Biological Membranes Flashcards
Where are plasma membranes located?
The surface of cells
What is a plasma membrane?
A barrier between the cell and its environment that controls which substances enter and leave
What is a membrane within a cell?
A barrier between the organelle and the cytoplasm
What can membranes inside a cell form?
Vesicles
What term is used to describe the structure of a membrane?
Fluid mosaic
What part of the phospholipid is hydrophilic? What does that mean?
The phospholipid head - it attracts water
What part of the phospholipid is hydrophobic? What does that mean?
The fatty acid tails - it repels water
What do phospholipids do in a membrane?
Act as a barrier to dissolved substances because of its hydrophobic bilayer
What does cholesterol do in membranes?
Makes the membrane less fluid and more rigid
What happens to cholesterol and membranes at lower temperatures?
Cholesterol prevents the phospholipids from packing close together, increasing fluidity
What do channel proteins do?
Allow small or charged particles through
What do carrier proteins do?
Transport molecule and ions across the membrane by active transport and facilitated diffusion
How do glycoproteins and glycolipids stabilise the membrane?
By forming hydrogen bonds with surrounding water molecules
How do cells communicate with each other?
1) Cell releases messenger molecule (hormone)
2) Molecule travels to another cell
3) Messenger detected by cell as it binds to receptor on the cells membrane
What proteins on the cell membrane act as receptors?
Membrane bound receptors
What do temperatures above 45°c do to a membrane?
Phospholipid bilayer breaks down and proteins denature, making the membrane more permeable.
What do temperatures between 0-45°c do to a membrane?
Phospholipids can move around and the membrane is partially permeable
What do temperatures below 0°c do to a membrane?
Phospholipids have little energy so cannot move and are packed closely together, making the membrane rigid. Proteins denature, increasing the permeability of the membrane.
What is a solvent?
A substance (molecule) with the ability to dissolve other substances (solutes) to form a solution
What do solvents (ethanol) do to a membrane?
Increase the permeability because it dissolves the lipids and the membrane loses its structure
What is diffusion?
The net movement of particles from an area of high concentration to low concentration
What is the concentration gradient? Which way do particles diffuse?
Path from an area of high concentration to an area of low concentration. Particles diffuse down the gradient.
Why is diffusion a passive process?
No energy is needed for it to happen
What molecules diffuse through the membrane?
Small non-polar molecules like O and CO2
What polar molecule can diffuse through plasma membranes and why?
Water because it is small enough to diffuse through via osmosis
What effect does the concentration gradient have on the rate of diffusion?
The higher it is, the faster the rate of diffusion
What effect does the thickness of the exchange surface have on the rate of diffusion?
The thinner the surface the faster the rate of diffusion
What effect does the surface area have on the rate of diffusion?
The larger the surface area the faster the rate of diffusion
What effect does the temperature have on the rate of diffusion?
The warmer it is the faster the rate of diffusion (particles more kinetic energy)
What colour is phenolphthalein in alkaline soloutions?
Pink
What colour is phenolphthalein in acidic soloutions?
Pink
What are channel proteins?
Proteins that form pores (channels) for charged particles to diffuse through via facilitated diffusion
What are carrier proteins?
Proteins that move large molecules into or out of the cell via active transport
What is active transport?
Moving molecules and ions across plasma membranes against a concentration gradient using energy (ATP)
What are the steps of a carrier protein moving a large molecule?
1) Large molecule attaches to carrier protein
2) The protein changes shape
3) The molecule is released on the opposite side of the membrane
What is endocytosis?
If a molecule is too large for proteins a cell will surround a molecule with a section of its membrane and form a vesicle
Does endocytosis use energy?
Yes, ATP
What is exocytosis?
Vesicles containing substances leave the golgi apparatus and fuse with the plasma membrane to release their contents outside the cell
Does exocytosis use energy?
Yes, ATP
What is osmosis?
The diffusion of water molecules across a partially permeable membrane down a water potential gradient
What is water potential?
The likelihood of water molecules to diffuse into or out of a solution
What has the highest water potential?
Pure water
What happens when an animal cell is in a solution with a higher water potential?
The cell will bust because net moment of water is into the cell
What happens when an animal cell is in a solution with a lower water potential?
The cell will shrink because the net movement of water is out of the cell
What is a hypotonic solution?
A solution with a higher water potential than the cell
What is a hypertonic solution?
A solution with a lower water potential than the cell
What is an isotonic solution?
A solution with the same water potential as the cell
What happens when an animal cell is in a hypotonic solution?
The vacuole swells as net movement of water is into the cell. The cell becomes turgid.
What happens when an animal cell is in a hypertonic solution?
The cell becomes flaccid as net movement of water is out of the cell. The cell is flaccid. Plasmolysis also occurs.
What is plasmolysis?
When a plant cell is in a hypertonic solution, the cytoplasm and the membrane pull away from the cell wall.
