The diagram represents a container divided by a partially permeable membrane. The dots show particles of a dissolved substance a short time after it was add...
Question 1 Report
The diagram represents a container divided by a partially permeable membrane. The dots show particles of a dissolved substance a short time after it was added.
(a) Define diffusion. [3]
(b) Using the diagram, state the direction of the net movement of the particles. [1]
(c) State why the particles are able to move without the cell using energy. [1]
(d) State what happens to the net movement of the particles once they are evenly spread throughout the container. [1]
Answer Details
(a) Definition of diffusion [3]
Diffusion is the net movement of particles (molecules or ions) [1]; from a region of their higher concentration to a region of their lower concentration [1]; that is, down a concentration gradient [1].
(b) Direction of net movement (from the diagram) [1]
From region P to region Q, i.e. from the crowded, higher-concentration side towards the sparse, lower-concentration side.
(c) Why no cell energy is needed [1]
The particles already move by their own random motion (kinetic energy), so diffusion is a passive process that does not use energy from the cell.
(d) Once the particles are evenly spread [1]
There is no longer a concentration gradient, so the net movement stops and equilibrium is reached (the particles still keep moving randomly, but with no overall direction).
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