Movement of Substances - OCR Biology

Movement of Substances Chapter 3  Learning Objectives... DIFFUSION define diffusion discuss its importance in nutrient uptake and gaseous exchange in plants and humans. OSMOSIS define osmosis discuss the effects of osmosis on plant and animal t...

Movement of Substances Chapter 3  Learning Objectives... DIFFUSION define diffusion discuss its importance in nutrient uptake and gaseous exchange in plants and humans. OSMOSIS define osmosis discuss the effects of osmosis on plant and animal tissues. ACTIVE TRANSPORT define active transport discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, – E.g.: ion uptake by root hairs – E.g.: uptake of glucose by cells in the villi Movement of Substances Diffusion Osmosis Active Transport  What are these items??? Movement of Substances Diffusion Osmosis Active Transport  What happens when you spray air freshener in one corner of the room? Movement of Substances Diffusion Osmosis Active Transport  Movement of air particles... The gas particles spread out from the source to the rest of the room. Movement of Substances Diffusion Osmosis Active Transport  Movement of air particles... The gas particles spread from a region of higher concentration to a region of lower concentration. Movement of Substances Diffusion Osmosis Active Transport  Movement of air particles... Air freshener particles spread from a region of higher concentration to a region of lower concentration. The two regions of different concentrations form a concentration gradient. Movement of Substances Diffusion Osmosis Active Transport  Movement of air particles... Air freshener particles will keep moving down the concentration gradient until the particles are evenly spread out. The particles are then said to be in dynamic equilibrium – The particles are in constant random motion – But there is no net movement of particles This movement of particles down the concentration gradient is known as DIFFUSION. Movement of Substances Diffusion Osmosis Active Transport  Defining Diffusion... DIFFUSION is the NET MOVEMENT of particles from a region of HIGHER CONCENTRATION to a region of LOWER CONCENTRATION down a CONCENTRATION GRADIENT. Movement of Substances Diffusion Osmosis Active Transport  Defining Diffusion... DIFFUSION is the NET MOVEMENT of particles from a region of HIGHER CONCENTRATION to a region of LOWER CONCENTRATION down a CONCENTRATION GRADIENT. Diffusion stops when particles reach DYNAMIC EQUILIBRIUM. Movement of Substances Diffusion Osmosis Active Transport  Diffusion of a Dissolved Substance Investigation 3.1 TB Pg 32 Place a drop of potassium permanganate solution at the bottom of a beaker of water. Observe the changes in the colour of the water. OBSERVATIONS Potassium permanganate particles move up the water from a region of higher concentration to regions of low concentration. Over time, a homogeneous solution will be obtained. Movement of Substances Diffusion Osmosis Active Transport  Question! Copy and complete the sentence... Diffusion is the NET movement of particles from a HIGHER concentration to a LOWER concentration until they reach DYNAMIC EQUILIBRIUM, whereby the particles are spread out EVENLY. Movement of Substances Diffusion Osmosis Active Transport  Question! Answer on a sheet of foolscap paper... “You can smell food when molecules from the food enter your nose.” Explain how the molecules get from the food to your nose. Movement of Substances Diffusion Osmosis Active Transport  Question! Moths emit chemicals (called pheromones) to attract a mate. a) Which process is responsible for the distribution of these chemicals through the air? b) If a moth detects pheromones, how might it work out which direction they are coming from? c) What would be the advantage of a moth releasing the pheromones on a night when there was little wind? Movement of Substances Diffusion Osmosis Active Transport  Diffusion across a Membrane Diffusion can occur across a permeable membrane. At the end, there will be equal concentrations of all ions on both sides of the membrane. Movement of Substances Diffusion Osmosis Active Transport  Diffusion across a Membrane Sugar molecules diffuse across the membrane to the right side. Water molecules will diffuse across the membrane to the left side. Movement of Substances Diffusion Osmosis Active Transport  Diffusion in Cells Diffusion is an important way by which oxygen and carbon dioxide move into and out of cells. food and oxygen diffuse in carbon dioxide and waste products diffuse out An amoeba Movement of Substances Diffusion Osmosis Active Transport  Diffusion in Cells In the lungs, Oxygen diffuses from the lungs into blood vessels Carbon dioxide diffuses out of the blood vessels into the lungs Gaseous exchange in the lungs Movement of Substances Diffusion Osmosis Active Transport  Diffusion in Cells In the root hair cell, Oxygen diffuses into the root hair cell Carbon dioxide diffuses out of the root hair cell oxygen diffuses in carbon dioxide diffuses out A root hair cell Movement of Substances Diffusion Osmosis Active Transport  What affects the RATE of diffusion? Steepness of concentration gradient – The steeper the concentration gradient, the faster the rate of diffusion Heat – Heat causes particles to gain kinetic energy and move faster. – The higher the temperature, the faster the rate of diffusion. Movement of Substances Diffusion Osmosis Active Transport  What is Osmosis? Movement of Substances Diffusion Osmosis Active Transport  Solute molecules cannot diffuse across a partially permeable membrane. Water molecules move from the left arm to the right arm of the U-tube. Level of solution in the left arm falls, while the level of solution in the right arm rises. Net result: both arms contain the same concentration of solution Movement of Substances Diffusion Osmosis Active Transport  Defining Osmosis... OSMOSIS is the NET MOVEMENT of WATER MOLECULES from a solution of HIGHER WATER POTENTIAL to a solution of LOWER WATER POTENTIAL through a PARTIALLY PERMEABLE MEMBRANE. Movement of Substances Diffusion Osmosis Active Transport  What is Water Potential? Water potential is a measure of the tendency of water to move from one place to another. – A dilute solution has more water molecules per unit volume than a concentrated solution, thus it has a higher water potential Movement of Substances Diffusion Osmosis Active Transport  What is Water Potential? When a partially permeable membrane separates 2 solutions of different water potentials, a water potential gradient is established. Water always moves down a water potential gradient. partially permeable membrane Movement of Substances Diffusion Osmosis Active Transport  Demonstrating Osmosis Investigation 3.2 TB Pg 35 Expected Observation: The liquid level inside the thistle funnel rises. thistle funnel water sucrose solution cellophane paper (partially permeable membrane) Movement of Substances Diffusion Osmosis Active Transport  Demonstrating Osmosis Investigation 3.2 TB Pg 35 Expected Observation: The liquid level inside the thistle funnel remains the same. thistle funnel water water cellophane paper (partially permeable membrane) Movement of Substances Diffusion Osmosis Active Transport  Test Yourself! TB Pg 36 Movement of Substances Diffusion Osmosis Active Transport  3 Types of Solutions If two solutions have the same water potential, they are isotonic. Movement of Substances Diffusion Osmosis Active Transport  3 Types of Solutions If one solution has a higher water potential than another, it is hypotonic. The solution with lower water potential is hypertonic. Note: The terms apply only to animal systems and not plant systems Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Living Organisms Plant and animal cells are surrounded by a living, partially permeable cell surface membrane. The enclosed nucleus and cytoplasm are a complex mixture of various dissolved substances. Osmosis occurs in and out of the cell across the cell surface membrane. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Animal Cells When placed in a solution of high water potential... Cell cytoplasm has a lower water potential than that of the solution outside the cell. Water enters the cell by osmosis. The animal cell will swell and may even burst. in solution with high water potential cell expands and bursts Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Animal Cells When placed in a solution of the same water potential... There will be no net movement of water across the cell surface membrane. There will be no change in size or shape. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Animal Cells When placed in a solution of low water potential... Cell cytoplasm has a higher water potential than that of the solution outside the cell. Water leaves the cell by osmosis. The animal cell shrinks, forming spikes on the cell surface membrane. This process is known as crenation. in solution with lower water potential crenated cell Movement of Substances Diffusion Osmosis Active Transport  Osmosis in the Hagfish The hagfish lives in sea water. To prevent water leaving or entering the fish, its body fluid is as salty as the sea water in which it lives. Its body fluid is considered to be isotonic to its surrounding fluid. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Plant Cells When placed in a solution of high water potential... Cell sap has a lower water potential than that of the solution outside the cell. Water enters the cell by osmosis. The vacuole increases in size and pushes the cell contents against the cell wall. The cell wall is strong and inelastic. It exerts an opposing pressure as water enters the cell, preventing it from over-expansion. The plant cell expands and becomes turgid. The cell does not burst because it is protected by the cell wall. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Plant Cells When placed in a solution of high water potential... in solution with high water potential cell becomes turgid, cell wall prevents cell from bursting The turgidity of the cell with water is called turgor. The pressure exerted by the water on the cell wall is the turgor pressure. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Plant Cells When placed in a solution of the same water potential... There will be no net movement of water across the cell surface membrane. There will be no change in size or shape. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Plant Cells When placed in a solution of low water potential... Cell sap has a higher water potential than that of the solution outside the cell. Water leaves the cell by osmosis. The vacuole decreases in size. The rigid cell wall does not change its shape. The cytoplasm shrinks away from the cell wall. This is known as plasmolysis. The cell is said to be plasmolysed. Movement of Substances Diffusion Osmosis Active Transport  Osmosis in Plant Cells When placed in a solution of low water potential... in solution with low water potential plasmolysed cell If not too badly damaged, the cell can be restored by placing it in water or in a solution with high water potential. Movement of Substances Diffusion Osmosis Active Transport  Turgor in Plants If the cell is plasmolysed, its tissues become flaccid. Cells will be killed if they remain plasmolysed for too long. Question: why is it not advisable to add too much fertiliser around the roots of the plant? Movement of Substances Diffusion Osmosis Active Transport  Turgor in Plants Turgor is important in maintaining the shape of soft tissues in plants. Most leaves and stems are able to remain firm and erect because of the turgor pressure within their cells. When there is high rate of evaporation of water from the cells, they lose their turgidity and the plant wilts. Movement of Substances Diffusion Osmosis Active Transport  Turgor in Plants Movements of certain plant parts are due to changes in turgor. – Certain flowers open during the day and close at night (and vice versa) – The leaves of the Mimosa plant fold when they are touched. Caused by changes in turgor of the cells. – Changes in turgor of the guard cell to cause the opening and closing of stomata. Movement of Substances Diffusion Osmosis Active Transport  Test Yourself! TB Pg 37 Movement of Substances Diffusion Osmosis Active Transport  Exchange of Materials in Cells Surface area to volume ratio is important for cell efficiency. Cells exchange materials across their cell surface membranes: – Enter cell: oxygen, nutrients – Leave cell: carbon dioxide, waste If cells do not exchange materials quickly enough, they will die. Movement of Substances Diffusion Osmosis Active Transport  Surface Area to Volume Ratio A B C Surface area Surface area : Cube Volume /cm3 /m2 volume A B C Movement of Substances Diffusion Osmosis Active Transport  Surface Area to Volume Ratio As the cell becomes bigger, surface area to volume ratio decreases. The largest cell of the same shape has the smallest surface area to volume ratio. The rate of movement of a substance across the surface of a cell depends on how big the area of cell surface membrane is. The greater the surface area to volume ratio, the faster the rate of diffusion for a given concentration gradient. Movement of Substances Diffusion Osmosis Active Transport  Surface Area to Volume Ratio The activities that the cell carries out for survival is known as metabolism. Actively growing (or metabolizing) cells are usually small – Large surface area to volume ratio As the cells grow in size, their metabolism slows down. Cells stop growing when they reach a maximum size. Movement of Substances Diffusion Osmosis Active Transport  Cells for Absorption Some cells are specifically adapted to absorb materials. Root hair cell has a long protrusion to increase absorption of water and mineral salts from the soil. The red blood cell has a flattened biconcave shape increases surface area to volume ratio which increases the rate of oxygen uptake. Movement of Substances Diffusion Osmosis Active Transport  Cells for Absorption Epithelial cells in the small intestine have microvilli to increase surface area to volume ratio of the cell for absorbing digested food substances. Movement of Substances Diffusion Osmosis Active Transport  Active Transport Living cells are able to absorb substances against a concentration gradient. Definition: Active transport is the process in which energy is used to move particles of a substance against a concentration gradient. Movement of Substances Diffusion Osmosis Active Transport  Active Transport Only occurs in living cells: – Living cells respire and release energy which is used in active transport. In plants: – Root hairs take in dissolved mineral salts by active transport – Water enters the cell by osmosis In animals: – Glucose and amino acids are quickly absorbed by the small intestine by active transport. Movement of Substances Diffusion Osmosis Active Transport