AQA GCSE (Separate Science) Unit 4 - Bioenergetics Foundation - Photosynthesis and Respiration - practical method

Sep 5, 2026

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AQA GCSE (Separate Science) Unit 4 Bioenergetics Foundation explains how photosynthesis in chloroplasts converts carbon dioxide and water into glucose and oxygen using light energy, and how limiting factors such as light intensity, temperature and carbon dioxide affect reaction rate. It links glucose to respiration, describing aerobic and anaerobic pathways, energy release, fermentation and oxygen debt in exercise. The resource includes an experiment using pondweed and sodium hydrogen carbonate to measure bubble production, identifying independent, dependent and control variables.

LanguageEnglish

CategoryExam

FormatPDF

Pages2

Reading Time5 min

AccessFree to download

Photosynthesis

Effect of light intensity on rate (RPI)

Limiting factors

Respiration

Aerobic vs anaerobic

Metabolism

How energy supports cell processes

Effect of exercise

Practical method: pondweed bubbles experiment

| AQA GCSE (Separate Science) Unit 4: Bioenergetics Foundation | | | | | --- | --- | --- | --- | | Photosynthesis | The Effect of Light Intensity on the Rate of Photosynthesis (RPI) | | Respiration | | Photosynthesis is a chemical reaction which takes place in plants. It converts carbon dioxide and water into glucose and oxygen. It uses light energy to power the chemical reaction, which is absorbed by the green pigment chlorophyll. This means that photosynthesis is an example of an endothermic reaction. The whole reaction takes place inside the chloroplasts which are small organelles found in plant cells.
Plants acquire the carbon dioxide via diffusion through the stomata of their leaves. The water is absorbed from the soil through the roots and transported to the cells carrying out photosynthesis, via the xylem.

The glucose made in photosynthesis is used for respiration, stored as starch, fat or oils, used to produce cellulose or used to produce amino acids for protein synthesis.
The Rate of Photosynthesis and Limiting Factors
A limiting factor is something which stops the photosynthesis reaction from occurring at a faster rate. Temperature, light intensity and carbon dioxide level are all limiting factors.
Increasing the temperature of the surroundings will increase the rate of reaction, but only up to around 45°C. At around this temperature, the enzymes which catalyse the reaction become denatured.
Increasing the light intensity will increase the rate of reaction because there is more energy to carry out more reactions. Increasing the carbon dioxide concentration will also increase the rate of reaction because there are more reactants available. | The amount of light a plant receives affects the rate of photosynthesis. If a plant receives lots of light, lots of photosynthesis will occur. If there is very little or no light, photosynthesis will stop. | | Respiration is the chemical reaction which occurs inside the mitochondria of all living cells to release energy for living functions and processes, e.g. movement, warmth and building larger molecules for growth and repair. The reaction is exothermic, meaning that energy is released to the surroundings.
Respiration can be either aerobic (using oxygen) or anaerobic (without using oxygen) .

In anaerobic respiration, the glucose is not completely oxidised. This means that there is less energy released than in aerobic respiration.

In plants and yeast, anaerobic respiration makes some different products. The reaction is also called fermentation and is used in bread-making and beer-brewing.

ethanol
C 2 H 5 OH | | | Method |
Boiling tube (clamped in place)
Pondweed weighted
with paperclip
Metre ruler
| | | | 1. Measure 20cm³ of sodium hydrogen carbonate solution and pour into a boiling tube.
2. Collect a 10cm piece of pondweed and gently attach a paper clip to one end.
3. Clamp the boiling tube, ensuring you will be able to shine light onto the pondweed.
4. Place a metre rule next to the clamp stand.
5. Place the lamp 10cm away from the pondweed.
6. Wait two minutes, until the pondweed has started to produce bubbles.
7. Using the stopwatch, count the number of bubbles produced in a minute.
8. Repeat stages 5 to 7, moving the lamp 10cm further away from the pondweed each time until you have five different distances.
9. Now repeat the experiment twice more to ensure you have three readings for each distance.
The independent variable was the light intensity.
The dependent variable was the amount of bubbles produced. Counting the bubbles is a common method, but you could use a gas syringe instead to more accurately measure the volume of oxygen produced.
The control variables were same amount of time and same amount of pondweed. A bench lamp is used to control the light intensity and the water in the test tube containing the pondweed is monitored with a thermometer to check and con

FAQs

What is photosynthesis and where does it take place in plants?

Photosynthesis is a chemical reaction that converts carbon dioxide and water into glucose and oxygen using light energy. It occurs inside chloroplasts in plant cells.

How do light intensity, temperature, and carbon dioxide affect the rate of photosynthesis?

Higher light intensity increases the rate, up to higher availability of energy for reactions. Increasing temperature raises the rate up to around 45°C, after which enzymes denature. Increasing carbon dioxide concentration increases the rate by providing more reactants.

What is the difference between aerobic and anaerobic respiration, and how does it relate to exercise?

Aerobic respiration releases more energy using oxygen, while anaerobic respiration occurs without oxygen and releases less energy. During exercise, insufficient oxygen demand leads to anaerobic respiration, producing lactic acid and causing oxygen debt.

Sep 5, 2026

Upload by Levi