3. Movement in and out of cells

3.1 Diffusion

• Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement 

• State that the energy for diffusion comes from the kinetic energy of random movement of molecules and ions 

• State that some substances move into and out of cells by diffusion through the cell membrane 

• Describe the importance of diffusion of gases and solutes in living organisms 5 Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance 

3.2 Osmosis

• Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport 

• State that water diffuses through partially permeable membranes by osmosis 

• State that water moves into and out of cells by osmosis through the cell membrane 

• Investigate osmosis using materials such as dialysis tubing 

• Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations 

• State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall.

Supplement 

• Describe osmosis as the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane 

• Explain the effects on plant cells of immersing them in solutions of different concentrations by using the terms: turgid, turgor pressure, plasmolysis, flaccid 9 Explain the importance of water potential and osmosis in the uptake and loss of water by organisms.

3.3 Active transport

• Describe active transport as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration Supplement 

• Explain the importance of active transport as a process for movement of molecules or ions across membranes, including ion uptake by root hairs 

• State that protein carriers move molecules or ions across a membrane during active transport.