Transport across cell membranes
Transport across cell membranes
Responsible for the transport of glucose and other amino acids across the membrane.
Sodium ions are actively transported from the epithelial cells into the blood using a specific carrier protein and energy from the hydrolysis of ATP
Glucose or amino acids and sodium ions are co-transported from the lumen of the small intestine into the epithelial cell across the membrane by facilitated diffusion down the sodium ion concentration gradient.This involves a specific carrier protein that will only carry glucose and sodium ions
The glucose or amino acid then moves into the blood via facilitated diffusion using a specific carrier protein as it is going from an area of high concentration to an area of low concentration
If ATP production is inhibited then Active transport can not occur preventing sodium ions from leaving the cell. This means the concentration of sodium ions will rise in the cell which would stop the absorption of glucose because sodium ions won't be able to diffuse down the concentration gradient. Preventing facilitated diffusion from the lumen.
This is used to transport molecules against the concentration gradient
From an area of high concentration to an area of low concentration
It requires a specific carrier protein
It requires energy from the hydrolysis of ATP
Cells that use active transport will have lots of mitochondria for respiration and production of ATP for its hydrolysis
Rate of diffusion
Factors that effect rate of diffusion
Temperature: Increases the kinetic energy of the molecules so they move faster.
Surface area: Larger area for molecules to pass through therefore the rate is faster.
Concentration gradient: As concentration difference increases the rate increases.
Diffusion distance: The thinner the surface the faster the molecules will travel across it
Diffusion is a passive process and does not require energy from the hydrolysis of ATP
Diffusion is the net movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane
Free water molecules collide with the membrane which creates pressure on the membrane. This is know as water potential and because it is pressure it is measured in kPa.
Pure water has the highest water potential because it has the most free water molecules and is given the value of 0.
The larger the concentration of water molecules the closer the water potential is to 0.
Therefore by adding a solute it makes the water potential more negative
Hypotonic: results ion the cell swelling and lysis (bursting an destruction of the cell). This occurs when there is a high water potential outside the cell and a low water potential inside the cell.
Hypertonic: Results in the cell shrivelling. High water potential inside the cell low water potential outside the cell.
Isotonic: No net movement of water in or out of cells the water potential is the same inside and outside the cell.
Osmosis is the net movement of water molecules from a solution with a high water potential to a solution with a low water potential through a partially permeable membrane
Hydrophillic substances cannot pass through the hydrophobic phospholipid bilayer. Instead they move through the membrane via channel proteins or carrier proteins
Channel proteins are specific due to their tertiary structure which means they only transport specific molecules