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12286909
Cell Membrane
Description
A2 Biology (Section 2) Mind Map on Cell Membrane, created by Dominic Weston on 15/02/2018.
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biology
section 2
a2
Mind Map by
Dominic Weston
, updated more than 1 year ago
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Created by
Dominic Weston
over 6 years ago
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Resource summary
Cell Membrane
Membranes
All cells surrounded by membranes
In eukaryotics surrounds some organelles too
Acts as a barrier to control what enters or leaves
Partially permeable - allows some molecules through
Can move through by diffusion, osmosis or active transport
Fluid mosaic model
Composed of lipids, proteins, carbohydrates
Phospholipids form a continuous bilayer
Bilayer is fluid as it moves continuously
Cholesterol are present in the membrane
Proteins scattered throughtout like a mosaic
Polysaccharides can attach to proteins and lipids
Glycolipid, Glycoprotein
Different components play different roles
Phospholipids form a barrier to dissolved substances
As hydrophobic centre of bilayer repels water
Cholesterol provides stability
Cholesterol is present in all cell membranes except bacteria
Does this by binding between phospholipids to the hydrophobic tails
Causes them to pack closer together, restricting movement making it more ridgid
Important for animal cells with no cell wall
Important for RBC that arent supported by other cells
Proteins in membranes have many functions
Include channel proteins, carrier proteins, and receptor proteins
Permeability test
Changing temperature changes the membrane permeability
Below 0
Phospholipids pack close together and become rigid
Channel and carrier proteins deform, increasing permeablility
Any ice that forms can pierce the membrane causing very high permeablility
0-45 celsius
Phospholipids move around and the higher the temp the more permeable it is
Above 45
Bilayer starts to melt
Water expands, puts pressure on membrane
Proteins deform increasing permeability of cell membrane
Simple Diffusion
Net movement of particles, molecules, or ions from an area of high to low conc down its conc gradient
Can diffuse across membranes as long as they can move freely through the membrane
When diffusion directly across a membrane its called simple diffusion
Higher conc gradient the faster the rate of diffusion
Microvilli increase surface area for faster diffusion
Passive process - no energy used
Osmosis
Net Diffusion of water molecules across a partially permeable membrane
From an area of high water potential to low water potential
Water potential (WP) is likelihood of water molecules to diffuse in or out of a solution
Equal WP of solution said to be isotonic
Rate depends on factors
WP gradient, Higher gradient, faster conc
As solutions undergo osmosis, difference in WP decreases
Rate of osmosis levels off over time
Thickness of exchanged surface
Thinner the osmosis path the faster rate of osmosis
Surface area of exchange surface
Larger S.A. the higher rate of osmosis
Investigating WP Using serial Dilutions
Make five serial dilutions of sucrose solution by a known factor
Add identical potato cylinders in solutions
After 20 mins, dry chips and weight each chip
Calculate the % change in mass
Net movement of water from a less negative WP to a more negative WP
Active Transport (AT)
Active process - uses energy in form of ATP
Usually movement of molecules and ions against a conc gradient
Carrier proteins used to move molecules from low to high conc
Molecule attaches to protein, causing it to change shape, moving molecule across membrane
Co-transporters are a type of carrier protein used in AT
Bind two molecules at a time
High to Low conc gradient used for one of the molecules used to move the other one against its conc gradient
Facilitated Diffusion
Passive
Large molecules, ions, and polar molecules diffuse slowly across membranes
Number of Channel and carrier proteins increase rate of diffusion of these molecules/ions
Higher conc gradient the faster the rate of diffusion
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