Required practical 1

• Describe how to prepare a microscope slide

  1 ● Plant eg. onion cells: peel off thin layer of tissue

  using forceps, place on water drop on slide

  ● Animal eg. cheek cells: swab inside cheek with a

  cotton bud, smear onto centre of slide

  2 Add a drop of stain with a pipette

  3 Lower coverslip at an angle without trapping air bubbles
• Describe how to use a microscope to view cells

  1 Clip slide onto stage and turn on light

  2 Select lowest power objective lens (usually x 4 )

  3 a. Use coarse focusing dial to move stage close to lens

  b. Turn coarse focusing dial to move stage away from

  lens until image comes into focus

  4 Adjust fine focusing dial to get clear image

  5 Swap to higher power objective lens, then refocus
• How is the total magnification of a microscope calculated?

  Magnification of eyepiece lens x magnification of objective lens
• Why use a stain? (1)

  To make sub-cellular structures visible
• Why is a thin layer of onion tissue used? (1)

  To let light pass through
• Why is the cover slip lowered at an angle? (1)

  To avoid trapping air bubbles
• Why is it easier to view cells using the low power

  objective lens first? (1)

  ● Biggest / widest field of view

  ● Easier to focus
• A student collected a sample of cells by taking a

  saliva swab on the inside of their cheek. Explain

  one safety measure that the student should take

  during this procedure. (2)

  1. Wear gloves / wash hands

  ● Because stain is an irritant

  2. Disinfect work surfaces / dispose of used swabs

  ● To prevent spread of possible infection
• How could a student observe structures within a

  cell in greater detail? (1)

  Use a higher power objective lens (or use an electron

  microscope but a student wouldn’t have access)