The cell membrane of an animal cell is 7.5 nm7.5\ \text{nm}7.5 nm thick. The animal cell is 15 μm15\ \mu\text{m}15 μm wide.
Calculate the ratio of the width of the cell to the thickness of the cell membrane.
Give the thickness of the cell membrane in picometres. Give your answer in standard form.
A water molecule is about 2.8×102 pm2.8 \times 10^{2}\ \text{pm}2.8×102 pm wide.
Calculate the number of water molecules that would fit in a line across the thickness of the cell membrane. Give your answer to the nearest whole number.
48 exam-style questions on Edexcel GCSE Biology 1.2 Number, size and scale, covering 1.2.1 Number, size and scale with estimations and 1.2.2 Quantitative units in relation to cells. Each one has a worked solution and a mark scheme showing where the marks go.