role of membranes at the surface of the cell
-substances leave and enter via the cell
-partially permeable
-substances move via diffusion, active transport and osmosis
-allow cell signalling
role of membranes within cells
-compartmentalisation
-provide attachment site for enzymes
-site of chemical reactions
fluid mosaic structure
-describes the arrangement of molecules in the membrane
-contains a bilayer
-“fluid” because its constantly moving
-cholesterol is present
-protein molecules are scattered like tiles in a mosaic
-proteins have polysaccharide chains ->glycoprotein
-lipids have polysaccharide chains ->glycolipids
role of the mosaic components for phospholipid
phospholipid:
-hydrophobic tail and hydrophilic head
-arrange themselves in a bilayer
-centre is hydrophobic so doesn’t allow water substances-acts as a barrier
-fat soluble substances can dissolve in the bilayer
cholesterol:
-lipid
-fit between phospholipids
low temp.->prevents phospholipids from packing to closely together (increases fluidity)
high temp.->causes them to pack too closely together, makes the membrane less fluid
role of the cholesterol for mosaic components
cholesterol:
-lipid
-fit between phospholipids
low temp.->prevents phospholipids from packing to closely together (increases fluidity)
high temp.->causes them to pack too closely together, makes the membrane less fluid
role of the mosaic components for proteins
channel proteins-allow small or charged particles through
carrier proteins-transport big molecules and ions across the membrane via active transport and facilitated diffusion
role of the mosaic components for glycolipids and glycoproteins
-stabilise the membrane by forming H bonds with surrounding water molecules
-site where drugs, hormones and antibodies bind
-act as receptors for cell signalling
-antigens
how temperature affects membrane permeability
below 0C:
-pack closely together and rigid
-channel and carrier proteins deform, increasing the permeability.
-ice crystals pierce the membrane making it highly permeable when it thaws
between 0C-45C
-phospho. can move around
-membrane is partially permeable
-as temp. increases, the permeability increases too
above 45C
-phospho. start to melt and become more permeable, water in cell expands
-channel and carrier proteins deform-increases the permeability of the membrane
how solvents affect the membrane permeability
solvents e.g ethanol increase the permeability
-solvents dissolve the lipids so they lose their structure
-some solvents increases cell permeability more than others e.g ethanol increases more than methanol
-increasing the conc. of the solvent increases the permeability
practical for factors affecting membrane structure
diffusion as a passive method of movement
-net movement of particles from an area of high conc to a lower conc.
-molecules diffuse both ways, but net movement is to a lower conc.
-no energy is needed
-particles diffuse down a concentration gradient
factors affecting diffusion rates in modal cells-practical
factors that affect the rate of diffusion
-the concentration gradient
-thickness of exchange surface
-the surface area
-temperature
facilitated diffusion
-when molecules move particles down a concentration gradient via carrier and channel proteins (for large molecules, ions and polar molecules) in a cell membrane
-passive process
active transport
-uses energy to move molecules and ions across plasma membranes against a conc. gradient, involves a carrier protein
-molecule attaches to carrier protein ,protein changes shape and moves across the membrane, releasing it on the other side
-ATP is used to move the solute against the conc gradient
endocytosis
-molecules can be too large to be taken into cells via a carrier protein
-A cell can surround a substance with a section of its plasma membrane
-membrane pinches off to form a vesicle containing ingested substances inside
-uses ATP for energy
exocytosis
Exocytosis is the process by which materials are removed from, or transported out of, cells
The substances to be released (such as enzymes, hormones, or cell wall building materials) are packaged into secretory vesicles formed from the Golgi body
These vesicles then travel to the cell surface membrane
Here, they fuse with the cell membrane and release their contents outside of the cell
movement of water across membranes by osmosis
-diffusion of water molecules across a partially permeable membrane down a water potential gradient
-water move from an area of higher water potential to a lower water potential
-water potential is the potential of water molecules to diffuse in and out of a solution
-pure water has the highest water potential of 0
effect solutions of water have on animal cells
hypotonic solution - solution has a higher water potential than the cell (net movement of water is into the cell, cell bursts)
hypertonic solution - solution has a lower water potential than the cell (net movement of water is out of the cell, cell shrinks)
isotonic solution-solution has the same water potential was the cell (water pass into and out of the cell in equal amounts, cell stays the same)
effect solutions of water have on plant cells
hypotonic solution-net movement is into the cell, vacuole swells cell becomes turgid
hypertonic solution- net movement is out of the cell, cell becomes flaccid cell is plasmolysed
isotonic solution-water molecule ,moves into and out of the cell in equal amounts, cell stays the same
explain how anomalous result affects the precision of data obtained
- reduces repeatability of data
- increases the standard deviation
What are the 2 types of endocytosis
pinocytosis and phagocytosis
whats phagocytosis
This is the intake of pathogen by a cell ( phagocyte)
whats pinocytosis
This is the bulk intake of liquids
