Membranes - Diffusion , Osmosis, and 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
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
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 pressure
What happens to the volume of cytoplasm when a plant cell is placed in a hypertonic solution?
volume of cytoplasm decreases
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
