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What is diffusion?. Diffusion and concentration. Why can the student smell the sock from a distance?. The sock can be smelt because sweat and other molecules are moving away from it and spreading out in the air . This is called diffusion . Where is the smell strongest?.
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Diffusion and concentration Why can the student smell the sock from a distance? The sock can be smelt because sweat and other molecules are moving away from it and spreading out in the air. This is called diffusion. Where is the smell strongest? The smell is strongest at the sock. The smell becomes weaker further away from the sock.
solid (e.g. ice) liquid (e.g. water) gas (e.g. steam) Moving molecules In which states are molecules able to diffuse? Molecules in liquids and gases are constantly moving and bumping into each other. This means that they tend to spread out.
high concentration low concentration Changing concentrations During diffusion molecules move from an area of high concentration to an area of low concentration. They are said to move down a concentration gradient. Diffusion is a passive process which means that no energy is needed. Molecules diffuse until they are evenly spaced apart and equilibrium is reached. The rate of diffusion depends on several factors, such as the distance the particles have to travel and the difference in concentration.
Why is diffusion important to life? Diffusion is the main way in which substances move over short distances in organisms. What substances need to move? Oxygen, food and waste products are some of the substances that move by diffusion. In animals, how do these vital substances get to where they are needed? The substances are transported in the bloodstream, from where they can diffuse in and out of cells.
Diffusion and breathing Breathing involves the exchange of gases in the lungs; a process that occurs by diffusion. What happens when you breathe in? Oxygen in inhaled air diffuses through the lungs and into the bloodstream. The oxygen is then transported throughout the body. Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from body tissues into the bloodstream and is exhaled via the lungs. Where does gas exchange take place in the lungs?
alveolus capillary red blood cell Cross-section through an alveolus Alveoli are the tiny air sacs at the end of the bronchioles, in which gas exchange occurs. air in/out deoxygenated blood (from body tissues) oxygenated blood (to body tissues)
How are alveoli adapted? Alveoli have several adaptations that help to make gas exchange very efficient: • They are very thin – only one cell thick. • They are covered by a network of fine capillaries, enabling gases to pass almost directly between the lungs and bloodstream. • They are moist, encouraging gas molecules to easily dissolve. • They have a large combined surface area, allowing large amounts of gases to be exchanged with each breath.
Diffusion and digestion Carbohydrates, proteins and fats are made up of large molecules that cannot be readily absorbed by the body. Digestion breaks down large food molecules into smaller molecules such as glucose, amino acids and fatty acids that can be easily absorbed. In which part of the digestive system is most food absorbed? Small food molecules are usually absorbed in thesmall intestine, diffusing across the intestine wall and into the bloodstream.
capillary network villus small intestine blood vessels How is the small intestine adapted? The wall of the small intestine is lined with many tiny finger-like projections called villi. These are very thin and increase the surface area of the small intestine, both of which increase the speed of diffusion.
glucose Diffusion and the small intestine How does the initial concentration of dissolved food molecules in the small intestine compare with the concentration of the blood in the villi? The concentration of dissolved food molecules is higher in the small intestine than in the blood entering the villus. This means that the dissolved food molecules diffuse from the small intestine into the blood, moving from higher to lower concentration.
Diffusion and the placenta The placenta is an organ that develops in the uterus of female mammals during pregnancy. The umbilical cord connects the placenta to the fetus. The placenta enables nutrients and oxygen to pass from the mother to the fetus by diffusion, and waste substances to diffuse from the fetus back to the mother. The placenta can filter out certain molecules and bacteria, but is unable to stop many harmful substances such as alcohol, chemicals and some types of virus from reaching the fetus.
blood to mother low in O2/nutrients, high in CO2/waste umbilicalcord placental villiincrease surface area for diffusion umbilicalartery blood from mother high in O2/nutrients, low in CO2/waste umbilicalvein Diffusion and the placenta How does the placenta work?
synaptic cleft neurotransmitter neurotransmitter receptor nerve impulse Diffusion and nerves impulses A synapse is a junction between two neurones across which electrical signals must pass. Neurotransmitter molecules diffuse from vesicles towards the neurotransmitter receptors, moving from an area of high concentration to low concentration.
partially-permeable membrane (visking tubing) water glucose What is osmosis? Osmosis is the diffusion of water moleculesfrom a low concentration solution to high concentration solution, across a partially-permeable membrane. A partially-permeable membrane has holes in it that permit water molecules through but are too small to allow larger molecules through. Osmosis can be demonstrated using visking tubing filled with a solution and placed in a beaker of pure water.
pure water concentrated solution dilute solution Dilute vs. concentrated During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions. • Dilute solutions have a high concentration of water molecules. • Concentrated solutions have a low concentration of water molecules.
plasma membrane cell wall Osmosis and cells Plant and animal cells are surrounded by a partially-permeable plasma membrane. This allows water and other small molecules to diffuse across. Plant cells additionally have a strong cell wall surrounding the membrane which offers support and protection. red blood cell plant cell
Osmosis and animal cells Animal cells do not have a cell wall. This means they respond differently to plant cells to the gain and loss of water. In dilute solutions, osmosis can cause animals cells, such as red blood cells, to swell up and burst. This is called lysis. In concentrated solutions, water loss causes the cells to shrink. When this happens to red blood cells, it is called crenation.
hypothalamus Osmosis and animal cells In order to remain healthy, animal cells need to maintain an isotonic water balance. This means that the water concentration both inside and outside the cell are equal. The concentration of water and salt in the blood are controlled by the kidneys. The kidneys are controlled by the portion of the brain called the hypothalamus.
Movement in and out of cells Substances move in and out of cell by passive and active transport. Which methods of transport are illustrated?
What is active transport? Substances can move passively in and out of cells by diffusion until the concentration on both sides of the cell membrane reaches an equilibrium. Substances can continue to move in and out of a cell using a process called active transport. During active transport, protein carriers in the cell membrane ‘pick up’ particles and move them against the concentration gradient. As the name suggests, active transport requires energy from the cell, which is made available by respiration.
minerals Active transport in plants Plants need to absorb mineral elements such as nitrogen, phosphorus and potassium from the soil for healthy growth. When the concentration of minerals in soil is lower than inside the plant, active transport is used to absorb the minerals against the concentration gradient. What would happen if the plant relied on diffusion to absorb minerals? The cells would become drained of minerals because they would travel down the concentration gradient.
glucose Active transport in humans During digestion, the villi in the small intestine absorb the soluble nutrients. Over time, the concentration of nutrients in the villi reach an equilibrium with the concentration in the gut. Active transport is used to continue the transport of the small amounts of remaining nutrients against the concentration gradient.
Glossary (1/2) • active transport – The movement of molecules against a concentration gradient, and which requires energy. • alveoli – The tiny air sacs at the end of the bronchioles in which gas exchange takes place in mammals. • concentration gradient – The difference in concentration across a given area. • crenation – The shrinking of animal cells in response to water loss by osmosis. • diffusion – The movement of molecules from an area of high concentration to low concentration. • osmosis – The diffusion of water molecules from a dilute solution to a more concentrated solution.
Glossary (2/2) • partially-permeable membrane – A membrane that allows only certain sized molecules to pass through it. • placenta –The organ that transports oxygen, nutrients and waste products to and from the developing fetus. • turgid –The state caused by high water uptake in plant cells. • villi – Tiny finger-like projections on the inner surface of the small intestine, across which nutrients diffuse.
