Cell Biology: Diffusion

• Partially Permeable:


  Only some molecules can diffuse through
• What is the definition of diffusion?


  Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.
• Diffusion is a passive process (which means no energy is required).
• Here the perfume particles are moving from the area of higher perfume concentration to the area of lower perfume concentration and therefore spreads throughout the air particles.

  A) Diffusion

  
• What are the 3 factors that affect the rate of diffusion?


  Concentration Gradient

  Temperature

  Surface Area
• It is important to remember that the particles:

  • will move in both directions, but there will be a net movement from high to low concentration
  • will end up evenly spread throughout the liquid or gas, but will continue to move
• Simple organisms take in substances over their body surface. Their needs are determined by their volume. As organisms increase in size, their surface area does not increase at the same rate as their volume. For example, the surface area to volume ratio of a puppy is several times greater than that of an adult dog.
• The rate of diffusion can be affected by a number of factors:

  • The concentration gradient: The greater the difference in concentration, the quicker the rate of diffusion.
  • The temperature: The higher the temperature, the more kinetic energy the particles will have, so they will move and mix more quickly.
  • The surface area of the cell membrane separating the different regions: The greater the surface area, the faster the rate of diffusion.
• Diffusion in Leaves:

  A) O2 moves out of cells by diffusion

  B) High O2 Concentration

  C) Low CO2 Concentration

  D) CO2 moves into the cells by diffusion

  E) Sunlight

  F) Palisade Mesophyll

  G) Spongy Mesophyll

  H) Guard Cell

  
• In plants, stomata open when it’s light and close when it’s dark. This means that photosynthesis only occurs during daytime hours. Stomata also open when water levels are high inside the plant and close when water levels are low inside the plant. This helps prevent dehydration.
• Oxygen diffusion through leaf tissue

  1. Reaches guard cells surrounding stoma

  2. Enters intercellular spaces between mesophyll cells

  3. Diffuses across thin walls of mesophyll cells

  4. Diffuses down concentration gradient towards chloroplasts in palisade mesophyll cells
• Photosynthesis in chloroplasts

  Carbon dioxide and oxygen combine to form glucose
• Glucose transport

  1. Leaves chloroplasts

  2. Enters cytoplasm of mesophyll cells

  3. Diffuses out of cells via intercellular spaces

  4. Back into atmosphere
• When the sun shines on the leaves, chloroplasts absorb some of its energy. Chloroplasts contain chlorophyll molecules which trap sunlight energy. This energy is used to convert carbon dioxide and water into glucose and oxygen.
• Oxygen diffuses through the leaf tissue until it reaches the air spaces between the mesophyll cells where it enters the atmosphere. Carbon dioxide diffuses across the cell wall and into the guard cells which surround the stoma (the opening). When carbon dioxide enters the guard cells, they become turgid and this causes them to push against one another and pull apart slightly. This opens the stoma wider allowing more carbon dioxide to enter the leaf.
• Diffusion in Alveolus:

  A) Air Out

  B) Air In

  C) Alveolus

  D) Blood from the body high in CO2 and low in O2

  E) Blood to the body high in O2 and low in CO2

  F) CO2 diffuses from blood to alveolus

  G) O2 diffuses from alveolus to blood

  
• Diffusion in Liver Cells:

  A) Liver Cells

  B) High Concentration of Urea

  C) Low Concentration of Urea

  D) Blood Vessel in Liver

  E) Urea is filtered from the blood by the kidneys