6. Biological Membranes Flashcards
(34 cards)
What is the function of plasma (cell surface) membranes?
Regulates transport into and out of the cell.
Contains enzymes involved in metabolic pathways.
Contains antigens that the body recognises as ‘self’ so it does not attack.
Contains receptors for chemical signal, so is a site for cell communication.
What is the fluid mosaic model?
Proposed that the fabric of the membrane consists of a phospholipid bilayer with proteins floating in it. The lipids and some proteins can move, giving it fluidity.
What structures are present in the phospholipid bilayer?
phospholipids, glycoproteins, carrier proteins, channel proteins, cholesterol, glycolipids, protein receptor sites
What are the different proteins within membranes?
Some have pores and act as channels to allow ions to pass through.
Some proteins are carriers and, by changing their shape, carry specific molecules across the membrane.
What is the function of cholesterol in a cell surface membrane?
Helps to regulate fluidity, maintain stability and resist the effects of temperature on the membrane’s structure.
What is the total thickness of a cell membrane?
Between 5 and 10 nm
What is the distribution of proteins in neurones?
A myelin sheath covering the axon formed by flattened cells contains protein.
This allows the conduction of electrical impulses along its length.
What is the function of proteins in white blood cells?
Protein receptors in their plasma membrane enable them to recognise antigens on foreign cells.
What is the distribution of proteins in root hair cells?
They have many carrier proteins to actively transport nitrate ions from the soil into cells.
What is diffusion?
When molecules move down the concentration gradient until they reach equilibrium. It may or may not be across a membrane. It does not involve metabolic energy (ATP)
How is a concentration gradient maintained in cells?
The molecules are used for metabolic reactions which keeps more of the molecules entering the cell.
How does temperature affect the rate of diffusion?
As temperature increases, molecules have more kinetic energy, so their rate of diffusion will increase and vise versa.
How does diffusion distance affect the rate of diffusion?
The thicker the membrane across which the molecules have to diffuse, the slower the rate of diffusion.
How does surface area affect the rate of diffusion?
More diffusion can take place across a larger surface area.
How does the size of diffusing molecule affect the rate of diffusion?
Smaller ions or molecules diffuse more rapidly than larger ones.
How does concentration gradient affect the rate of diffusion?
The steeper the gradient, the faster the diffusion to the side where there are fewer molecules, down the gradient.
What is facilitated diffusion?
The movement of molecules down the concentration gradient across a partially permeable membrane via protein channels or carriers.
It does not involve metabolic energy (ATP)
What is a solution?
Solute molecules dissolved in a solvent. Water is the solvent in aqueous solutions.
What is osmosis?
The passage of water molecules down their water potential gradient, across a partially permeable membrane.
What is water potential?
Measure of the tendency of water molecules to diffuse from one region to another.
It is represented by Ψ (psi) and measured in kPa.
Pure water has the highest water potential of 0kPa.
Dissolved solutes lower the water potential.
What does hypotonic mean?
High water potential (more water than solute)
What does hypertonic mean?
Low water potential (more solute than water)
What does isotonic mean?
When a solution has the same concentration of water and solute.
What happens when animal cells are placed in a solution with a higher water potential?
Water molecules move by osmosis into the cell, the cell will swell and burst as the plasma membrane breaks.
This is cytosis.
