to control?

Concentration of CO2, Surrounding temperature.

3. Describe the relationship between the distance the lamp is from the pondweed and the volume of oxygen produced

As the distance between the lamp and the pondweed increases, the volume of oxygen produced decreases (answers could vary depending on data).

4. What does this relationship tell us about the relationship between light intensity and the rate of photosynthesis? As light intensity decreases, the rate of photosynthesis decreases.As light intensity increases, the rate of photosynthesis increases.

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5. Was this what you expected? Explain you answer

Answers will vary depending on data collected.

Student should explain that more light lead to a faster rate of photosynthesis, as light energy is required to transform carbon dioxide and water into glucose and oxygen.

CHALLENGE QUESTION: Look at the graph below

Why does the graph plateau?

Maximum rate has been reached, light intensity is no longer a limiting factor.

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v1 January 2018 Published on the qualification pages

Version 1.1 – January 2018 10 © OCR 2018

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Light intensity

Rate

of p

hoto

synt

hesi

s

Biology PAG 5: Photosynthesis

Combined Science PAG B4: Photosynthesis

Suggested Activity 3: Investigating how light intensity can affect the rate of photosynthesis

Learner ActivityIntroductionPhotosynthesis is a process used by plants, algae and some bacteria. Light energy is used transform carbon dioxide and water to glucose and oxygen.

Therefore, increasing the light available to a plant, will increase the rate of photosynthesis.

carbon dioxide + water glucose + oxygen

6CO2 + 6H2O C6H12O6 + 6O2

Other factors that will affect the rate of photosynthesis are temperature and carbon dioxide concentration.

AimsIdentify variables in an investigationMeasure the rate of photosynthesis by the production of oxygen in aquatic plants

Equipment Lamp Metre stick 10ml measuring cylinder 200ml measuring cylinder 250ml beaker Funnel 1 strand of Hornwort pondweed 185ml pond water or 185ml of 1% sodium hydrogen carbonate Plastic gloves (If using 1% sodium hydrogen carbonate)

Version 1.1 – January 2018 11 © OCR 2018

Chlorophyll

Light

Chlorophyll

Light

Method Equipment should be setup as shown by the diagrams.

Here are step by step instructions on how to do that;

1. Use the 200ml measuring cylinder to measure out 175ml of pond water or 1% sodium hydrogen carbonate

2. Pour the 175ml of pond water or 1% sodium hydrogen carbonate into the 250ml beaker

3. Place your strand of hornwort pondweed into the beaker

4. Place your lamp next to the beaker

5. Place the funnel into the beaker, over the hornwort pondweed, with the spout pointing up

6. Fill the 10ml measuring cylinder with pond water or 1% sodium hydrogen carbonateIf using 1% sodium hydrogen carbonate, now put on your gloves

7. Place your thumb over the 10ml measuring cylinder

Version 1.1 – January 2018 12 © OCR 2018

8. Invert (turn upside down) the measuring cylinder and place it over the spout of the funnel. Keep your thumb over the measuring cylinder as close to the spout as you can to keep as much of the liquid in as you can

9. Record in the table (under level before) the level of pond water/1% sodium hydrogen carbonate in the 10ml measuring cylinder.

10. Start the stop clock to and time 10 minutes

11. After 10 minutes, record in the table (under level after) the level of liquid in the 10ml measuring cylinder.

12. Work out the difference between the levels of liquid after step 9 and step 11, record this in your table under Displacement (Difference in levels)

13. Using the metre stick to measure the distance, move the lamp 80cm away from the beaker

14. Repeat steps 9 – 12. Repeat again with the lamp at 160cm and 240cmYou may need to repeat 6-8, depending on how much liquid was displaced.

It is unlikely that you will have enough class time to repeat your test. However, as the rest of your class are following the same method, you can use results from peers.

Results Collect your results in the table below

Table 1

Distance of lamp from plant (cm)

Displacement of Pondwater/1% NaHCO3 (cm3)

Test 1 Test 2 Test 3 Average Displacement

Level befor

e

Level

after

Displacement

(Difference in levels)

Level befor

e

Level

after

Displacement

(Difference in levels)

Level befor

e

Level

after

Displacement

(Difference in levels)

0

80

160

240

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The volume of liquid displaced, tells us the volume of oxygen produced. Add you averages to this table (this will help with you graph drawing)

Table 2

Distance of lamp from plant (cm)

Average Volume of Oxygen collected (cm3)

0

80

160

240

Plot the results from table 2 onto a graph

Activity 1. Identify the variables in this experiment

Independent variable

Dependent variable

Control variables

2. Which control variable with be difficult to control?

3. Describe the relationship between the distance the lamp is from the pondweed and the volume of oxygen produced

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4. What does this relationship tell us about the relationship between light intensity and the rate of photosynthesis?

5. Was this what you expected? Explain you answer

CHALLENGE QUESTION: Look at the graph below

Why does the graph plateau (level off)?

DfE Apparatus and Techniques coveredThe codes used below match the OCR Practical Activity Learner Record Sheet (Biology / Combined Science) and Trackers (Biology / Combined Science) available online. There is no requirement to use these resources.

Biology Combined Science1-iv 1-vi 1vii 3-i 1-iv 1-vi 1vii 3-i3-ii 4-i 4-ii 5-i 3-ii 4-i 4-ii 5-i

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Light intensity

Rate

of p

hoto

synt

hesi

s