Biology Experiments for Teachers – Enzymes: Catalase

Safety. Although the hazards in the following experiments are negligible, you are advised to consult the latest edition of ‘Safeguards in the School Laboratory’ published by The Association for Science Education (ase.org.uk) before embarking on any experiment.

Outline. Catalase is an enzyme which occurs in the cells of many living organisms. Certain of the energy-releasing reactions in the cell produce hydrogen peroxide as an end-product. This compound, which is toxic to the cell, is split to water and oxygen by the action of catalase. 2H2O2 = 2H2O + O2

Samples of liver and yeast are dropped into hydrogen peroxide. Oxygen is evolved and the student is asked to extend the experiment to try and decide if an enzyme in the tissues is responsible. The experiments and the questions take about one hour.

Prior knowledge. The existence of inorganic catalysts; enzymes denatured on boiling; oxygen relights a glowing splint.

Advance preparation and materials – per group

20 volume hydrogen peroxide 50 cm3

splint

liver, about 1 cm cube

distilled water 20 cm3

dried yeast about 1 g

clean sand about 1 g

activated charcoal granules, about 1 g

Apparatus – per group

test-tube rack and 4 test-tubes

forceps or seeker for pushing liver into test-tube

4 labels or spirit marker

filter funnel

Bunsen burner

filter paper

test-tube holder

mortar and pestle

Experiment

The investigation below is a fairly critical examination of plant and animal tissues to see if

they contain catalase.

(a) Label three test-tubes 1-3.

(b) Pour about 20 mm (depth) hydrogen peroxide into each tube.

(c) Cut the liver into 3 pieces.

(d) To tube 1 add a small piece of liver, and to tube 2 add a pinch of dried yeast.

(e) Insert a glowing splint into tubes 1 and 2, bringing it close to the liquid surface or into the upper part of the froth.

1 Describe what you saw happening and the effect on the glowing splint.

2 How do you interpret these observations?

3 Is there any evidence from this experiment so far, to indicate whether the gas is coming from the hydrogen peroxide or from the solid?

4 Is there any evidence at this stage that an enzyme is involved in the production of gas in this reaction?

(f) In tube 3 place a few granules of charcoal and observe the reaction.

5 Could charcoal be an enzyme? Explain your answer.

6 Assuming (i) that the gas in (f) is the same as before and (ii) that the charcoal is almost pure carbon, does the result with charcoal help you to decide on the source of the gas in this and the previous experiments?

(g) Suppose the hypothesis is advanced that there is an enzyme in the liver and yeast, which decomposes hydrogen peroxide to oxygen and water; design and carry out a control experiment to test this hypothesis.

7 Record (i) the experiment, (ii) the reasons which led you to conduct it, (iii) the observed

results and (iv) your conclusions.

(h) Wash out the test-tubes. Design and carry out an experiment to see if the supposed enzyme in the plant and animal material can be extracted and still retain its properties. The experiment should include a control.

8 Describe briefly your procedure, your results and your conclusions.

9 Assuming that liver and yeast each contain an enzyme which splits hydrogen peroxide, is there any evidence to show that it is the same enzyme? What would have to be done to find this out for certain?

Discussion – answers

1 Effervescence should be observed in each case but it is more vigorous with yeast than with liver. The glowing splint should relight.

2 Oxygen is being produced.

3 There is no evidence to indicate whether the liquid or solid is giving the gas. If the students think that a solid is unlikely to give off a gas they could be reminded of marble and hydrochloric acid in which it is the solid producing the carbon dioxide. It seems less likely, however, that yeast and liver would both give off oxygen when treated with hydrogen peroxide, than that hydrogen peroxide should give oxygen when treated with diverse substances.

4 So far, there is no evidence of an enzyme being involved.

5 A gas will come off but not sufficiently rapidly to relight a glowing splint. Charcoal could not

be an enzyme because (a) it is an element and (b) it has been produced by very high temperatures that would destroy enzymes.

6 Charcoal, as an element, could not be giving off oxygen. The gas must be coming from the

hydrogen peroxide.

7 (i) The experiment should involve boiling the tissues and then putting them into hydrogen peroxide.

(ii) If an enzyme is involved,

(iii) no gas will be produced.

8 The student should grind the samples with a little sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will be evolved with a vigour proportional to that witnessed when the original substances were tested.

The student should boil half of each extract and show that it loses its activity.

9 There seems no fundamental reason why yeast and liver should not have different enzymes which catalyse the decomposition of hydrogen peroxide. To be certain on this point, the enzymes would have to be extracted and their chemical composition determined.

Biology Terms: Countershading

Many marine creatures are countershaded, which is a type of camouflage for them. What exactly is countershading?

Imagine that you are in a boat on the ocean and looking down. The ocean water looks dark blue. If you were an animal in the ocean, what color should you be to hide from animals in the sky, or higher up in the ocean, than you are?

Now, imagine you are SCUBA diving on the bottom of the ocean floor and look up, toward the sky. During the daytime, the sunlight filters into the water. What color should an animal be so it can blend into the water and hide from the animals below it in the water?

Animals selected for countershading

Animals that are darkly colored on their top part and lightly colored on their underside are said to be countershaded.

Animals that are darkly colored on their top part, where their dorsal fins are located, are less likely to be found and eaten by sky creatures or ocean animals higher up in the ocean than they are. Their dark colored skin blends into the color of the ocean around them and they have higher survival rates than animals that are lightly colored on the top.

Animals that are lightly colored on their underside blend into the ocean better when looking from the ground upward. They are found and eaten less often by the fish and animals underneath them in the water, so they have better survival rates than animals with darker colored under sides.

So, animals with both of these features have an even better chance of living to an age that they can reproduce.

What kind of animals are countershaded?

Countershading of the type, where the animal blends into its background, is most prevalent with marine animals. Sharks, dolphins, porpoises, fish, and penguins all present this kind of countershading.

Another type of countershading has the same type of principles, but the animals don’t blend completely into their background. Instead, their coloring makes it difficult for predators to see where their bodies start and end. Some lizards and caterpillars present this type of countershading.

What have we learned from the animals?

An artist and naturalist named Abbott Thayer studied countershading. He described and published his nature studies regarding countershading in 1892. In fact, sometimes countershading is called Thayer’s law. Thayer made his contribution in World War I by suggesting that the military paint their ships using countershading techniques.

Countershading and camouflage techniques are used frequently by the military. Clothing fashions are also influenced by these types of color schemes.

Beyond Biology

Three disparate things that I read recently made me sit up and take another look at the threat that biotechnology poses to the future of humankind. The first was an announcement made by scientists of the J Craig Venter Institute on their work on genome transplantation that enabled them to transform one kind of bacteria to another type. This is the first time in history that a completely synthetic organism has been created. The second was a declaration made by Sir Martin Rees, Astronomer Royal and former President of British Association for the Advancement of Science – considered to be one of the most eminent scientists of today. He states “I have staked one thousand dollars on a bet: That by the year 2020, an instance of bio-error or bio-terror will have killed one million people.” The third was that scientists at the Shanghai Second Medical University have created the first human/animal Chimera (animal containing genetic material from parents of two or more distinctly different species) fusing together cells from humans and rats.

The first piece of information shows that biotechnology is racing ahead at breakneck speed and has the ability to change things in a fundamental way. This ability has already been translated into the development of drugs and other products – biotechnology now produces 40 per cent of the drugs that the US Food and Drug Administration approves of every year.

The second indicates that scientists of the calibre of Sir Martin Rees believe that it is likely that this ability could be used with malicious intent. Bio-weapons are the ideal weapons for terrorist and/or anarchists. The cost of setting up a laboratory for biotech research is significantly smaller than that of developing nuclear or chemical weapons. The manufacture of lethal toxins requires modest equipment, essentially the same as is needed for medical or agricultural programmes: the technology is “dual use”.

Research teams have been able to reconstitute the polio virus, as well as the 1918 pandemic influenza virus (that killed somewhere between 20 to 40 million people) using only published DNA information and raw material from mail order services. This knowledge and technology is already dispersed among hospital staff, academic research institutes and factories. Bioterrorism is thus a real possibility in the next decade with the invention of ways of killing that had previously existed only in the realm of science fiction.

Sir Martin Rees also mentions the possibility of error on the part of otherwise responsible laboratories and agencies. Ed Hammond of the Sunshine Project in Texas that monitors the use of biological agents says that lab accidents happen a lot more frequently than the public knows. In recent years, the spread of Foot and Mouth Disease in the UK (2007), the death of a lab worker at Texas A&M ( 2006) due to brucellosis after cleaning a high containment container, the exposure of 3 researchers at Boston University Medical Centre (2004) to tularaemia or rabbit fever have occurred.. All these laboratories are well run and subject to many regulations. The same cannot be said for other laboratories in different parts of the world. Perhaps the worst bio-error took place in 1979 in the former Soviet Union when weapons-grade anthrax escaped from a facility in Sverdlovsk, now known as Yekaterinburg, killing 68 people. The accident was covered up by the authorities and came to light only in 1998.

If there is a major outbreak in the future, there may be severe clamping down by governmental authorities on the kind of research and agents that can be used in experimentation. This however would not have impact on research in rouge laboratories or by anti-social elements.

The Human Chimera experiment in China is one that could not have been able to be carried out in any other country in the world. Most do not, at least at present, have the scientific capability. Those that do, such as the US and Western Europe have strict codes of ethics and regulations in place that expressly forbid such experimentation. Even between the US and Europe however, there is a vast difference in the regulatory framework. In the US, products of biotechnology have been extensively tested and marketed. In the EU, few biotechnology products have received regulatory approval while most have faced a de facto moratorium.

Many countries do not have any kind of regulatory framework relating to biotechnology or restrictions on the kind of research that can be carried out. Frightening experiments could be conducted, without the knowledge of the rest of the world, or authorities within the countries themselves. These could even attract groups to set up research facilities in the future- the same principle that attracts groups and individuals to tax havens such as Barbados, St Kitts, Canary Islands etc.

The advancements made in the field of biotechnology have the potential to change the life of humankind for the better by impacting health, eradicating disease and creating miracle drugs. But we need to also ponder seriously on what we need to do to prevent Sir Martin Rees’ wager coming true.

Biology – Why Are Penguins Birds If They Can’t Fly?

Everyone knows what a bird is, right? If I ask my seven-year-old son what a bird is, he’ll respond with something like “a bird is an animal that has a spine, wings, two feet, hollow bones, and can fly.” Or, if her remembers the little military chant his dad made for him, he might say, “hollow bones and scaly feet, feathered wings and goes tweet tweet.”

Well, penguins can’t fly. They have wings, feathers, two feet, and a spine, and they swim well but they cannot fly. Ostriches can’t fly either, but both penguins and ostriches are considered birds. How is that possible? What’s the deal?

It’s all in the definition

There’s a difference between the common usage of the word “bird” and the scientific use of the word. The common definition is based on features of the animal you can see with your eyes and discern with your other senses like feathers, wings, number of legs, and being warm-blooded. My seven-year-old son knows the common definition of the word “bird.”

Scientists use a slightly different definition.

Evolutionary birds

The scientific taxonomy of birds is a bit different than common usage. The scientific groups are made based on fossil evidence and other biological evidence such as DNA and mitochondrial DNA when the DNA can be obtained. Birds are in the Domain Eukaryotes, the Phylum Chordata meaning vertebrates, and the Class Avians. Avians have descended from theropod dinosaurs. More specifically, birds have descended from Archaeopteryx, which existed in the late Jurassic period.

Many scientists think of birds as the only type of dinosaur that didn’t go extinct 65 million years ago. In fact, my daughter who is obsessed with dinosaurs, calls birds “tiny dinosaurs.”

Scientifically, birds today are descended from dinosaurs, have feathers, a beak with no teeth, and they lay eggs with hard shells. Birds have a high metabolic rate, meaning they need to eat a lot to maintain their body temperature. (Some refer to them as warm blooded.) They have a four-chambered heart (like mammals), and they have lightweight, strong skeletons. Most birds can fly, but flying isn’t a requirement to be a bird.

And that’s the crux of it. The scientific definition of “bird” does not require the ability to fly.