Ch 5 Diffusion Osmosis Active Transport Notes 2024.pdf

Chapter 5: Diffusion, Osmosis and Active Transport Name: _______________________( ) Class: __________ Date: ________ CHAPTER OVERVIEW Movement of Particles Any particles...

Chapter 5: Diffusion, Osmosis and Active Transport Name: _______________________( ) Class: __________ Date: ________ CHAPTER OVERVIEW Movement of Particles Any particles Only water molecules Diffusion Active Osmosis Transport - Down a concentration - Against a concentration - Down a water potential gradient gradient gradient - From higher concentration - From lower concentration - From higher water potential to lower concentration to higher concentration to lower water potential - No energy required - Energy is required - Through a SELECTIVELY permeable membrane - No energy required Learning Outcomes: Students will be able to: 1. define diffusion as the movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient. 2. define osmosis as the passage of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane. 3. distinguish between diffusion and osmosis in terms of the type of molecules and the presence/absence of a partially permeable membrane (*for cell membranes, must use selectively permeable membrane). 4. define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi. 5. describe the effects of osmosis on plant cells (including turgidity, flaccidity and plasmolysis) and animal cells. Advanced: 1. apply the concepts of the movement of particles to solve related data analysis problems. Page 1 of 12 Diffusion Sometimes, while studying in the living room, you may get distracted by the smell of your mother's cooking from the kitchen. On the street, you may smell the unpleasant odour of rubbish before seeing the rubbish truck. All these can be explained if we think of these smells as made up of tiny atoms or molecules constantly moving from where they are more concentrated to where they are less concentrated. The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, is called diffusion. - Concentration refers to the number of particles per unit volume - The concentration gradient is the difference in concentration between two regions. Particles move down a concentration Particles continue moving but the gradient until concentration is uniform concentration remains uniform throughout Page 2 of 12 The photographs below were taken at different intervals of time after a crystal of potassium permanganate was placed in a jar of water. Source: https://chemstory.files.wordpress.com/2013/06/kmn04_diffusion.jpg The purple colour of the potassium permanganate spread slowly, eventually filling the whole jar of water even when there was no stirring. This is because the particles in the crystal separated from one another as the crystal dissolved in water. Water molecules then collide with these particles as they move slowly through water, spreading them out in all directions. Diffusion occurs spontaneously and does not involve any energy taken in or given out, i.e. there is no gain or loss of energy. The movement of particles during diffusion is random and continuous, with each moving in a different direction, as shown in the figure below. Source: Cambridge University Press Let's Think… Which state of matter (solids, liquids or gases) will diffusion occur the fastest? Why? From solids to liquids to gases, particles move further apart and can move randomly with less forces of attraction between them. Page 3 of 12 The rate of diffusion depends upon: ♦ The concentration gradient The greater the difference in concentration between two regions of a substance, the higher the rate of diffusion. In other words, the steeper the diffusion gradient for a substance, the greater the rate of diffusion. ♦ The distance over which diffusion takes place The shorter the diffusion distance between two regions of different concentrations, the greater the rate of diffusion. ♦ The area over which diffusion takes place The larger the surface area, the higher the rate of diffusion. Diffusion surfaces frequently have structures for increasing their surface area, hence the rate at which they exchange materials. These structures include microvilli on cells lining the small intestine. ♦ The size and nature of the diffusing molecule Small molecules diffuse faster than large ones. Fat-soluble molecules diffuse more rapidly through cell membranes (consisting of fats and proteins) than water-soluble molecules. Page 4 of 12 Osmosis (A special case of diffusion) A water molecule comprises two hydrogen atoms and one oxygen atom. Hydrogen atoms are the smallest atoms that exist. Oxygen atoms are not very large. Thus, water molecules are smaller than most solute molecules. For example, a long chain of starch is much larger than a water molecule. Source: http://www.nuffieldfoundation.org/sites/default/files/PB_evaluating-visking-tubing-2.jpg The diagram above shows a starch and glucose (small sugar molecules from starch) solution separated from pure water by a thin piece of membrane such as a visking tubing. The membrane has many tiny pores in it. The pores are big enough to allow water and glucose molecules through, but not the larger starch. A membrane such as this, which will allow some molecules through but not others, is called a selectively permeable membrane. The water molecules on both sides also move around, colliding with other molecules and the membrane. Water molecules from both sides of the membrane will cross to the other side. There is a two-way traffic of water molecules from one side of the membrane to the other. The movement of particles in one direction does not hinder the movements of other particles in the opposite direction. There are far more water molecules in the pure water than sugar solution. Hence, more water molecules from the pure water will pass through the pores in the membrane. We say that the water molecules have moved from the pure water into the sugar solution. This net movement of water molecules through a selectively permeable membrane, from a region of a higher water potential to a region of a lower water potential, down a water potential gradient is called osmosis. Osmosis through the selectively permeable membrane of the Visking tubing will continue until the water potential is uniformly distributed between the two solutions. When the two solutions are of equal water potential, there is no net movement of particles in any particular direction. Osmosis is just a special kind of diffusion. In osmosis, water molecules diffuse through a selectively permeable membrane. On the other hand, diffusion generally involves any type of molecules, and a selectively permeable membrane needs or does not need to be present. Page 5 of 12  In living cells, the cell membrane is selectively permeable. This is because the cell membrane not only allows water to move across by osmosis, but it also has special channels and carrier proteins that allow other molecules to pass through. Osmosis is important to living organisms as water enters and leaves the cells through their cell membranes. Effect of Osmosis From the diagram below, there is a net movement of water molecules from 10% solute solution (hypotonic solution) to 20% solute solution (hypertonic solution) through a selectively permeable membrane. When equilibrium is reached, i.e. water potential is equal on either side of the selectively permeable membrane, a difference in solution level is observed on both sides. higher water potential lower water potential Page 6 of 12 Application: Osmosis in Living Things Osmosis is an important process for all living things. When a unicellular organism like the Paramecium adapts to living in the pond, the water in the pond is hypotonic to the cell. The Paramecium needs to osmoregulate control the water balance between its cellular environment and the external environment. It has developed a contractile vacuole that can pump water out of the cell as fast as it enters by osmosis. This prevents the Paramecium from bursting in a hypotonic environment. In plants, when water molecules enter the plant cells across the selectively permeable cell membrane, from a region of higher water potential to a region of lower water potential, the plant cell will not burst due to the presence of the tough cellulose cell wall. The cell wall prevents overexpansion of the cell by exerting an opposing pressure preventing the entry of more water molecules. The pressure exerted by the water on the cell wall is called turgor pressure. For example, when a potato strip is immersed in distilled water, the potato cells will become turgid and the potato strip will increase in length. The root hair cell absorbs water and dissolved mineral salts from the soil. Water molecules enter the root hair cell by osmosis. The path taken by the water from the root hair cell to the xylem is shown in the figure below. Source: Cambridge University Press Page 7 of 12 Application: Diffusion in Living Things Respiration: As oxygen is used up in a living cell for respiration, the concentration of oxygen in the cell is lowered. When the concentration of oxygen in a cell becomes lower than that in its surroundings, oxygen from the surroundings will diffuse into the cell through the cell membrane, as shown in the figure below. Diffusion of oxygen into a cell. The red dots represent oxygen molecules. Source: Cambridge University Press Carbon dioxide is constantly produced as a waste product of respiration in living cells, and it diffuses out from the cells to the surroundings which have a lower concentration of carbon dioxide. Photosynthesis: During photosynthesis, cells in green leaves take in water and carbon dioxide to form glucose and oxygen. Carbon dioxide from the surrounding air diffuses into the cells of green leaves through the stomata and oxygen produced from the cells diffuses out into the surrounding air. Page 8 of 12  Effect of different types of solutions on living cells Types of Solution (ONLY APPLICABLE TO ANIMAL CELLS) Isotonic solution: "Iso-" means equal. Isotonic solutions have equal water potential. Hypotonic solution: A solution that has a higher water potential (lower concentration of solute) than the other solution. Hypertonic solution: A solution that has a lower water potential (higher concentration of solute) than the other solution. Animal Cell in: Plant cell in: Case 1: Hypotonic solution Solution of higher water potential (eg. distilled water) (eg. distilled water) Osmosis occurs. Osmosis occurs. Higher water potential in extracellular Higher water potential in extracellular solution solution than intracellular solution. than intracellular solution Water molecules enter the animal cell Water molecules enter the plant cell across across the selectively permeable cell the selectively permeable cell membrane membrane and the cell swells. and the cell swells. Net gain of water molecules from Net gain of water molecules from extracellular extracellular solution into the cell. solution into the cell. As more and more water molecules Central vacuole increases in size and plant cell enter the cell, it swells. start to swell. The cell membrane has to stretch as Plant cells do not burst due to its tough the cell gets bigger. cellulose cell wall. Until the strain is too large, the cell will When the cellulose cell wall is stretched to its burst and release the contents of the maximum, the plant cell cannot take in any cell. more water and is said to be turgid. This breaking up of a cell is called lysis, resulting in a lysed cell. Page 9 of 12 Case 2: Hypertonic solution Solution of lower water potential (e.g. Concentrated salt solution) (eg. Concentrated salt solution) Osmosis occurs. Osmosis occurs. Lower water potential in extracellular Lower water potential in extracellular solution solution than intracellular solution than intracellular solution Water molecules leave the animal cell Net loss of water molecules from the cell into across the selectively permeable cell extracellular solution. membrane, and the cell shrinks. Firstly, the cell shrinks slightly and becomes Net loss of water molecules from the flaccid. cell into extracellular solution. Central vacuole decreases in size. If a large amount of water leaves the Then, the selectively permeable cell cell, it will become shrivelled. membrane starts to pull away from the When cells shrink and shrivel, the cellulose cell wall. process is called crenation. This leaves a visible gap between the cell wall and the cell membrane. This process is called plasmolysis. Plants with plasmolysed cells will wilt and die if water is not supplied. Cell appearance is described as flaccid. For example: Onion cells in a concentrated salt solution. The cytoplasm has shrunk inwards, leaving big gaps between the cytoplasm and the cellulose cell walls. Plasmolysis has occurred. Page 10 of 12 Case 3: Isotonic solution Solution of same water potential Equal water potential in extracellular Equal water potential in extracellular solution solution and intracellular solution and intracellular solution. No net gain or loss of water molecules No net gain or loss of water molecules. Summary of the effect of different types of solutions on living cells: Animal cells: Hypotonic solution Isotonic solution Hypertonic solution (e.g. distilled water) (eg. Concentrated salt solution) The net into the cells no net movement out of the cells movement of water molecules Effect cells swell and burst no net change in size or cells become shrivelled (lysed cells) shape Plant cells: Solution of higher water Solution of same water Solution of lower water potential potential potential (e.g. distilled water) (eg. Concentrated salt solution) Net movement of into the cells no net movement out of the cells water molecules Effect cells swell no net change in size cells become flaccid and then become turgid or shape plasmolysed. Page 11 of 12 Active Transport Living cells can absorb certain substances from the external environment even though these substances are of higher concentration inside the cell than they are in the environment. This means that the cells are absorbing substances against a concentration gradient, and energy is required. Active transport is the process in which energy is used to move the particles of a substance against a concentration gradient, that is from a region of lower concentration to a region of higher concentration. Active transport requires energy released from the process of respiration in living cells. Active transport is carried out by a series of carrier proteins within the cell membrane. These have a binding site, allowing a specific dissolved substance to bind to the side of the membrane where it is at a lower concentration. Examples of active transport 1. Root hair cells in plant roots use active transport to absorb nitrate ions from the soil, although the concentration of nitrate ions inside the root hair cell is higher than the concentration in the soil. 2. In the small intestine, glucose and amino acids are actively transported from the lumen of the intestine into the cells of the villi. Cells of small intestine take in Root hair cells take in dissolved mineral glucose through diffusion as salts through diffusion as well as active well as through active transport. transport. Differences between diffusion and active transport Diffusion Active transport Transports dissolved substances from higher to Transports dissolved substances from lower to lower concentration higher concentration Requires no additional energy input Requires energy from respiration in living cells. Page 12 of 12