9700 · 13.2
Investigation of limiting factors flashcards
Revision flashcards for Cambridge 9700 Investigation of limiting factors (syllabus 13.2). Flip, recall, then mark a real past-paper question.
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What is the principle of limiting factors?
The rate of a physiological process that depends on several factors is limited by the factor that is in shortest supply.
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Name the three main limiting factors of photosynthesis.
1. Light intensity 2. Carbon dioxide concentration 3. Temperature
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In an experiment investigating limiting factors of photosynthesis, what is a common dependent variable and how is it measured?
The rate of photosynthesis. It can be measured by: 1. The volume of oxygen produced per unit time (using a gas syringe or counting bubbles from an aquatic plant like *Elodea*). 2. The rate of carbon dioxide uptake per unit time (using a CO₂ sensor or bicarbonate indicator).
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How would you ensure temperature is controlled when investigating light intensity as a limiting factor for an aquatic plant?
Place the beaker containing the aquatic plant inside a larger water bath. The large volume of water in the bath has a high specific heat capacity, which helps maintain a constant temperature by absorbing excess heat from the lamp.
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On a graph of photosynthetic rate vs. light intensity, what does the plateau indicate?
The plateau indicates that light intensity is no longer the limiting factor. Another factor, such as carbon dioxide concentration or temperature, is now limiting the rate of photosynthesis.
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What is the role of DCPIP in investigating the light-dependent stage of photosynthesis?
DCPIP acts as an artificial electron acceptor, taking the place of NADP. It is blue when oxidised and becomes colourless when reduced by electrons from the electron transport chain. The rate of its decolorization is a measure of the rate of the light-dependent reaction.
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Explain why temperature becomes a limiting factor for photosynthesis at very high levels.
At very high temperatures (e.g., above 45°C), enzymes involved in photosynthesis, such as RuBisCO, begin to denature. The enzyme's active site changes shape, reducing its efficiency and causing the rate of photosynthesis to decrease rapidly.
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How can a commercial grower in a glasshouse manipulate limiting factors to maximise crop yield?
They can use: 1. **Artificial lighting:** to extend photosynthesis beyond daylight hours. 2. **Heaters:** to maintain the optimum temperature for photosynthetic enzymes. 3. **CO₂ generators:** to increase carbon dioxide concentration in the air.