BIOLOGY FORM 4 CHAPTER 3
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The document discusses the movement of substances across the plasma membrane in living cells. There are two main types of movement: passive transport, which moves substances down their concentration gradient without requiring energy, and active transport, which moves substances against their concentration gradient using energy from ATP. Passive transport includes simple diffusion, osmosis, and facilitated diffusion. Active transport is required to uptake nutrients from areas of lower concentration and pump out waste products against gradients.
BIOLOGY FORM 4 CHAPTER 3
- 1. MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE
- 2. Subtopics 2 01 02 03Movement of Substances Across the Plasma Membrane Understanding the Movement of Substances Across the Plasma Membrane in Everyday Life Appreciating the Movement of Substances Across the Plasma Membrane
- 3. Learning Objective To describe the permeability of the plasma membrane To state the substances required by living cells To state the substances that have to be eliminated from cell To explain the necessity for movement of substances across the plasma membrane To describe the structure of the plasma membrane 3
- 4. NECESSITY FOR MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE To provide nutrients for metabolism & growth supply oxygen for respiration regulate solute concentration & suitable pH for maintaining a stable internal environment for optimal enzymatic activities maintain an ion concentration gradient required for nerve & muscle cell activities eliminate toxic waste products such as urea & carbon dioxide secrete useful substances, for example, digestive enzymes & hormones4
- 5. SUBSTANCES CAN MOVE INTO OR OUT OF A CELL BY : 5 PASSIVE TRANSPORT ACTIVE TRANSPORT Simple diffusion Osmosis Facilitated diffusion
- 7. Movement of substances across the plasma membrane would depend on Selectivity of the partially permeable membrane The difference in concentration between the cell & extracellular fluiD
- 9. All cells are covered by a thin plasma membrane It separates the cell contents from the surrounding 1972, S.J. Singer & G.L. Nicolson proposed the fluid-mosaic model of plasma membrane The plasma membrane is dynamic & fluid. The phospholipid molecules can move thus giving the membrane its fluidity & flexibility The proteins are scattered in the membrane giving it a mosaic appearance
- 10. The membrane consists of a phospholipid bilayer (2 molecules thick) The non-polar hydrophobic hydrocarbon fatty acid tails face inwards, away from water The polar hydrophilic heads outer layer face outwards, chemically attracted to the watery surrounding There are proteins on the outer & inner surfaces of the plasma membrane Some proteins penetrate partially through the membrane, others penetrate completely The phospholipid bilayer is permeable to diffusion of small uncharged molecules such as O2 & CO
- 16. Channel / pore proteins Other carrier proteins Some carrier proteins 2 TYPES OF TRANSPORT PROTEIN 16 have pore to facilitate diffusion of particular ions / molecules across the PM have binding sites that bind to specific molecules such as glucose @ amino acids alter their shape to facilitate the diffusion of solutes function in active transport an energized carrier protein actively pumps the solute across the cell membrane against the concentration gradient.
- 18. Cholesterol molecules stabilise the structure of PLASMA MEMBRANE
- 19. selectively permeable to small molecules such as water & glucose MECHANISM OF MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE MECHANISM 19 semipermeableDoes not permit large molecule to move through it egg membrane, plasma membrane of living cells & cellaphone membrane of the Visking tubing permeable to the many solvent (water) & solute molecules permeable membrane Example : cellulose cell wall of plant cell impermeable membrane not allow substances to diffuse through it Example : the impermeable polythene membrane
- 20. LEARNING OUTCOMES 20 03 04 To explain the movement of substances across the plasma membrane through the process of passive transport To explain the movement of water molecules across the plasma membrane by osmosis To explain the movement of substances across the plasma membrane through the process of active transport To explain the process of passive transport in living organisms using examples
- 21. The movement of particles (molecules/ions) within a gas or liquid across the plasma membrane from a region of higher concentration to a region of lower concentration & does not require expenditure of energy from ATP. The substances move down their concentration gradient through different ways : Phospholipid bilayer Pore protein/ channel protein Carrier protein
- 26. The bigger the concentration gradient the faster the rate of diffusion These substances will diffuse down the concentration gradient if there is a concentration gradient. (until an equilibrium is reached) Examples : gaseous exchange between the alveolus & the blood capillaries, blood capillaries & body cells The net movement of molecules / ions from a region of higher concentration to a region of lower concentration until an equilibrium is reached Substances Small non-polar molecules ,eg: O2 & CO2 Water molecules SIMPLE DIFFUSION 26 Lipid-soluble substances,eg: vitamins ADEK, steroids & alcohols
- 29. OSMOSIS OSMOSIS A special type of diffusion Examples Absorption of water from soil solution by plant root hairs Reabsorption of water by kidney tubules The diffusion of water molecules (solvent) from a region of higher water concentration (diluted solution) to a region of lower water concentration (concentrated solution) through a semi-permeable membrane until an equilibrium is reached 29
- 31. FACILITATED DIFFUSION THE MOVEMENT OF MOLECULES / IONS DOWN THEIR CONCENTRATION GRADIENT ASSISTED BY TRANSPORT PROTEINS (CHANNEL PROTEIN / PORE PROTEIN) ACROSS THE PLASMA MEMBRANE WITHOUT USING ENERGY THE TRANSPORT PROTEINS FACILITATE & INCREASE THE RATE OF DIFFUSION ACROSS THE PLASMA MEMBRANE NOT REQUIRE ENERGY 31 THE RATE OF FACILITATED DIFFUSION DEPENDS ON THE NUMBER OF TRANSPORT PROTEIN MOLECULES IN THE MEMBRANE & HOW FAST THEY CAN MOVE THEIR SPECIFIC SOLUTE ONLY ALLOWS SMALL CHARGED MOLECULES SUCH AS MINERAL IONS TO PASS THROUGH THE PORE PROTEIN CARRIER PROTEIN : ALLOWS LARGER UNCHARGED POLAR MOLECULES GLUCOSE & AMINO ACIDS TO CROSS THE MEMBRANE
- 33. THE MECHANISM 33 The solute moves to the binding site of the specific carrier protein The carrier protein returns back to its original shape The solute binds to the carrier protein at the binding site & triggers the carrier protein to change its shape The carrier protein changes its shape & moves the solute across the membrane 01 02 03 04
- 34. FACILITATED DIFFUSION The solutes can be transported by carrier proteins in either direction but the net movement is always down the concentration gradient Examples : the transportation of glucose, amino acids & mineral ions across the membrane of the vilus at the ileum & body cells
- 35. ACTIVE TRANSPORT The movement of substances across the plasma membrane from a region of low concentration to a region of high concentration (against the concentration gradient) by using metabolic energy The substances move across a membrane against the concentration gradient, using metabolic energy Perform by a specific protein embedded in the plasma membrane Require energy (ATP) to change the shape of the protein such that the substance can be pumped across the membrane Example : absorption of potassium ions from pond water by algae Nitella sp. against a concentration gradient, the intake of mineral ions by the plant root hairs, Na+/ K+ protein pumps in the plasma membrane of neurons transport Na+ & K+ against their concentration gradients 35
- 38. PASSIVE TRANSPORT SIMILARITIES ACTIVE TRANSPORT o Transport of substances across the plasma membrane o Need a difference of concentration gradient between extracellular environment & the cell DIFFERENCES Follow Concentration gradient Against Does not expend energy Cellular energy Need to expend energy Until an equilibrium is reached Outcome of the process Depends on the cells requirement (no need to reach an equilibrium) Non-living & living organisms Occurs in Living organisms only Simple diffusion, osmosis, facilitated diffusion Name of process Active transport