Chapter 5: Plasma Membranes Flashcards
Effect of low temperature on active transport + osmosis + phloem loading?
- Molecules –> little KE (move slowly) –> less respiration/ATP produced.
- Less active transport of sugars/sucrose into sieve tube elements.
- Less osmosis of water into sieve tube element.
- Less hydrostatic pressure (HP) created.
Effect of increasing temperature on active transport + osmosis + phloem loading?
- Molecules –> more KE (move quickly) –> more respiration/ATP produced.
- More active transport of sugars/sucrose into sieve tube elements.
- More osmosis of water into sieve tube elements.
- More HP generated/created.
Effect of VERY HIGH temperature on active transport + osmosis + phloem loading?
- Enzymes denatured.
- Shape change to precise 3D shape of tertiary structure of enzymes.
- Carrier/Channel proteins denature.
- No longer complementary to substrate.
- No longer bind to substrate.
Roles of proteins in cell surface membranes?
- Glycoproteins –> cell adhesion/recognition/signalling/receptor sites/attach to water molecules.
- Channel proteins –> transport by facilitated diffusion.
- Carrier proteins –> transport by active transport.
Roles of different lipid components of plasma membranes?
- Phospholipids –> form bilayer.
- Non-polar hydrophobic fatty acid tails in bilayer –> hydrophobic core that prevents diffusion of polar molecules/ions.
- Hydrophobic barrier –> compartmentalisation/isolation of contents of organelles –> separates different areas.
- Bilayer –> allows diffusion of non-polar molecules (O2) easily through cell surface membrane.
- Glycolipids –> cell recognition.
- Cholesterol –> regulates membrane fluidity + stabilises membrane –> dual hydrophilic/hydrophobic properties + waterproofs the skin.
Why is alcohol used in antiseptic wipes?
- Alcohol disrupts cell surface membrane of bacteria –> pure alcohol dissolves the membrane.
- Helps prevent infection.
Define Simple Protein.
Protein without prosthetic group.
Describe (using beetroot) how you would use a colorimeter to investigate how cell membrane permeability changes with temperature.
- Use beetroot –> contains betalain dye.
- Cut beetroots into cubes of equal size/area.
- Place beetroot cubes in sample of water at different temps.
- At least 5 different temps.
- Sample water after set time.
- Use filter in colorimeter.
- Calibrate/zero colorimeter.
- Read absorbance.
How do water molecules cross selectively permeable membranes by simple diffusion?
- Water molecules small.
- Moving fast between phospholipid molecules.
- Through transient gaps.
Why is the cell surface membrane described as selectively permeable and not semi-permeable?
- Only certain ions/molecules can cross cell surface membranes.
- Depends on size (larger = slower), charge (partial +ve or -ve (polar) repelled by hydrophobic core of bilayer), presence of transport protein.
- Semi-permeable does not give the idea of selectivity.
Outline the general process of active transport.
- Molecule/ion to be transported binds to receptors on channel of carrier proteins on outside of cell.
- On inside of cell ATP binds to carrier proteins and is hydrolysed to ADP + phosphate.
- Binding of phosphate molecule to carrier protein causes protein to change shape –> opening up to inside of cell.
- Molecule/ion released inside cell.
- Phosphate molecule released from carrier protein + recombines with ADP to form ATP.
- Carrier protein returns to original shape.
Outline the process of exocytosis.
- Vesicles formed by Golgi apparatus move towards + fuse with cell surface membrane.
- Contents of vesicle released outside cell.
Outline process of endocytosis.
- Cell surface membrane invaginates when it comes into contact with material to be transported.
- Membrane enfolds material until it fuses forming a vesicle.
- Vesicle pinches off and moves into cytoplasm to transfer material for further processing in cell.
