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2.3 transport across membranes - Coggle Diagram
2.3 transport across membranes
lesson 1: phospholipids & membrane structure
phospholipid's form bilayers in water with a hydrophobic core, the hydrophilic heads point towards water and the hydrophobic tails point away from water
plasma membrane structure
cholesterol
adds strength to membrane, prevent water loss, reduce lateral movement/fluidity of membrane, phospholipid bilayer
channel proteins
water filled tubes, completely span phospholipid bilayer, have a hydrophilic channel through the center, allow water soluble/polar ions to diffuse acorss the membrane (also help adhere cells together and provide structural support)
carrier proteins
embedded in phospholipid bilayer, span the membrane, have a binding site specific to a particular molecule or ion, bind to ions or molecules like glucose and amino acids then change shape in order to move molecules across membrane, allow active transport
glycoproteins and glycolipids
act as a recognition site and cell surface receptors for hormones and neurotransmitters, help maintain stability of the membrane
fluid mosaic model
called fluid as phospholipids and components can move laterally and mosaic as the components are embedded unevenly in the phospholipid bilayer
what makes it a model? scientists and researchers have agreed upon the fluid mosaic model based on experimental and chemical data
lesson 2: diffusion
the movement of particles of a substance down a concentration gradient from an area of high concentration to an area of low concentration
diffusion is passive - does not require energy from ATP
simple diffusion
diffusion across a phospholipid bilayer, non polar (lipid soluble) molecules can diffuse across the phospholipid bilayer, small uncharged polar molecules can also diffuse across the bilayer (not as efficiently though)
facilitated diffusion
passive, involves either carrier or channel proteins
channel proteins
provide a specific polar route through the membrane, only open if a specific ion is present, remain closed if not
allow charged/polar substances to diffuse through the membrane
carrier proteins
provide specific pathways for large molecules, specific molecule binds to carrier protein which causes the tertiary structure to change shape which allows the molecule to be released on the other side of the membrane
lesson 3: osmosis
the net movement of water molecules from a region of high water potential to low water potential across a selectively permeable membrane until water potential is the same on both sides of the membrane
water potential
the pressure created by molecules as they collide with the membrane
pure water has a potential of 0kpa so the more solutes that are dissolved in water the more negative the water potential will become
animal cells in different solutions
hypertonic solution
solution outside the cell has a lower water potential than inside the cell
water molecules leave cell via osmosis
cell becomes shrunken and shrivelled. haemoglobin is more concentrated so cell appears darker. crenation of cell membrane
isotonic
solution inside and outside the cell has the same water potential
no net movement of water molecules by osmosis
cell is normal sized
hypotonic
solution outside the cell has higher water potential than solution inside the cell
water molecules enter the cell by osmosis
hydrostatic pressure increases inside. cell swells and potentially bursts (cytolysis) . contents including haemoglobin are released.
plant cells in different solutions
hypertonic solution
the solution outside the cell has a lower water potential than inside the cell
net movement of water molecules: water leaves the cell
cell shrivels - protoplast completely pulls away from cell wall- cell is plasmolysed
isotonic solution
solution outside the cell has the same water potential
no net movement of water molecules
protoplast jut beginning to pull away from cell wall- cell is in incipient plasmolysis
hypotonic solution
solution outside the cell has a higher water potential than the solution inside the cell
net movement of water molecules: water moves into the cell
cell swells - protoplast pushed up against the cell wall and cell I turgid
lesson 4: active transport
the movement of molecules or ions in or out of a cell from a region of lower concentration to a region of higher concentration
process
molecule binds to receptor sites on carrier protien
ATP attaches to the membrane of the carrier protein on inside the cell
this causes hydrolysis of ATP into ADP and Pi, the hydrolysis of ATP releases energy
carrier protein changes shape tertiary structure changes due to phosphate ion binding to membrane
this results in the carrier protein becoming open to the inside of the cell but closed to the outside and the particle is released
molecule is released into cell against their concentration gradient, phosphate molecule is released and carrier protein reverts back to original shape
hydrogen ion pumps
lesson 5: co transport
the movement of ion/molecule against its concentration gradient by coupling it to the facilitated diffusion of another ion/molecule down its concentration gradient
co transport in the ileum
microvilli
provide more surface area for the insertion of carrier proteins through which diffusion and active transport can take place
key ideas/points
most glucose is absorbed by facilitated diffusion
the concentration gradient of glucose is constantly maintained as carbohydrates are digested/hydrolysed continuously therefore there is a high concentration in the ileum - glucose is constantly circulated in the blood and used in respiration therefore concentration gradient is maintained
however diffusion result in equilibrium so not all glucose can be absorbed by facilitated diffusion
process
1) glucose absorbed by facilitated diffusion into epithelial cells lining the ileum then absorbed from the epithelial cells to the bloodstream - down concentration gradient
2) as more glucose moves into epithelial cells the concentration gradient falls
3) sodium potassium pump actively transports sodium ions out of epithelial cells into the bloodstream and at the same time actively transports potassium ions into the epithelial cells
4) concentrations gradient between epithelial cells and ileum is established
5) sodium ions diffuse into epithelial cells via sodium glucose transporter down their concentration gradient - glucose is coupled with sodium/ also transported through sodium glucose transporter