Unit4.1:Cells(book 1B ,p.2-22)

• Cells are the basic units of living things
• Some living things are made up of many cells and are called multicellular organisms (e.g. celery, rose, human)
• Some living things are made up of only one cell and are called unicellular organisms (e.g. Amoeba, E. coli, yeast)
• We can use a microscope to observe cells in detail
• Comparison between light microscopes and electron microscopes:

  • Light microscopes have lower magnifying power (up to 1600 times) and produce less detailed, coloured images
  • Electron microscopes have higher magnifying power (up to 1,500,000 times) and produce more detailed, black and white images
• Parts of the light microscope:

  • Eyepiece: lens nearest to our eyes
  • Objective: lens nearest to the slide
  • Coarse adjustment knob: used for large focusing adjustments
  • Fine adjustment knob: used for small focusing adjustments
  • Stage translational control: used to move the slide
  • Diaphragm: used to adjust light entering the microscope
  • Light source/mirror: shines light onto the slide
• Total magnification of a microscope = magnification of eyepiece × magnification of objective
• Steps in using the light microscope:

  • Put the microscope on the bench and turn on the light source
  • Choose a low-magnification eyepiece and objective
  • Clip the slide onto the stage and adjust the stage translational control
  • Use the coarse adjustment knob to focus without touching the slide
  • Use both eyes to slowly raise the objective with the coarse adjustment knob
  • Use the fine adjustment knob for a sharp image
• The image formed in the light microscope is magnified and inverted
• The direction of movement of the image under the light microscope is opposite to that of the slide
• The higher the magnification of the microscope, the smaller and dimmer the field of view
• Structures in a plant cell and an animal cell:

  • Cell wall: in plant cells only, protects and supports the cell
  • Cell membrane: in plant and animal cells, controls movement of substances
  • Cytoplasm: in plant and animal cells, allows transport and chemical reactions
  • Nucleus: in plant and animal cells, contains genetic materials
  • Vacuole: in plant cells (large) and animal cells (small), stores water and minerals
  • Chloroplast: in cells of green plants, contains chlorophyll for photosynthesis
• Skills in preparing a slide:

  • Place specimen on a clean slide
  • Add water or stain to the specimen
  • Cover with a cover slip, remove air bubbles, and soak up excess liquid with tissue paper
• Points to note in making biological drawings:

  • Draw smooth, continuous lines without sketching or shading
  • Draw different parts in proportion
  • Use straight labelling lines for labels without crossing
  • Include a title with the specimen name and magnification power