Form 4 Paper 2 Chapter 2

Paper 3

Aim: To compare the structure of an animal cell and a plant cell.

Problem statement: Are plant cells different from animal cells?

Hypothesis: The structure of plant cells have certain similarities and some differences to animal cells.

Variables: Manipulated : cell types (epidermal cells of onion and human cheek cells)

Responding: cell structure

Constant: power of microscope

Apparatus: Toothpicks, a scalpel, a pair of forceps, microscope slides, cover slips, needles, a dropper, filter paper and a light microscope.

 Materials: An onion bulb, Cheek cells (scraping from the inner lining of the mouth), distilled water.

Cell stains: iodine solution for plant cells and methylene blue solution for animal cells.

Technique: Observing onion cell and cheek cell under light microscope and comparing the epidermal cell of onion and the cheek cells.

Procedures: A: Observing epidermal cells of onion

1 A succulent leaf of an onion bulb is cut by using a scalpel.

2 A piece of thin epidermis from the inside of the leaf is peeled off by using a pair of forceps.

3 The piece of the epidermis in a drop of water is placed on a microscope slide. This is a wet mount. (Precaution: Try to avoid folding the epidermal tissue.)

4 The cover slip is put carefully onto the epidermis layer using a needle to prevent the formation of air bubbles.

5 A drop of iodine solution is added onto one side of the glass slip and the solution

is allowed to spread under the glass slip by holding a piece of fi lter paper at the opposite end. This is known as the irrigation technique.

6 The slide is examined under a light microscope using low magnifi cation (x4) and then followed by higher magnifi cation. (x10).

7 The structure of an onion epidermal cell is drawn and labelled.

B: Observing human cheek cells

1 Some tissues are scraped off gently from the inside of your cheek with a clean and flat toothpick.

2 The tissues in a drop of water is placed on a microscope slide.

3 A drop of methylene blue solution is added.

4 Mount is mixed with a toothpick.

5 The mount is covered with a glass slip by using a needle.

6 The fi lter paper is placed at the edges of the cover to absorb the excess solution.

7 The slide is examined under a light microscope using low magnification followed by higher magnification.

Discussion:

• Under the light microscope, both plant cell and animal cells have these cellular component:   

            -nucleus, cytoplasm and cell membrane.

• Plant cells have regular shape (due to the presence of cellulose wall), whereas animal cells have irregular shape.

• The onion epidermal cell have no chloroplast because it is a vegetative reproductive organ, found growing underground. Therefore no photosynthesis occur.

Conclusion : The results of the experiment show that both plant cells and animal cells have certain similarities and some differences. Therefore, the hypothesis is accepted.