Ultima settimana di preparativi
Le modifiche rispetto al progetto iniziale, suggerite dai tempi a disposizione, dall'esperto dott. Marco Testa, dai fallimenti nelle prove effettuate sono ancora in via di definizione
Da dietro le quinte l'insegnante di turno seguirà i ragazzi, guide volontarie (più o meno volontarie) che avranno il compito di presentare al pubblico l'attività
Negli ultimi pomeriggi bisognerà mostrar loro, passo passo, lo svolgersi degli esperimenti, magari prevedendo le domande più strampalate che i visitatori generalmente pongono e suggerire risposte accettabili
Scopo di tutto il laboratorio è mostrare che siamo cotituiti da unità molto piccole, le cellule (osservazioni con la lente di ingrandimento e il microscopio); che tali cellule si comportano seguendo le leggi della fisica (fenomeni osmotici) e della chimica (reazioni con la catalasi)
Scartato l'uso delle carote e delle patate ci rimangono cipolla, foglie e fegato.
Sicuramente quello che resterà più nella memoria sarà il "giochino" per riconoscere la presenza di tracce di sangue su un tessuto per la sua spettacolarità.
Per chi volesse la procedura ufficiale, trascrivo la scheda di laboratorio per studenti.
Investigators often find blood stains during their examination of a crime scene.
They also find stains that could be either blood or some other similar substance,
like reddish-brown paint. What other things can you think of that might look like
blood? How would you test a stain to see if it is blood?
Have you ever used hydrogen peroxide to clean a cut or a scrape? What
happened when the hydrogen peroxide came in contact with the blood from the
wound?
Blood contains an enzyme called catalase, which breaks down hydrogen
peroxide into water and oxygen gas.
2H2O2 2H2O + O2
catalase
When this reaction occurs, the oxygen gas is released as bubbles. The catalase
enzyme performs an important function to living organisms because hydrogen
peroxide is very toxic to living cells. Other organisms, including plants and some
bacteria, also make catalase.
If you place a few drops of hydrogen peroxide on a substance that contains
catalase, it will bubble profusely. These substances that bubble with the addition
of hydrogen peroxide are said to test positive for catalase.
Criminal investigators do not typically use the catalase test at crime scenes.
Other simple tests are better at detecting very dilute concentrations of blood –
sometimes so dilute the human eye can longer see the stain. These tests (listed
below), while more reliable, require more expensive chemicals.
Benzidine
Leucomalachite green
Phenolphthalein
Takayama test
Tetra-methyl bezidine
Luminol
and Spectrophotometric tests.
Most of these tests rely on the activity of peroxidase enzymes in blood to react
with a chemical stain causing it to change color, or in the case of luminol, glow in
the dark.
In this activity, you will be comparing the results of the catalase test using
hydrogen peroxide with the phenolphthalein test, to see how each reacts with
blood and other substances.
They also find stains that could be either blood or some other similar substance,
like reddish-brown paint. What other things can you think of that might look like
blood? How would you test a stain to see if it is blood?
Have you ever used hydrogen peroxide to clean a cut or a scrape? What
happened when the hydrogen peroxide came in contact with the blood from the
wound?
Blood contains an enzyme called catalase, which breaks down hydrogen
peroxide into water and oxygen gas.
2H2O2 2H2O + O2
catalase
When this reaction occurs, the oxygen gas is released as bubbles. The catalase
enzyme performs an important function to living organisms because hydrogen
peroxide is very toxic to living cells. Other organisms, including plants and some
bacteria, also make catalase.
If you place a few drops of hydrogen peroxide on a substance that contains
catalase, it will bubble profusely. These substances that bubble with the addition
of hydrogen peroxide are said to test positive for catalase.
Criminal investigators do not typically use the catalase test at crime scenes.
Other simple tests are better at detecting very dilute concentrations of blood –
sometimes so dilute the human eye can longer see the stain. These tests (listed
below), while more reliable, require more expensive chemicals.
Benzidine
Leucomalachite green
Phenolphthalein
Takayama test
Tetra-methyl bezidine
Luminol
and Spectrophotometric tests.
Most of these tests rely on the activity of peroxidase enzymes in blood to react
with a chemical stain causing it to change color, or in the case of luminol, glow in
the dark.
In this activity, you will be comparing the results of the catalase test using
hydrogen peroxide with the phenolphthalein test, to see how each reacts with
blood and other substances.
La nostra sarà una dimostrazione molto più casalinga
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