Year 8 Science Cells and Microscopes

• The classical cell theory was proposed by Theodor Schwann


  1839
• Classical cell theory


  1. All organisms are made of cells

  2. Cells are the basic units of life

  3. Cells come from pre-existing cells that have multiplied (described by Rudolf Virchow in 1858)
• Since the formation of classical cell theory, technology has improved, allowing for more detailed observations that have led to new discoveries about cells
• Modern cell theory


  1. DNA is passed between cells during cell division

  2. The cells of all organisms within a similar species are mostly the same, both structurally and chemically

  3. Energy flow occurs within cells
• Eukaryotic cells


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotic cells


  Cells that lack a nucleus and membrane-bound organelles
• Prokaryotic organisms


  • Archaea
  • Bacteria
• Prokaryotic cells


  • Reproduce asexually, copying themselves
  • Single-celled organisms, with only a few exceptions
  • Smaller cell sizes
• Eukaryotic organisms


  • Animals
  • Plants
  • Protists
  • Fungi
• Eukaryotic cells


  • Reproduce sexually through meiosis, which allows for genetic variance
  • Most are multicellular, with some exceptions
  • Larger cell sizes
  • Contain membrane bound organelles
  • Contain a nucleus (brain of cell) – capable of specialised functions
• Nucleoid


  Area of the cytoplasm where DNA sits in prokaryotic cells
• Prokaryotic cells


  • Lack membrane bound organelles
  • Lack a nucleus (brain of cell) – incapable of specialised functions
  • Contain ribosomes (makes proteins)
  • Have a simple cell membrane
• Eukaryotic cells


  • Contain organelles enclosed in membranes
  • Contain a nucleus to store DNA in chromosomes
  • Contain ribosomes
  • Have a more complex cell membrane
• Most cells are too small to be seen without a microscope
• Micrometre (μm)


  One millionth (1/1,000,000) of a metre or one thousandth (1/1,000) of a millimetre
• Measuring cell size under a microscope

  1. Set up the microscope with the lowest power objective lens

  2. Place the ruler on the stage and focus the microscope on the ruler markings

  3. Line up the ruler so that it crosses the full diameter of the field of view (FOV)

  4. Count the markings on the ruler to get the diameter

  5. Record the FOV Diameter for each of the 3 lenses in mm and μm
• Estimating cell size under a microscope

  1. Position your specimen on the stage and centre in the field of view (FOV)

  2. Estimate how many of the objects viewed with this lens can fit across the circular area (FOV) at its widest

  3. Divide the FOV Diameter by the number of objects that fit across
• Estimating microorganism length


  • Field of view diameter is 400 μm
  • Field of view diameter is 450 μm
• Parts of the cell

  • Cell wall
  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Chloroplast
  • Lysosomes
  • Vacuole
  • Mitochondria
  • Endoplasmic reticulum
  • Ribosomes
• Organelles in animal and plant cells

  • Cell wall (plant only)
  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Chloroplast (plant only)
  • Lysosomes
  • Vacuole
  • Mitochondria
  • Smooth endoplasmic reticulum
  • Rough endoplasmic reticulum
  • Ribosomes
• Stem cells have the ability to develop into different cell types in the body
• Embryonic stem cells


  Stem cells derived from donated embryos
• Induced pluripotent stem cells

  Stem cells reprogrammed from adult tissue cells
• Embryonic stem cells and induced pluripotent stem cells

  Both have pluripotent capabilities, but embryonic stem cells are derived from embryos while induced pluripotent stem cells are reprogrammed from adult cells
• Stem cells have many potential uses in medicine