What is required for simple diffusion in terms of energy, particles and proteins?
Energy - ATP is not needed as particles are moving along the conc’n gradient (passive transport)
Particles - small, no charge, (H2O exception)
Proteins - not used
How do you increase the rate of simple diffusion?
- increase temperature as this increases kinetic energy
- increase surface area of membrane
- increase the conc’n gradient
What is required for facilitated diffusion in terms of energy, particles and proteins?
Energy - ATP is not needed as particles are moving along the conc’n gradient (passive transport)
Particles - large (eg glucose -> carrier), charged particles eg polar molecules/ions (ions -> channel)
Proteins - yes - carrier and channel - intrinsic proteins
What increases the rate of facilitated diffusion?
- increase temp as it increases kinetic energy
- increase number of transport proteins
- increase conc’n gradient
What is osmosis?
The diffusion of water
What diffusion does osmosis use?
Simple diffusion which is slower
OR
Facilitated diffusion using aquaporines (channel proteins)
What is required for active transport in terms of energy, particles and proteins?
Energy - ATP is needed as particles are moving against the conc’n gradient
Particles - any that move against conc’n gradient
Proteins - yes - protein pumps
What is required for cotransport in terms of energy, particles and proteins?
Energy - indirectly, (ATP needed for pumping Na+ out of cell)
Particles - 1st stage = glucose accompanied by Na+/K+. 2nd stage: Na+/K+
Proteins - yes cotransport proteins and Na+/K+ pump
What is the definition of diffusion?
The net (or overall) movement of particles from an area of higher concentration to an area of lower concentration (down/along concentration gradient)
When is equilibrium reached during diffusion?
When particles are evenly distributed
What do intrinsic proteins allow in facilitated diffusion?
It allows hydrophillic substances to cross the membrane without having to interact with hydrophobic centre of phospholipid bilayer
How does active transport work with the carrier proteins?
The molecule/ions to be transported attatches to the receptor site on carrier protein, ATP binds to carrier protein. ATP undergoes hydrologist producing phosphate + ADP. Phosphate attatches to protein causing it to change shape causing transport of molecule/ions to other side of membrane where it’s released. Phosphate leaves protein so it goes back to shape. ADP and Phosphate will later reform ATP in respiration.
Carrier proteins in active transport are specific so will only reansport 1 type of molecule/ions.
What is the ileum?
A part of the small intestine that absorbs molecules produced by digestion including glucose.
What’s the structure of the ileum?
Epithelial cells line the ileum. Glucose is absorbed by the lumen of the ileum into the epithelial cells and it then moves into the bloodstream.
Why does cotransport occur in the ileum?
Glucose molecules are diffused from lumen into epithelial cells however facilitated diffusion can’t absorb all available glucose so some is absorbed via active transport
How does cotransport occur in the ileum?
- Sodium potassium pump (a type of carrier protein) uses ATP to actively transport sodium ions out of epithelial cells into the bloodstream. At the same time potassium ions are transported into the epithelial cells. Now there’s a lower concentration of sodium ions in epithelial cells, lumen contains a higher concentration.
- the membrane of epithelial cells has a protein: sodium glucose transporter. Sodium ions can diffuse along concn gradient so they bind with glucose (which goes against concn gradient). This ensures glucose is absorbed at a faster rate. Energy for this comes indirectly from concn gradient of sodium ions.
Why do epithelial cells contain lots of mitochondria?
To synthesise ATP providing energy for the active transport.
What is an adaptation of the membrane to increase rate of active transport?
It is folded into a large number of microvilli which increases surface area
Why is there a steep conc’n gradient between epithelial cells and blood?
Because the glucose absorbed are rapidly carried away by the bloodstream
What is active transport?
The net movement of molecules from a region of low concentration to a region of high concentration (against their concentration gradient). Requires ATP and is mediated by specific transport proteins (pumps)
What is cotransport?
The movement of 2x substances simultaneously. 1 substance moves along the concentration gradient providing energy indirectly to transport another substance (going against its concentration gradient). Thus indirectly using ATP.
What is an example of active transport?
Na+/K+ pump moves 3 Na+ ions out of cells and 2 K+ ions into cell. Against concn gradients so using ATP.
Why is active transport necessary?
To maintain concentration gradients of ions/molecules that are essential for all functions eg nutrient absorption (which can’t happen through facilitated diffusion alone)
