Limiting factors in photosynthesisAQA A-Level Biology: Mind map

Exam questions on Limiting factors in photosynthesis

1. A grower measures the rate of photosynthesis of tomato plants in a glasshouse at a constant 20 °C, which is close to the optimum for the plants' enzymes, and a carbon dioxide concentration of 0.04%. As the light intensity is increased the rate rises steadily, then levels off at high light intensities.
   Explain why the rate of photosynthesis at a high light intensity increases when the glasshouse carbon dioxide concentration is raised to 0.1%.2 marks
2. The rate of photosynthesis of pondweed was measured at a range of temperatures, with light intensity and carbon dioxide concentration both kept high. The rate roughly doubled between 10 °C and 20 °C, was greatest at about 35 °C, and fell to almost zero at 55 °C.
   Explain why light intensity and carbon dioxide concentration were both kept high throughout the experiment.2 marks
3. A grower compares lettuce yields in three glasshouses of the same size over one growing season. Glasshouse X has no extra heating, lighting or carbon dioxide. Glasshouse Y is heated to 25 °C and enriched with carbon dioxide. Glasshouse Z has the same heating and carbon dioxide enrichment as Y, plus supplementary lighting. The mean yields were 4.0 tonnes (X), 6.2 tonnes (Y) and 7.1 tonnes (Z). The extra running costs compared with X were £1500 for Y and £3800 for Z. Lettuce sells for £1200 per tonne.
   Calculate the net financial gain per season of heating and carbon dioxide enrichment (Glasshouse Y) compared with Glasshouse X.3 marks