AS Level AQA unit 1: Topic 3 Movement In and Out of Cells
- 1. Topic 3: Membranes, Absorption and Cholera By Tahmida Chowdhury
- 2. Lipids What 3 elements do lipids contain? A: carbon, hydrogen and oxygen Describe the solubility properties of lipids A: soluble in organic solvents but insoluble in water What are the 5 main roles of lipids? (PIPEW) A: plasma membranes A: insulation A: protection A: energy source A: water-proofing
- 3. Triglyceride What is a triglyceride made out of? A: 3 fatty acid chains and glycerol When a triglyceride forms how many molecules of water are removed and why? A: 3 because one for each fatty acid joining to the glycerol What is a fatty acid chain? A: a long chain of carbon atoms each bonded to hydrogen atoms What is meant by a saturated fatty acid? A: the bonds between carbon and carbon are singularly bonded What is meant by an unsaturated fatty acid? A: there is one double bonded carbon atom What is meant by a poly-saturated fatty acid? A: when there is more than 1 double bonded carbon atom
- 4. Phospholipid In what way is a phospholipid different to a triglyceride A: it has a phosphate group and 2 fatty acid chains What 2 parts is a phospholipid made out of? A: a hydrophilic head (polar) and hydrophobic tail (non-polar) Why is the tail hydrophobic? A: because it doesn’t interact with water Why is the head hydrophilic? A: because it interacts with water In cell-surface membranes what do the phospholipids form? A: a phospholipid bilayer sheet
- 5. Lipids Test What is the test for lipids called? A: emulsion test Describe the 3 steps taken (ESW) 1) Add 5cm of ethanol to 2cm of sample in a test tube 2) Shake the tube to dissolve any lipids in sample 3) Add 5cm of water and shake What is the indication for a positive result? A: a cloudy white colour
- 6. Membrane Structure What do the phospholipids allow to enter and leave the cell? A: lipid soluble substances What do the phospholipids prevent entering and leaving the cell? A: water soluble substances Where can extrinsic (peripheral) proteins occur on the phospholipid bilayer? A: on the surface or partly embedded to it What are the 2 roles of extrinsic proteins? A: to act as cell receptors and provide structural support Where do intrinsic (integral) proteins occur on the phospholipid bilayer? A: they span the whole way through the bilayer What is the role of intrinsic proteins? A: to act as protein carriers (transporting water soluble substances across the membrane) and create ion channels to allow Na and K through via active transport
- 7. Membrane Structure What are glycoproteins? A: branched carbohydrates attached to the surface of the embedded proteins Why is the fluid mosaic model described as fluid? A: because the individual phospholipids can move relative to one another Why is the model mosaic? A: because the embedded proteins vary in shape, size and structure What does cholesterol do to the membrane? A: adds strength What are glycolipids involved in? A: involved in recognition
- 8. Diffusion Define diffusion A: the random, passive movement of molecules from a high concentration to a low concentration What is equilibrium? A: when the particles are evenly distributed on both sides What 3 factors increase the rate of diffusion? A: thin exchange surface area, larger surface area, difference in concentration Sum this into an equation A: rate of diffusion = DP (surface area X difference in concentration) length of diffusion path
- 9. Facilitated Diffusion Define facilitated diffusion A: diffusion of complementary large molecules and charged ions through specific carrier proteins in the plasma membrane What kind of molecules do carrier/channel proteins diffuse? A: large, water soluble ions What two molecules are transported by carrier proteins? A: sodium ions and glucose ions Describe the 3 steps taken in how a carrier protein works (ASR) 1) The molecule attaches onto the protein 2) The protein changes shape 3) The molecule is released How do channel proteins work? A: they form pores in the membrane to let specific ions through
- 10. Osmosis Define osmosis A: the net movement of water from a high water potential to a low water potential across a partially permeable membrane What is the unit for measuring water potential? A: kPa Define solution A: a solute dissolved in a solvent makes a solution What value must the water potential of a solution always be? A: 0 KPa What energy process is required for this type of transport? A: kinetic What kind of value means that there is a lower water potential? A: the more negative, the lower the water potential
- 11. Active Transport Define active transport A: the movement of molecules/ions against the concentration gradient using ATP from energy and carrier proteins How does the protein transport molecules against the concentration gradient? A: the protein attaches to ATP, the protein changes shape, the molcules is released on the other side. What are the 2 adaptations for cells which are adapted for active transport? A: numerous mitochondria to provide ATP and microvilli to increase the surface area for more carrier proteins
- 12. Exchange Surfaces What are four properties of the villi that enables efficient absorption in the small intestine? 1) They provide a large surface area 2) They have thin walls 3) They move which maintains the concentration gradient 4) They have a rich blood supply
- 13. Absorption of Glucose How are Na ions pumped into the blood from out the epithelial cells? A: in the Na/k pump via active transport Why do the Na ions diffuse back into the epithelial cells through the co-transport protein? A: there is lower concentration of Na in the epithelial than the lumen (concentration gradient) When sodium diffuses back into the cell what does it attach with and how? A: it attaches with glucose and through a co-transport protein When does glucose diffuse out the epithelial cell into the blood? A: When the concentration of glucose is higher in the epithelial cell than blood How does it diffuse out? A: with a specific channel protein via facilitated diffusion
- 14. Cholera What can cause the transmission of cholera? A: ingestion of un-purified water, & contaminated food containing faeces What does cholera secrete when it enters the small intestine? A: toxins What do the toxins bind to? A: specific receptors on the cell surface membrane of the epithelial cell What does the toxin cause the chloride channel ions to do & what does this cause? A: for the channels to open. This causes large amounts of chloride ions to diffuse into the lumen
- 15. Cholera continued… What affect does this have on the W.P of the lumen? A: it is lowered, so more water moves in by osmosis from the epithelial cells (and causes diarrhoea) What other 3 factors can cause diarrhoea? A: damage to epithelial cells A: loss of microvilli A: excessive secretion of water due to toxins What causes the dehydration? A: the loss of so much water in the lumen Why is just drinking water on its own ineffective for treating diarrhoea? A: it won’t replace the lost ions from the epithelial cells
- 16. Oral Rehydration Therapy What is the purpose of ORT? A: to replace the lost chloride ions and water loss Name the 4 substances an oral rehydration solution contains A: water, sodium, glucose, potassium Why is water needed? A: for rehydration Why are sodium and potassium needed? A: to replace the lost ions Why is glucose needed? A: for energy and to stimulate the uptake of sodium ions by co-transport