P20. MITOSIS

OBJECTIVES

The aim of this practice is to identify the phases of the mitosis in the root of an onion.

MATERIAL 

• Microscope

• Slide and coverslide

• Dropper

• Watch glass.

• Beaker

• Forceps

• Filter paper

• Scissors

• Bunsen burner

• Lighter.

• Needles. 

• Distilled water

• Orcein A

• Orcen B

• Onions

• Water

PROCEDURE

• We keep in a glass the bulb of an onion for a few days, the glass must contain water that is in contact with the roots until the roots measure 3mm.

• Then, we cut the roots and we put them in a watch glass and we add 2mL of Orcein A.

• Heat the watch glass with the orcein until we see gray vapors.

• Take the root and put it on the slide and add drops of orcein B. 

• We place the slide on filter paper, wrapping and tighting it.

• We cover it with the coverslide and we observe the results on the microscope. 

P19. (EXTRA) ANATOMY OF A LIZARD

P18. YOGURT BACTERIA

OBJECTIVES:

To reveal bacteria that stay in yogurt such as Streptococcus Thermophilus and Lactobacillus Bulgaricus and to know how to do the Gram Stain in order to reveal them.

MATERIAL

• Crystal violet

• Ethanol

• Distilled water

• Safranin

• Three beakers

• Dropper

• Bunsen burner

• Lighter

• Forceps

• Slide and coverslide

• Dissection needle

• Iodine (Lugol)

• Petri dish

PROCEDURES

Take the dissection needle and burn it in the Bunsen burner and then spread it on the yogurt.

Put the yogurt on a slide, then take a dropper and throw a few drops of Chrystal violet, wait for 1 minute and 30 seconds.  After that clean the slide with some distilled water.

Now do the same with Iodine, throw on it few drops and wait for 1 minute, then clean it with water again.

Wash it well with ethanol.

Now you have to dye the slide with safranin and to put again some water, after that add the coverslide and put it into the microscope. 

RESULTS

QUESTIONS

EXPLANATION OF GRAM STAIN

Gram-positive bacteria have a thicker peptidoglycan (disaccharides and amino acids) cell wall than gram-negative bacteria. The latter contain a layer of lipopolysaccharide (lipids and polysaccharides) as part of their cell wall. When applied to both gram-positive and gram-negative cells, crystal violet and then iodine readily enter the cells. Inside the cells, the crystal violet and iodine combine to form the crystal violet-iodine (CV- I) complex. This complex is larger than the crystal violet molecule that entered the cells and because of its size, it cannot be washed out of the intact peptidoglycan layer of gram-positive cells by alcohol. Consequently, gram-positive cells retain the color of the crystal violet dye. In gram-negative cells, however, the alcohol wash disrupts the outer lipopolysaccharide layer and the CV- I complex is washed out through the thin layer of peptidoglycan . As a result, gram negative cells are colorless until counterstained with safranin, after which they are pink.

OBSERVATION OF G+ OR G- 

The first membrane belongs to Gram + and the second to Gram -.

 

P17. CROMATOGRAPHY

OBJECTIVES

• To know the bases of chromatographic analysis.

• To learn the procedure for separating the photosynthetic pigments.  

MATERIAL:

• Test tubes
• Rack 
• beakers 250ml
• mortar
• funnel
• petri dish
• spatula
• filter paper
• spinach
• water
• and many products quimics

PROCEDURES

• Wash the spinach and cut them, then dry them.

• Grind the spinach in a mortar and add 50 ml of ethanol and a small amount of calcium carbonate, which fits at the tip of the spatula.

• Filter the mixture into a funnel with filter paper.

• Put a part of the mixture in a Petri dish (3-4 mm high).

• Put a rectangle of paper for chromatography in form V, and wait for the pigments to be differentiated.

RESULTS

The different pigments that are from bottom to top are:
Beta carotene (red - orange)
Chlorophyll alpha (bluish green)
Chlorophyll beta (bright light green)
Xanthophylls (yellow)


QUESTIONS

Why do we add calcium carbonate?

To avoid the degradation of the pigments.



Which is the colour of every pigment

• Beta carotene (red - orange)

• Chlorophyll alpha (bluish green)

•  Chlorophyll beta (bright light green

For what purpose it does have different colour pigments?

To know the different solubility of photosynthetic pigments in an organic solvent such as ethanol, which is miscible with water.



Why do they separate in the paper? 


When the alcohol is placed with the pigments dissolved by a chromatography paper, the different pigments are separated as the medium is increasingly poorer in ethanol and richer in water.