Term Definition
Passive Transport Does not require a cell to use energy
Active Transport Requires a cell to use energy to move molecules through its cell membrane
Facilitated Diffusion The passive movement of a particle across a cell membrane via a channel
protein
Osmosis A net movement of water molecules from a region of low solute concentration to
a region of high solute concentration, through a partially-permeable membrane
Factors affecting the rate of diffusion
- Diffusion gradient (The steeper the diffusion gradient, the higher the rate)
- Size of molecules or ions (The smaller the size, the higher the rate)
- Temperature (The higher the temperature, the higher the rate)
- Diffusion medium (Rate in gas > rate in liquid > rate in solid)
- Surface area (The larger the surface area the higher the rate)
Outline the ways in which substances move passively across membranes
- Diffusion
- Channel proteins for facilitated diffusion
- Movement down the concentration gradient
- Membrane must be permeable to the substance diffusing
- Oxygen can diffuse through membranes
- Osmosis is the movement of water through a membrane from a region of higher to lower water
potential
- Membranes are always freely permeable to water
Describe the process of active transport
- Requires energy (ATP)
- Goes against concentration gradient
- Requires carrier protein
- Hydrolysis of ATP
- Involves a conformational change in the pump/protein
- Sodium-Potassium Pump
- Moves ions
- Maintains chemical gradient
How sodium-potassium pumps reduce blood sodium concentration, if
there is sufficient potassium in the diet
- The sodium-potassium pump transports three sodium atoms out of the cell and two potassium
atoms into the cell
- More potassium means more sodium can be sent out of the cell
- A fall in potassium means more sodium remains in the cell
- Higher concentration of potassium in the cell
Distinguish between active and passive movements of materials across
plasma membranes
- Passive movements includes diffusion, facilitated diffusion and osmosis. Active movement
includes active transport, exocytosis and phagocytosis
- Passive transport does not require energy, active transport requires energy from ATP
- Passive transport is down the concentration gradient, active transport is against
- Passive transport does not need pumps, active transport needs pumps
- Oxygen across alveoli/secretion of substance into bloodstream
- Na-K pump/glucose absorption in ileum
Describe four different types of transport of substances across a
membrane
- Diffusion when molecules move down concentration gradient directly through membrane
- Facilitated diffusion through channel proteins
- Osmosis of water from low solute concentration to area of high solute concentration
- Active transport against a concentration gradient using protein pumps
Describe the process of endocytosis
- Membrane encloses
- Fluidity of membrane allows endocytosis
- Plasma membrane forms pit
- Membrane seals back on itself
- Vesicle formed
- Inside of membrane becomes outside of vesicle membrane
- Vesicle breaks away from plasma membrane
- Endocytosis requires energy
- Example: Clean up foreign materials (Bacteria)
Describe the process of exocytosis
- Vesicles carry material to plasma membrane and fuse with membrane
- By joining phospholipid bilayers
- Fluidity of membrane allows exocytosis
- Material released from the cell
- Membrane flatterns
- Example: Release of cortisol
Explain the role of vesicles in transportation of materials within cells
- Vesicles are membrane bound packages formed by pinching off a piece from a membrane
- Can carry proteins
- rough ER synthesises proteins
- Proteins accumulate inside the ER
- Transported to Golgi apparatus for processing
- Transported to specific cellular organelles
- Fuse with membrane of organelle so contents of vesicles join the organelle
- Transported to the plasma membrane
- Fuses with plasma membrane and secretes content
- Exocytosis
