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H2O2
dissociates
H2O + O2
This reaction happens slowly by itself without any additional input of
energy.
This reaction can be sped up many times with the help of an enzyme
called CATALASE.
First
2
CATALASE
1
H2O2
Second
3
O2
CATALASE H2O2
(tube expands)
No O2
Bubbles
Third
H2O
O2
The oxygen produced from the first reaction now breaks down the tissues of the
potato through a process called OXIDATION. The potato decays and turns black.
You see this around the house if fruits and vegetables are left out too long.
Points of Discussion
1. In what ways did this lab demonstrate characteristics of a cell?
The dialysis tubing represented a cell membrane and the concept of
selective permeability. Hydrogen peroxide was able to pass through the
membrane according to the law of diffusion, which says that substance will
move from an area of greater concentration to an area of lesser
concentration. The enzyme catalase could not escape from inside the "cell"
because it was too big. If it could have escaped, you would have seen white
foaming bubbles in the beaker and the color of the solution turning brown.
2. Could you live without enzymes? Explain.
Life could not function without enzymes. Enzymes accelerate vital chemical
reactions thousands of times faster than the reaction would occur without
them. Without enzymes the amount of energy required to make these
reactions go fast enough would be counterproductive and destroy the very
products the reactions create.
3. Why do people apply hydrogen peroxide to wounds?
When you are wounded, you are threatened by a variety of bacteria / viruses
that are around you all the time, looking for a way to get into your body.
Application of hydrogen peroxide reacts with catalase in your blood plasma
to create oxygen gas in large quantities. That's right…. the same enzyme
that is in potatoes courses through your body!! Bacteria and viruses are
destroyed by the high concentration of oxygen gas.
4. As most bacteria will tell you, oxygen gas is one of the most toxic substances
on Earth. Is this true for humans and most other organisms on Earth?
The answer is yes and no. On the one hand our cells have evolved over
billions of years to use oxygen to break down the food we eat. On the other
hand, we can not ignore the destructive characteristics of oxygen. The
toughest iron bar will turn to reddish dust over time due to oxidation. The
same thing is happening to us. That is to say, the biochemical price of
breathing oxygen is aging; or, we "rust".
5. Can we "rustproof" ourselves and protect our bodies from the damaging
effects of oxygen?
Yes. Certain vitamins (vitamin C for example) and compounds found in
certain foods (green vegetables, and green tea) are high in
ANTIOXIDANTS. Antioxidants react with rogue oxygen atoms, called “free
radicals”, to make harmless compounds that can be eliminated by the
excretory system. Regular exercise also encourages cells to manufacture
antioxidants. So, a healthy diet and regular exercise can slow down
oxidation, but eventually we'll all look like the wrinkled black goo inside the
tubing!