A LABORATORY PROTOCOL ON THE BIOLOGY EXPERIMENT CARRIED OUT AT “IIS NELSON MANDELA”, CASTELNOVO NE’ MONTI, ITALY

PHOTOSYTHESIS AND OBSERVATION OF VEGETAL TISSUES

Part One

Experimental procedure

a) Pour some water into the beaker and add a few drops of gentian violet (the solution must not be too colored) and mix

b) Cut the onion and leaf through the bulb, take a fragment of the film present on the inside of the leaves of the bulb.

c) place the sample on the slide and add a drop of solution taken from a small beaker, cover with the coverslip and press lightly with absorbent paper

d) Place the slide on the microscope slide and observe starting from the lower magnification and then moving on to the higher ones

Expected results

• the cell wall made up of cellulose is observed. Cellulose is a complex glucose polymer with a structural function in plants.

• The cell nucleus is observed: it contains the genetic material (DNA and RNA) of the species (and variety)

Conclusions:

The nucleus can be found in the central area of the cell or near the wall.

• a great part of the cell can be occupied by the vacuole which contains various organic and inorganic substances

Second part (VEGETAL TISSUES)

1.Experimental Procedure:

1. Pour some distilled water into the beaker and add a drop of methylene blue; mix well.

2. Use the bisturi to make a square incision (4-5 mm side) on the epidermis of the lower page of a cyclamen leaf; you must act gently without pressing; then with the tweezers, detach the squares of the epidermis, starting from an angle.

3. Place the sample on the slide, add a small drop of colored solution taken with the dropper from the small beaker and cover with the cover slide; press gently and wipe with the absorbent paper the excess liquid leaking around the cover slide.

4. Put the slide on the slide holder of the microscope. Look at the sample, starting with the smallest magnification, then moving on to more powerful targets.

2.Expected results

1.Note the cell walls of the cells; their shape is peculiar, they look like pieces of a “puzzle.”

2. Note the numerous STOMES present in the epidermis, each delimited by two GUARD CELLS.

Conclusions:

3. The gas exchanges that allow the passage of carbon dioxide (CO2), water in the form of steam and oxygen take place through the stomata.

4.Through these natural openings the plant can absorb the carbon dioxide needed for photosynthesis, as well as release oxygen (essential role for life on planet Earth).

5.The opening and closing of the stomata are regulated by the guard cells, according to the climatic conditions to which the plant is subjected. The stomata also allow the elimination of water vapour, the end product of cellular respiration.