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(a) What is a membrane?
Structure that separates the contents of cells from their environment
(a) What is compartmentalisation?
The formation of separate membrane-bound areas in a cell
(a) Why do certain organelles need to be compartmentalised?
Metabolism includes many different and often incompatible reactions and environments - chemical gradients
(a) Give another name for the cell surface membrane
Plasma membrane
(a) What are membranes formed from?
phospholipid bilayer
(a) What, in the phospholipid bilayer, forms the inner and outer surface of the plasma membrane?
Hydrophilic phosphate heads
(a) What is inside the membrane?
Hydrophobic core of fatty acid tails
(a) Why are phospholipid bilayers suited as membranes?
The outer surfaces of the hydrophilic phosphate heads can interact with water (cells are in aqueous environments)
(b) What is a glycoprotein?
Branched carbohydrate attached to protein - recognition site for chemicals (hormones)
(b) What is a glycolipid?
Lipid with carbohydrate attached - acts as a recognition site
(b) What is an extrinsic protein?
Protein molecule partially embedded in/lying on the surface of membrane
(b) What is an intrinsic protein?
Protein molecule spanning the phospholipid bilayer
(a) Give three roles of membranes in a cell
Partially permeable barriers between the cell and its environment (or organelles); sites of chemical reactions; sites of cell communication
(b) Give two examples of intrinsic proteins
Channel proteins and carrier proteins
(b) What is a channel protein?
a protein that allows the passive transport of specific substances across a cell membrane
(b) What is a carrier protein?
an active and passive transport molecule that changes shape to allow the molecule to pass across the membrane
(b) What is a glycoprotein an example of?
Intrinsic protein
(b) Give two examples of cell signalling (glycoprotein)
Receptors for neurotransmitters at nerve cell synapses; peptide hormones
(b) What is the role of a glycolipid?
Antigens that can be recognised by the immune system as self/non-self
(b) What is the role of an extrinsic protein?
Interaction with polar heads of phospholipids/intrinsic proteins
(b) What is cholesterol?
Lipid with a hydrophilic and hydrophobic end (like a phospholipid)
(b) What is the role of cholesterol?
Regulates the fluidity of membranes
(b) How does cholesterol keep membranes stable?
hydrophilic end interacts with the phosphate heads, and the hydrophobic end interacts with the fatty acid tails - pulls them together
(b) How does cholesterol prevent the membranes becoming too rigid?
Stops the phospholipid molecules from grouping too closely and crystallising
(a) How are proteins similar to enzymes in chemical reactions?
Proteins in the membrane have to be in particular positions for chemical reactions to take place
(c) What happens to the cell membrane when the temperature is increased?
Phospholipids will have more kinetic energy and will move more, makes the membrane more fluid - loses its structure
(c) What happens to the membrane if the temperature continues to increase?
Cell will break down completely
(c) What does the loss of structure mean for the membrane?
Increases membrane permeability - makes it easier for particles to cross it
(c) What happens to intrinsic proteins at higher temperatures?
Denaturation - involved in transport so will affect membrane permeability
(c) What happens to cells when they are exposed to organic solvents?
dissolve the membrane - disrupting cells
(c) How do less concentrated solutions of alcohols affect cells?
Non-polar alcohol molecules can enter cell membrane - presence between phospholipids disrupts membrane
(d) What is diffusion?
The net movement of particles from a region of high concentration to a region of low concentration
(d) True or false: diffusion is passive and does not require ATP
True
(d) What is equilibrium?
When there is no difference in the concentration of the two regions
(d) Why does diffusion occur?
Because molecules constantly move and collide with each other
(d) Why is diffusion over short distances fast?
Particles are constantly colliding, which slows down their overall movement
(d) Why are cells microscopic?
Movement of particles within cells depends on diffusion - large cell leads to slow rates of diffusion
(d) Give two factors affect the rate of diffusion
temperature and concentration difference
(d) How does higher temperature affect the rate of diffusion?
The higher the temperature the higher the rate of diffusion - particles have more kinetic energy and move at higher speeds
(d) How does a bigger concentration gradient affect the rate of diffusion?
The greater the difference in concentration between two regions, the faster the rate of diffusion - overall movement from higher conc to lower conc will be larger
(d) Diffusion takes place ______ the concentration gradient
Down
(d) What is simple diffusion?
Diffusion in the absence of a barrier or membrane
(d) What is diffusion across membranes?
Involves particles passing through phospholipid bilayer - only if membrane is permeable to the particles
(d) Why can't ions pass through the bilayer?
Hydrophobic interior of the membrane repels ions so they cannot easily pass through
(d) Why is the diffusion of water slow?
Polar molecules (water) have partial +ve and -ve charges
(d) Give two factors that affect the rate of diffusion across membranes
Surface area and thickness of membrane
(d) How does surface area affect the rate of diffusion across membranes?
The larger the surface area, the higher the rate of diffusion
(d) How does the thickness of the membrane affect the rate of diffusion across membranes?
The thinner the exchange surface, the higher the rate of diffusion
(d) What is facilitated diffusion?
Diffusion across a membrane with the help of a channel or carrier protein
(d) What does selectively permeable mean?
Only allows certain molecules to pass through
(d) Give 5 factors that affect the rate of facilitated diffusion
temperature, concentration gradient, membrane surface area, membrane thickness, and number of channel/carrier proteins
(d) Give 2 examples of passive diffusion
Simple diffusion and facilitated diffusion
(d) What is active transport?
The net movement of molecules into/out of a cell from a region of lower concentration to a region of higher concentration which requires energy in the form of ATP and carrier proteins
(d) Step 1 of active transport from outside to inside a cell
Molecule/ion to be transported binds to receptors in channel of the carrier protein on outside of cell
(d) Step 2 of active transport from outside to inside a cell
On the inside of the cell ATP binds to carrier protein and hydrolysed into ADP and phosphate
(d) Step 3 of active transport from outside to inside a cell
Binding of the phosphate molecule to carrier protein causes the protein to change shape - opening up to inside of cell
(d) Step 4 of active transport from outside to inside a cell
Molecule is released to inside of cell
(d) Step 5 of active transport from outside to inside a cell
Phosphate molecule is released from carrier protein and recombines with ADP to form ATP
(d) Step 6 of active transport from outside to inside a cell
The carrier protein returns to its original shape
(d) Why is active transport selective?
Specific substances transported by specific carrier proteins
(d) When is bulk transport used?
Large molecules such as enzymes, hormones and whole cells like bacteria need to be transported
(d) What is endocytosis?
bulk transport of material into cells
(d) What are the 2 types of endocytosis?
phagocytosis and pinocytosis
(d) How does endocytosis occur?
Plasma membrane invaginates to form pseudopods, enfolds the material until membrane fuses to form a vesicle - moves into cytoplasm to process material
(d) How does exocytosis occur?
Vesicles (usually Golgi) move towards and fuse with plasma membrane - contents released outside the cell
(d) When is ATP required in endo and exocytosis?
Movement of vesicles along the cytoskeleton, changing shape of cells to engulf materials, and fusion of membranes as vesicles form/as they meet plasma membrane
(d) What is phagocytosis?
Cell eating
(d) What is pinocytosis?
Cell drinking
(d) Give 3 cellular processes that require ATP
active transport, endocytosis and exocytosis
(e) What is osmosis?
diffusion of water across a partially permeable membrane
(e) What is water potential?
the pressure exerted by water molecules as they collide with a membrane or container
(e) What is water potential measured in?
kilopascals (kPa)
(e) What is the water potential of pure water?
0
(e) Why can't you have a positive value for water potential?
All solutions have negative water potentials
(e) How does the concentration of solution affect the water potential?
The more concentrated the solution, the more negative the water potential
(e) What is hydrostatic pressure?
diffusion of water into a closed system increases the volume, and therefore the pressure in the system
(e) What is the effect on an animal cell with a higher water potential than that of the cytoplasm?
Water will move into the cell by osmosis, increasing the hydrostatic pressure inside the cell, causing cell to burst (cytolysis)
(e) What is the effect on an animal cell when it is placed in a solution that has a lower water potential than the cytoplasm?
Water will move out of the cell by osmosis, reducing the volume of the cell, causing cell to shrink and crentate
(e) What happens to a plant cell when it is placed in a solution that has a higher water potential than the cytoplasm?
Water will move into the cell by osmosis, increasing hydrostatic pressure, and causing turgor
(e) What happens to a plant cell when it is placed in a solution that has a lower water potential than the cytoplasm?
Water will move out of the cells by osmosis, reducing the volume of cell, and causes plasmolysis
(e) What is a hypotonic solution?
has a lower concentration of solute compared to the cell
(e) What is an isotonic solution?
Contains equal concentrations of solutes on both sides.
(e) What is a hypertonic solution?
Solute concentration is greater than that inside the cell
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