2. cell membranes

lipids

diverse group of non polar molecules including fatty acids, triglycerides, phospholipids and cholesterol, they only dissolve in organic (non polar) solvents

emulsion test

test for lipids by adding ethanol, shaking then pouring in to cold water, turns white if lipids present

fatty acid

either saturated or unsaturated, have a hydrocarbon chain and a COOH group at one end

triglycerides

formed by condensation reaction to join 3 fatty acids to glycerol forming 3 ester bonds

fat

triglycerides with mostly saturated fatty acids, store in animals

oil

triglycerides with mostly unsaturated fatty acids, store in plants

triglycerides use

energy store (adipose tissue in animals/seeds and fruits in plants)

thermal insulation (layer beneath skin)

provides buoyancy

protection- shock absorber for vital organs

lipase

enzyme which breaks down triglycerides into fatty acids and glycerol

phospholipid

contains 2 fatty acids joined to a glycerol by ester bonds and has a phosphate group

phospholipid bilayer

double membrane made up of phospholipids with hydrophilic heads on outside and hydrophobic fatty acid tails in centre, act as barrier to movement of polar molecules and ion say allow non polar molecules across

glycolipids

modified phospholipids with a carbohydrate chain (sugar) instead of phosphate group, act as antigens for recognition and adhesion to form tissues

choline and serine

example of what can be added to phospholipids

cholesterol

small non polar molecule with a single polar -oH group at one end, used for synthesis of steroid hormone and in membrane between phospholipids which stabilises them by binding to fatty acid tails, controls fluidity and prevents polar molecules and ions crossing membrane 

fluid mosaic model

used to represent the plasma membrane as the molecules are able to move around within monolayer (unless anchored by cytoskeleton) and describes the appearance of the different molecules

outer surface

side which contains carbohydrate chains of glycolipids and glycoproteins that project from cell surface to from glycocalyx

proteins

act ac channels or carrier for polar molecules and ions across membrane by facilitated diffusion or active transport, also act as enzymes eg ATP synthase

glycoproteins

modified in Golgi apparatus by addition of carbohydrate chain, act as antigens for cell recognition as self or non self, act as receptors for chemical signals like hormones, cell adhesion to form tissues

intrinsic

proteins which are embedded in phospholipid bilayer and often span the bilayer

extrinsic

proteins are not embedded in phospholipid bilayer but are associated with one side of the membrane

passive trasport

process of molecules moving by simple diffusion requiring no addition energy

fascinated diffusion

large molecules which cannot pass through membrane without a specific transport protein, they move down their concentration gradient

channel proteins

provide a hydrophilic channel or pore though hydrophobic interior of phospholipid bilayer, specific to small molecule or ion, either open all the time or gated by a ligand or voltage

carrier proteins

bind to specific polar molecule and change shape to relate molecule on other side of membrane

active transport

transport of a molecule from low to high concentration against the gradient, requires specific carrier protein or pump and energy (ATP)

bulk transport

movement of large quantities of materials into or out the cell using vesicles, requiring ATP

exocytosis

movement out the cell eg hormones secretion

endocytosis

movement into the cell eh phagocytosis

4, 1, 3, 2, 5

process of endocytosis and exocytosis


1. Lysosome containing hydrolytic enzymes fuses with phagocytic vesicle
2. Soluble products of digestion are absorbed into the cytoplasm
3. Lysosome releases digestive enzymes into vesicle; these break down the

nutrient particles
4. Nutrient particle is taken up by endocytosis, plasma membrane surrounds the nutrient particle and fuses with itself, pinching off to form a phagocytic vesicle
5. Insoluble, undigested material is removed from the cell by exocytosis as the vesicle fuses with the plasma membrane

surface area

allows more diffusion to take place, resulting in faster rate of diffusion

distance

molecules take longer to move further so slows rate of diffusion

concentration gradient

greater the difference between the sides the faster the diffusion

temperature

provides molecules with kinetic energy to move more and increase rate of diffusion

size of particle

larger molecules move slower and don’t fit as easily between phospholipids so slow rate of diffusion

type of particle

non polar can diffuse directly through bilayer, large polar pr charged molecules and ions require transport protein to cross membrane so rate if effected by number or proteins

agar block

used to measure rate pd diffusion by adding pH indicator phenolphthalein and seeing how the block changes from pink to colourless has H+ diffuse from centre

visking tubing

used to separate a solution of starch from the spring iodine and water solution, starch turns blue black after 20 mins and solution turns yellow brown when tested with iodine solution

effect of temperature on membrane fluidity

use beetroot cylinders in different water baths and use a colorimeter to determine the colour change in the water

unsaturated

kind of phospholipid which makes the membrane more permeable and fluid cell

cell signalling

chemical signal binds to receptor in plasma membrane which may lead to production of second intracellular messenger inside the cell to trigger cellular response