An Introduction to Enzymes

Enzymes first make an appearance in Year 9 and although most students at this level quickly grasp that these globular proteins speed up chemical reactions there are always a number of stubborn misconceptions about exactly what they are and how they work. Below are a few ideas for class practicals (tried and tested – enzyme experiments are notoriously fickle) and activities that can help at Key Stage 3 and beyond.

Practical 1 – Factors affecting the activity of catalase

Science is about discovery and students should be given opportunities to actually be scientists by discovering things for themselves. Too often teachers feel that they have to tell students everything, explaining exactly what will happen in an experiment and leaving nothing to be explored. So instead I turn the topic of enzymes on its head and start with this class practical investigating factors which affect the activity of catalase.

At the end of the lesson ask the students to describe what has happened and make some simple deductions; they will have seen that both liver and potato share a curious ability to break down hydrogen peroxide and release bubbles of gas, but that boiling them removes their ability to do so – why? By the time you start talking about enzymes, the lock and key theory and denaturing, the students’ curiosities will have been stirred and they will want to know how on Earth it all works.

You will need per group:

  • 6 boiling tubes in a test tube rack
  • 4 watch glasses
  • 30 cm3 hydrogen peroxide (20%) solution
  • 10 cm3 measuring cylinder
  • Forceps
  • Dropping pipette
  • Boiling water bath
  • Ruler
  • Raw liver, cut into  5 g cubes
  • Raw potato, skin removed and cut into 5 g cubes
  • Glass rod
  • Pestle and mortar
  • Stopwatch

Steps:

  1. Label the boiling tubes A, B and C and the watch glasses B and C.
  2. Measure out 5 cm3 of hydrogen peroxide solution into each boiling tube.
  3. Place a 5 g cube of raw liver into the boiling water bath and leave for two minutes.
  4. Use the forceps to carefully remove the cube from the water bath, and place it on watch glass B.
  5. Grind one raw liver cube with the pestle and mortar, and transfer the paste to watch glass C.
  6. Add the remaining raw cube of liver to boiling tube A and after one minute record the height of froth in the boiling tube.
  7. Repeat with the boiled cube in boiling tube B and the raw liver paste in boiling tube C.
  8. Repeat the experiment using potato cubes instead of liver (the potato cubes are difficult to grind in a pestle and mortar so you may need to cut them up into smaller pieces first).
  9. Record the results in a suitable table.

Modelling enzyme action

Follow the class practical by modelling the protein structure of enzymes, discussing the lock and key theory and demonstrating what happens when an enzyme is denatured.

Locked out

Begin the lesson by purposely locking yourself and the students out of the classroom. Produce a big handful of keys and make a fuss about finding the right key to fit the lock. Once inside, introduce the lock and key theory of enzyme action.

Complementary pairs

Another good starter activity is to cut large pieces of paper into complementary enzyme and substrate molecules then hand one out to each student as they enter the classroom and ask them to find their partner.

complementary sites

Amino acid necklace

Give each student a shoelace or a long piece of string and a handful of different coloured beads. Ask them to thread the beads onto the shoelace in any order they wish in order to make a colourful necklace. Explain that enzymes are large protein molecules made of many amino acids joined together in a long chain, a bit like the beads on their necklace.

beads

Ask the students to screw the necklace into a tight ball to make an ‘enzyme’. Highlight that everyone in the class has made a different type of enzyme because the sequence of ‘amino acids’ on their necklace and the 3D shape of the balls are all different.

necklace

Plasticine models

Make two or three enzymes with different shaped active sites using plasticine or modelling clay. Demonstrate that the substrate molecule only fits the active site of one type of enzyme, before reshaping the plasticine to show what happens when the enzyme is denatured.

Student enzyme models

Nominate two or three students to play the role of enzymes by standing up and putting out their hands in front of them to model an active site. Use a piece of scrap paper as the substrate molecule and move from one student to another until you find the complementary enzyme (in truth this can be any one of the students but it helps to reinforce the specificity of enzyme action).

Model digestive enzymes by gesturing for the chosen student to rip the paper in two before throwing the products dramatically into the air so that their active site is free to accept a second substrate molecule.

found-two-bits-of-paper-while-doing-some-sorting-out-yesterday-that-uEnPFm-clipart

You can also model the action of anabolic enzymes by asking the student to hold two ‘substrate molecules’ together in their active site while a bond forms between them (using sellotape). Again, encourage the student to throw the product dramatically into the air, leaving their active site free to repeat the process.

High five collisions

This is a very simple yet effective way of demonstrating the effect of temperature on an enzyme-catalysed reaction. With reference to a graph of enzyme activity against temperature explain that at low temperatures the average kinetic energy of the enzyme and substrate molecules is low and as such they move very slowly and collide only infrequently. Model this by asking the students to trudge slowly around the classroom and to high five one another on the odd occasion that they meet.

Now turn up the temperature. Ask the students to move around the room a little more quickly, again high fiving when they collide. The students should be able to hear that the number of successful collisions has now increased.

Increase the temperature further still. The students will now be whizzing around the room (careful!) and high fiving almost constantly. The noise of substrate molecules and enzymes colliding will be deafening. This is of course the optimum temperature and the enzyme’s catalytic activity is at its greatest.

Finally, raise the temperature beyond the optimum, denaturing the enzyme and inhibiting the formation of enzyme-substrate complexes. Ask the students to lower their hands so that they can no longer high five. They will still be whizzing about (in fact, faster than before) and will certainly collide but the collisions will no longer be successful. The classroom will fall silent, the reaction has stopped.

Flowmap donuts, zoetropes and flickbooks

Instead of using linear flowmaps to illustrate the stages of an enzyme-catalysed reaction use flowmap donuts, zoetropes or flickbooks to highlight that enzymes remain unchanged by the reaction and can be used again. The students could even animate their plasticine models using stop motion applications such as Stop Motion Studio.

zoetrope 2

Practical 2 – Investigating the effect of temperature on the activity of lipase

A simple protocol which provides reliable, unambiguous results. The investigation can be carried out as a demonstration at two different temperatures, or in groups of five or six students with each student working at a different temperature, allowing enough time to collect repeat data. A nice extension is to add washing-up liquid to the solution in order to emulsify the fats and provide a larger surface area for enzyme action (demonstrating the effect of bile salts in the digestive system).

Full teaching notes and student sheets are available to download from the Nuffield Foundation.

Practical 3 – Investigating the effect of pH on amylase activity

Another reliable class practical from the Nuffield Foundation, this time measuring the time taken for amylase to completely break down starch at different pHs. Again, students can work in groups of five or six with each student working at a different pH before pooling results.

Virtual lab

However, if time is tight, one alternative is to use the excellent Virtual Lab from McGraw-Hill Education, in which students can investigate both the effect of pH and substrate concentration on an enzyme-catalysed reaction from their computer or tablet.

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BBC Bitesize

A nice video from BBC Bitesize which can be used to summarise much of the Key Stage 3 and Key Stage 4 content on enzymes.

Van de Graaff Pie Cases

There is no need to fear the Van de Graaff generator (although advice from CLEAPSS should  always be followed). However, a fun alternative to charging up students is to stack aluminium pie cases on top of the metal dome and watch them fly off in all directions as the electrostatic charge accumulates.

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Forces Dance Mat

This is a great activity for introducing students to drawing force diagrams and resultant force. I have taken the idea directly from TES (the hugely popular original is available here) but I have made my own version in order to emphasise that the length of the arrow shows the size of the force. Obviously any music can be used to accompany it but I have always found that Gangnam Style works well (some of the students even do the dance moves as they jump about!).

Start the music, start the presentation and then jump in the direction of the resultant force. Have fun!

Motion Obstacle Course

I have just started the topic of Motion with my Year 9 students and used an obstacle course as an active way to introduce speed, distance and time equations.

obstacle course

The students set up an obstacle course in the sports hall (balance beams, hopscotch, cones, a wall to climb over etc.) Then, working in pairs, one member of each team tackled the course whilst the other timed them and recorded how long it took to complete each section. The students also recorded the length of each section using a measuring tape e.g. balance beam = 3m, hoops = 8m.

Now that the students knew the distance and the time taken, they could work out the speed at which they completed each obstacle. Finally, the students were asked to plot a distance-time graph (which lead nicely onto the follow-up lesson in which we looked at motion graphs using DynaKars).

Canva

Canva is a free online graphic design tool which can be used to make beautiful posters, infographics, presentations and many other things. It is extremely simple to use and features a vast library of templates, fonts and photographs to choose from.

My AS level biology students have recently used Canva to create eyecatching infographics summarising the structure and properties of biological molecules. I think they look great!

Squishy Circuits – Electrical Play Dough

Capture

A wonderful idea from the Playful Learning Lab at the University of St. Thomas in Minnesota.

Play dough is a semisolid which contains salt and is naturally electrically conductive. However, replace the salt with sugar and the play dough becomes an insulator! Both can be made easily and cheaply using flour, vegetable oil, water and salt or sugar. Students can then roll the dough into ‘wires’ or build more elaborate shapes into which they can then connect components. Great fun!

The recipes in metric units are available here.

The Squishy Circuits Classroom Guide contains the recipes as well as basic instructions and sample worksheets. There are also lots of fun ideas for using squishy circuits in electronics education on the Tinkering Studio website.

Desert Island Apps for Teachers

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There are thousands of websites and apps aimed at teachers but if you had to pick just 10 that you couldn’t live without – the digital bare essentials of a 21st Century classroom, your desert island apps – what would they be?

Here, in no particular order, are mine.

1. Google Drive and Google Classroom

Google Drive includes Google Docs, Sheets, Slides and Forms as well as many other GAFE (Google Apps for Education). Google Classroom is a learning platform for schools which brings it all together in a secure online environment. Drive and Classroom allow students to collaborate and share files quickly and teachers to create and distribute assignments, flip learning, grade work, and post notices. Indispensable.

2. Kahoot!

Without doubt this would be the students’ choice. Kahoot! is an enjoyable, game-based learning platform with many similarities to (the also excellent but less jovial) Socrative. Use it to build fast paced multiple-choice quizzes and class surveys or pose questions at hingepoints during a lesson to receive instant feedback from all. Formative assessment at its most fun.

3. TES Teaching Resources

If you didn’t already know, TES Teaching Resources is a vast online library of mostly free lesson plans and classroom resources uploaded by teachers from around the world. To be honest, it’s not all great but there are some real gems in there which are more than worth the rummage. The site is also home to Teachers’ TV; a source of high quality videos on teaching and learning in Early Years, Primary, Secondary and FE, as well as films to help with continued professional development.

4. Adobe Voice

This one is relatively new on the scene but I love the simplicity of this application for making short, highly-professional-looking animated videos. I have written about it many times in this blog and confess to being a huge fan.

5. Online-Stopwatch.com

This site provides a variety of different stopwatches and clocks which can be used to add a sense of urgency to any starter activity or plenary, help keep younger students on task, or be clearly displayed during classroom-based tests.

6. Educreations

There are now a huge number of apps for creating video tutorials on the iPad but I have mostly remained faithful to Educreations as it works seamlessly with Google Drive and is so simple and intuitive to use. As well as making tutorials, I find it useful for providing feedback on larger pieces of student work (e.g. posters or models). I simply take a photograph, import it into Educreations, and then comment and annotate over it before sharing with the student via Classroom.

7. Twitter

We all know that Twitter is essentially a virtual staffroom for sharing resources, airing opinions and generating discussion but it can also be used to support learning in the classroom. For example, I have used it to provide a running news feed, tracked hash tags, connected with other classrooms and industry professionals, and encouraged students to send live Tweets during field trips. There are lots of possibilities. Not convinced? Here is a useful post by the brilliant @ICTEvangelist on the dos and don’ts of getting started in the pedagogical Twittersphere.

8. Armoured Penguin

The best site I have found for making crosswords and other simple word games. All free and easily converted into PDF.

9. YouTube

Create playlists of videos on particular topics, import videos into Google Forms as a flipped learning activity, post video tutorials, find sound effects to really bring your lessons to life, or simply mine this vast resource for educational audio visuals. TeacherTube, TedEd, How Stuff Works, BBC and Sick Science are just some of my favourite channels.

10. Visible Body 3D Human Anatomy Atlas

This is the only subject-specific entry on my list and a costly one (at the time of writing £18.99 from App Store) but it is a simply stunning piece of kit with an impeccable 3D interface offering students a far greater appreciation of anatomical structures than the flat drawings of a textbook ever could. The high-resolution graphics offer smooth zooming, panning and rotating capabilities and the concise labelling (showing the name of each structure and the system hierarchy to which it belongs) make it particularly useful for older students during organ dissections and demonstrations. Brilliant.

So there you have it, my top 10 teaching websites and apps. I would love to hear about your own desert island choices!

 

Awesome Lesson Starters

Start the lesson with a bang!

What students experience in the first couple of minutes of a lesson makes a crucial difference in how well they engage with the learning intentions and as such, starter activites should be exciting, enthusing and unpredictable.

Here are some ideas for creating that ‘hook’ and maintaining the curiosity of students from the get-go.

  • Start the lesson with a fun or even explosive demonstration which ties in to the main body of the lesson. Sick Science has lots of great ideas.
  • Pass around mystery objects inside sealed bags. Ask the students to guess what they are and what they do.
  • Display apparatus, interesting objects and photographs around the room.
  • Play a short video on a loop and hand out questions about its content. This is even better if it is a video that you or the students have made. For example, a time-lapse video to recap the previous lesson or the steps of a practical investigation presented in Adobe Voice.
  • Write a true / false question or a statement on the board. As pupils arrive ask them to choose whether they think it is ‘true’ or ‘false’ or whether they ‘agree’ or ‘disagree’ and to stand to one side or another of an imaginary line down the middle of the room.
  • Display a picture and a question. Alternatively, you can display a number of different pictures related to a theme and simply ask ‘What have I Googled?’
  • Play ‘Backs to the Board.’ Divide your students into two or three teams. One volunteer from each team sits in a chair with their backs to the board, facing their friends. Write a key word on the board, making sure that the players in the ‘hot seats’ can not see it. After you say ‘Go!’, the members of each team must try to elicit the word from the volunteer without saying the word or giving any clues as to its spelling. The players in the ‘hot seats’ then swap with another member of their respective teams.
  • Arrange for a guest speaker to be standing in the room as the students arrive.
  • Recap the last lesson by displaying true / false statements or multiple choice questions and asking students to answer on mini whiteboards.
  • Use Socrative or Kahoot to prepare a fun quiz or questionnaire.
  • Play a song relating to the lesson as the students arrive.
  • Display multiple choice questions around the room. Give the students a time limit (these classroom timers are fun) and get them to move around the room looking for and answering the questions.
  • Set up apparatus for the lesson and display one or more questions about what it might be for and how it works. Alternatively, hide the appartus under a cloth and, before revealing it, ask questions about what it might be.
  • When they arrive, hand each student or pair of students a mystery object and ask them to come up with ideas about what it might be used for.
  • Greet the students at the classroom door wearing full protective equipment including visor or goggles.
  • Hand each student a question or an answer to a question and ask them to find their pair.
  • Play the ‘Who Am I?’ game but instead of a famous person designate each student a key word relating to the current topic. Remember, participants can only use ‘Yes’ and ‘No’ questions to work out who or what they are.

No matter how you start the lesson try to involve the students whenever you can and make sure it does not go on for too long. Link the activity to the main body of the lesson and allow time for questions and answers. Have fun!