3.1.4 Transport into and out of Cells Flashcards
What is a cell-surface membrane?
(Partially permeable) barrier between cell and its environment, controlling which substances enter and leave the cell
What is the functions of membranes around organelles?
- Act as barriers between organelle and cytoplasm
- Also control what comes in and out + partially permeable
Describe the phospholipids arrangement in a plasma membrane
- Bilayer
- Hydrophobic tails to inside
- Hydrophilic heads to outside
Describe how the plasma membrane acts as a barrier to water-souble substances
Centre of bilayer is hydrophobic ∴ membrane doesn’t allow water-souble substances (like ions) through it
Name 3 functions of phospholipids in plasma membranes
- Allow lipid-soluble substances to enter & leave the cell
- Prevent water-soluble substances entering and leaving the cell
- Makes membrane flexible
Cholesterol is present in all cell membranes expect _____ ____ ________
bacterial cell membranes
Where are cholesterol molecules found in cell membranes?
Between phospholipids
What is the role of cholesterol in cell membranes?
Controls the fluidity of the membrane
(provides stability e.g. helps to maintain shape of animal cells)
Describe how cholesterol gives cell membranes stability
- Cholesterol molecules bind to hydrophobic tails of phospholipids = causes them to pack more closely together
- Restricts movement of phospholipids
- Makes membrane less fluid and more rigid
What model is used to describe the arrangement of molecules in membrane?
Fluid mosaic model
Why is the bilayer is ‘fluid’?
∵ phospholipids are constantly moving
How are proteins arranged in the cell membrane?
They’re scattered through bilayer (like tiles in mosaic)
What are extrinsic proteins?
Proteins are partly embedded in bilayer (occur either on surface of it)
What are intrinsic proteins?
Proteins that span entire bilayer from one side to the other
What do channel proteins and carrier proteins allow?
Allow large molecules and ions to pass through membrane
What do receptor proteins on the cell-surface membrane do?
Detect chemicals released from other cells
(chemicals signal to cell to respond in some way)
Some proteins can ___ _______ through bilayer & others are _____ __ _____
Some proteins can move sideways through bilayer & others are fixed in position
What are glycoproteins?
Proteins that have a polysaccharide chain attached
What are glycolipids?
Lipids that have a polysaccharide chain attached
Increasing the temperature ____ membrane permeability
INCREASES
Temperatures below 0°C: Describe and explain the membrane permeability
- Phospholipids don’t have much energy = can’t move much
- Packed closely together & membrane is rigid
- BUT channel proteins and carrier proteins deform = increasing permeability of membrane
- Ice crystals may form and pierce the membrane = makes highly permeable when it thaws
Temperatures between 0 and 45°C: Describe and explain the membrane permeability
- Phospholipids can move around & aren’t packed as tightly together = membrane is partially permeable
- As temperature increases = phospholipids move more ∵ have more energy = increases permeability of membrane
Describe the effect of high temperature on cell membranes
- Phospholipids have more kinetic energy
- Movement makes membranes more fluid and leaky
- Increases no. of gaps between phospholipids
- Glycoproteins/channel & carrier proteins denature
All increases permeability of membrane as substances can enter and leave that wouldn’t normally
Sketch a graph showing how increasing the temperature affects membrane permeability
Surrounding cells in an increasing concentration of solvent (e.g. acetone) will _______ membrane permeability
INCREASE
Why does surrounding cells in an increasing concentration of solvent (e.g. acetone) increase membrane permeability?
∵ the solvent dissolves lipids in the cell membrane, causing it to lose its structure
What could you use to investigate how different conditions (e.g. temperature and solvent concentration) affects membrane permeability?
Beetroot → higher permeability of membrane = more pigment leaks out of cell
Define diffusion
Net movement of particles from an area of higher concentration to area of lower concentration
Diffusion is a ____ process
passive
Particles diffuse ___ a concentration gradient
DOWN
What type of particles can diffuse through cell membranes?
Small and non-polar particles
Polar molecules have… & non-polar molecules don’t
partial postive and negative charges
Why are small particles able to diffuse through the cell membrane?
∵ they can pass through spaces between phospholipids
Why are non-polar particles able to diffuse through the cell membrane?
∵ they can dissolve in the hydrophobic bilayer as being non-polar makes them soluble in lipids
What is simple diffusion? (in membrane terms)
When molecules diffuse directly through cell membrane