RP1: Required practical activity 1: Microscopy

Specimen: cell structure of onion epidermal cells (plant) and prepared animal cell slides.

Recorded: appearance and relative size of cell structures; total magnification calculated and written below each drawing.

Quality controls:

very thin specimen

no trapped air bubbles under coverslip

slide kept still when changing objective lens

coarse focus used on low power only (never on high power)

Place one drop of water onto a clean microscope slide.

Peel a thin layer of epidermal tissue from the inner surface of an onion.

Use forceps to lay the tissue flat on the drop of water.

Add two drops of iodine solution to stain the cells.

Lower the coverslip at an angle — place one edge down first, then slowly lower the other edge using forceps — to prevent trapping air bubbles.

Blot away excess liquid from around the coverslip with paper.

Place the slide on the microscope stage.

Select the lowest power objective lens. Looking from the side (not through the eyepiece), use the coarse focus to lower the lens close to the slide.

Now look through the eyepiece and slowly raise the lens with the coarse focus until the cells come into view.

Use the fine focus to sharpen the image at low power, then rotate to a higher power objective and use fine focus only.

Make a large, clear pencil drawing of several cells, using single unbroken lines and no shading.

Label all visible structures (cell wall, nucleus, vacuole, cytoplasm, cell membrane) with straight, ruled label lines that do not cross.

Calculate and write the total magnification below the drawing: eyepiece magnification × objective magnification.

Iodine solution is an irritant — wear safety goggles throughout; wash any spills off skin immediately with water.

Glass slides and coverslips can break and cause cuts — handle carefully, never apply excessive pressure to the coverslip, and report any breakages to the teacher immediately.