Transport across the CSM

CSM transport Phospholipid bilayer creates effective barrier against water soluble molecules and ions Prevents aqueous contents from escaping Some essential transport is achieved through diffusion, facilitated diffusion, osmosis, active transport and bulk transport

Diffusion Diffusion: net movement, as a result of random motion of its molecules or ions, of a substance from a region of high concentration to a region of low concentration Particles move down a concentration gradient

Rates of Diffusion ‘steepness’ of concentration gradient: greater difference = higher rate Temperature: higher temperature = higher rate Surface area of diffusion: greater surface area – higher rate Nature of molecules/ions: small molecules = greater rate

Diffusion Respiratory gases cross membrane by diffusion (uncharged and nonpolar) Water (even though it is polar) can cross because molecules are very small

Facilitated diffusion Diffusion that takes place with the help of a certain protein molecule Channel proteins Carrier proteins

Channel proteins Water-filled pores Fixed shape Allow charged substances (usually ions) to diffuse through membrane Gated to allow for selectivity and control of movement

Carrier proteins Flips between shapes to alternately open binding sites on interior/exterior of membrane Direction of movement depends on concentration gradient inside and outside of cell

Osmosis Type of diffusion involving water molecules only

Water potential Water potential: tendency of water molecules to move from one place to another Measured by Greek symbol psi Ψ

Water potential Water potential for pure water is 0 Solutes make water potential less than 0, the more solute, the more negative the water potential The amount that solutes lower the water potential is called solute potential

Pressure potential Increasing pressure increases water potential The contribution made by pressure to water potential is called pressure potential and is given by symbol Ψp Pressure potential makes water potential less negative (more positive)

Water potential in animal cells

Osmosis in plant cells

Active Transport Active transport moves molecules/ions against concentration gradient Achieved by carrier proteins (specific for structure of particular ion/molecule) Requires ATP for energy, supplied by cellular respiration Can occur into or out of the cell

Sodium-potassium pump Found in CSM of all animal cells Use ~30% avg cell energy and ~70% neuron cell energy Pump 3 Na+ ions out of the cell and 2 K+ ions into the cell Net result: inside of cell become more negative than the outside

Sodium-potassium pump Difference in charges between inside membrane and outside creates a potential difference (p.d.) which allows nerve cells to propagate a signal

Active transport Important in re-absorption in the kidneys, where certain useful molecules and ions have to be re-absorbed into the blood after filtration into the kidney tubules Involved in absorption of products of digestion in the gut

Active transport Used to load sugar from photosynthesizing cells of leaves into phloem tissue for transport around the plant

Active transport http://www.youtube.com/watch?v=Kd3LorZcJew&feature=related

Bulk transport Bulk transport involves the mechanism of moving large quantities of molecules into the cell (endocytosis) or out of the cell (exocytosis) Large molecules such as proteins or polysaccharides, part of cells, or even whole cells may be transported across the membrane

Endocytosis Involves the engulfing of material by the CSM to form a small sac, or endocytic vacuole Two forms: phagocytosis and pinocytosis

phagocytosis ‘cell eating’ Bulk up take of solid material Cells specializing in this are called phagocytes and the vacuoles are called phagocytic vacuoles Ex: engulfing of bacteria by immune cells

endocytosis http://www.youtube.com/watch?feature=fvwp&NR=1&v=a4aZE5FQ284 http://www.youtube.com/watch?v=JnlULOjUhSQ

Pinocytosis ‘cell drinking’ – bulk uptake of liquid into cell Vacuoles ( vesicles) formed are often extremely small, in which the process is called micro-pinocytosis Human egg cells take up nutrients from cells that surround it by pinocytosis http://www.youtube.com/watch?v=InG6xF9D4EM

exocytosis Process by which bulk material is removed from a cell Ex: how plants transport materials out of CSM to make cell wall Ex: secretion of digestive enzymes of the pancreas Secretory vesicle from the Golgi carry the enzymes to the CSM and release their contents

Bulk transport http://www.youtube.com/watch?v=aWItglvTiLc&feature=related http://www.youtube.com/watch?v=pvOz4V699gk&feature=fvwrel

Homework Pg 81 #5,6,7 (ING Pg 34)