Diffusion , osmosis and active transport

• Cells need to obtain substances from their surroundings in order to survive like water and oxygen. But need to removed waste products like CO2
• What is diffusion?


  Movement of particles from an area of high concentration to a low concentration
• What three ways can you increase the rate of diffusion?


  Increase the temperature (particles have more kinetic energy)

  Increase the concentration gradient

  Increase the surface area
• What are three examples of diffusion?

  Cells carrying out respiration

  Plant cells carrying out photosynthesis

  Transport of urea in the blood
• Multi-cellular organisms require specialised exchange surfaces to provide an efficient supply of materials. This is because of the surface area to volume ratio
• A smaller object has a bigger surface area to volume ratio
• What does having a large surface area to volume ratio do?


  Increases the rate of diffusion

  Makes it easier absorbing essential substances
• What is active transport ?


  Movement of particles from a low concentration for high concentration which requires energy
• Active transport requires energy so cells that are specialised to carry out active transport have many ribosomes
• What are two examples of active trabsport?

  Absorption of glucose in the small intestine

  Absorption of minerals ions in plant roots
• Active transport can’t happen without oxygen as respiration releases energy
• What is osmosis ?


  Movement of water from a high concentration of water to a low concentration of water across a partially permeable membrane
• How do you calculate percentage change ?


  Change/Original X 100
• What are exchanged surfaces ?


  Adaptations that enable substances to move quickly in and out of the body and are required because larger organisms have a small surface area to volume ratio
• The alveoli are the site of gas exchange in the mammals. Oxygen diffuses into the blood and carbon dioxide diffuses out of the blood
• Each alveolus has a good blood supply, thin walls, large surface area and are well ventilated
• The villi are the site of nutrient absorption in the small intestine.
• Each villus have a good blood supply, thin walls and a large surface area
• The root hair cells are the site of water and nutrient absorption in plants. They have a large hair like structure that increases the surface area for absorption
• Root hair cells have thin walls, large surface area and a steep concentration gradient
• The gills are the site of gas exchange in fish. Water passes over the gills and oxygen diffuses into the blood from the water
• Gills have a good blood supply, thing walls, large surface area and a steep concentration gradient