| what are the properties of gas exchange surfaces? | surface area to volume ratio
concentration gradient
diffusion distance |
| Fick's Law | rate of diffusion ∝ (surface area x difference in concentration)/thickness of exchange surface |
| how is the mammalian lung adapted for rapid gaseous exchange? | large network of capillaries surrounds a lot of alveoli to provide large surface area
capillaries and alveoli are each 1 cell thick so short diffusion distance
constant blood circulation and breathing maintains concentration gradients |
| cell membrane role | protects the cell from its surroundings
controls what enters and exits the cell
has receptors that receive chemical messages from other cells to help signal processes that need to occur in the functioning of the whole organism |
| structure of a cell membrane | phospholipid bilayer, channel proteins, glycoproteins, glycolipids, aquaporins, cholesterol |
| what is the phospholipid bilayer? | the main component of the cell membrane
made of hydrophilic phosphate polar heads and hydrophobic fatty acid non-polar tails
the heads point outwards whilst the tails point inwards |
| meaning of hydrophobic | does not like water |
| meaning of hydrophilic | likes water |
| what are channel proteins? | proteins integrated into the phospholipid bilayer that allow certain molecules to pass through as they cannot enter the cell by simple diffusion
involved in facilitated diffusion |
| what are glycoproteins? | a carbohydrate chain attached to membrane proteins
involved in cell to cell recognition and binding of other molecules |
| what are glycolipids? | carbohydrate and lipid chain attached to the phospholipid heads
involved in cellular recognition
can acts as receptors for viruses |
| what are aquaporins? | a type of channel protein involved in the transportation of water into and out of cells |
| what is cholesterol in a cell membrane? | the part protein-part lipid molecule embedded within the phospholipid bilayer that regulate membrane fluidity |
| what are carrier proteins? | membrane protein involved in facilitated diffusion and active transport |
| what is the fluid mosaic model? | the model used to describe the cell membrane structure
'fluid' - because the membrane is able to move quite freely
'mosaic' - because the membrane is made up of many molecules that follows no distinct pattern or symmetry |
| who proposed the fluid mosaic model? | Singer and Nicholson |
| what other models were proposed before the fluid mosaic model? | Davson-Danielli model |
| how was the Davson-Danielli model proposed? | electron micrograph images inspired the model
3 layer protein lipid sandwich |
| why was the Davson-Danielli model wrong? | the electron micrograph image showed the membranes of two adjacent cells instead of the phospholipid bilayer
researchers showed that some proteins were able to disassociate whilst other not, implying some proteins were embedded into the bilayer
added label proteins only bound to the outside of the bilayer proving the sides were asymmetrical |
| membrane permeability experiment | can be done using temperature or alcohol concentration
5 water baths from 0 to 50
cut 5 beetroot cores must be from the same source and cut to the same length
rinse off the beetroot so excess membrane/pigment is washed away
place beetroot in test tubes in each water bath and wait for 30 mins
set the colorimeter to blue-green filter
syringe a sample of each beetroot solution into a cuvette
place each cuvette sample into the colorimeter and record the absorbance value
after each reading zero the colorimeter with a cuvette of distilled water
repeat these steps to get a mean average reading of absorbance |
| osmosis | the free movement of water molecules through a partially permeable membrane from an area of low solute concentration to an area of high solute concentration |
| passive transport | diffusion and facilitated diffusion
no energy is provided for the movement of the molecules across the membrane
down the concentration gradient - molecules move from an area of high concentration to an area of low concentration |
| diffusion | the passive movement of small, non-polar, lipid-soluble molecules, like carbon dioxide and oxygen, through a partially permeable membrane from an area of high concentration to an area of low concentration - down the concentration gradient |
| facilitated diffusion | the movement of polar, charged, water-soluble molecules across a partially permeable membrane
require a channel protein in the cell membrane
down the concentration gradient: moves from an area of high concentration to an area of low concentration |
| active transport | the movement of molecules across a membrane from an area of low concentration to an area of high concentration - against the concentration gradient
requires energy in the form of ATP provided by the cell
uses carrier proteins in the membrane |
| endocytosis | bulk transport of large molecules into the cell via vesicle formation
requires energy in the form of ATP
vesicle forms around the molecules as it enters the cell
examples: phagocytosis and pinocytosis |
| exocytosis | the bulk movement of large molecules out of the cell
vesicle full of molecules will fuse with the membrane and release the molecules
requires energy as ATP because its an active process |
