Investigation of limiting factors
Cambridge A-Level Biology (9700) · Unit 13: Photosynthesis · 8 flashcards
Investigation of limiting factors is topic 13.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 13 — Photosynthesis , alongside Photosynthesis as an energy transfer process. In one line: The rate of photosynthesis can be limited by light intensity, carbon dioxide concentration, and temperature. These factors can restrict the photosynthetic rate if they are below their optimal levels.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 1 definition and 7 key concepts — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Three environmental factors that can limit the rate of photosynthesis
The rate of photosynthesis can be limited by light intensity, carbon dioxide concentration, and temperature. These factors can restrict the photosynthetic rate if they are below their optimal levels.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- state that light intensity, carbon dioxide concentration and temperature are examples of limiting factors of photosynthesis
- explain the effects of changes in light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis
- describe and carry out investigations using redox indicators, including DCPIP and methylene blue, and a suspension of chloroplasts to determine the effects of light intensity and light wavelength on the rate of photosynthesis
- describe and carry out investigations using whole plants, including aquatic plants, to determine the effects of light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Investigation of limiting factors
- › In C4 plants, PEP carboxylase is in the mesophyll cells to fix CO2, while Rubisco is restricted to the bundle sheath cells.
- › Note that if the action spectrum for photosynthesis is higher than the absorption spectrum of one pigment, other accessory pigments must be present.
- › Clearly state that respiration occurs continuously in plants, both in the dark and in the light.
- › When describing a graph where the x-axis is temperature or pH, use 'above/below' or 'at higher/lower values', not temporal language.
- › Remember that chloroplasts produce their own ATP via chemiosmosis on the thylakoid membrane specifically for the Calvin cycle.
State three environmental factors that can limit the rate of photosynthesis.
The rate of photosynthesis can be limited by light intensity, carbon dioxide concentration, and temperature. These factors can restrict the photosynthetic rate if they are below their optimal levels.
Explain how increasing light intensity affects the rate of photosynthesis up to a certain point.
Initially, as light intensity increases, the rate of the light-dependent reactions increases proportionally, leading to a higher overall rate of photosynthesis. However, beyond a certain point, other factors become limiting, and increasing light intensity no longer increases the rate.
Describe how increasing carbon dioxide concentration affects the rate of photosynthesis, assuming other factors are not limiting.
As carbon dioxide concentration increases, the rate of the light-independent reactions (Calvin cycle) increases, leading to a higher overall rate of photosynthesis. This continues until another factor, such as light intensity or temperature, becomes limiting.
Explain the impact of increasing temperature on the rate of photosynthesis up to its optimum.
Increasing temperature increases the rate of enzyme-catalyzed reactions in photosynthesis, up to a certain optimal temperature. Above this optimum, enzymes denature, and the rate of photosynthesis decreases rapidly.
Outline the procedure for investigating the effect of light intensity on the rate of photosynthesis using DCPIP.
Prepare a chloroplast suspension. Add DCPIP, expose to different light intensities, and measure the time taken for DCPIP to decolourise. Faster decolourisation indicates a higher rate of photosynthesis (electron transport).
What does the rate of DCPIP decolourisation indicate in an experiment investigating photosynthesis?
The rate of DCPIP decolourisation indicates the rate of electron transport during the light-dependent reactions of photosynthesis. Faster decolourisation implies a higher rate of electron transport and therefore, a higher rate of photosynthesis.
Describe a method to investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant.
Place an aquatic plant in water with a known concentration of CO₂. Vary the distance of a lamp from the plant (changing light intensity) and count the number of oxygen bubbles produced per unit time. This bubble count indicates the rate of photosynthesis.
How can you investigate the effect of carbon dioxide concentration on the rate of photosynthesis using an aquatic plant?
Use solutions of varying concentrations of dissolved carbon dioxide (
More topics in Unit 13 — Photosynthesis
Investigation of limiting factors sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Investigation of limiting factors deck
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