Sunday, 21 October 2012

Using food in science lessons - some ideas.

I enjoying teaching the Edexcel Physics units called Good Enough to Eat and Spare Part Surgery. As I teach in an all-girls school I want to ensure that my practicals appeal to the girls and using food to illustrate physics principles manages that.

During this term I have used golden syrup to calculate viscosity and strawberry laces in a Hooke’s Law investigation. Using Crunchie bars to represent bones is also part of the scheme of work. The strawberry laces doesn’t need to be restricted to an A-level scheme of work, and could be used to extend Year 7 or primary students too. If you find the strawberry laces are not strong enough on their own then it is possible (if a bit sticky) to plait them to make them stronger. Of course, this also leads to a second possible experiment finding the relationship between ultimate tensile stress and number of strawberry laces used.

Some of the students I teach are from Hong Kong. Using sweets as props to go over the key language relating to material science has been very useful. One student explained to me that tough, strong and stiff all have the same meaning when using her translating device.

However, my experience using sweets doesn’t stop there. My step-daughter’s history teacher asked the class to create a model of a castle, she created one out of cake and biscuits, as cooking is turning into a big hobby of hers. This particularly caught my imagine when I saw the same thing being done by  science teachers when asking students to make a model cell cell cake via a link on pinterest and again when a student of a friend brought to school a “sweet” pathogen model. I am reliably informed that asking students (and indeed student teachers) to build models helps to bring out misconceptions. 

I have also seen “sweetie” blood produced by teachers in the past, a recipe I found on the internet suggests the following:
To represent plasma use water
To represent ions use sugar, salt, oil and protein shake mix 
To represent red blood cells use red jelly beans
To represent white blood cells use mini marshmallows and
To represent platelets use white rice.

A colleague has also used sweets to create models of the atom, including strawberry laces for electron shells. A different version is shown in the image to the left.
I have been using golden syrup in other ways to demonstrate the movement of plate tectonics using biscuits on golden syrup. This is an idea from the website:

I feel that it shows brilliantly how the tectonic plates move slowly as it is difficult to see the pieces of biscuit move, yet taking a photo on a digital camera before and after can show the the pieces of biscuit do move. I have used this demonstration already this year with a group of Year 6 students who are following the theme of “underground”.

Physics Experiments
Asking colleagues and searching the Internet has revealed a huge number of science experiments that either involved food directly or have an alternative that uses foodstuffs and sweets.

Several colleagues use skittles or (chocolate) M&Ms to model radioactive decay. This is especially useful if the school doesn’t have enough dice to share between the students and overcomes the issue of students putting the dice that have “decayed” back in with the “unstable” dice, as the students will eat those that land writing-side up. An alternative is to use ditalini pasta, which students would not be as keen to eat and disrupt the lesson.

Measuring the speed of light is possible using a microwave with the turntable turned upside-down to disable the turning effect. For those who haven’t seen this experiment, the standing waves inside the microwave cause two melted spots on a slab of chocolate (cheese slices can also be used). The melted spots are half a wavelength apart. The frequency of the microwaves can either be found in the manual or on a sticker on the back. Speed of light = frequency x wavelength.

Putting marshmallows into a vacuum flask and pumping out the air is a great way to demonstrate the effects of air pressure.

The National STEM centre has a great video explanation by Alom Shaha of the jelly baby wave machine here: A brilliant way to demonstrate transverse waves and their properties.

Not quite sweets, but I also love demonstrating the luminescence of tonic water under UV light, tap water doesn’t glow.

Lastly in my list of possible physics experiments a colleague has suggested using Oreos (as an alternative to jaffa cakes) to model the phases of the moon.

Creativity in Biology
During my career I haven’t taught many biology units, so I turned to my colleagues and friends for ideas of where sweets can be used during biology practical activities:
It is possible to create DNA from sweets as the image above shows. There are various different methods for this activity.
It is possible to use gummy bears in osmosis experiments by measuring the gummy bear before and after immersing in water and salt water.

An example I have used is using sweets as san object for Year 7 students to use and write keys about in their classification modules. Quality street are good for this, or Dolly Mixtures if you are on a budget. It gives something a little more interesting than lab equipment or pictures of aliens. 

A popular experiment with interesting results is investigating the effect of pH on chicken bones. 

A lot of my biology teacher friends talk about “Reebots”. The Reebops activity helps to demonstrate how genetics is responsible both for similarities and variation among members of the same species. There is a worksheet here: and the practical biology website has a good example too. 

Chemistry Practical Activities
If you use the Wikid scheme of work in Year 7 then you will be aware that there is an entire scheme of work dedicated to food called “Cook”. Some of the topics covered relate to heat transfer and change of state, but students also get to make ice cream, investigate British vs American pancakes and look at cooking in the context of physical and chemical changes. I am a big fan of the majority of the wikid scheme.

Using food as a context for science is not just restricted to key stage 3. I teach the OCR Gateway specification at GCSE and there are sections of the first chemistry module dedicated to the chemistry of cooking. 

One of the examples involves baking powder. Instead of heating and showing the decomposition of sodium hydrogen carbonate, it is also possible to make sponge cakes in the microwave during a lesson with and without baking powder to demonstrate the purpose of adding baking powder when baking cakes.

I love carrying out the experiment where the students boil potato and see who it’s consistency changes with time and I demonstrate cooking pieces of potato in a microwave. I enjoy it because the potato usually gets so dry it sets on fire in the microwave, which excites the students. 

The scheme of work also involves students using egg white as an emulsifier.

This term Year 7 have been studying Acids and Alkalis and there are a lot of links to food in the this topic. Whether it be eating foods to establish that acids are sour, to investigating the perfect sherbet recipe, my students have found the link between chemistry and real life interesting at this early stage in tehir secondary education. I also really enjoy the lessons where students test different vegetables to see which one makes the best indicator. (I really like Ribena, but it isn’t as fun as making indicator using red cabbage).

Of course there are lots of “kitchen chemsitry” experiments that involve food, from volcanoes to making invisible ink and creating crystals with sugar. See for more ideas.

A big favourite of a chemistry teacher colleague of mine is making elephant dung using concentrated sulphuric acid and sugar.

Practical Investigations
A colleague told me of an experiment she carried out with a class to establish if a Jaffa Cake is a cake or a biscuit. Cakes get drier as they get older and biscuits go soggy. 

Using food is a great way to engage students in science.

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