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Instead of counting bubbles, a pupil collects the gas from a sprig of pondweed in a gas syringe. With the lamp at 15 cm, 2.6 cm³ of gas collects in 4 minutes. (a) Calculate the rate of gas production in cm³ per minute. Give your answer to two decimal places. (b) At the same rate, calculate how long it would take to collect 3.0 cm³ of gas. Give your answer to one decimal place.
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Scope and sources
Cambridge IGCSE Biology 0610 · 2026–2028 v3 · Original learning materials.
The effects of light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis, investigated with pondweed (6.1.8); gas exchange of an aquatic plant in light and dark with hydrogencarbonate indicator (6.1.9); limiting factors in different conditions (Supplement 6.1.11); the large, thin leaf (6.2.1); the structures of a dicotyledonous leaf in diagrams and images (6.2.2) and how they adapt it for photosynthesis (6.2.3). Bubble counts and indicator colours in the experiment come from a teaching model.
Apparatus, amounts and times in the experiment are illustrative. Real practical work follows a teacher-approved safety method.
Official Cambridge syllabus