L. 19 CELLS ORGANELLES

Tomato chromoplasts (400X)

Potato amyloplasts, stained with lugol (1000X)

Chloroplasts of vallisneria

Carrot (1000X)

red cabadge cloroplasts (400X)

Red cabadge (100X)

Red cabadge stoma (1000X)

L.18 LIFE IN A DROP OF WATER

L.17 GRAM STAINING

OBJECTIVES:

- Differenciate yogurt bacteria.
- Relate the staining procedure with the structure of the cells.

MATERIALS:

- 1 Slide
- 1 Cover slip
- Tongs
- Needle
- Gram stain: crystal violet, iodine and safranin.
- Descolorize reagent: ethanol 96%
- Microscope
- Yogurt

PROCEDURE:

- Prokariotic cell observations: GRAM STAINING

1. Prepare a heat-fixed sample of the bacteria to be stained.
2. Cover the smear with crystal violet for an exposure of 1 min.
3. Rinse with distilled water.
4. Apply Iodine solution for 1 min.
5. Rinse the sample with distilled water.
6. Decolorize using ethanol. Drop by drop until the purple stops flowing. Wash immediately with distilled water.
7. Cover the sample with the safrain stain for an exposure time of 45 seconds.
8. Rinse the sample with distilled water.
9. Gently dry the slide with paper.

=> Gram staining is a method of differentiating bacterial species into two large groups: Gram positive and Gram negative. This differentiation is based by the chemical and physical properties of their cell walls by detecting a peptidoglycan, which is present in a thick layer in gram-positive bacteria. The result is:

> Gram-negative: stain pink or reddish color.
> Gram-positive: stain purple color. 

Gram stain:
- Complete the table that you have below:

	GRAM POSITIVE	GRAM NEGATIVE
Crystal violet: Color?	Violet	Violet
Iodine	Contrast	Contrast
Ethanol: Decolorize?	No,  too thick retaining the dye	Yes, open the pores and the Coloring goes.
Safranin: Color?	No	Reddish

L.16 EPIDERMIS CELLS

OBJECTIVES:

- Identify the shape of epidermis cells.
- Identify and explore the parts of a stoma.
- Measure dimensions of the entire cell and the stoma.

MATERIALS:

- 1 Slide

- 1 Cover slip
- Distilled water
- 10% Salt water
- Scissors
- Needle

PROCEDURE:

Plant cells observation:
1. Cut the stalk of the leek.
2. In the place of the cut, pull out the transparent part of the epidermis using forceps.
3. Using the brush, place the peel onto the slide containing a drop of tap water.
4. Take a cover slip and place it gently on the peel with the aid of a needle.
5. View it in the microscope.
6. Describe the change in the shape of the cells.
7. Draw a diagram with the parts of a stome: stoma,cell guards,epidermis cells.

Salt treatment:
1. Prepare a 10% of salt solution.
2. Put the salt with a dropper on the left part of the slide.
3. Place a piece of cellulose paper in the opposite part of the cover slip, and let the dissolution to go though your sample.

RESULTS AND CONCLUSIONS:

1. What is the major function of a cell membrane?
The basic function is to maintain the plasma membrane via the differential intracellular environment. The combination of active and passive transport makes the plasma membrane selective barrier that allows the cell to differentiate medium.
2. What is the major function of the cell wall?
Cell wall protects the cell contents and gives rigidity to the cellular structure.
3. How does salt affect the cells shape? And the stomes?
altering the sodium concentration gradient both outside and inside the cell ions.