Unit 1.3 - Cell Membranes And Transport Flashcards
List the 6 functions of the cell membrane
-The boundary that separates the living cell from its non-living surroundings
-Cell recognition
-Controls which substances pass into and out of the cell
-Controls the uptake of nutrients
-Allows waste products to pass out of the cell
-Is responsible for secreting substances such as enzymes and glycoproteins
How does cell recognition work?
It’s to do with the surface pattern of the cell - The immune system recognises a parasite by scanning its surface pattern and immune system cells attack and destroy it for being a foreign cell
What is the cell membrane made up of?
Almost entirely phospholipids and proteins embedded
What can the phospholipids within the cell membrane do?
Form bilayers, with one sheet of phospholipid forming over another
What can the phospholipid bilayer be described as?
The basis of membrane structure
What is the basis of membrane structure?
The phospholipid bilayer
What type of molecules does the phospholipid bilayer allow to enter and leave the cell through the cell membrane?
Lipid soluble (non-polar) molecules (e.g - 02, C02)
Examples of lipid soluble (non-polar) molecules that the phospholipid bilayer allows to enter and leave the cell
02, C02
Describe the phosphate head of a phospholipid molecule
Hydrophillic (polar) - has an electrical charge
Is attracted to other polar molecules (e.g - water)
Describe the fatty acid tails of a phospholipid molecule
Hydrophobic (non-polar) = repels water
How do we know about the existence of the phospholipid bilayer?
By looking under an electron microscope (T.E.M. - transition electron microscope, that looks at a thin slice of cell) and adding a water soluble stain, we would see the hydrophilic parts accepting the stain and appearing as a stained dark layer, whereas each side of a hydrophobic layer would reject the stain and appear as an unstained white layer
What’s the name of the space between cells?
Intercellular space
Under what type of microscope would be see the staining of the hydrophobic and Hydrophilic parts of the phospholipid bilayer?
T.E.M - transition electron microscope
What does a T.E.M. (Transition electron microscope) look at?
A thin slice of cell
What is the diameter of the cell membrane and which type of microscope revealed this?
7-8nm
T.E.M (transition electron microscope)
What was one of the original structure theories of the cell membrane? How accurate was this?
A phospholipid bilayer with proteins on the outside -this theory is incorrect
What type of microscope and process allowed us to advance from the original theory of the proteins on top of the phospholipids structure?
S.E.M. (scanning electron microscope)
Freeze-fracture
S.E.M
Scanning electron microscope
A type of electron microscope that scans the surface with a focused beam of electrons to create a high resolution image
T.E.M meaning
Transition electron microscope
What has the S.E.M and freeze fracture allowed us to see?
That on the surface of the cell, protein molecules are embedded in the surface, not on it, as we’ve seen little bumps in the freeze-fracture image
Freeze fracture
To rapidly freeze the specimen and then crack it on a plane through the tissue
-Fractures occur on weak parts of the tissue such as membranes or organelle surfaces
On which parts of the tissue do fractures occur during freeze fracture?
Weak portions of the tissue such as membranes or organelle surfaces
Which model did the S.E.M and freeze fracture imaging lead to in terms of the structure of the cell membrane?
The fluid Mosaic model
Which scientists discovered the fluid mosaic model?
Singer and Nicholson
Draw and label the fluid mosaic model
(Check notes)
What forms the glycocalyx?
Glycolipids and glycoproteins
What do glycolipids and glycoproteins form?
they glycocalyx
What are all the parts to label on the fluid mosaic model?
-Intrinsic proteins (+channel)
-Extrinsic proteins (+surface proteins)
-Cholestrol
-Glycoprotein
-Glycolipid
-Glycocalyx
-Phospholipid bilayer
Glycolipid
A branched polysaccharide attached to a phospholipid
Glycoprotein
A branched polysaccharide attached to an extrinsic protein
What function do both the glycolipids and glycoproteins have?
Form external patterns to help in cell recognition
Glycocalyx
A Glycolipid and glycoprotein covering that surround the cell membrane of cells
What’s the name for the glycolipid and glycoprotein covering that surrounds the cell membrane of cells?
Glycocalyx
The branched polysaccharide attached to a phospholipid
Glycolipid
The branched polysaccharide attached to an extrinsic protein
Glycoprotein
What type of protein is a glycoprotein attached to?
Extrinsic protein
Extrinsic protein
Sits in one half of the membrane or on its surface (surface proteins are an example)
What type of proteins are surface proteins?
Extrinsic proteins
Intrinsic proteins
Stretch from one end of the membrane to the other, completely spanning it
-Has to have Hydrophillic parts on the outside - exposed to liquid
-Has the have non-polar centre - no rejection from the non-polar, fatty acid tails
What features does the intrinsic protein have to have and why?
-Hydrophillic parts on the outside - exposed to liquid
-Non-polar centre - avoid rejection from the non-polar, fatty acid tails
Cholestrol
Helps stabilise some regions of the membrane that are less fluid
Channel
Allows charged polar molecules to pass through the membrane (e.g - glucose)
Give an example of a charged particle that the channel of an intrinsic protein would allow through
Important charged polar molecules, such as glucose, which is necessary to the cell
Where are the channels within the fluid mosaic model?
In the intrinsic proteins
What makes the channels in the cell membrane selectively permeable?
If a protein is too big, it won’t be allowed through - the channel doesn’t allow all polar molecules across
What does the fact that the channel within the cell membrane doesn’t allow all charged polar molecules, for example if they’re too big, make it?
Selectively permeable
Why ‘fluid’ mosaic model?
All parts of the membrane move relative to each other consistently (very dynamic + proteins can change position)
How do the proteins within the membrane move?
Relative to each other, consistently + can change position
Why fluid ‘mosaic’ model?
Proteins dotted around the membrane like mosaic tiles
What are the 5 different ways of movement across the membrane for molecules and particles?
-Simple diffusion
-Facilitated diffusion
-Active transport
-Osmosis
-Exocytosis/Endocytosis
-Cotransport
What are two types of passive transport across the membrane for proteins and molecules?
Simple and facilitated diffusion
What type of molecules does simple diffusion allow to freely pass through the membrane?
Small, uncharged molecules such as 02 and C02
Which type of movement across the membrane allows small, uncharged particles such as 02 or C02 to freely pass through?
Simple diffusion
Examples of small, uncharged particles
02, C02
(Move through the membrane through simple diffusion)
Diffusion
The movement of molecules or ions from a region where they’re in high concentration to a region of lower concentration until they’re evenly distributed
Until which point do molecules and ions move from a region where they’re in high concentration to a region of lower concentration during diffusion?
Until they’re equally distributed
What do molecules move down during diffusion?
A concentration gradient
What type of process is simple diffusion?
Passive (doesn’t require ATP from the cell)
Passive processes
Don’t require ATP from the cell
What will eventually occur during simple diffusion?
Unless the molecule is used up by the cell, equilibrium will be reached
When would equililbirum not be reached during simple diffusion?
If the molecule is used up by the cell
What does it mean if equilibrium has been reached during simple diffusion?
Concentration of molecules is equal on either side of the membrane in both directions, but there’s no net movement in any particular direction
What does the rate of diffusion depend on?
How steep the concentration gradient is
(Steeper = faster)
What’s affects the rate of diffusion?
How steep the concentration gradient is (steeper = faster rate of diffusion)
Facilitated diffusion
Diffusion in or out of cells helped by an intrinsic protein
What does facilitated diffusion still rely on and why?
The concentration gradient (requires no ATP) as it’s a type of diffusion
What type of process is facilitated diffusion?
Passive - doesn’t require ATP from the cell
What type of particles and molecules does facilitated diffusion help?
Charged particles/ions and large molecules such as glucose and protons
What is glucose an example of and which method does it use for movement across the membrane?
A large molecule
Facilitated diffusion
What are 02 and C02 examples of and which method do they use for movement across the membrane?
Small, uncharged molecules
Simple diffusion
Which protein has two types? What are they?
2 types of facilitating proteins
-Channel proteins
-Carrier proteins
What are the 2 facilitating proteins and which process do the help in?
Channel and carrier proteins
Facilitated diffusion
How do channel proteins work?
-Consist of pores lined with polar groups (Hydrophillic)
-Allows charged particles (such as Na+) to pass through - each one is specific to 1 type of ion
-Can open and close depending on the needs of the cell (gated channels)
What do channel proteins consist of and why?
Pores lined with polar groups (Hydrophillic) to allow charged particles to pass through
What can channel proteins do depending on the needs of the cell? What are these called?
Can open + close
Gated channels
Do all channel proteins open and close (gated channels)?
No, it depends on the needs of the cell
Example of a charged particles that channel proteins allow to pass through
Na+
What type of molecules do carrier proteins allow the facilitated diffusion of?
Larger polar molecules (e.g - sugars and amino acids)
What type of molecules are sugar and amino acids an example of and what type of proteins help transport them across the membrane?
Larger polar molecules
Carrier proteins allow their facilitated diffusion
Can channel proteins carry multiple different ions across the membrane?
No, they’re specific to one type
Can carrier proteins carry multiple different types of molecules across the cell membrane?
No, they’re specific to a particular molecule
How do carrier proteins work?
A particular molecule attaches to a carrier protein at its binding site and causes the carrier protein to change shape or rotate within the membrane to release the molecule on the other side of the membrane (not an open channel)
Why do carrier proteins have to change shape or rotate to transport the molecule across the membrane?
They’re not open channels
Where does the molecule attach to a carrier protein?
At its binding site
What type of molecules is active transport used to transport?
Relatively small molecules
Does active transport require ATP? What does this make it?
Yes, so it’s not a passive process
Does active transport use the concentration gradient? Why?
No - its not a type of diffusion
Molecules and ions are moved across membranes against a concentration gradient
In which direction to the concentration gradient are molecules and ions moved during active transport?
Against it
In which direction in relation to diffusion can molecules and ions move during active transport?
The opposite direction
What carries out active transport?
A specific intrinsic protein - a pump
What is the pump?
A specific intrinsic protein that carries out active transport
How does active transport work?
-Molecule or ion that needs to be transported combines with a specific intrinsic protein - a pump
-ATP transfers a phosphate group to the pump on the inside of the membrane, causing the pump to change shape and transport the ion across the membrane and release it into the cell
What does ATP transfer to the pump during active transport and what does this do?
A phosphate group - causes it to change shape to transport the ion across the membrane
Examples of processes that use active transport
-Protein synthesis
-Muscle contraction
-Nerve impulse transmission
-Absorbance of minerals (e.g - nitrates by plant root hair cells)
Which minerals do plant root hair cells absorb and which process does this require?
Nitrates through active transport
What type of transport occurs through exocytosis and endocytosis?
Bulk transport
What is bulk transport done through?
Endocytosis and exocytosis
How does endocytosis work?
-Large particles or liquid enter the cell
-Plasma membrane folds inwards
-Plasma membrane engulfs the material
-Plasma membrane fuses to enclose the material, forming a membrane bound vesicle in the cytoplasm
What type of materials undergo endocytosis?
Particles and liquids
What does endocytosis form and where within the cell?
A membrane bound vesicle in the cytoplasm after the plasma membrane fuses
What can lysosomes do to the vesicles produced during endocytosis?
Fuse with it and digest the small digestive molecules, whilst the vesicle becomes part of the membrane again - reusing!
What are the 2 types of endocytosis?
Phagocytosis
Pinocytosis
What are phagocytosis and pinocytosis the 2 types of?
Endocytosis
Phagocytosis
‘Cell eating’ - the movement of solids
The movement of which type of particles does phagocytosis involve?
Solids
2 examples of phagocytosis
-White blood cell (phagocytes) swallowing a bacterial cell
-Amoeba engulfing a paramecium
Pinocytsosis
Involves entry of liquid into the cell
Example of exocytosis
Within the Golgi Body, when vesicles fuse with the membrane to release its contents outside of the cell
Exocytosis
The opposite of endocytosis - particles such as hormones and enzymes secreted from cells when the vesicle containing particles migrate to the cell membrane and fuse with it, releasing particles outside the cell
What type of particles undergo exocytosis?
Hormones and enzymes
As the concentration gradient increases, what happens to the rate of transport in simple diffusion?
Continues increasing
As the concentration gradient increases, what happens to the rate of transport of facilitated diffusion?
Increases up to a point - the number of protein channels limit the rate
What limits the rate of transport for facilitated diffusion?
The number of protein channels
What is it that increases the rate of transport for active transport?
Concentration difference across the membrane (higher = higher rate of transport)
What’s the affect of adding cyanide during active transport? Why?
The rate of transport drops to zero - cyanide is a respiratory inhibitor, and active transport requires ATP
Give an example of a respiratory inhibitor
Cyanide
What is cyanide?
A respiratory inhibitor
What type of transport is osmosis?
Passive (type of diffusion)
Osmosis
When water molecules diffuse through the cells selectively permeable membrane from a solution of high concentration of water molecules to a solution of lower concentration of water molecules
What does amoeba engulf during phagocytosis?
Paramecium
What’s the name for white blood cells? What do they digest?
Phagocytes
Bacterial cells
Phagocytes + their role
White blood cells, which digest bacterial cells
How do we figure out the surface area of a membrane if given the surface area of a phospholipid monolayer?
Halve it, as phospholipids form bilayers in membranes, not monolayers
What type of molecules can diffuse through the bilayer through simple diffusion? Give three examples
Non-polar molecules
02
C02
Fat-soluble vitamins (A, D, E and K)
Name four fat-soluble vitamins and state how they’re transported through the membrane
Vitamins A, D, E and K
Simple diffusion
What happens to the membrane if there’s too much Cholestrol? Why?
It becomes too rigid
Cholesterol is responsible for stabilising the regions of the membrane that are less fluid
Where did the evidence for the ‘mosaic’ part of the fluid mosaic model come from?
Freeze-fracture electron microscopy
Where did the evidence for the ‘fluid’ part of the fluid mosaic model come from?
From experiments (e.g - hybridisation of cells)
Example of an experiment that proved the ‘fluid’ part of the fluid mosaic model
Hybridisation of cells (fuse two cells together)
Hybridisation of cells
Fuse two together
Give examples of large particles that would enter a cell through endocytosis
-Whole cells
-Large protein molecules
Does bulk transport via endocytosis or exocytosis require energy?
Yes
With increased concentration differences, how does this affect the protein channels and how does this affect facilitated diffusion?
Channels are simultaneously (saturated with molecules)
= limits facilitated diffusion
What are channels if they’re simultaneously busy?
Saturated with molecules
What are protein channels if they’re saturated with molecules?
Simultaneously busy
Is cotransport a passive or non-passive process and why?
Passive as it depends on a concentration gradient
Where does glucose-sodium cotransport occur?
In the kidney tubules and small intestine
(In the digestive system - absorb glucose from our food into our blood)
What’s the cotransport example that we end to remember?
Glucose-sodium
What’s the purpose of glucose-sodium cotransport in our digestive system?
To absorb glucose from our food into our blood
What do the sodium ions and glucose attach to in the first stage of cotransport?
A carrier protein - a cotransporter
What’s the name for the carrier protein that sodium ions and glucose attach to in the first step of cotransport?
A cotransporter
What’s a cotransporter?
A carrier protein that allows the transport of two different species across the membrane simultaneously
What happens to the sodium ions and glucose once they’ve attached to a carrier protein in the cell membrane during the first step of cotransport?
Carrier protein changes shape and deposits the sodium ion and glucose molecule into the cell
Sodium ion and glucose molecule diffuse separately across the cell to the opposite membrane
How do the sodium ion and glucose molecule diffuse across the cell during cotransport?
Separately across the cell to the opposite membrane
What type of cells do sodium ions and glucose molecules enter during cotransport?
Epithelial cells
How do the sodium ions exit the epithelial cells?
Pumped out by active transport
What happens inside the epithelial cell once sodium ions are pumped out by active transport?
Lowers the sodium ion concentration inside the cell, maintaining the concentration gradient needed for the diffusion of sodium ions from the gut lumen into the cell
What’s the sodium ion concentration gradient inside the epithelial cell required for?
The diffusion of sodium ions from the gut lumen into the cell
What carries out the active transport for the sodium ions to exit the epithelial cells during cotransport and what does it use?
Na+/K+ pump uses ATP
What does the Na+/K+ pump do during cotransport?
Turns ATP into ADP whilst pumping out the sodium ions out of the epithelial cells by active transport
How does glucose leave the epithelial cells during cotransport?
By facilitated diffusion
Where does glucose enter after leaving the epithelial cells through facilitated diffusion?
The blood in the capillaries
What need to be ensured in order for glucose to be able to enter the blood? Why?
That the glucose concentration in the blood is low
To create a concentration gradient between the cell and the blood
Which uses active transport and which uses facilitated diffusion during cotransport?
Na+ ions
Glucose molecules
Na+ ions - Active transport
Glucose molecules - Facilitated diffusion
What are most cell membranes permeable to?
Water and certain solutes only
What is the name of the weird fork Greek letter for water potential?
psi
Water potential
The tendency of water molecules to move from a high to a low concentration of water
What’s the unit of water potential?
kPa
What is water potential actually a measure of?
The pressure exerted by water molecules on the membrane (hence it being measured in kPa, units of pressure)
Osmosis
The movement of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane
Which phrase do we use to define osmosis instead of ‘concentration’ and why?
Potential, as water is a solvent
What’s the water potential of pure water?
0kPa
What does a higher concentration of water molecules mean in terms of energy?
Higher concentrations of water molecules = greater potential energy
What can water molecules do if they have greater potential energy?
They’re completely free to move around
Give an example of a solute that could be dissolved in water
Sugar
What’s a solute’s concentrations relationship with water potential?
Higher concentration of a solute = lower water potential
If a solution has a high concentration of water, how is its water potential?
High
If a solution has a low concentration of water, how is its water potential?
Low
If a solute, such as sugar, is dissolved in water, how does this affect the water potential of the solution and why?
Water potential of the solution is lowered (becomes more negative)
Proportionally fewer water molecules to move about
What actually happens to the water potential figure if the water potential is lowered?
Becomes more negative
Describe the values of all water potentials and what is the exception for this?
All water potentials have negative water potential values, except pure water
What does a ‘more concentrated’ solution actually mean?
More solutes dissolved in it
What does dissolving more solutes in a solution make it?
More concentrated
How does the concentration affect the water potential of a solution?
The more concentrated a solution (the more solutes dissolved in it), the more negative the water potential
How does a lower water potential affect the number of free water molecules there are?
lower water potential = fewer free water molecules
What happens when a solution has a high water potential?
Greater tendency of water to leave the system by osmosis
Where does water diffuse to and from during osmosis in terms of water potential?
Diffuses from a region of higher (less negative) to lower (more negative) water potential
Symbol for pressure potential
ψp
Symbol for solute potential
ψs
What’s ψp the symbol for?
Pressure potential
What’s ψs the symbol for?
Solute potential
Pressure potential
As the outward pressure builds up, the cell wall in plant cells develops an opposing force - pressure potential.
(The resistance the cell has to expanding)
Is pressure potential a positive or a negative number?
Usually a positive number
What does pressure potential do?
Pushes against the cells tendency to swell
Solute potential
The concentration of dissolved substances inside the cell vacuole - the water potential of what’s inside the cell
Is solute potential a positive or a negative number?
Always a negative value
Describe the properties of a plant cell wall and explain why it’s like this
Inflexible and Inelastic - won’t allow the cell to expand and stretch
Made of cellulose (strong microfibrils)
What type of pressure pushes outwards on the cell wall when water enters a plant cell vacuole by osmosis?
A hydrostatic pressure
Describe the process of a plant cell becoming turgid
-Water enters the plant cell vacuole by osmosis
-Hydrostatic pressure is set up and pushes outwards on the cell wall
-The cell swells
-Inflexible cell wall resists the cell from expanding too much
-Cell becomes turgid
What is a plant cell’s healthy, natural state?
When it’s turgid
In what state is a plant cel when it’s turgid?
In its healthy, natural state
What helps a plant stay upright?
Turgidity from a hypotonic external medium
What does turgidity help a plant do?
Stay upright
Symbol for water potential of a cell
ψcell
ψcell meaning
Water potential of a cell
Water potential equation
ψcell = ψs + ψp
Water potential of a cell = solute potential + pressure potential
What are thee types of external medium a cell can be within?
Hypotonic
Hypertonic
Isotonic
Hypotonic external medium
Water potential of external medium is higher than the solution inside the cell
Hypertonic external medium
Water potential of external solution is lower than the solution inside the cell
Isotonic external medium
External solution has the same water potential as the cell’s contents
What happens in terms of osmosis when a cell is in a hypotonic external medium?
Water moves into the cell by osmosis
What happens in terms of osmosis when a cell is in a hypertonic external medium?
Water moves out of the cell by osmosis
What happens in terms of osmosis when a cell is in an isotonic external medium?
No net movement of water by osmosis
What happens to an animal cell in a hypotonic external medium?
The cell swells and may lyse (bust) as they don’t have a cell wall to protect them from bursting
What’s the phrase for an animal cell bursting in a hypotonic external medium?
Lysis
Why is there a risk of animal cells undergoing lysis (bursting) when in a hypotonic external medium?
They don’t have a cell wall to protect them from bursting
What’s the phase for red blood cells bursting in a hypotonic external medium?
Haemolysis
Haemolysis
Red blood cells bursting when in a hypotonic external medium
What could lead to Haemolysis?
Kidney problems leading to too much water in the plasma
What happens to a plant cell in a hypotonic external medium?
The cytoplasm and vacuole swell and push against the cell wall - cell wall becomes turgid
Turgid plant cells support plant tissues and structures (optimal for plant cells)
What’s optimal for plant cells?
Turgidity
What do turgid plant cells do?
Support the plant tissues and structures
What happens to an animal cell in a hypertonic external medium?
The cell shrinks
What happens to a plant cell in a hypertonic external medium?
The cytoplasm and vacuole shrink, causing the cell membrane to pull away from the cell wall
= plasmolysed and flaccid (floppy) cells (plasmolysis)
What shrinks in a hypertonic external medium and what swells in a hypotonic external medium in plant cells?
Cytoplasm and vacuole
Flaccid
Floppy cell
(Plant cell in a hypertonic external medium)
Plasmolysis
The cytoplasm and vacuole shrinking, causing the cell membrane to pull away from the cell wall when a plant cell is in a hypertonic external medium
What will happen to a plant when it undergoes plasmolysis?
Usually fatal to them - the whole plant will wilt
What’s the phrase for the cytoplasm and vacuole to shrink, causing the cell membrane to pull away from the cell walls when a plant cell is in a hypertonic external medium?
Plasmolysis
What maintains the situation of an animal cell remaining in an isotonic external medium and what does this ensure?
Homeostasis
Ensures there’s no water loss or gain
Animal cell in an isotonic external medium
Naturally - their bathing medium
What’s the natural external medium of a plant cell?
Hypotonic
What’s the natural external medium of an animal cell?
Isotonic
What happens to a plant cell in an isotonic external medium?
Cells become flaccid (floppy)
The point of incipient (beginning to happen) plasmolysis
Describe the potential of the water, solute and pressure in a plant cell when in an isotonic external medium
ψp = 0kPa
ψcell= ψs
Crenation
The formation of abnormal notchings around the edges of a cell after expose to a hypertonic solution
In what type of solution does cremation occur to a cell?
Hypertonic
What’s the phrase for the formation of abnormal notchings around the edges of a cell after exposure to a hypertonic solution?
Crenation
Describe a solution in an isotonic external medium
Equilibrium, with no net movement
What’s the net movement in an isotonic external medium?
There is none
How does the size of a molecule affect how lipid-soluble it is and its rate of diffusion?
Smaller =
More lipid soluble
Faster rate of diffusion
Overall movement
Net movement
Net movement
Overall movement
How do you remove the cell debris after a pigment has been released into the surrounding solution following Haemolysis?
By centrifugation
How can you measure the depth of colour of pigment released following Haemolysis?
-Remove cell debris by centrifugation
-Measure with a colourimeter
What do we use to measure depth of colour?
A colorimeter
Where is the overall water potential of blood cells taken?
Where 50% of the cells have burst
What does each cell have within a tissue?
Its own water potential
What does the fact that each cell has its own water potential mean?
The cells plasmolyse at different sucrose concentrations
At different what do cells plasmolyse?
Different sucrose concentrations
Incipient plasmolysis
The point where the water potential of solution and tissue are equal
(When 50% of the cells are plasmolysed)
At which point do we know that the water potential of solution and tissue are equal in a plant cell?
When 50% of the cells are plasmolysed (incipient plasmolysis)
What has happened when 50% of the cells have plasmolysed?
The water potential of solution and tissue are equal
= incipient plasmolysis
What’s the name of the state where 50% of cells are plasmolysed - the point where the water potential of solution and tissue are equal?
Incipient plasmolysis
Which factors is the rate of diffusion dependant on?
-Surface area of the membrane
-Length of diffusion pathway
-Steepness of concentration gradient
-Temperature
-Membrane permeablity
What causes an increase in the surface area of a membrane?
Folds in the cell membrane
How does the surface area of the membrane affect the rate of diffusion?
A higher surface area gives more places over which diffusion can happen, therefore it increases the rate of diffusion
How does the length of a diffusion pathway affect the rate of diffusion?
The shorter it is, the faster the rate of diffusion
Flattened cells, thinner membranes and less layers of cells all decrease diffusion pathways
Which factors decrease a diffusion pathway?
Flattened cells, thinner membranes and less layers of cells
How does the steepness of a concentration gradient affect the rate of diffusion?
Larger difference between high and low concentrations = faster diffusion
Increased by circulation and ventilation
What increases the steepness of a concentration gradient?
Circulation and ventilation
How does the temperature affect the rate of diffusion?
Higher temperatures = more kinetic energy = faster particles = faster rate of diffusion
Which factors affect membrane permeability?
Salt concentration
Presence of detergents
Organic solvents
What do salt concentrations, presence of detergents and organic solvents all affect?
Membrane permeability
How do we describe the direction of water molecules between cells?
From ____ to ____
Not “out of”
How is the pressure potential inside a cell built up?
Water passes into the cell via osmosis
Cytoplasm expands
Cell becomes turgid as cytoplasm and contents push against the cell wall
Inelastic cell wall resists further expansion
When a cell wall expands, which pressure is built up?
Pressure potential
What do all cells have different?
Water potentials
What is the rate of active transport affected by?
-Respiration rate
-Temperature
Why is the pressure potential of a cell in incipient plasmolysis zero?
The cell membrane is pulled away from the cell wall
When the cell membrane is pulled away from the cell wall during incipient plasmolysis, what does this cause?
The pressure potential to be zero
What do we NOT mention when a question asks about PASSIVE transport?
Carrier proteins or active transport
What is diffusion proportional to?
Surface area x concentration gradient
——————————————————
Diffusion distance
What is surface area x concentration gradient proportional to?
—————————————————
Diffusion distance
Diffusion
What forms the largest vesicles- phagocytosis or pinocytosis?
phagocytosis
What do both endocytosis and exocytosis require?
Energy in the form of ATP
Draw a turgid cell vs a plasmolysed cell
(See notes)
How do we increase our confidence in data?
Repeat and calculate a mean
Exclude anomalies
Describe extrinsic proteins in the fluid mosaic model of the plasma membrane
Embedded in the lipid layer
Where is there already a high Na+ concentration when thinking of cotransport and why?
In the lumen, from dietary sources
Why should we use thermostatically controlled water baths as opposed to carrying out experiments at room temperature?
Room temperature varies, and this reduces reproducibility
