3 By the end of the lesson, you should be able to OBJECTIVESBy the end of the lesson, you should be able todefine and describe diffusion, osmosis and active transportto describe the idea of a partially permeable membraneassess the importance of water potential gradient in water uptake by plantsexplain the effects of osmosis in plant and animal tissuesdefine and discuss importance of active transport in ion-uptake by root hairs and glucose uptake by cells in the villi
4 Introduction Recall: ~ A cell is the basic unit of life ~ Many complex reactions take place inside the cell~This means that many raw materials must be brought into the cell~ And new products formed by the chemical reactions, and waste materials, must exit the cell.
5 How? How do the raw materials get into the cell? How do the new products leave the cell?How are the waste materials removed from the cell?Answer:Materials move across the partially permeable cell membraneBy processes called _________, _________ and _______________diffusionosmosisactive transport
6 DiffusionDiffusion is the net movement of ions or solute molecules from a region of higher concentration to a region of lower concentration, down a concentration gradientmolecule moves from a region of high concentration to that of low concentrationconcentration gradientregion of high concentration of molecule Xregion of low concentration of molecule X
7 Diffusion Diffusion in gases Gas molecules move from a region of higher concentration to that of a lower concentrationB.The movement continues until they are evenly spread
8 Diffusion Diffusion in liquids A.B.Dissolved particles of a substance in a liquid move from a region where they are more concentrated to a region where they are less concentrated.The particles continue to move until they are evenly distributed.
9 Importance of Diffusion Initially, the concentration of a substance outside the cell is higher than inside the cell.The particles diffuse across the cell membrane.Later, an equal concentration of the substance inside and outside the cell is attained.
10 Importance of Diffusion Living cells continuously use up oxygen during aerobic respiration.The concentration of oxygen inside the cell falls.Oxygen molecules diffuse into the cell until the oxygen concentration is raised again.During respiration, carbon dioxide is produced.The concentration of carbon dioxide rises and creates a concentration gradient.carbon dioxideoxygenOxygen is supplied to Amoeba by diffusion. Diffusion enables metabolic wastes such as carbon dioxide to be excreted out.
11 Diffusion Factors which Affect the Rate of Diffusion Temperature: An increase in temperature results in a higher rate of diffusion.Temp Molecules move faster Rate of diffusion Size of particles: Small molecules or ions diffuse faster than large ones.Particle size Energy to move particle Rate of diffusion Thickness of the barrier: Membranes of plant and animal cells are of about the same in thickness and permeability. Plant cell walls vary in their thickness. The thicker the cell walls, the slower the rate of diffusion.Thinner membrane Higher rate of diffusionConcentration gradient: The greater the concentration gradient, the higher the rate of diffusionSteeper concentration gradient Higher rate of diffusionSurface area: The rate of diffusion into a cell depends on the total surface area of the cell membrane. surface area rate of diffusion.
13 Diffusion in our bodyRecall: Our cells have a partially permeable membranePartially permeable membraneAllows some substance through and not othersHow do these substances pass through?via DIFFUSION
14 Practical Application Kidney dialysisWaste products are removed from the blood by diffusing across artificial membrane in the machineBlood cells and other large protein are retained
15 selectively-permeable membrane OsmosisOsmosis is the diffusion of water across a selectively permeable membrane, from a high water potential to a low water potential.selectively-permeable membraneThe selectively permeable membrane on the side of the water is being continuously bombarded by water molecules which pass through.This causes an increase in the volume of sucrose solution and a decrease in the volume of water.water moleculessucrose moleculewatersucrose solution
16 Osmosis Water Potential The water potential of a solution is a measure of the tendency of water molecules to move from one place to anotherA dilute solution has a higher water potential than a concentrated solutionThe difference in water potential between two solutions is known as the water potential gradient
17 Osmosis Osmosis and Plant Cells In plant cells, the cell sap contains dissolved salts and sugar. If the cell sap has a lower water potential than that of the surrounding fluids, water from the outside enters by osmosis.Turgor pressure – The outward pressure which the cell sap exerts against the inside wall of the cellTurgor – A state when a cell is firm or turgid due to water entering the cell, causing it to swell.
18 Importance of Turgor in Plants Changes in turgor of the guard cell causes the opening of the stomata
19 Turgor (II)Changes in turgor of the pulvinus (small swelling at the base of the leaflets) causes the folding of leaflets in the Mimosa
20 Osmosis Osmosis and Plant Cells cell sap more concentrated than outside solutionTurgid cells. The cytoplasm is pressed against the cell wall. The cell swells up and is prevented from bursting by the cellulose cell wall.water enters by osmosiscellulose cell wallplasma membranecell sap less concentrated than outside solutionwater leaves by osmosisPlasmolysed cells. Water is lost from its vacuole, the cytoplasm shrinks and is withdrawn from the cell wall.cytoplasm
22 Fertilizer - Good or Bad? Too much fertilizer added will cause the plant to wiltSoil solution becomes very concentratedWater moves out of rootPlant will wiltSufficient water must be added to ensure plant survival
23 Osmosis Osmosis and Animal Cells normal red blood cellChanges observed under a microscope when blood is dropped into hypertonic and hypotonic solutions.in hypertonic solutionin hypotonic solutioncell shrinkscell swellscell becomes crenatedcell bursts and cell is said to be haemolysed
24 carrier protein changes shape Active TransportActive transport is an energy-consuming process by which substances are transported from regions of low concentration to regions of high concentration against a concentration gradient.binding sitesubstrate moleculeOUTSIDEcarrier proteincell membranerestorationINSIDEbindingcarrier protein changes shapesubstrate releasedenergy from ATP used
25 Ion uptake by root hair is facilitated by active transport Plants need to absorb mineral salts from the soil. They are present as charged ions which cannot diffuse across partially-permeable membranes.soil particlehigh concentration of ionslow concentration of ionsDirection of active transportIon uptake by root hair is facilitated by active transport
26 Uptake of glucose by cells in the villi Active TransportActive transport enables absorption of glucose and amino acids through the inner surface of the small intestine.The presence of microvilli increases the surface area over which active transport occurs.microvilluscell lining the villusUptake of glucose by cells in the villiglucose moleculedirection of active transport