Flashcards in 2B - Cell Membranes Deck (36):
What is a cell surface membrane
A partial permeable barrier between the cell(or organelle) and its environment, controlling the substances which enter and leave it.
How do molecules move across a membrane
Another name for a cell surface membrane
What is a cell membrane composed of
What is the fluid mosaic model
Phospholipid molecules form a continuous bilayer(Double layer) which is 'fluid' as they are constantly moving. Proteins, such a carrier and channel proteins, are scattered across the layer like a mosaic. Receptor cells on the membrane allow the cell to detect chemicals from other cells.
What is a protein with a carbohydrate attached called?
What is a lipid with a carbohydrate attached called?
Describe the arrangement of phospholipid molecules in the plasma membrane.
The molecules are arranged in a bilayer with the hydrophilic heads facing away from the centre and towards the water in the cells and outside of the cells.
The hydrophobic tails point towards the centre of the bilayer as they are repelled by the water molecules on each side.
What substances cant diffuse through the bilayer?
Water soluble substances such as ions and polar molecules as the centre is hydrophobic.
What is the role of cholesterol in the plasma membrane?
Gives the membrane stability by binding to the hydrophobic tails of the phospholipids and causing them to pack closer. This restricts their movement and so makes the layer less fluid and so helps to maintain the shape of the cell membrane.
The effect of temperatures below 0 on plasma membranes.
Phospholipids don't have much energy and so cant move very much. They are packed close together making a rigid membrane. Channel and carrier proteins denature, increasing permeability.
Ice crystals form and puncture the membrane which makes it highly permeable once thawed.
The effect of temperatures between 0 and 45 on plasma membranes.
Phospholipids are fluid and can move more as the temperature increases
The effect of temperatures above 45 on plasma membranes.
Bilayer starts to melt
Water inside the cell expands which puts pressure on the membrane
Channel and carrier proteins denature
All of which increase permeability.
the net movement of molecules from an area of high concentration to an area of lower concentration.
If diffusion is said to be passive what does this mean?
It requires no energy
Factors affecting the rate of diffusion.
Concentration gradient - larger will increase the rate
Length of diffusion pathway - thinner surfaces increase the rate
Surface area - increasing S.A will increase diffusion
What is facilitated diffusion
When large or polar molecules that cant diffuse through the bilayer are moved across a membrane by carrier or channel proteins.
Describe the action of a carrier protein.
Large molecule attaches to a carrier protein
Carrier protein changes shape
Releases molecule on the other side of the membrane.
Describe the action of a channel protein.
The form pores in the membrane which allows charged molecules to diffuse through.
Which proteins moves laree molecules
Carrier protein - channel proteins move charged particles
Factors that affect facilitated diffusion
Concentration gradient - Higher increases the rate
Number of channel/carrier proteins - more increase diffusion
What is osmosis?
The diffusion of water across a partially permeable membrane from an area of higher water potential to an area of lower water potential.
What is water potential?
The likelihood of water molecules diffusing out of or into a solution.
What is the water potential of pure water?
What does adding solute do to the water potential.
Lowers it and makes t more negative.
If two solutions have the same water potential they are...
Solutions with a higher water potential than inside the cell are called....
Solutions with a lower water potential than inside the cell are called....
In a hypertonic solution the net movement of water is...
Out of the cell
In a hypotonic solution the net movement of water is...
Into the cell
The factors affecting osmosis
The same as those for diffusion.
What is active transport
Using energy to move molecules against a concentration gradient.
Active transport by carrier proteins.
Molecule attaches to protein
Protein changes shape
Molecule released on the other side.
This is the same process as facilitated diffusion apart from ATP is used to move the molecule against the concentration gradient
Active transport with Co-transporters
Same process as carrier proteins apart from two molecules bind to the same protein and the concentration gradient of one is used to move the other against its own.
How is glucose absorbed from the ileum?
1) Sodium ions are actively transported out of epithelial cells and into the blood by a potassium sodium pump, creating a concentration gradient.
2) Sodium ions diffuse from the ileum and into the epithelial cells, via sodium glucose co-transporters. The co-transporters also carry glucose into the cell which increases the concentration of glucose in the epithelial cells.
3)Glucose diffuses out of the cell an into the blood down its concentration gradient through a protein channel by facilitated diffusion.