State two differences in structure between plant and animal cells.

Outline how molecules move across a membrane by simple diffusion.

Explain the role of protein pumps in active transport.

Answers do not need to be shown in a table format.

membranes are porous/permeable allowing diffusion;
diffusion is (passive) movement (of particles) from high to low concentration;
due to random motion/kinetic energy of molecules / no ATP involved;
diffusion continues until concentrations are equal (across the membrane);

(can) move solutes against a concentration gradient;
using energy/ATP;
specific for the solute/molecule transported;
protein pumps change shape (as they transport molecules);

 Most candidates knew structural differences between plant and animal cells. Answers usually mentioned that chloroplasts and cell walls exist in plant cells but not animal cells. That plants have chlorophyll and animal cells do not was unacceptable since chlorophyll is not a structure.  Unless the wording was careless, some shocking misconceptions were revealed when candidates wrote that “plant cells have cell walls while animal cells have cell membranes” or that “plant cells have chloroplasts while animal cells have mitochondria.”

An easy 2 marks were gained by many candidates who mentioned that membranes are permeable/porous to allow diffusion and that diffusion is movement of particles from high to low concentration. Many candidates stated that diffusion happens without the need for energy instead of without the need for ATP.  

Most candidates stated that active transport goes against the concentration gradient and requires ATP. Unfortunately, some candidates thought protein pumps produce/provide ATP and some confused change in the shape of protein pumps with exocytosis and endocytosis.  Though candidates did give the example of the sodium potassium pump, they did not mention that protein pumps are specific for the solute/molecule they transport.