Carbon dioxide diffuses from a fish's blood into the water across its gills. The fish swims from a still pool into a current. Away from the fish, the water in both places has the same temperature and carbon dioxide concentration. Its circulation and gill structure do not change.
Which statement correctly describes and explains the change in the rate of carbon dioxide diffusion across the gills when the fish enters the current?
The current gives carbon dioxide particles more kinetic energy, making them cross the gill surface more frequently.
The unchanged gill structure means the factors controlling diffusion are constant, so the diffusion rate remains unchanged.
The current lowers the water's carbon dioxide concentration, making the concentration gradient smaller and decreasing diffusion.
The current prevents carbon dioxide building up beside the gills, keeping a steep concentration gradient and increasing diffusion.
102 exam-style questions on Edexcel GCSE Biology 8.1 Exchange surfaces and diffusion, covering 8.1.1 Introduction to exchange and transport, 8.1.2 Alveoli adapted for gas exchange, 8.1.3 Factors affecting rate of diffusion, and 8.1.4 Rate of diffusion using Fick's law. Each one has a worked solution and a mark scheme showing where the marks go.