Guide to the practical teaching
of biology and genetics

Chemical composition

TASK 1: Proof of enzyme – amylase

Flush your mouth with water (saliva contains enzyme amylase, which splits starch into simple sugars), filtrate it using a funnel, wet filtration paper and beaker. Prepare six tubes. The first one will contain 1 ml of saliva (concentrated amylase), second to fifth tubes will contain 1 ml of decreasing concentrations (1/2, 1/4, 1/8, 1/16) of amylase prepared by diluting saliva with physiological solution (0.9 % NaCl). The sixth tube will be a control containing 1 ml of physiological solution. Add 2 ml of starch to each tube including the control tube. Incubate the tubes at 40°C in a water bath for 5 min. Add Lugol’s solution to the control tube to permanent blue color and add the same amount to all other tubes. Evaluate the color of all tubes and explain why the color changed.

TASK 2: Proof of starch

Press a piece of potato against a slide (or scrape off some juice from a cut half of potato), add a drop of water and cover with the cover glass. Observe starch grains consisting of concentric layers. Add Lugol’s solution (KI + I₂ + H₂O) and observe the blue color of the stained starch.

Fig.: Starch grains.

TASK 3: Proof of fat

PP: histological section of fatty liver tissue stained by Sudan III red dye "lipidy"

Observe the orange-red lipid vacuoles inside the liver cells.

Fig.: Lipid vacuoles in liver cells.

TASK 4: Proof of DNA in the nucleus of onion

NP: internal epidermis of onion

Put an internal epidermis of onion onto the slide, fix it with 1 % acetic acid for few minutes, then stain it with 1 % methyl-green dye for 5 minutes and cover it with the cover glass.

TASK 5: Proof of protein (after Heller)

Pour 2 ml of nitric acid into the tube and slowly add egg white (the two liquids must not mix). You can observe a white ring of denatured protein between both layers.

Fig.: Proof of protein (ater Heller).