cell membrane

phospholipids make up the plasma membrane they have the same structure as triglycerides but have a phosphate group instead of one of the fatty acid tails the membrane is made up of two layers of phospholipids which mirror eachother. the phosphate head is hydrophillic so is on the outside (exposed to extracellular fluids) and the fatty acid tails are hydrophobic so are on the inside

• allows lipid soluble substances to enter and leave the cell • to prevent water soluble substances from entering and leaving the cell • to make the membrane flexible and self sealing

channel proteins allow water soluble/polar/large molecules to pass through the membrane carrier proteins allow active transport across the membrane

cholesterol is very hydrophobic so prevents loss of water and dissolved ions from the cell. cholesterol also pulls the fatty acid tails of the bilayer together to provide structure and make the membrane less fluid in high temperatures

glycolipids are lipids with a carbohydrate chain covalently bonded to it they extend through the bilayer into the extracellular fluid to act as a receptor for chemicals they act as recogntion sites and provide structure to the membrane

glycoproteins are proteins with a carbohydrate chain bonded to it found on the surface of the embrane they act as receptors for hormones and neurotransmitters and also cell recognition- identidying cells as the organisms own cells

• to provide structural support • to act as receptors for chemicals e.g hormones • cell recognition

fluid refers to the way the molecules move relative to eachother- the membrane can be described to have a ‘liquid crystalline structure’ mosaic refers to the different components of the membrane- glycolipids, glycoproteins, phospholipid bilayer, cholesterol. channel and carrier proteins

the net movement of particles from a high concentration to a low concentration the particles will move both ways but the net movement will be to the area of low concentration until equilibrium is reached particles move down a concentration gradient diffusion is a passive process- no energy is required

small or lipid soluble molecules can pass straight through the membrane without the need for a carrier or channel protein

facilitated diffusion requires the use of channel or carrier proteins to allow polar/ water soluble or large molecules to pass through the membrane polar molecules are water soluble so would diffuse through the membrane slowly as the centre of the bilayer is hydrophobic

• a large molecule attaches to the carrier protein • the protein changes its shape • the molecule is released on the opposite side of the membrane

channel proteins form pores for charged particles to pass through the membrane, down a concentration gradient. different channel proteins facilitate the diffusion for different charged particles

• concentration gradient- the higher the concentration grafient, the faster the rate of diffusion. the net movement of particles will be down the gradient, but they will move both ways until equilibrium is reached • thickness of the exchange surface- the thinner the surface, the shorter the diffusion patheay therefore the rate of diffusion is quicker • surface area- the larger the surfae area, the faster the rate of diffusion e.g microvilli increase surface area

• concentration gradient- the higher the concentration gradient the faster the rate of diffusion. the particles will diffuse down the concentration gradient until equilibrium is reached • number of carrier/ channel proteins- if all the carrier/ channel proteins are in use, the rate of diffusion cant increase any more even if the concentration gradient is increased. so the more carrier/ channel proteins there are, the faster the rate of diffusion

osmosis is the net movement of water molecules from an area of high concentration to an area of low concentration through a partially permeable membrane

water potential is the likelihood of water molecules to diffuse in/out of a solution pure water has the highest water potential. all other solutions have a lower water potential

• water potential gradient- the higher the gradient, the faster the rate of osmosis • thickness of the exchange surface- the thinner the exchange surface is, the faster the rate of osmosis • surface area- the larger the surface area, the faster the rate of osmosis

• line up 5 test tubes in a rack • add 10cm of the sucrose solution to the first test tube. • add 5cm of distilled water to the other 4 test tubes • using a pipette, draw 5cm of the sucrose solution from the first test tube and place it in the second test tube. this test tube now has 10cm of solution half as concentrated as the first test tube (1M) • repeat this process for the other three test tubes to create solutions of 0.5M, 0.25M and 0.125M you’re diluting each solution by a factor of 2

• cut the potato into cubes that are roughly the same size • weigh the initial mass of each cube using a balance and record in your results table • place each cube in one of the 5 solutions of different concentrations • leave them in the solution for at least 20 mins then take out and pat dry with a paper towel to remove any excess water make sure all the cubes stay in their solution for the same amount of time • reweigh the potato cubes and record their final mass in your results table • calculate the change in mass of the potato cubes the potato chips will gain water in solutions with a higher water potential than the chips and lose water in solutions with a lower water potential

active transport uses energy (ATP) to move molecules and ions across membranes against a concentration gradient

carrier proteins are used for active transport in a similar way theyre used for facilitated diffusion a molecule attaches to the carrier protein, causing the protein to change shape. the molecule is moved across the membrane and released on the other side

1) active transport moves molecules from a low to high concentration (against the concentration gradient)- facilitated diffusion always moves molecules from high to low concentration 2) active transport requires energy- ATP is a common source of energy in the cell as it is produced by respiration ATP can also undergo hydrolysis into ADP and P (inorganic phosphate) which releases energy so molecules can be transported

1) the speed of the individual carrier proteins- the faster they work, the faster the rate of active transport 2) the number of carrier proteins present- the more proteins there are, the faster the rate of active transport 3) the rate of respiration in the cell and the availability of ATP- if respiration is inhibited, active transport cant take place