Unit 2 - Diffusion/osmosis/active transport Flashcards
Define diffusion
The net movement of particles from an region of higher concentration to a region of lower concentration
Is diffusion active or passive?
Passive
Define passive transport
Movement of substances that does not require energy
Define osmosis
The movement of water from a region of high water potential to a region of low water potential across a partially permeable membrane
Define facilitated diffusion
Diffusion across a plasma membrane through protein channels
Is facilitated diffusion passive?
Yes
Is osmosis passive or active?
Passive
Define active transport
The movement of molecules from an area of low concentration of that molecule to an area of high concentration of that molecule. This movement requires ATP
What sort of molecules tend to move via diffusion across a membrane?
- small molecules (e.g. gases)
- lipid soluble molecules
- non-polar molecules
How does water tend to move across membranes?
Through aquaporins (via osmosis)
Why can steroid hormones easily cross a membrane by simple diffusion?
- They are lipid soluble
- They are non-polar
Which 2 factors affect the rate of diffusion?
Temperature
Concentration difference
What effect does an increase in temperature have on the rate of diffusion?
It increases the rate of diffusion
What effect does a greater difference in concentration of two regions have on the rate of diffusion?
It increases the rate of diffusion
Why does a higher temperature increase rate of diffusion?
-higher temperature means particles have more kinetic energy and move at higher speeds
Why is it easier for oxygen to diffuse across a membrane than water?
- oxygen molecules are small and non-polar whereas water molecules are polar
- the hydrophobic interior of the phospholipid bilayer repels the charged molecules
- water is only partially charged so is still able to diffuse through the membrane, though only slowly
What 4 factors affect the rate of diffusion across a membrane?
- temperature
- concentration gradient
- surface area
- thickness of membrane
An increase in surface area of an exchange surface has what effect on rate of diffusion?
increases rate of diffusion
An increase in membrane thickness has what effect on the rate of diffusion?
Decreases rate of diffusion
Why are membranes containing protein channels selectively permeable?
- Most protein channels are specific to one molecule or ion
- Therefore only these specific molecules/ions are able to move across the membrane
What does facilitated diffusion allow to move across a membrane?
- larger molecules
- lipid insoluble molecules
- small charged particles
Give an example of a small charged particle that moves across membranes via facilitated diffusion
Na+
Give an example of a large molecule that moves across membranes via facilitated diffusion
Glucose or amino acids
What happens to carrier proteins when a specific molecule binds to them?
They change shape
How do protein channels allow charged particles to move through the membrane?
They provide a hydrophilic channel for charged particles
What are the 5 factors which affect the rate of facilitated diffusion?
- temperature
- concentration gradient
- membrane surface area
- membrane thickness
- number of channel proteins
Which type of movement of particles requires ATP?
Active transport
Bulk transport
What does active transport require to occur?
ATP
Carrier proteins
Describe how active transport occurs with aid of a carrier protein
- molecules/ions bind to receptors in the channel of the carrier protein
- ATP binds to the opposite side of the carrier protein
- ATP is hydrolysed to form ADP and phosphate
- the phosphate molecule binds to the phosphate molecule to the carrier protein causes the protein to change shape
- carrier protein opens, allowing molecules through
- phosphate molecule is released and recombines with ADP to form ATP
- carrier protein returns to original shape
Why is active transport considered to be selective?
-specific substances are transported by specific carrier proteins
Define endocytosis
the bulk transport of material into cells
Define pinocytosis
the bulk transport of liquids into cells
Define phagocytosis
the bulk transport of solids into cells, most commonly the process by which white blood cells engulf pathogens
Define exocytosis
the bulk transport of materials out of a cell
Does bulk transport require ATP?
Yes
Why would a molecule be moved by bulk transport?
It is too big for channel or carrier proteins
Name 3 things which are moved by bulk transport
Enzymes, hormones, bacteria
Outline how phagocytosis occurs
- the cell surface membrane invaginates when it comes into contact with a bacterium
- the membrane then enfolds around the bacterium forming a vesicle around it
- the vesicle then pinches off and moves into the cytoplasm towards lysosomes
Outline how exocytosis occurs
- vesicles are usually formed by the golgi apparatus
- vesicles move towards and fuse with the cell surface membrane
- contents of the vesicle are then released outside of a cell
Name an example of exocytosis
Excretion
Why are ions only able to cross a membrane through a protein channel?
- protein channels provide a hydrophilic channel through the membrane
- ions cannot pass through membranes without them due to the hydrophobic centre of the phosphoplipid bilayer
How can the effect of surface area on the rate of diffusion be investigated?
- agar made with phenolpthalein and NaOH is pink as NaOH is alkai
- cubes of different sizes are placed in HCl
- In HCl the cubes will go colourless
- Leave for 5 minutes
- measure the volume of cube that is still pink
- calculate % diffusion
How can the effect of temperature on the rate of diffusion be investigated?
- an artificial cell is made from dialysis tubing
- solution is placed in cell
- cell is placed in water bath at different temperatures
- indicators can be used to see the rate of diffusion (e.g. iodine for starch or benedict’s solution for glucose)
What is the effect of a higher surface area to volume ratio on the rate of diffusion?
It increases the rate of diffusion
What is the symbol of water potential?
Ψ
What are the units of water potential?
kPa
What is water potential?
The pressure exerted by water molecules as they collide with a membrane or container
What is the Ψ of pure water?
0
Why does water potential decrease as solute is added?
- when a substance is dissolved in water the kinetic energy of the water is lowered
- because water molecules aggregate around the solute
- movement of water molecules is partially impeded
- so a lower pressure is exerted
What is a hypertonic solution?
having a higher concentration of solute relative to another solution
What is an isotonic solution?
having the same concentration of solute relative to another solution
What is a hypotonic solution?
having a lower concentration of solute relative to another solution
What is the usual water potential in animal cells?
About 50kPa
What would be the effect of placing a red blood cell in a hypotonic solution?
- net movement of water into the cell
- cell swells and bursts
- causing haemolysis
- cell contents lost, haemoglobin released
What would be the effect of placing a red blood cell in a hypertonic solution?
- net movement of water out of the cell
- cell shrinks and shrivels
- becomes darker in colour as haemoglobin is more concentrated
- crenation
What would be the effect of placing a plant cell in a hypotonic solution?
- net movement of water into cell
- cell becomes turgid
- protoplast pushed against cell wall
What would be the effect of placing a plant cell in a hypertonic solution?
- net movement of water out of cell
- contents shrink
- cell plasmolysed
- protoplast completely pulled away
When a plant cell is placed in a hypertonic solution, what fills the space between the cell wall and the protoplast?
the external solution with a more negative water potential
Why do plant cell walls not burst from osmosis?
- they have strong cellulose walls
- which are able to resist the hydrostatic prssure
What happens to the volume of cytoplasm when a plant cell is placed in a hypertonic solution?
-volume of cytoplasm decreases
How can the concentration of a potato be determined?
- weight pieces of equal size potato
- place in different concentrations of solution
- leave potato for the same time
- blot potato dry and reweigh
- calculate % change in mass
- plot on graph
- where line of best fit crosses 0 on x-axis shows concentration of potato
Define precision
the closeness of two or more measurements to each other
Define accuracy
the closeness of a measured value to a standard or known value
Define repeatbility
if you repeat the experiment, how close are you results to other results you have collected
Define reproducility
if someone else repeats the experiment how close are their results to yours
Describe the routes that water molecules take through the cell surface membrane
- diffuse between phospholipids
- move through aquaporins
