Studying Pond Water in the Classroom

Fig. 1 - Rotifers

The best method for preparing pond water suitable for observation under the microscope is to make a hay infusion. Here, a sample of natural water from a pond, creek or other source is collected and poured into a glass jar or beaker. A handful of cut hay or grass, which will provide nutrients for any microbes present, is then added to the jar.

Organisms Visible in Pond Water Using the Light Microscope

If left for several weeks, a succession of microbes can be observed as one species replaces the next in this mini ecosystem. Initially, a prepared drop from the surface of the pond water should reveal several types of bacteria (spiral, rod shaped or spherical) swimming around.

After around a week, protozoans such as Paramecium (see figure 2) and Euglena may be visible. Further examples of this group of microbes, including ciliates such as Stentor and Vorticella and algae such as Volvox, diatoms and Chlamydomonas ,should appear in the next four or five weeks.

Students should be encouraged to research the Monera and Protista kingdoms, as most of the organisms they observe will belong to these groups. The Monera , which include bacteria and blue green algae, are much smaller than other microbes (around 2 micrometres in diameter) and do not possess a true membrane bound nucleus or ‘organelles’ (small structures within the cell that carry out specialised functions).

The Protista are essentially a loose grouping of single celled organisms that do possess a membrane bound nucleus and organelles. They are much larger than the Monera, averaging around 40-100 micrometres in diameter.

An interesting multicellular microbe that may be found among decaying vegetable matter in the pond water is the Rotifer (see figure 1). These organisms are around 0.1-0.5mm long and possess a distinctive corona of small hairs (cilia) at their apex. These cilia sweep food into the rotifer’s mouth in a motion that resembles a wheel rotating (giving rise to its common name of ‘wheel animal’).

Observing Pond Water – Materials and Teaching Method

A standard light microscope with magnification of up to 400x is required in this activity. Students may prefer to observe their pond water at 100x magnification, as this provides greater resolution and covers a larger field of view.

The following materials and equipment are required per group of around four students:

Figure 2 - Paramecium

•                light microscope and microscope lamp

•                glass slide and coverslip

•                Pasteur pipette or eyedropper

•                glass jar of pond or creek water

•                handful of hay or cut grass

Students should be instructed to copy down the following directions, which should be followed by a teacher-led explanation.

•                Place the hay or grass in the pond water and leave for a week in a warm place.

•                Use the eyedropper or pipette to draw up a sample of water from the surface of the jar.

•                Place this drop on a glass microscope slide and cover with a cover slip.

•                Place the slide on the microscope stage and focus first using the low power objective (10x). This will give a total magnification of 100x when combined with the magnification of the lens in the microscope’s eyepiece.

•                Observe and draw any organisms visible – if bacteria are the only things present the higher power objective may need to be used.

•                Repeat this procedure for water in the middle of the jar and the detritus at the base of the jar, as different types of microbes are often found in each region.

The following questions could be written on the board after students write up the experiment and their observations:

1.             Use resource material to name as many of the microbes you have drawn.

2.             Identify any microbes you observed that belong to the kingdom Monera.

3.             Identify any microbes you observed that belong to the kingdom Protista.

4.             Rotifers are multicellular organisms. To what kingdom do they belong?

5.             Research information on rotifers to describe their method of locomotion, eating habits and reproductive behaviour.

If the pond solution contains a reasonable number of Paramecia, students could add a drop of yeast that has been stained with congo red dye to the microscope slide. This will allow them to observe the Paramecia ingesting the yeast and to track the movement of the yeast through the cell. Interestingly, the yeast may change to a blue colour as the pH changes in the organism’s gullet.

References

Microbus, 2007, 'Pond water Critters That You Can See With a Microscope' microscope.org

Proscope Digital Microscope, 2010, 'Biology Experiment: Microbes From a Hay Infusion', bodelin.com

Making a Battery From Fruits and Vegetables

Fig. 1 - Potato battery

Alessandro Volta and Luigi Galvani pioneered the science behind this experiment. Both realised that current electricity is produced when two different metals are placed in contact with a conducting solution, or "electrolyte," and connected with a wire.

In 1771, Galvani discovered that a frog’s legs twitched when placed between two different metals. Volta concluded in 1800 that electricity could be created in a similar fashion by placing brine solution between alternating copper and zinc discs that were arranged in a pile and connected with wire. The famous "Voltaic Pile" was then further adapted in 1836 by John Daniell, who created the "Daniell Cell."

The Chemistry of Wet Cell Batteries

The Daniell Cell, a typical "wet cell" battery, consists of two half cells; in one, a zinc electrode is immersed in a solution of zinc sulphate, while in the other cell a copper electrode is placed in a solution of copper sulphate. The half cells are connected by a salt bridge (see figure 2).

When the zinc and copper are connected by a wire, electrons flow through the wire from the zinc to the copper while positive and negative ions move through the solutions to balance the resulting charge difference. This phenomenon is the result of an oxidation-reduction reaction between the two metals – as zinc is more active than copper it tends to lose electrons through the wire (oxidation) while the copper accepts these electrons (reduction).

How a Lemon Can Act as a Battery

Lemons and other fruit and vegetables contain acidic juices that can act in a similar way to the electrolytes in the Daniell Cell. If two different metals are pushed into the skin of a lemon, for instance, and connected with an insulated wire, an electrical circuit is produced because positive and negative ions present in the juice can move to each metal to balance the charges.

Unlike a Daniell Cell, however, the less active metal is not reduced: instead, hydrogen ions in the juice are reduced to form hydrogen gas. When the two different metals are a galvanised (zinc) nail and a copper coin, the reactions that occur are:

At the galvanised nail: Zn→ Zn2+ + 2 e-

At the copper coin: 2H++ 2e- → H2

The copper coin in effect acts as an electrode to direct the electrons from the nail to the hydrogen ions.

Making a Lemon Battery – Materials and Teaching Method

A copper coin or a piece of copper wire and a galvanised nail are used as the two different electrodes in this experiment, but other combinations could be trialled. To achieve the maximum amount of voltage both should be rubbed with steel wool prior to the activity. In addition, the more lemons connected in series to each other, the more power will be generated. One single lemon cell will produce up to 0.9 volts if copper wire is used instead of a coin.

The following materials and equipment are required per group of around four students:

•                3 or 4 lemons

•                connecting wires and alligator clips

•                steel wool

•                calculator with dry cell removed or LED bulb

•                galvanised nails

•                copper coins or wire

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Rub the nails and coins/copper wire with steel wool.

•                Push a nail in one end and a coin in the other end of each lemon. If you are using copper wire, use lengths of around 5cm. Coil each length up into a circular shape and push one free end into the lemon skin.

•                Pull the wires in the battery compartment of the calculator out at each side of the calculator. Connect the negative end to a length of insulated wire. Connect the other end of the insulated wire to the galvanised nail in one of the lemons.

•                Now connect another insulated wire between the nail and the copper metal of this first lemon.

Fig.2 - Galvanic Cell

•                Take a further insulated wire and join the copper electrode of the first lemon to the nail in the second lemon.

•                Repeat the two steps above until you have three or four lemons connected in series. Join the last copper electrode to the positive wire emerging from the calculator.

Alternatively, the free ends of the lemon battery can be connected to a LED light bulb. The flat side of the LED should be attached to the galvanised nail (anode) end of the lemon cell. Potatoes, in which phosphoric acid present in the juice acts as an electrolyte, can be used instead of lemons to create comparable voltages.

The following questions could be written on the board after students write up the experiment and their observations.

1.             What is an electrolyte?

2.             Name the electrolyte present in a) lemons; b) potatoes.

3.             Explain how Galvani made the frog’s leg twitch in his famous "animal electricity" experiment.

4.             Name the two different metals and the electrolyte used in Volta’s "Voltaic Pile."

5.             Define: a) oxidation; b) reduction; c) anode; d) cathode.

6.             What acts as the anode in these experiments?

Making a Lemon Battery – Follow-Up Activities

Students could try using apples, kiwi fruit, pears or tomatoes to create electricity instead of lemons and potatoes. A typical calculator and LED light bulb both require around 1.5 volts. Additional current can be produced by connecting pairs of fruit pieces in parallel and then connecting each pair together in series. Note that the more each electrode is pushed into the fruit, the greater is the surface area exposed to the electrolyte.

References

"Battery History," 2010, inventors.about.com

Construct a Vinegar Battery, 2010, hilaroad.com videos

Hila Research Centre, Lemon Battery, hilaroad.com

Knowlera Media, How to Make a lemon Battery, 2010, monkeysee.com

Knowlera Media, How to Make a Potato Battery, 2010, monkeysee.com

Extracting Metal on a Match Head

 Match Head

Most metals, with the exception of gold, silver and in some cases, copper, do not occur in a pure state in nature. Instead, they are usually combined with other elements such as sulphur and oxygen to form naturally occurring compounds known as ores. Examples of ores include cassiterite (tin oxide), haematite (iron oxide), galena (lead sulphide) and malachite (copper carbonate hydroxide)

The Magic of Metal Production

So how do we produce a solid, shiny metal with a high melting point from what appears, in most cases, to be a brownish sample of dirt? The answer lies in a chemical process termed "reduction." Reduction involves the addition of negative electrons to a positively charged atom (or "ion") to form a neutral atom of a particular element.

When metals occur as ores, they are in the form of positive ions combined with negative non-metal ions such as oxides and sulphides. When electrons are supplied to these metal ions, they form metal atoms and acquire all the properties typical of metals. Before this process can occur, however, a source of electrons is required.

Oxidation and Reduction Reactions

Carbon can act as such a source because it is a more reactive element than many metals and consequently has a greater tendency to lose electrons. When this happens, we say that carbon has been "oxidised" and the metal ions which accept these electrons have been "reduced."

Less reactive metals are relatively easy to extract from their ores in this manner – in the case of copper and iron, for instance, the pure metal can be produced by simply heating the ore in the presence of carbon. The equation for the reduction of iron is:

Iron(III) oxide + carbon → iron + carbon dioxide

2Fe2O3(s) + 3C(s) → 4Fe(s) + 3CO2(g)

Iron Extraction on a Match Head – Materials and Teaching Method

The charcoal that remains after burning a match provides a source of carbon in this experiment, while the sodium carbonate powder provides an interface between the iron oxide and the carbon when it melts.

The following materials and equipment are required per group of around four students:

•                watch glass

•                iron (III) oxide powder

•                sodium carbonate

•                spatula

•                matches

•                magnet

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Immerse the head of a match in water. Roll the match first in sodium carbonate and then in iron oxide powder.

•                Using metal tongs, hold the match in a Bunsen flame until it catches fire. Allow to burn until about half way down the length of the match.

•                Place the match on a watch glass and crush the blackened head with a spatula. Spread the resulting particles evenly over the surface of the watch glass.

•                To test whether any metallic iron has been produced, move a magnet around under the watch glass. Any iron particles should move with the magnet.

The following questions could be written on the board after students write up the experiment and their observations.

1.             How do you know whether or not iron has been produced?

2.             What did the charcoal from the burnt match help to do?

3.             In this oxidation-reduction reaction, what was oxidised and what was reduced?

4.             Name one other metal that can be extracted by heating in the presence of carbon.

5.             How are more active metals such as aluminium extracted from their ores?

Iron Extraction on a Match Head – Follow Up Activities

Copper can be extracted from black copper oxide powder in a similar manner. For best results, one spatula of copper oxide powder should be placed in a test tube above one spatula of charcoal powder. After heating for several minutes in a Bunsen flame a copper coloured ring should appear at the junction between the two powders.

References

Dunne, Kevin, 2003, 'Metal Ores', caveman chemistry.com

Iron Extraction on a Match Head, youtube.com

Royal Society of Chemistry, 2010, ‘The extraction of Iron’ rsg.org

Making Ginger Beer in the Science Classroom

Fermentation is a type of anaerobic respiration (respiration in the absence of oxygen) carried out by yeasts and other living cells to produce energy for growth and metabolism. In this process, glucose is converted into carbon dioxide, ethanol and energy according to the following equation:

glucose → ethanol + carbon dioxide + energy

When yeast is provided with a source of sugar, water and ginger, it will begin to ferment to produce a bubbly mixture generally incorrectly referred to as a ginger beer "plant" (yeast is a type of fungus). This mixture is supplied with ginger and sugar over several days and is then diluted and bottled. The bottled liquid is then allowed to mature for around one week before it is opened.

The History of Ginger Beer

Ginger beer was first manufactured in Great Britain in the mid 1700s and was introduced to North America by British colonists towards the end of the 18th Century. The original brew had an alcohol content of around 11%, but this was reduced to a much lower percentage during the Prohibition years in America in the 1930s. By 1935 there were around 3000 breweries in Britain, 1000 in Canada and 300 in the U.S.A. The British developed specially glazed stoneware bottles that could effectively transport the ginger beer to countries throughout the British Empire. These included the Ionian islands, Kenya and Tanzania.

Making Ginger Beer – Materials and Teaching Method

Step 1 – Making the Ginger Beer Plant

The following materials and equipment are required per group of around four students:

•                ½ teaspoon dried yeast

•                1 rounded teaspoon ground ginger

•                1 rounded teaspoon sugar

•                1 cup lukewarm water

•                old stocking

•                glass jar

•                rubber band

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Mix all ingredients together in a jar, cover with a piece of stocking and secure with a rubber band.

•                Each day for the next week, add 1 teaspoon sugar and 1 teaspoon ground ginger.

Step 2 – Making Up the Ginger Beer

To make up the ginger beer, each group requires the following materials:

•                2 cups of sugar

•                2.5 litres of warm water

•                1/4 cup strained lemon juice

•                2 empty 1.25 litre soft drink bottles with lids

•                A clean bucket or other plastic container

Students could also copy down the following directions:

•                Rinse the bottles with boiling water to sterilise them.

•                Add the sugar, water and lemon jiuce to the bucket to make a base syrup.

•                Strain the ginger beer plant through the stocking.

•                Pour the resulting liquid into the syrup and mix well.

•                Bottle and seal. The ginger beer should be consumed within one week.

Making Ginger Beer – Further Investigations

Note that because the ginger beer contains live yeast it has a short shelf life. Students could investigate ways of removing the yeast before bottling as a means of extending the life of the drink. They could also do some research to discover why ginger beer has such a low alcohol content (this is partly because it is only allowed to ferment for a limited period, but also because the added sugar creates an osmotic effect that dehydrates the yeast cells).

References

Madden, Dean. "Ginger Beer- A traditional Fermented Low Alcohol Drink." scienceinschool.org, 2008

Yates, Donald. "Root Beer and Ginger Beer Heritage." The Federation of Historical Bottle Collectors, fohbc.com, 2003.