IBDP CORE>TOPIC 1.4>MEMBRANE TRANSPORT
ASSESSMENT STATEMENT
Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
U1. Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.
Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.
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Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.
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Passive transport across membranes by simple diffusion and facilitated diffusion.
The cell membrane is hydrophobic inside thus hydrophobic (lipid soluble) molecules will pass through easily. This is by simple diffusion. However hydrophilic molecules and charged particles will not be able to cross the cell membrane. They will need the help of protein channels, this is facilitated diffusion.
Simple diffusion involves the diffusion of molecules through the phospholipid bilayer while facilitated diffusion involves the use of channel proteins embedded in the membrane. Water moves through by osmosis which is also by passive transport. Osmosis involves the movement of water molecules from a region of low solute concentration, to a region of high solute concentration. So if the solute concentration is higher inside the cell than outside the cell, water will move in and vice versa. |
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Protein pumps and ATP in active transport across membranes.
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U2. The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles move materials within cells.
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The fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
The plasma membrane is held together by the relatively weak hydrophobic associations between phospholipids. This allows membrane fluidity and flexibility.
Thus the breaking and remaking of membranes is possible, allowing larger substances access into and out of the cell. There are two processes based on the entry and exit of substances. Endocytosis
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Application: Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
Application: Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis.
- Organs placed in hypotonic solution or hypertonic solution would damage cells, therefore isotonic solutions are used (same osmolarity as inside the cell)
- Isotonic solution: A solution that has the same salt concentration as cells and blood.
Isotonic solutions commonly used during medical procedures-
- Intravenously infused fluids in hospitalized patients.
- Saline eye drops
- Packing organs for transplant
- During skin grafts, used to keep damaged area moist
Skill: Estimation of osmolarity in tissues by bathing samples in hypotonic and
hypertonic solutions. CLICK HERE
References-
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
All picture have been downloaded from Google images for educational purpose only
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
All picture have been downloaded from Google images for educational purpose only