Cell membranes and transport Flashcards
Diffusion definition
net movement as a result of random motion of its molecules of a substance from a region of higher to lower concentration
How does steepness of concentration gradient affect rate of diffusion
about how large the difference is in concentration between two sides of the molecule
if one side is of much greatewr concentration of molecules, more molecules will have random motion so more going from high to low
diffusion rate increases
how does temperature affect the rate of diffusion
increased kinetic energy of molecules
faster movement so increased rate of diffusion
how does surface area affect rate of diffusion
greater number of molecules can diffuse at any given time
so Rate increases
can be caused by folding of cell membrabe
as SA:V ratio increases with size of cell, rate of diffusion slows as the distance becomes too large to diffuse through cell
size of molecule or ion affect on rate of diffusion
decreases rate as more energy is required for molecules to move
facilitated diffusion
transports what molecules
large
polar
charged
two types of proteins that enable facilitated diffusion:
channel and carrier
what are channel proteins
water-filled pores
allow charged substances to diffuse through the cell membrane
pores can open and close (gated) - this means that they control the exchange of ions
what are carrier proteins
carrier proteins switch between two shapes
only one binding site of the protein is open at a time
direction that molecules will diffuse through carrier proteins depends on the concentration of ions
osmosis definition
net diffusion of water molecules from high to low water potential
through a partially permeable membrane
water potential definition
tendency of water to move out of a solution.
water potential of a dilute solution
high
water potential of a concentrated solution
low
water potential of pure water
0Kpa
cell membrane of plants and animal cells with relation to osmosis
partially permeable with phospholipid bilayer - water is free to move by osmosis
cell wall of plants (relating to osmosis)
composed of cellulose
fully permeable
what happens when a plant cell is placed into a solution with low water potential
water leaves the cell through cell membrane
volume of cell decreases
protoplast pulls away from the cell wall
cell is plasmolysed
what happens when an animal cell is placed into a solution with low water potential
water leaves cell through membrane
volume of cell decreases
cell shrivels
what happens when a plant cell is placed into a solution with high water potential
water enters cell
protoplast expands against the cell wall
cell is turgid as cell wall withstands pressure
no more water can enter
what happens when an animal cell is placed into a solution with high water potential
water enters cell through cell membrane by osmosis
volume of cell increases
no cell wall to withstand turgor pressure
cell membrane bursts
Experiment for investigating the water potential using calibration curves
Immersing plant tissues in different solutions of different water potentials
Use results to estimate the water potential of plant tissue itself
Potato cycling’s water potential calibration curve test method
Cut all potatoes to same length and shape
Blot dry
Record initial mass
Place potatoes into solution for 30min at 30degrees
Remove and dry excess liquid
Final mass of each potato cylinder is recorded
Plot a graph of change of mass and concentration of sucrose
Results achieved from calibration curve osmosis experiment
For both 0 percent sucrose and 0.2 , the potato cylinders gained weight. This is as water moves from the higher water potential solution into the lower water potential potato.
All other sucrose concentrations, the potato loses mass. This is as there is a lower water potential outside than inside the plant tissue. This means that water moves out of the cell.
How to calculate percentage change
(Final mass -initial mass) / initial mass. X 100
Active transport definition
Movement of molecules and ions through a cell membrane from a region of lower to higher concentration using ATP
What type of protein in the cell membrane does active transport use
Carrier proteins
Specific for a particular type of molecule of ion
How does AT use carrier proteins
ATP makes the carrier proteins change shape allowing it to transfer the molecules or ions across the cell membrane
factors which rate of diffusion depends on
temperature
thickness of exchange surface
surface area of exchange surface
concentration gradient
affect of surface area on rate of diffusion (simple)
the larger the SA, the higher the rate as more molecules can diffuse at a given time
affect of concentration gradient on rate (simple)
rater increases with increasing concentration gradient as higher conc on one side.
as diffusion occurs, conc gradient slowly decreases thus decreasing rate
affect of TOES on rate (simple)
thicker = longer diffusion distance which decreases rate
affect of concentration gradient on rate
(facilitated)
higher rate with more conc on one side
dependant on the number of carrier and channel proteins available
number of channel or carrier proteins affect on rate of diffusion facilitated
these proteins are required. Once all the carrier and channel proteins are used up , rate cannot increase any further. more channel and carrier proteins = more rate
root hair cells adaptations to diffusion
adapted for the absorbtion of water and mineral ions from soil
shape increases the surface area - rate of water uptake by osmosis is greater
thinner walls means less diffusion distance
permanant cell vacuole containing cell sap which is more concentrated that high water potential gradient is maintained
experiment for factors affecting membrane fluidity method
cut 5 equal size cubes of beetroot
rinse the beetroot peices
add pieces to 5 test tubes containing same vol of water
put each tube in different temp water baths
leave 30min
remove beetroot pieces leaving just liquid
use a colorimeter to test how permeable the membrane is
experiment for factors affecting membrane fluidity results
as temperature increases, membrane permeability increases
as phospholipids gain more energy so move more and are less tightly packed
temperature also affects the 3D shape of proteins as at high temperatures the inter molecular forces between amino acids are broken.
how does PH affect membrane fluidity
Excess OH and H ions disrupts the amino acids in the proteins which disrupts function.
fluid mosaic model explains
movement of molecules
cell to cell interactions
cell signalling
phospholipid structure
phosphate head (polar and hydrophilic) and 2 fatty acid tails (non polar and hydrophobic)
forms a bilayer
phospholipids can move (FLUID mosaic)
cholesterol function
regulate the fluidity of the cell membrane
glycolipid function
lipids with carbohydrate chains added.
project out whatever fluid is surrounding the cell
glycoprotein function
proteins with carbohydrate chains added
also project out whater fluid is covering the cell
