Practical activity: To prepare temporary slides
Temporary slides are those prepared for immediate use and are not stored.
The epidermal cells of onion bulbs can be used to prepare temporary slides.
Requirements
- Onion bulb
- Scalpel
- Glass slide and cover slip
- Dissecting needle
- Forceps
- Iodine or methylene blue stain.
Procedure
- Cut the onion bulb vertically into 4 sections
- Remove one fleshy leaf and cut out a piece measuring 0.5cm. x 0.5 cm.
- Using the forceps, remove the thin epidermis from the inner surface of the piece of a leaf as shown below
- Place the drop of water on the glass slide and gently spread the epidermis on the slide
- Place a drop of iodine or methylene blue stain on the epidermis on the glass side
- Use the mounting needle to gently place the cover slip on the epidermis. Ensure you do not trap air bubbles.
- Observe under low power objective lens. For more details, change to medium power objective and then to high power objective lens.
Note:
While preparing temporary microscopic slides, we;
(i) Cut very thin sections of specimen to make it transparent thus allow light to pass through over a short distance.
(ii) Mount the specimen on a drop of water to make the cells turgid and prevent dehydration.
(iii) Stain the specimen to make certain parts appear distinct hence increase visibility.
(iv) Use a sharp blade when making thin sections to avoid damaging the cells.
(v) Cover the specimen with a coverslip to spread out the specimen on the slide and prevent dehydration.
Observation
(a) Human cheek cell
(b)Onion epidermal cell
