Key Area 2: Transport Across Cell Membranes Flashcards
Phospholipids
Make up the cell membrane along with proteins. Give the membrane flexibility
Proteins
Make up the cell membrane along with phosophilids. Some respond to specific signals. Some transport substances across the membrane.
Selectively permeable.
Means the cell membrane controls which molecules enter the cell by only allowing certain molecules to move across. It selects those that enter or leave the cell.
Passive transport
Occurs down a concentration gradient and does not require energy.
eg. Diffusion and osmosis
Diffusion
The movement of molecules down a concentration gradient from a higher to lower concentration. Until the concentrations become equal.
Osmosis
The movement of water molecules from a higher water concentration to a lower water concentration through a selectively permeable membrane.
Burst and Shrink
Animals cells can burst and shrink. Solutions of different concentrations will have different effects on cells.
Turgid and Plasmolysed
Plant cells can become turgid or plasmolysed. Solutions of different concentrations will have different effects on cells.
Active transport
Requires energy for membrane proteins to move molecules and ions across the cell membrane against the concentration gradient.
Concentration gradient
High concentration of water to lower concentration of water
Examples of active transport.
Sodium/potassium proteins pumps are important in neuron responses.
Iodine protein pumps in seaweed keep iodine levels much higher internally than in the external seaweed.
A higher water concentration solution will?
Always lose water
A lower water concentration solution will?
Always gain water
A solution with equal water concentration will?
Neither gain nor lose water
Substances can cross the cell membrane by
osmosis, diffusion or active transport
