A student places a lamp 10 cm from some pondweed. Light intensity is inversely proportional to the square of the distance from the lamp. The student wants to reduce the light intensity at the pondweed to one ninth of its value. At what distance from the pondweed should the student place the lamp?
3.3 cm3.3\ \text{cm}3.3 cm
19 cm19\ \text{cm}19 cm
30 cm30\ \text{cm}30 cm
90 cm90\ \text{cm}90 cm
117 exam-style questions on OCR GCSE Biology 1.4 Photosynthesis, covering 1.4.1 Photosynthesisers as biomass producers, 1.4.2 Factors affecting the rate of photosynthesis, and 1.4.3 Limiting factors in photosynthesis. Each one has a worked solution and a mark scheme showing where the marks go.