2.5 Biological Membranes Flashcards
What is the role of membranes within cells and at cell walls?
- Partially permeable barriers between the cell+ its environment, between organelles and cytoplasm, within organelles
- Site of chemical reactions
- Site of cell communication
Describe membranes within cells
- Membranes around organelles divide cells into different compartments - barrier between organelle and cytoplasm - makes functions more effective
- Form vesicles to transport substances
- Controls what enters + exits (partially permeable)
- Can get membranes within organelles
- Can be site of chemical reactions
Describe the fluid mosaic model
The fluid mosaic model was suggested to describe the arrangement of molecules in the membrane.
•phospholipid molecules form a bilayer
•bilayer is fluid as phospholipids are constantly moving
•cholesterol molecules are present within the bilayer
•some proteins have a polysaccharide chain attached - glycoproteins
•some lipids also have a polysaccharide chain attached - glycolipids
What factors affect membrane permeability and structure?
•Temperature
Cold - phospholipids can’t move
Hot - bilayer melts
•Changing the solvent
Surrounding cells in a solvent (e.g ethanol) increases permeability of their cell membranes
What is diffusion?
The net movement of particles from an area of higher to lower concentration
Describe diffusion in a cell
- diffusion will continue until particles are evenly distributed
- particles diffuse down the concentration gradient
- passive process - no energy required
- small, non-polar molecules are able to diffuse easily through spaces between phospholipids
What is facilitated diffusion?
- Larger molecules don’t diffuse through the phospholipid bilayer
- Instead they diffuse through carrier proteins or channel proteins in the cell membrane
- particles move down a concentration gradient
- passive process - doesn’t use energy
What is osmosis in terms of water potential?
Water moves via osmosis from a region of higher to lower water potential, DOWN the water potential gradient
What is active transport?
•Moves substances against a concentration gradients
•Involves carrier proteins
(Low - high)
Energy needed
What happens if you put an animal cell in a solution with high water potential
Net movement of water molecules is into the cell. Cell bursts.
What happens if you put an animal cell in a solution with the water potential as the cell
Water molecules pass into and out of the cell in equal amounts. The cell stays the same.
What happens if you put an animal cell in a solution with low water potential
Net movement of water molecules is out of the cell. The cell shrinks.
What happens if you put a plant cell in a solution with high water potential
The cell becomes turgid (swollen) as water moves into the cell
What happens if you put a plant cell in a solution with the same water potential as the cell
Cell stays the same
What happens if you put a plant cell in a solution with low water potential
Cell becomes flaccid (limp)
