Different types of transport in cells AS Biology

Diffusion is the movement of of mmolecules or ions from an area of high concentration to an area of low concentration until  they are equally spread out

things that affect the rate of diffusion

• how steep the concentration gradient is
• the size of the particle
• the thickness and surface area of a membrane
• the distance between the 2 regions
• temperature  ( Only a little bit )

the difference in the concentration of the two sites is called the concentration gradient

this is where proteins are used to move particules down the concentration gradient these proteins are called carrier proteins or channel proteins ( they are not the same thing but they do the same job)

Channel proteins help to move IONS which normally can not move through the membrane because of the hydrophobic tails in the centre of the membane the chennel membranes have polar groups in side them to aid diffusion the channel memebranes are often specific to a certain ion

carrier prtoeins are for biggrer molecules like sugars and amino acids. They bind to  the binding site and the protein then moves/ changes shape to move the molecule across the membrane  like the channelprotein the carrier protein only works for one molecule

in both of these cases the ion or molecule can travel in either direction across the membrane

this is a special type of diffusion which only occurs with water molecules

osmosis is the diffusion of water molcules from and area of high water potential ( a dilute solution) to an area of low water potenetial  ( a concentrated solution )through a partially permeable memebrane

a partially permeable mebrane is one that lets some things through but not all things

this is a particually important process in plants as it allows tham to maintain their structure and for this to happen a plant cell must be turgid  ( full , swollen) they can get to this state as they have cellulose cell walls however animal cells can not reach this state as they do not have cell walls so if a red blood cell was placed into pure water it will burst

a solution which is dilute has a high water potential ( a high tenancy to move about) where as a concentrated solution has a low water potential water will diffuse to the one with low water potential

Active transport requires energy - this is where you move something against its concentration gradient, this process gets its energy from ATP produced during respiration by mitochondria

this is done by specific carrier proteins but this time energy is needed 

• the ion /molecule binds 
• a phosphate group is knocked off an ATP molecule
• the change of shape happens on the carrier proteins
• and the molecule/ion ends up on the opposite side of the membrane 

here are a few processes which use this type of transport 

• roots when they take up nutrients
• protein synthesis 
• muscle contraction