Chapter 3

• Learning Objectives


  - diffusion

  - osmosis

  - Active Transport
• Partially Permeable Cell Membrane

  - restrict passage of molecules that exceed a particular size

  - vital for osmosis since only H2O is allowed to pass thru

  - an artificial form of this is a visking tube
• Diffusion


  the net movement of molecules and ions from a region of higher concentration, to a region of lower concentration, as a result of their random movement
• Diffusion in Cells


  A partially permeable cell membrane controls the movement of substances- substances diffuse in and out of a cell through this
• Importance of Diffusion in Cells

  - obtaining necessary requirements needed for metabolism

  - getting rid of waste and toxic substances
• Diffusion During Photosynthesis


  - Atmosphere has a higher concentration of CO2 and leaves have lower concentration

  - carbon dioxide diffuses into the leaves and into the mesophyll tissue
• Diffusion During Pollination


  - insect pollinating flowering plants use diffusion to send out the nectar scent to attract insects
• Osmosis


  - diffusion of H2O molecules from a region of high to low water potential, down the concentration gradient, thru a partially permeable membrane
• Osmosis in Plant Cells

  Low Water Potential (concentrated solution)

  - plants become plasmolysed as they have a higher water potential than their surroundings

  
  

  High Water Potential (dilute solution)

  - plant cell becomes turgid but doesn't burst bc it has a tougher cell wall
• Osmosis in Animal Cells

  Low Water Potential (concentrated solution)

  - cells shrink since they have a higher water potential than their surroundings

  
  

  High Water Potential (dilute solution)

  - cell bursts as their surrounding solution has a higher water potential ---> the water enters the cell to the extent where the cell BURSTS
• Examples of Osmosis in Animals

  1. Water moves from the digestive system into blood

  2. Water moves from blood to tissue cells
• Examples of Osmosis in Plants

  1. water moves from soil into root hair cells

  2. Water moves from xylem into leaf cells
• Active Transport


  - energy consuming process where substances are transported against their concentration gradient when cells need to take in substances which are in small quantities around them

  - the energy used is provided by respiration in the cells
• Active Transport Steps


  1. Substance, present at lower concentration, combines w/ carrier protein

  2. Carrier proten changes shape and transports substance across membrane using energy produced during respiration

  3. Substance released into cells