AQA A Level Biology: Transport Across Cell Membranes Flashcards
What is the structure of the cell membrane?
- Phospholipid bilayer with hydrophobic tails and hydrophilic heads.
- Contains proteins, cholesterol, glycoproteins, and glycolipids.
What is the function of the cell membrane?
- Controls the movement of substances in and out of the cell.
- Provides structural support and cell recognition.
What is the fluid mosaic model?
- Fluid: Phospholipids move laterally, giving flexibility.
- Mosaic: Proteins are scattered throughout the bilayer.
What is the role of phospholipids in the membrane?
- Form a bilayer that acts as a barrier to water-soluble substances.
- Allows passage of non-polar, small, and lipid-soluble molecules.
What is the role of cholesterol in the membrane?
- Reduces fluidity by restricting movement of phospholipids.
- Provides stability and prevents leakage of water and ions.
What are the two types of proteins in the cell membrane?
- Intrinsic (integral) proteins: Span across the bilayer, involved in transport.
- Extrinsic (peripheral) proteins: On the surface, used for cell recognition and signaling.
What is the role of glycoproteins and glycolipids?
- Glycoproteins: Act as receptors and help with cell signaling.
- Glycolipids: Involved in cell recognition and stability.
What is diffusion?
The net movement of particles from a region of high concentration to low concentration down a concentration gradient.
What factors affect the rate of diffusion?
- Surface area – Larger surface area increases rate.
- Concentration gradient – Steeper gradient increases rate.
- Distance – Shorter distance increases rate.
- Temperature – Higher temperature increases kinetic energy and rate.
What is facilitated diffusion?
- The passive movement of substances across the membrane via channel or carrier proteins.
- Used for polar or large molecules that cannot diffuse through the bilayer.
How do channel proteins work?
Form hydrophilic pores that allow specific ions to pass through by diffusion.
How do carrier proteins work?
Bind to specific molecules, change shape, and move them across the membrane.
What is osmosis?
- The diffusion of water molecules across a partially permeable membrane.
- From an area of high water potential to low water potential.
What is water potential?
The pressure created by water molecules; pure water has a potential of 0 kPa.
What happens to an animal cell in a hypertonic solution?
- Water moves out of the cell by osmosis.
- The cell shrinks and becomes crenated.
What happens to an animal cell in a hypotonic solution?
- Water moves into the cell by osmosis.
- The cell swells and may burst (lysis).
What happens to a plant cell in a hypertonic solution?
- Water moves out of the cell.
- The cell becomes plasmolysed (cytoplasm shrinks).
What happens to a plant cell in a hypotonic solution?
- Water moves into the cell.
- The cell becomes turgid (swollen but does not burst due to the cell wall).
What is active transport?
- The movement of molecules against a concentration gradient using ATP and carrier proteins.
- Moves substances from low to high concentration.
How does active transport work?
- Molecule binds to a specific carrier protein.
- ATP is hydrolyzed to release energy.
- Carrier protein changes shape and moves the molecule across the membrane.
What is co-transport?
A type of indirect active transport where two molecules move together, often involving one molecule moving down its gradient to help the other move against its gradient.
How does sodium-glucose co-transport work?
- Sodium ions move down their concentration gradient into the cell.
- Glucose moves against its concentration gradient, alongside sodium.
What is endocytosis?
The bulk movement of substances into the cell by forming vesicles from the membrane.
* Phagocytosis: Solids.
* Pinocytosis: Liquids.
What is exocytosis?
The bulk movement of substances out of the cell by vesicles fusing with the membrane and releasing contents.
What is the role of ATP in active transport?
Provides the energy needed to change the shape of carrier proteins and move substances across the membrane.
