<ul><li>The net movement of particles from an area of high concentration to an area of low concentration </li></ul><ul><li>Due to the random movement of particles </li></ul><ul><li>A passive process which means that no energy is needed </li></ul>
HIGH concentration LOW concentration A difference in concentration between 2 areas is called a CONCENTRATION GRADIENT . What effect might the gradient have on speed of diffusion?
Fast Steep concentration gradient Shallow concentration gradient Rate of Diffusion Draw both sets of diagrams, write how the rate of diffusion changes when the concentration gradient changes Slow
<ul><li>Concentration gradient </li></ul><ul><li>Temperature </li></ul><ul><li>Distance particles must travel </li></ul><ul><li>Faster Diffusion When... </li></ul><ul><li>Large concentration gradient </li></ul><ul><li>Higher Temperature </li></ul><ul><li>Short distance </li></ul>
The particles are separate when first put together. They slowly start to mix due to their random motion. The particles are now nearly fully diffuse. The particles are fully diffuse. Draw the diagrams next to each other and copy the captions Has diffusion stopped completely? Explain your answer
<ul><li>Dissolved substances have to pass through the partially permeable cell membrane to get into or out of a cell. </li></ul><ul><li>Diffusion is one of the processes that allows this to happen.. </li></ul>What substances are we talking about?
All living cells rely on diffusion to live. They use it for: <ul><li>Getting raw materials for respiration (dissolved substances and gases) </li></ul><ul><li>Removing waste products (eg. from respiration) </li></ul><ul><li>Plants use of photosynthesis (raw materials in, waste products out) </li></ul>Examples…
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?
deoxygenated blood (from body tissues) oxygenated blood (to body tissues) air in/out Alveoli are the tiny air sacs at the end of the bronchioles, in which gas exchange occurs. alveolus capillary red blood cell
Alveoli have several adaptations that help to make gas exchange very efficient: <ul><li>They are very thin – only one cell thick. </li></ul><ul><li>They are covered by a network of fine capillaries , enabling gases to pass almost directly between the lungs and bloodstream. </li></ul><ul><li>They are moist , encouraging gas molecules to easily dissolve. </li></ul><ul><li>They have a large combined surface area , allowing large amounts of gases to be exchanged with each breath. </li></ul>
Digestion breaks down large food molecules into smaller molecules such as glucose, amino acids and fatty acids that can be easily absorbed. Small food molecules are usually absorbed in the small intestine, diffusing across the intestine wall and into the bloodstream.
blood vessels capillary network Villi small intestine
<ul><li>The small intestine has these things called villi. The best way of explaining them, is that they look like millions of little sausages. </li></ul><ul><li>The villi INCREASE THE OVERALL SURFACE AREA of the small intestine, thus increasing the volume of substances which can be absorbed by diffusion. </li></ul><ul><li>The villi have a very GOOD BLOOD SUPPLY as each contains a capillary, which leads to the main blood supply, so when substances diffuse, they can go straight to the bloodstream. </li></ul><ul><li>Attached to each villi are thousands and thousands of MICROVILLI. These are exactly the same as the villi, except a lot smaller. </li></ul><ul><li>Again, the purpose of these is to further increase the surface area. Like before, as well, this increasing the volume of substances which can be absorbed. </li></ul><ul><li>So, the main points to remember are: </li></ul><ul><li>The villi and microvilli result in a LARGE SURFACE ARE A, for maximum absorption. </li></ul><ul><li>The villi also give a GOOD BLOOD SUPPLY to absorb the nutrients. </li></ul>
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.
<ul><li>The placenta is an organ that develops in the uterus during pregnancy. </li></ul><ul><li>The umbilical cord connects the placenta to the foetus. </li></ul><ul><li>It enables nutrients and oxygen to pass from the mother to the foetus by diffusion, and waste substances to diffuse from the foetus back to the mother. </li></ul>
<ul><li>The placenta can stop certain molecules and bacteria from diffusing through </li></ul><ul><li>It is unable to stop many harmful substances such as alcohol, chemicals and some types of virus from diffusing through, reaching the foetus. </li></ul>
How does the placenta work? umbilical cord umbilical artery umbilical vein
<ul><li>Carbon dioxide diffuses in through the stomata </li></ul><ul><li>Oxygen and water diffuse out of the stomata </li></ul>carbon dioxide + water oxygen + glucose <ul><li>During photosynthesis, the level of CO 2 is low inside the leaf </li></ul><ul><li>This creates a big concentration gradient so CO 2 diffuses into the cell </li></ul>