1.3 Flashcards
Why do phospholipids form a bi-layer in water and describe how they’re arranged
Due to the hydrophilic head and hydrophobic tails
Polar heads face outwards interacting with water outside the cell and inwards interacting with the water in the cytoplasm
What is an extrinsic protein
Found on either surface of the bilayer
Function of extrinsic proteins
Act as receptors for hormones and as recognition sites
What is an intrinsic protein
Proteins that are found within the membrane and extend across both layers
What are the 2 kinds of intrinsic proteins
Channel and carrier
Why is the membrane said to be representative of the fluid-mosaic model?
Fluid - phospholipids are free to move
Mosaic - random assortment of protein molecules
Animal or plant cell membrane contains cholesterol and what does it do
Animal
Stabilises the membrane
Function of glycoproteins
Act as antigens
Function of glycolipids
Act as receptor sites for molecules eg hormones
What kind of molecules pass through simple diffusion
Non-polar molecules and small molecules
They can dissolve in the fatty acid tail and diffuse across the membrane
What is diffusion
The passive movement of molecules from a high concentration to a low concentration until they’re equally distributed
What does passive mean
Doesn’t require ATP
Does simple diffusion transport individual molecules
Yes
Factors affecting diffusion
- concentration gradient
- diffusion distance
- surface area of the membrane
- thickness of the exchange surface
- increase in temperature
How does increase in concentration gradient affect rate of diffusion
More molecules can diffuse in a given time so collisions with membrane are more likey
How does decrease in diffusion distance increase rate of diffusion
Less time for molecules to diffe
How does increase in surface area of the membrane increase rate of diffusion
More molecules can diffuse in a given time
How does thickness of the exchange surface affect rate of diffusion
Increases with a shorter distance as less time is taken to diffuse
How does increase in temperature increase rate of diffusion
Molecules possess more kinetic energy so they move faster and collide with the membrane more frequently
Graph of simple diffusion is
Directly proportional
What kind of molecules pass through facilitated diffusion?
Polar, water soluble and large
What is facilitated diffusion
Passive transfer of molecules/ions down a concentration gradient, across a membrane, by transport proteins in the membrane
Which kind of intrinsic protein allows charged molecules through
Channel
Which kind of intrinsic protein allows large and water soluble molecules through
Carrier
What is active transport
Movement of ions/molecules across the membrane from a low to high concentration against the concentration gradient, this is an ATP requiring process
Carrier proteins
How does cyanide affect active transport?
Prevents aerobic respiration and ATP production
Without ATP active transport cannot occur
Why does the graph of facilitated diffusion and active transport plateau after a while
The proteins are saturated
What is co-transport
Type of facilitated diffusion that brings molecules + ions into cells together on the same carrier protein
Example of co-transport
Glucose and sodium ions
Mechanism by which glucose is absorbed in the ileum of mammals
What is osmosis
the net passive diffusion of water molecules across a selectively
permeable membrane from a region of higher water potential to a region of lower water potential.
What is water potential
A measure of the tendency of water molecules to move from a high to low concentration of water
What is pressure potential
represents the pressure exerted by the cell contents on the cell wall.
It can be OkPa or higher.
What does a turgid plant cell mean
the plant cell can hold no more
water, as the cell wall cannot expand further.
What is a hypertonic solution
Has a lower water potential than the solution inside the cells
Water flows out of the cell
What is a hypotonic solution
Higher water potential than the solution inside the cell
Water flows into the cell
What is an isotonic solution
Has the same water potential to the solution inside the cell
No net water movement
What is solute potential
Concentration of dissolved substance in the cell vacuole
When is a plant cell said to be flaccid and how does it happen
When plasmolysis is complete
When a plant cell is in a hypertonic solution so the vacuole shrinks and cytoplasm draws away from the cell wall
What is the point of incipient plasmolysis
Point at which the cell membrane just begins to move away from the cell wall
What is the pressure potential during incipient plasmolysis
0 kPa
What is the solute potential during incipient plasmolysis
= water potential
Why is being turgor important in plants - especially young seedlings
It provides support
Maintains their shape and holds them upright
What % of cells are plasmolysed during incipient plasmolysis
50
What will happen to red blood cells in a hypotonic solution
Haemolysis - burst
What will happen to red blood cells in a hypertonic solution
Said to be crenated
Why will animal cells burst but not plant
Lack of cell wall to resist bursting
What are 3 factors that affect permeability of membrane
Temperature , pH and ethanol
How does temperature and pH beyond normal range affect permeability
Denature the membrane’s proteins which makes gaps in the membrane and it is far more permeable
How does ethanol increase permeability of the membrane
Dissolves the lipid components of the membrane and makes holes in it
Which kind of transport doesn’t transport molecules or ions individually
Bulk - endocytosis and exocytosis
What does endocytosis involve
Engulfing of the material by infolding of the plasma membrane bringing it into cell enclosed within a vesicle
What are the 2 kinds of endocytosis
Phagocytosis- solid (that are too large)
Pinocytosis - liquid
How does exocytosis work
Substances leave the cell after being transported through the cytoplasm in a vesicle
Membrane width
7-8 nm
