Transport
- Created by: Charlotteeliseharrison
- Created on: 10-06-17 15:16
The cell membrane
The cell membrane is made from;
Phospholipids- hydrophillic heads point to outside of the cell and hydrophobic tails point into the center. Lipo-soluable can enter and leave thecells, prevent water soluable sources entering and leaving. Make the membrane flexible and self-sealing
Glycoproteins- recognition sites, maintain stability of membrane, help cells attach together to form tissues
Glycolipids- recognition sites, help cells recognise each other, helps cells attach together to form tissues
Proteins- protein carriers and channels, structural support, help adhere cells together, form receptors, transportation
The fluid-mosiac model shows the arrangement of materials in the cell surface membrane, the fluid is the flexible phospholipid and the mosaic is the proteins emmbedded.
Simple Diffusion
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distrubuted
This process involves no energy as it is passive
The particles move from an area of high concentration to an area of low concentration
Through the partially permeable membrane
Small, non polar molecules such as oxygen and carbon dioxide are the only molecules which can move using simple diffusion
Facilitated Diffusion
Some molecules can not diffuse that easily as they may be larger and polar so channel proteins and carrier proteins are needed.
This is still a passive process so without the use of ATP
Protein channels- form water-filled hydrophilic channels so water- soluable ions can pass through. These channels are selective so they open and close to allow molecules through
Carrier Proteins - the molecules are specific to each carrier protein so the molecule binds with the protein. This causes it to change shape so the molecule is released inside the cell
Osmosis
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
Solute- any substance dissolved in a solvent
Solution- a solute and a solvent together
Pure water has a water potential of 0
When a solute is added to water its water potantial decreases so becomes more negative
Only water can move by osmosis other molcules move using different transport systems
Water can move through proteins such as aquaporins
Animal cells such as red blood cells contain many solutes, if placed in pure water the cell will absorb the water by osmosis as water will travel to the lower water potential
Active Transport
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
ATP is used to directly move molecules
This ATP comes from aerobic respiration in the mitochondria
Up the concentration gradient from a low to high concentration
This process is very selective as only certain substances are transported and carrier proteins are used
Co-Transport
Co-Transport is a mixture of active transport and facilitated diffusion which moves more than one molecule at a time through the partially permeable membrane
Here a sodium Potassium pump is used to move two molecules - in this case sodium and glucose
Sodium ions are actively transported out of the epithelial cells, by the sodium- potassium pump, into the blood. This takes place in one type of protein carrier molecules
This maintains a much higher concentration of sodium ions in the lumen of the intestine than the epithelial cells
Sodium ions diffuse into the epithelial cell down the concentrayion gradient through a different (co transport) channel. As it diffuses through they carry a glucose molecule with them.
This glucose pass into the blood plasma by facilitated diffusion
Oral rehydration therepy
This is used to treat Diarrhoea.
There are many causes of diarrhoea from damage to the epithelial cells lining the intestine to loss of microvilli due to toxins.
To treat diarrhoea the patient needs to be rehydrated however just drinking water is uneffective as the water is not absorbed in the intestine and drinking water doesnt replace the electrolytes which are being lost from the cells.
A reydration solution needs to contain- water, sodium ions (to replace lost sodium), glucose (to stimute uptake of sodium via co-transport), pottassium (to replace those lost and stimulate appetite) and other electrolytes such as chloride and citrate.
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