topic 1 - cell biology

• Specialized exchange surfaces


  Parts of an organism over which they exchange substances with their environment
• Specialized exchange surfaces in humans

  • Alveoli
  • Villi
• Alveoli


  • Small sac-like things found in the lungs at the very ends of the bronchioles
  • Exchange oxygen and carbon dioxide between the air and the blood
• Villi


  • Finger-like things found on the inside lining of the small intestines
  • Help absorb nutrients like glucose and amino acids
• Specialized exchange surfaces in plants

  • Root hair cells
  • Leaves
• Root hair cells


  • Help absorb water and mineral ions from the soil
• Leaves


  • Help absorb the carbon dioxide they need from the air
• Common features of specialized exchange surfaces

  • Large surface area
  • Thin surfaces
  • Permeable to substances they need to exchange
  • Good blood supply (internal medium)
  • Good supply of external medium
• Large surface area


  Allows more molecules to diffuse across at the same time, increasing the rate of diffusion
• Thin surfaces


  Short diffusion distance, allowing faster diffusion
• Permeable


  Allows substances to diffuse across rather than blocking them
• Good blood supply (internal medium)


  Helps maintain a concentration gradient for substances to diffuse into the blood
• Good supply of external medium


  Helps maintain a concentration gradient for substances to diffuse into the organism, e.g. air for alveoli, food for villi
• Adaptations of Capillary network


  • Large surface area (about 75 m2)
  • Thin walls
  • Good blood supply
• Diffusion of gases in leaves

  1. Carbon dioxide diffuses into air spaces in leaf

  2. Carbon dioxide diffuses into cells for photosynthesis

  3. Oxygen and water vapour diffuse out through stomata
• Stomata


  • Little holes on underside of leaf
  • Controlled by guard cells to prevent water loss
• Flattened shape of leaf increases exchange surface area
• Air spaces inside leaf increase surface area for carbon dioxide to diffuse into cells
• Water vapour evaporates from cells and diffuses out of leaf
• Gills


  • Large surface area for gas exchange
  • Thin surface layer of cells
  • Blood and water flow in opposite directions
• Gas exchange in gills

  1. Water containing oxygen enters mouth and exits through gills

  2. Oxygen diffuses from water into blood

  3. Carbon dioxide diffuses from blood into water
• Gill filaments and lamellae

  • Increase the surface area for gas exchange
  • Covered in blood capillaries to speed up diffusion
• Oxygen concentration in water is always higher than in blood, so oxygen diffuses into the blood
• Steps of stem cell treatment

  1. Extract embryonic stem cells from early embryos.
  2. Grow them in a laboratory.
  3. Stimulate them to differentiate into whichever type of cell that we want.
  4. Give them to the patient to their replace faulty cells.
• What is the main part of the optical microscope where the slide is placed?

  The stage
• What is the function of the clips on the stage of the microscope?

  To hold the microscope slide in place
• What is located below the stage of the optical microscope?

  A lamp or a mirror
• How does the mirror in some optical microscopes function?

  It reflects light up through the microscope slide
• What are the lenses above the stage called?

  Objective lenses
• How many objective lenses do most microscopes have, and what are their typical magnifications?

  Three objective lenses with magnifications of four times, ten times, or forty times
• What is the magnification of the eyepiece lens?

  Ten times
• What are the final parts of the microscope mentioned in the video?

  The coarse focusing dial and the fine focusing dial
• What is the first step in using an optical microscope to view a prepared slide?

  Place the slide onto the stage and use the clips to hold it in place
• Which objective lens should be selected first when using an optical microscope?

  The lowest power objective lens, usually four times
• How do you position the objective lens when using an optical microscope?

  Turn the coarse focusing dial until the objective lens almost touches the microscope slide
• Why is it important to look at the microscope from the side while adjusting the objective lens?

  To avoid damaging the slide
• What should you do after positioning the objective lens close to the slide?

  Look down through the eyepiece and slowly turn the coarse focusing dial
• What is the purpose of the fine focusing dial?

  To bring the cells into clear focus
• How do you calculate the total magnification of the microscope?

  Multiply the magnification of the eyepiece lens by the magnification of the objective lens
• What is the total magnification when using a ten times eyepiece lens and a four times objective lens?

  Forty times