Practical - Making slides and observations

Aim

To prepare a microscope slide of cheek cells, stain them and examine them using a light microscope.

Method

  1. Set up the microscope using the lowest power objective lens.
  2. Wipe one side of the cotton bud down the inside of your cheek. The cotton bud will pick up cheek cells without damaging any tissue.
  3. Rub the side of the cotton bud with the cells on it onto the centre of a microscope slide.
  4. Put one drop of methylene blue stain on top of where the cells have been put on the slide.
  5. Carefully place one side of the coverslip into the methylene blue using a mounted needle.
  6. Slowly lower the other side of a coverslip onto the slide. Take care not to trap any air bubbles between the cover slip and the slide.
  7. Observe the slide under the microscope using low power. Then change the objective to a higher power magnification.
  8. Produce a scientific drawing of what you have observed.
Preparing a slide sample to examine under a microscope

Risk assessment

When carrying out any experiment, it is important to do a risk assessment. Methylene blue stains the DNA inside of your cheek cells. It is a low hazard substance but can stain skin and clothing. The inside of the cheek is delicate so the cotton bud should only be rubbed gently once along the surface to pick up some cells. The cotton bud should later be placed in disinfectant to stop the spread of any contagious diseases.

Producing scientific drawings

When scientists use a microscope to look at cells they often produce a scientific drawing of what they see. This is a record of their observations and what they have been studying.

When producing a scientific drawing:

  • only draw what you can actually see
  • use a sharp pencil
  • make the drawing large and fill as much of your paper as you can
  • use solid lines to draw - do not use feathery sketch lines
  • don't shade in the drawing
  • use a ruler to draw any label lines
  • make sure label lines don't overlap
  • include the magnification of your drawing
  • include a title for your drawing to let the person know what it is
Question

How could this scientific drawing be improved? [3 marks]

An incorrect way to draw and label a scientific drawing
  • Include a title
  • Include the magnification
  • Do not cross the label lines