Worksheets for Practicals

A worksheet is a good way to give instructions of how to carry out practical work safely and effectively. The students can refer to it whenever they are unsure of what to do next and they do not have to waste time copying out the method into their workbook – they can focus on the results and what they mean. However, one of the disadvantages of using worksheets containing detailed instructions is that students can end up following them passively, like a cookery recipe.

In view of this, I have started to develop worksheets for practicals that make extensive use of diagrams or photographs (images can be snipped from instructional videos on YouTube) and the minimum use of words. Furthermore, I include questions about what the students are doing and why they are doing it as discussion points at each stage of the process. Below is an example of one such worksheet that I made for an investigation of chlorophyll using paper chromatography.

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Food Chains and Food Webs

The feeding relationships of the different organisms in an ecosystem can be shown most simply in a food chain. However, in most communities, animals will eat more than one type of organism and as such, a food web gives a more complete picture of exactly what eats what. Below are just a few ideas of how to teach both.

Wildlife documentaries

Wildlife documentaries contain lots of examples of real life (and often quite bloody) food chains and food webs, and asking the students to watch a few snippets before identifying the feeding relationships in each can prove a useful starting point to the lesson.

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Hanging mobiles

One common mistake when drawing food chains and food webs is for students to put the arrows the wrong way round and it is crucial that you emphasise that they point in the direction of energy flow up the chain. Asking students to construct food chain and food web hanging mobiles can help. You can download templates here or ask the students to make their own.

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Energy transfer

Energy transfer in food chains is inefficient; the amount of energy that is passed on is reduced at every step (trophic level). However, great care must be taken to ensure that you do not refer to the energy being lost, since energy can be neither created nor destroyed but rather is converted into some other form or store.

In food chains, much of the energy is transferred to the environment as heat during respiration but obviously some of it is also used by the organism (before it is eaten) in life processes such as movement and growth. Furthermore, not all of a food item may be ingested during feeding and, even if it is, not all parts will be digestible (e.g. lignin and cellulose).

A nice way to demonstrate energy transfer in a food chain is to pour coloured water between paper, plastic or styrofoam cups (each representing a trophic level) and reducing the volume of water transferred each time.

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Begin by pouring just 10% of the total volume of water in the jug (the sun) into the first cup (producer). This demonstrates that only about 10% of the sunlight that falls on a plant is used in photosynthesis since most of it is transmitted or reflected, and some of it is simply not the correct wavelength to be absorbed by the photosynthetic pigments in the leaf (only red or blue light is absorbed).

Next, pour roughly 10% of the water in the first cup into the second (primary consumer) and the remainder into another container labelled ‘Respiration (movement, warmth, growth) and excretion’ (do not pour the water down the sink as this will only reinforce the misconception that energy is lost). Repeat this process along the food chain.

By the time you reach the final consumer, only a couple of drops of water will remain. This is a good point in the learning to ask the students why food chains are usually restricted to just three or four trophic levels and why the number of organisms generally decreases along the chain.

Dinner at the Reef

This is a fun game from Arkive in which students learn about food chains in a marine environment, predator-prey relationships and the fine balance of an ecosystem. Although primarily aimed at 7 – 11 year olds it can also be used at Key Stage 3.

Interactive learning websites

There are now a large number of interactive learning websites offering simulations and simple ‘drag and drop’ style games for teaching younger students about food chains and food webs. Simply click on any of the images below to link.

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Stop Motion Animated Movies

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I have recently discovered this wonderful app for making stop motion animated movies on the iPad. It is free to download from the App Store but includes a number of in-app purchases such as sound effects and movie themes which you may wish to invest in. Students can simply draw a sequence of images on paper to photograph or build models using plasticine, Lego or pipe cleaners etc. Most recently, my AS students (who are currently studying a unit on immunity) animated clonal selection and expansion in B-lymphocytes (below), phagocytosis and the action of antibodies.

Teaching Artificial Selection

Artificial selection is the process by which humans select animals and plants for breeding because of their useful characteristics e.g. high crop yield in cereal crops and meat quantity and quality in beef cattle. Artificial selection has been practiced for thousands of years to produce varieties of animals and plants with increased economic importance. At GCSE, students may not only be required to define the process of artificial selection (or selective breeding as it is also known) but also state the similarities and differences between natural and artificial selection, and outline the steps involved in ‘improving’ crop plants and domesticated animals over many generations.

I would actually suggest introducing artificial selection before broaching (or revisiting) natural selection, as students often find it easier to grasp the concept of humans acting as the selective agent, purposively picking and choosing which individuals survive to breed, than the environment. There are also many examples of weird and wonderful selectively-bred plants and animals with which the students will already be familiar. Indeed, I tend to open the lesson with a short quiz in which I display photographs of sausage dogs, Merino sheep, Belgian blue cows etc., and ask the students to guess why they look the way that they do.

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Thinking Maps

However, once the students are familiar with both artificial and natural selection, it is useful to compare and contrast the two using a card sort activity, Venn diagram or double-bubble map. The students should identify that both processes require genetic variation and result in individuals with particular phenotypic traits (characteristics) surviving to breed and pass on their genes, while others do not. At this stage it may also be useful to reinforce the concept of evolution as being a change in frequency of particular alleles within a population over time and that, as such, evolution occurs through artificial as well as natural selection (one common misconception is that natural selection and evolution are one and the same).

Selective Breeding Game

This is a fun game in which the students, as farmers, aim to selectively breed sheep with both plentiful wool and high quality meat. It is a particularly effective activity for demonstrating that artificial selection occurs over successive generations and that the farmer does not actually create anything (the alleles for the favourable characteristics already exist) but simply decides which individuals can breed and which can not. The game is available to download for free here.

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Wolf and Dog Handraising Project

This is a BBC documentary entitled ‘The Secret Life of the Dog’ which features an overview of a fascinating experiment carried out by researchers at Eötvöus Loránd University in Hungary between 2001 – 2003. The aim of the experiment was to investigate whether the relationship between humans and domesticated dogs could be replicated with wolf cubs if they were treated like puppies and raised in the home. It makes for a fantastic discussion point about ‘nature and nurture’ by highlighting the fact that artificial selection can result in changes to an animal’s temperament as well as their appearance. The relevant section begins at 32 minutes in.

The Ethics of Artificial Selection

The danger of artificial selection is that that there may be too much inbreeding between closely related individuals. This can result in harmful recessive alleles being inherited alongside the desired genes, and an overall reduction in genetic variation. Indeed, many breeds of dog suffer from the effects of inbreeding e.g. elbow and hip dysplasia, epilepsy and heart disease (further information is available from the Kennel Club, among other sources). Asking students to consider the ethics of artificial selection, can prove an engaging topic for debate, if carefully structured.

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Lego Telomeres

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Telomeres are located at the ends of chromosomes. They consist of multiple repeat sequences and their main function is to ensure that when DNA is replicated, the ends of the molecule are included in the replication and not left out. When teaching the significance of telomeres, I use Lego to build giant chromosomes as this allows me to demonstrate the loss of a short section of each telomere during cell division (by removing Lego bricks) and the role of telomerase in replenishing it (by adding Lego bricks).

Stem Cell Potency

A stem cell is a cell that can divide an unlimited number of times by mitosis. When it divides, each new cell has the potential to remain a stem cell or to differentiate into a specialised cell. The extent of the power of a stem cell to produce different cell types is variable and referred to as its potency. A simple yet enjoyable way to demonstrate the potency of different types of stem cell is to use plasticine or modeling clay.

Start by giving each student an identical ball of plasticine and ask them to model it into an animal of their choosing. As you can see, in today’s lesson we had a snail, a penguin, a pig, a cat, two fish and a snake. In other words, the plasticine has the potential to be absolutely any animal in the world. As such, it can be described as having high potency, much like the embryonic totipotent stem cells which can differentiate into any type of cell.

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Next, explain that some of the totipotent stem cells differentiate into specialised cells in the placenta (demonstrate this by removing a few of the now ‘specialised’ animals but provide their sculptors with a new ball of plasticine in order for them to continue with the activity) whereas others become a second type of stem cell, called pluripotent stem cells.

Pluripotent stem cells have lower potency than the totipotent cells but can still form all of the cells that will lead to the development of the embryo and later the adult. Demonstrate this reduced potency by asking the students to roll their plasticine back into a ball before modeling it into an animal of their choosing but stipulating that it must now be an animal with four legs. In case you were wondering, we now have an elephant, two pigs, two lizards, a tortoise, and a cat.

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Again, explain that many of the pluripotent stem cells differentiate into specialised cells (as before, remove some of the now ‘specialised’ animals and replace with a new ball of plasticine) but that some become multipotent stem cells, found in the organs and tissues of adults. Multipotent stem cells have far lower potency than embryonic stem cells and can typically only differentiate into a very small number of specialised cell types. So, once again, ask the students to roll their plasticine back into a ball before modeling it into an animal of their choosing…so long as that animal is either a dog or a cat!

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Limiting Factors and Super Cheesy Burgers!

This is a fun way to introduce the concept of limiting factors in photosynthesis at Key Stage 3.

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Explain to the students that they are working at McBoulton’s (please feel free to change the name!), a popular hamburger fast food restaurant. It is a particularly busy day in the restaurant and the students are working in teams to prepare the most popular item on the menu, the McBoulton’s Super Cheesy Burger. Each Super Cheesy Burger consists of a sesame seed bun, a 100% pure beef patty, a slice of cheddar cheese, and a crunchy lettuce leaf (simply print and laminate for durability). Delicious!

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To begin, provide each team with 12 sesame seed buns, 8 beef patties (the second limiting factor), 12 lettuce leaves, and just two slices of cheddar cheese. Challenge the teams to make as many Super Cheesy Burgers as they can in one minute. Go!

Of course, after just 10 seconds or so, the production line will ground to a halt. Ask the students to record the number of complete Super Cheesy Burgers they have made (i.e. two) and to discuss why they made so few (i.e. they ran out of cheese slices). Now repeat the challenge with four, six, eight, ten and finally twelve slices of cheese. Each time ask the students to record the total number of burgers they managed to make in one minute and to discuss exactly what stopped them from making more.

Ask each team to plot a line graph of the number of complete burgers against the number of cheese slices they were given. Next, ask the students to describe and explain the graph (i.e. at first, the number of cheese slices governed the rate at which Super Cheesy Burgers could be made but eventually, when there were plenty of cheddar cheese slices available, the amount of beef patties limited production instead).

At this stage I usually ask the students to compare their fast food production line with the process of photosynthesis (using bridge maps) by identifying the following in each:

  • Raw materials
  • Products
  • Site of production
  • Energy source

Finally, I show the students examples of limiting factor graphs in photosynthesis, highlight the similarities with their own graph, and then ask them to identify the limiting factor in each.

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.

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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.

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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.

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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.

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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.

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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.

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!