(U1) Cell Physiology Flashcards
What is simple diffusion? (2)
- The net movement of a substance
- down the concentration gradient
What factors affect simple diffusion and how? (5)
- concentration gradient: greater = faster diffusion
- size of molecule: smaller = faster diffusion
- temperature: higher = quicker (more kinetic energy)
- thickness of exchange surface: thinner = faster diffusion
- surface area of membrane: greater SA = faster diffusion
What proteins are involved in facilitated diffusion? (2)
- carrier proteins
- channel proteins
How do carrier proteins facilitate diffusion? (3)
- take in the polar diffusing molecule
- change shape due to specific receptor sites bonding to the molecule
- release molecules on the other side
How do channel proteins facilitate diffusion? (3)
- central pore allows polar molecules to pass through e.g. ions
- some permanently open, others gated
- gated channels open or close to control movement
What factor affects the rate of facilitated diffusion that doesn’t affect simple diffusion?
Number of channel or carrier proteins
Why does a graph showing increasing concentration and rate of uptake of a membrane for facilitated diffusion level off?
Lack of availability of carrier / channel proteins —> saturated membrane
What is active transport? (2)
- net movement of substances against the concentration gradient
- requiring ATP
What are the differences between active transport and facilitated diffusion? (2)
- AT: substances moved against concentration gradient, FD opposite
- AT requires ATP, FD does not
What does cytosis transport? (2)
- large molecules too big for carrier proteins
- bulk transport of smaller molecules e.g. water
What is endocytosis?
Movement of substances into the cell
Outline endocytosis (3)
- cell membrane invaginates around substance entering cell
- forming a vesicle which pinches off inside the membrane
- membrane reforms
What are the 2 types of endocytosis?
Describe both
- Phagocytosis: transport of solid material into cell e.g. engulfing bacteria by phagocytes
- pinocytosis: transport of fluid into cell
What is exocytosis?
Describe it
- Movement of substances out of the cell
- secretory vesicles fuse with cell surface membrane
- contents of vesicle released outside cell
State the equation linking solute potential, water potential and pressure potential
Ψcell = Ψs + Ψp
Water potential of cell = solute potential + pressure potential
What is osmosis? (4)
- net movement of water molecules
- through a selectively permeable membrane
- from a solution of less negative water potential / higher water potential
- to a solution of more negative water potential / lower water potential
What is the name of channel proteins that allow water through?
Aquaporins
What is the difference between hypotonic and hypertonic solutions?
- hypotonic = more water, hypertonic = less water
- hypotonic = lower solute potential, hypertonic = higher solute potential
What name is given to 2 solutions of equal concentration / water potential
Isotonic solutions
What is water potential? (3)
- tendency to take in water by osmosis
- from pure water
- across a selectively permeable membrane
What unit is water potential measured in?
KPa (kilopascals)
What the water potential of pure water?
Why?
- 0 kPa
- no water molecules form associations with other molecules
What do molecules of water form around solutes?
Hydration shells (largely made up of hydrogen bonds)
What is the impact of greater concentration on water potential?
What does this cause?
- More negative water potential
- cell is more likely to take in water by osmosis
What is solute potential? (2)
- potential of a solution to take in water by osmosis
- relates to solute concentration
What factor affects water potential, but doesn’t affect solute potential?
Space in a cell which alters pressure potential —> turgid cell means lower water potential
What is pressure potential? (2)
What values can it have?
1.
- the effect of pressure on the solution
- influences the ability of a cell to take in water
- +ve kPa, but can be 0kPa
What structure exerts pressure potential in a plant cell?
Cell wall
What is turgor? (2)
- The force exerted by the cell membrane on a cell wall
- by having a full vacuole
When are plant cells described as being flaccid? (2)
On a large scale what does this cause?
- when cells lack turgor pressure due to not having a full vacuole,
- therefore the cell membrane doesn’t press against the cell wall
- Wilting
What is plasmolysis? (3)
- vacuole loses water by osmosis
- shrinks the contents of the cell
- pulls membrane from the cell wall
What is incipient plasmolysis? (2)
- the point at which a plasmolysed cell membrane first makes contact with the cell wall
- or the last time a flaccid cell has its membrane touch its cell wall
What is the effect of increasing water potential outside a cell on:
- Ψcell
- Ψp
- Ψs
Inside a cell
(2)
(until incipient plasmolysis)
- as cell takes in water, contents become less concentrated, Ψs rises
- No Ψp to restrict water uptake as cell wall isn’t in contact with cell membrane, therefore Ψs = Ψcell (both rise together)
What is the effect of increasing water potential outside a cell on:
- Ψcell
- Ψp
- Ψs
Inside a cell
(2)
(at incipient plasmolysis)
- Ψp becomes positive and starts to hinder water entering the cell
- therefore Ψcell and Ψs diverge —> graphs don’t increase together
What is the effect of increasing water potential outside a cell on:
- Ψcell
- Ψp
- Ψs
Inside a cell
(3)
(at full turgor)
- max Ψp between cell membrane and cell wall
- Ψcell = 0 —> no further water can enter
- Ψs is still negative as solutes are still present in the cell
