Define cell membrane.
A flexible barrier that controls what enters and exits the cell.
What is a phospholipid bilayer?
A double layer of phospholipids that forms the basic structure of the cell membrane.
Define integral proteins.
Proteins that span the entire cell membrane.
What are peripheral proteins?
Proteins that sit on the surface of the cell membrane.
What is active transport?
Movement of substances across a cell membrane against their concentration gradient, requiring energy (ATP).
Define passive transport.
Movement of substances across a cell membrane down their concentration gradient, without requiring energy.
What is endocytosis?
The process by which cells engulf substances by inward folding of the cell membrane.
Define exocytosis.
The process by which cells expel substances by fusion of vesicles with the cell membrane.
What is primary active transport?
Active transport that uses ATP directly.
Define secondary active transport.
Active transport that uses the energy of an existing concentration gradient.
Describe the process of endocytosis.
1. Cell membrane surrounds the substance. 2. Membrane folds inward, engulfing the substance. 3. A vesicle forms, containing the substance inside the cell.
What are the steps of exocytosis?
1. A vesicle containing substances moves towards the cell membrane. 2. The vesicle fuses with the cell membrane. 3. The substances are released outside the cell.
Outline the function of the sodium-potassium pump.
1. Pump binds intracellular sodium. 2. ATP phosphorylates the pump. 3. Pump changes conformation and releases sodium outside. 4. Pump binds extracellular potassium. 5. Pump dephosphorylates. 6. Pump returns to original conformation, releasing potassium inside.
Compare and contrast active and passive transport.
Active transport: Requires energy (ATP), moves substances against the concentration gradient. | Passive transport: Does not require energy, moves substances down the concentration gradient.
What are the key differences between primary and secondary active transport?
Primary active transport: Uses ATP directly. | Secondary active transport: Uses energy from an existing concentration gradient.
