B1 cell structure and transport

• Living things are all made up of cells, but most cells are so small you can only see them using a microscope
• Units used for tiny specimens

  • Kilometre (km)
  • Metre (m)
  • Centimetre (cm)
  • Millimetre (mm)
  • Micrometre (μm)
  • Nanometre (nm)
• 1 km = 1000 m
• 1 m = 100 cm
• 1 cm = 10 mm
• 1 mm = 1000 μm
• 1 μm = 1000 nm
• A nanometre is 0.000000001 metres (or written in standard form as 1 x 10-9 m)
• First light microscopes were developed

  Mid-17th century
• Light microscopes


  • Use a beam of light to form an image of an object
  • Can magnify around 2000 times (x2000)
  • School microscopes usually only magnify several hundred times
  • Relatively cheap
  • Can be used almost anywhere
  • Can magnify live specimens
• Electron microscopes


  • Use a beam of electrons to form an image
  • Can magnify objects up to around 2000000 times
  • Transmission electron microscopes give 2D images with very high magnification and resolution
  • Scanning electron microscopes give dramatic 3D images but lower magnifications
  • Large
  • Very expensive
  • Have to be kept in special temperature, pressure, and humidity-controlled rooms
• Magnification


  Multiply the magnification of the eyepiece lens by the magnification of the objective lens
• When labelling drawings made using a microscope, make it clear that the magnification you give is the magnification at which you looked at the specimen
• Magnification formula


  magnification = size of image / size of real object
• A light microscope has a resolving power of about 200 nm
• A scanning electron microscope has a resolving power of about 10 nm
• A transmission electron microscope has a resolving power of about 0.2 nm
• The resolving power of a microscope affects how much detail it can show
• Advantages and disadvantages of using

  • Light microscope
  • Electron microscope
• Calculating the diameter of a capillary

  1. Measure the image diameter

  2. Know the magnification

  3. Calculate the actual diameter
• Calculating the magnification of an image

  1. Know the actual size of the object

  2. Know the size of the image

  3. Calculate the magnification
• Magnifying power


  • Height of an average person magnified by a light microscope would look about 3.5 km
  • Height of an average person magnified by an electron microscope would look about 3500 km
• Resolving power


  • Light microscope can distinguish objects 200 nm apart
  • Scanning electron microscope can distinguish objects 10 nm apart
  • Transmission electron microscope can distinguish objects 0.2 nm apart
• Make sure you can work out the magnification, the size of a cell, or the size of the image depending on the information you are given
• What is osmosis?

  Passive movement of water particles
• How does osmosis occur?

  From higher to lower water concentration
• How can you observe the effects of sugar solutions on plant tissues?

  • Cut innocent potato into cylindrical pieces
  • Use different sugar solutions
  • Compare effects on plant tissues
• What should one sugar solution be in the experiment?

  Pure water
• What should the other sugar solution be in the experiment?

  Highly concentrated sugar solution
• What concentrations can be used in the experiment?

  0.2 mol/dm³, 0.4 mol/dm³, 0.6 mol/dm³
• What should you measure after soaking the cylinders?

  Their masses
• What happens to the mass of cylinders in sugar solutions?

  It increases or decreases based on concentration
• What does increased mass indicate in the experiment?

  Water has entered the cylinders
• What does decreased mass indicate in the experiment?

  Water has left the cylinders
• What variables affect the osmosis experiment?

  • Volume of sugar solution
  • Temperature
  • Time of exposure
  • Type of sugar used
• What is the dependent variable in the osmosis experiment?

  The mass of the cylinders
• What is the independent variable in the osmosis experiment?

  The concentration of sugar solutions
• What is the purpose of measuring percentage change in mass?

  To analyze the effect of osmosis
• How do you calculate percentage change in mass?

  Percentage change = (final mass - initial mass) / initial mass
• What does a positive percentage change indicate?

  Mass has increased due to water uptake