Cell Structure: Notes and Sample Answers

The light microscope parts and functions:

  • Eyepiece lens: magnification
  • Nosepiece: holds the objective lenses
  • Objective lens: magnification
  • Clip: holds the slide in place
  • Stage: the slide is placed on the stage
  • Condenser: focuses light onto the slide
  • Diaphragm: used to adjust the amount of light shining on the slide
  • Light: supplies light to the slide
  • Stage height adjuster: allows the stage to be moved up and down
  • Coarse/fine focus knob: focuses the image on the slide

How to use a light microscope:

  • Lower the stage to the bottom
  • Place the slide onto the stage and clip into place
  • Use the lowest power objective lens first
  • Use the coarse focus knob to approximately focus the object on the slide
  • Use the fine focus knob to focus the object on the slide
  • Adjust the amount of light hitting the object using the diaphragm
  • Repeat with a higher power objective lens

The transmission electron microscope:

  • Instead of using light to view objects, electrons are fired at the object and bounce off of it, allowing us to see
  • Because the wavelength of electrons are much lower than that of light, a more detailed and higher resolution image is obtained

Calculating magnification:

  • Magnification is calculated by multiplying the power of the eyepiece lens by the power of the objective lens
  • For example, if the power of the eyepiece lens is 10x and the power of the objective lens is 3x, the overall magnification is 30 (3 x 10 = 30)

The cell:

  • The cell is the smallest functional unit of life
  • Ultrastructure: the structure of a cell that can be seen under an electron microscope.
  • Animal cells:
    • Cell membrane: composed of phospholipids and proteins. Allow for some substances to enter while keeping some substances out. It also supports the cell.
    • Cytoplasm: a viscous, jelly-like liquid that contains and stabilises the organelles. It is where the majority of metabolism occurs.
    • Mitochondria: provides energy during respiration. Has cristae (infoldings) for increased surface area and increased energy production.
    • Ribosomes: this is where proteins are made
    • Nucleus: contains DNA and RNA. Controls the cell processes.
    • Nucleolus: located inside the nucleus, contains chromatin. This is where ribosomes are made
    • Nuclear pores: areas in the nuclear membrane made of various proteins through which molecules can pass in and out of the nucleus.
    • DNA: stores our genetic material
  • Plant cells:
    • Have all of the above features of animal cells with the addition of the following:
    • Cell wall: gives the cell its shape, strengthens the cell and prevents it from bursting. Plant cell walls are made of cellulose
    • Vacuole: vesicles surrounded by a membrane that have various functions, such as storage and waste removal.
    • Chloroplast: this is where photosynthesis takes place. Contains the pigment chlorophyll to trap light.
  • Examine animal cells:
    • Using a cotton swab, run it along the inside of your cheek.
    • Spread onto the slide.
    • Apply methylene blue as a stain with a dropper. A stain is needed to be able to clearly see the cells.
    • Add a cover slip at a 45 degree angle to avoid air bubbles. The cover slip is needed to protect the lens and prevent the cells from drying out.
    • View under the microscope using the procedure outlined above.
  • Examine plant cells:
    • Pull a thin strip of epidermis from an onion or take a thin shaving of Elodea leaf/potato/moss
    • Place it on the slide
    • Apply iodine as a stain with a dropper
    • Add a cover slip at a 45 degree angle to avoid air bubbles. The cover slip is needed to protect the lens and prevent the cells from drying out.
    • View under the microscope using the procedure outlined above.
  • Protoplasm: The collective term for the cytoplasm and nucleoplasm.
  • Prokaryotes: Organisms whose cells do not have a membrane bound nucleus or membrane bound organelles, e.g. bacteria.
  • Eukaryotes: Organisms whose cells have a membrane bound nucleus and membrane bound organelles, such as mitochondria and chloroplasts, e.g. plants and animals

Diagrams and sample answers for this chapter are available in our full Biology guide

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  • Post published:August 31, 2016
  • Post category:Biology