The cell: the smallest working unit of a living organism.

Respiration is the release of energy from food.

Tissue: a group of similar cells working together to carry out a specific function e.g. muscle tissue.

Organ: a group of tissues working together to carry out the same function e.g. lungs, brain.

System: a number of organs working together to carry out a function e.g. circulatory system.

Organism: composed of a number of different systems e.g. humans, daffodil. An organism refers to a living thing.

To prepare and examine animal cells using a light microscope

Preparing the slide:

1. Scrape the inside of your mouth with a cotton bud.
2. Spread the smear of cheek cells on a glass slide.
3. Add two drops of methylene blue using a dropper, to stain the nucleus dark blue.
4. Using a mounting needle, slowly add a cover slip at a 45° angle (reduce air bubbles).
5. Note: The purpose of the cover slip is to protect the microscope lens.
6. Examine using the coarse focus wheel and then sharpen the image with the fine focus wheel.

Result:

• The nucleus is dark blue.

To prepare and examine plant cells using a light microscope

Preparing the slide:

7. Remove outer, dry scaly leaves of an onion.
8. Use tweezers to pull a strip of thin, translucent epidermis from the onion.
9. Place the epidermis on a microscope slide.
10. Add two drops of iodine using a dropper, to stain the nucleus (dark brown).
11. Using a mounting needle, slowly add a cover slip at a 45° angle (reduce air bubbles).
12. Note: The purpose of the cover slip is to protect the microscope lens.
13. Examine using the coarse focus wheel and then sharpen the image with the fine focus wheel.

Result:

• The nucleus is dark brown.
• The cell walls can also be seen.