Paper 1 AQA A level Biology 2022
Explain why plasma membranes are said to have a fluid mosaic structure. - ANSWER-1. Fluid because the
phospholipids are constantly moving. 2. Mosaic because the proteins are scattered throughout the
membrane-like tiles in a mosaic.
What effect does cholesterol have on the cell membrane? - ANSWER-1.Cholesterol molecules fit
between the phospholipids and bind to the hydrophobic tails of the phospholipids. 2.Causes them to
pack together more closely, restricting the movement of other molecules in the membrane.
3.Cholesterol makes the membrane less fluid and more rigid. 4.Cholesterol helps to maintain the shape
of animal cells, which is important because animal cells don't have cell walls (especially important for
cells which are not supported by other cells e.g. red blood cells).
State 3 functions of glycolipids in the cell membrane. - ANSWER-1. Act as recognition sites. 2. Maintain
the stability of the membrane. 3. Help cells attach to one another and so form tissues.
State 3 functions of glycoproteins in the cell membrane. - ANSWER-1.Act as recognition sites.2.Help cells
to attach to one another so form tissues.3.Allow cells to recognise one another e.g. lymphocytes can
recognise an organisms's own cells.
Describe the functions of membranes within cells. - ANSWER-1.Control the entry and exit of materials in
membrane-bound organelles such as mitochondria and chloroplasts.2.Separate organelles from
cytoplasm so that specific metabolic reactions can take place.3.Provide an internal transport system e.g.
endoplasmic reticulum.4.Isolate enzymes which could damage the cell e.g. lysosomes.5.Provide surfaces
on which reactions can occur e.g. protein synthesis on ribosomes on rough ER.
Suggest reasons why most molecules do not diffuse freely through the cell membrane. - ANSWER-
1.They're not lipid soluble.2.Too large to pass through protein channels.3.Have the same charge as the
charge on the protein channels, so they are repelled even if they are small enough to pass through the
channel.1
State two factors which affect the permeability of cell membranes - ANSWER-.1.Temperature2.Solvent
concentration
, How can substances move across a cell surface membrane? - ANSWER-1.Simple diffusion
(passive)2.Facilitated diffusion (passive)3.Osmosis (passive)4.Active transport (active)5.Co-transport
(active)
Describe how substances can move across a cell surface membrane. - ANSWER-1.Small/non-polar/lipid-
soluble substances can cross by simple diffusion down a concentration gradient.2.Large/polar molecules
- pass through channel proteins/carrier proteins, by facilitated diffusion, down a concentration
gradient.3.Water - moves by osmosis from an area of high water potential to an area of lower water
potential.4.Active transport - moves substances against a concentration gradient, involves protein
carriers and requires ATP.5.Glucose/amino acids can be co-transported across a cell membrane alongside
sodium ions.* DON'T EVER SAY THAT A MOLECULE MOVES 'ACROSS' OR 'ALONG' A CONCENTRATION
GRADIENT - MAKE SURE YOU SAY 'UP' OR 'DOWN' OR 'AGAINST'
Define diffusion. - ANSWER-The net movement of molecules or ions from an area of higher
concentration to an area of lower concentration until evenly distributed.Define osmosis.The movement
of water from a region of higher water potential to a region of lower water potential across a partially
permeable membrane.
Define active transport. - ANSWER-The movement of molecules from an area of lower concentration to
an area of higher concentration using ATP and carrier proteins.
State factors which affect the rate of diffusion. - ANSWER-1.Concentration gradient2.Area over which
diffusion takes place3.Thickness of exchange surface4.Temperature5.Size of molecules (smaller the
molecule, the faster the rate of diffusion).2
What is meant by the term simple diffusion - ANSWER-.The diffusion of molecules directly through a cell
membrane.(most molecules don't easily pass across the cell surface membrane - those that do are small,
non-polar molecules).
What is Ficks Law? - ANSWER-The rate of diffusion is proportional to : (Surface Area x Concentration)
Thickness1.The larger the SA, the faster the rate of diffusion.2.The higher the concentration gradient, the
faster the rate of diffusion.3.The thinner the exchange surface, the faster the rate of diffusion.
What is meant by the term passive process. - ANSWER-No energy is needed for it to happen.
Explain why plasma membranes are said to have a fluid mosaic structure. - ANSWER-1. Fluid because the
phospholipids are constantly moving. 2. Mosaic because the proteins are scattered throughout the
membrane-like tiles in a mosaic.
What effect does cholesterol have on the cell membrane? - ANSWER-1.Cholesterol molecules fit
between the phospholipids and bind to the hydrophobic tails of the phospholipids. 2.Causes them to
pack together more closely, restricting the movement of other molecules in the membrane.
3.Cholesterol makes the membrane less fluid and more rigid. 4.Cholesterol helps to maintain the shape
of animal cells, which is important because animal cells don't have cell walls (especially important for
cells which are not supported by other cells e.g. red blood cells).
State 3 functions of glycolipids in the cell membrane. - ANSWER-1. Act as recognition sites. 2. Maintain
the stability of the membrane. 3. Help cells attach to one another and so form tissues.
State 3 functions of glycoproteins in the cell membrane. - ANSWER-1.Act as recognition sites.2.Help cells
to attach to one another so form tissues.3.Allow cells to recognise one another e.g. lymphocytes can
recognise an organisms's own cells.
Describe the functions of membranes within cells. - ANSWER-1.Control the entry and exit of materials in
membrane-bound organelles such as mitochondria and chloroplasts.2.Separate organelles from
cytoplasm so that specific metabolic reactions can take place.3.Provide an internal transport system e.g.
endoplasmic reticulum.4.Isolate enzymes which could damage the cell e.g. lysosomes.5.Provide surfaces
on which reactions can occur e.g. protein synthesis on ribosomes on rough ER.
Suggest reasons why most molecules do not diffuse freely through the cell membrane. - ANSWER-
1.They're not lipid soluble.2.Too large to pass through protein channels.3.Have the same charge as the
charge on the protein channels, so they are repelled even if they are small enough to pass through the
channel.1
State two factors which affect the permeability of cell membranes - ANSWER-.1.Temperature2.Solvent
concentration
, How can substances move across a cell surface membrane? - ANSWER-1.Simple diffusion
(passive)2.Facilitated diffusion (passive)3.Osmosis (passive)4.Active transport (active)5.Co-transport
(active)
Describe how substances can move across a cell surface membrane. - ANSWER-1.Small/non-polar/lipid-
soluble substances can cross by simple diffusion down a concentration gradient.2.Large/polar molecules
- pass through channel proteins/carrier proteins, by facilitated diffusion, down a concentration
gradient.3.Water - moves by osmosis from an area of high water potential to an area of lower water
potential.4.Active transport - moves substances against a concentration gradient, involves protein
carriers and requires ATP.5.Glucose/amino acids can be co-transported across a cell membrane alongside
sodium ions.* DON'T EVER SAY THAT A MOLECULE MOVES 'ACROSS' OR 'ALONG' A CONCENTRATION
GRADIENT - MAKE SURE YOU SAY 'UP' OR 'DOWN' OR 'AGAINST'
Define diffusion. - ANSWER-The net movement of molecules or ions from an area of higher
concentration to an area of lower concentration until evenly distributed.Define osmosis.The movement
of water from a region of higher water potential to a region of lower water potential across a partially
permeable membrane.
Define active transport. - ANSWER-The movement of molecules from an area of lower concentration to
an area of higher concentration using ATP and carrier proteins.
State factors which affect the rate of diffusion. - ANSWER-1.Concentration gradient2.Area over which
diffusion takes place3.Thickness of exchange surface4.Temperature5.Size of molecules (smaller the
molecule, the faster the rate of diffusion).2
What is meant by the term simple diffusion - ANSWER-.The diffusion of molecules directly through a cell
membrane.(most molecules don't easily pass across the cell surface membrane - those that do are small,
non-polar molecules).
What is Ficks Law? - ANSWER-The rate of diffusion is proportional to : (Surface Area x Concentration)
Thickness1.The larger the SA, the faster the rate of diffusion.2.The higher the concentration gradient, the
faster the rate of diffusion.3.The thinner the exchange surface, the faster the rate of diffusion.
What is meant by the term passive process. - ANSWER-No energy is needed for it to happen.
