Plotting the Solar System on My Maps

capture-solar

This is a fun activity for imparting the vastness of the solar system. Start by placing a football on the centre spot of the school football field or at the front gate etc. and informing your students that it represents the sun. If the circumference of the football is approximately 70 cm and the circumference of the sun is 4.3 million kilometres, how big would each of the planets in our solar system be (I like to provide a selection of everyday objects such as a tennis ball, apple, ping pong ball, and various marbles etc. for comparison) and how far up the road would they be located? Once the calculations have been made (this can be scaffolded by providing a conversion table or similar) ask the students to plot each planet, centered around the football, on Google My Maps.

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.

capture-6

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.

capture-new-1

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.

capture-5capture-4capture-3

Hinge-Point Questions in Science

Hinge-point questions are diagnostic questions that are used at a particular point in a learning sequence when you need to check if your students are ready to move on and in which direction. Typically, hinge-point questions are multiple-choice and include wrong answers that challenge common student misconceptions. Critically, they are quick to answer and allow you to realistically view and interpret all students’ responses in 30 seconds or less.

Hinge-point questions should be used before you move from one key idea or learning intention to another, particularly if a solid understanding of the content before the hinge is a prerequisite for the next phase of learning. Apps such as Socrative, Kahoot and Plickers can all be used to provide instant feedback but mini-whiteboards or flashcards (below) also work well.

flashcards

Below are a couple of examples of hinge-point questions that I have used recently in my lessons. However, for more information, I highly recommend the free online course ‘Assessment for Learning in STEM Teaching’ offered by the National Stem Learning Centre via Future Learn.

Key Stage 3

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compund-3

GCSE

distance-time-graphs

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A Level Biology

dna

glycogen

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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.

selective-breeding

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.

art-selection-game

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.

bulldog

Atomic Structure

By the end of Key Stage 3 pupils are expected to be able to describe the structure of an atom, relate atomic structure to information given for each element in the Periodic Table and show the arrangement of electrons in shells around the nucleus. It is vitally important that pupils develop a secure knowledge of these fundamental concepts in chemistry since a superficial understanding can result in misconceptions and pose significant difficulties in understanding higher-order content such as ionic and covalent bonding at GCSE and beyond.

Take your time, break down the topic into bitesize chunks and use plenty of diagnostics such as hingepoint questioning to gauge the level of understanding of the whole class before moving forward together. In addition to the following activities, provide pupils with plenty of practice in relating atomic number and mass number to the number of protons, neutrons and electrons in a neutral atom, and drawing electron shells.

Hula hoop competition

Explain that all atoms consist of electrons orbiting a tiny nucleus then have a hula hoop competition! Who can keep their electrons orbiting for the longest?

Plasticine atoms

Provide pupils with laminated electron shells, an element symbol, a particle key and coloured plasticine. Ask them to build an atom of the element they have been given before taking a photograph and sharing it with the class via Padlet.

electrons

Models

Build giant models of atoms using foam balls, craft straws, pipe cleaners and wire etc. These make excellent mobiles which can be hung in order of atomic number along the length of the science corridor.

Atomic cookies

Alternatively, bake (or buy) cookies and decorate them with proton and neutron M&Ms and silver ball electrons.

Facebook profiles or cubes

Facebook profiles or these simple cubes can be used to present information on all manner of things in science (e.g. famous scientists, types of nuclear radiation, specialised cells). Ask the pupils to investigate the element for which they built their plasticine atom and then complete a Facebook profile or cube for it. Who discovered it? When was it discovered? Is it a metal, non-metal or semi-metal? What are its properties?

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What’s the Door Policy? Modelling Cell Transport.

doorman

When explaining how substances enter and leave cells, I use the different door policies of (fictional) exclusive restaurants and nightclubs to model the processes of simple diffusion, facilitated diffusion, active transport and osmosis. I often ask the students to act out each scenario (using various props) before asking them to identify the process, explain their reasoning, and discuss the limitations of each model.

Explanations are given in italics beneath each description.

Luigi’s

Luigi’s is a simple Italian restaurant which allows anyone in; so long as they are not being too noisy (really boisterous people tend to go to Jack’s instead). There are no doormen and it is free to enter. However, it is quite small inside and so it quickly fills up and then, once full, no one else can get in. There are usually an equal number of people waiting outside as there are inside but as one person leaves, another can enter so the actual number of diners never changes.

Luigi’s represents simple diffusion. Small, non-polar molecules can diffuse across living cell membranes (i.e. do not require transport proteins or ‘doormen’) but large, polar molecules (‘noisy people’) can not. Diffusion is passive (‘free to enter’) and net movement continues until equilibrium is reached (‘the actual number of diners never changes.’)

Havanna’s

rooftop

Havanna’s is an exclusive rooftop restaurant. It is free to enter but there are doormen who are notoriously fussy about who they let in; usually only the big names in town (who would never dream of going to Luigi’s or Jack’s). In fact, Havanna’s is so strict that the doormen actually accompany you up in the elevator all the way from the ground floor to the restaurant. As with Luigi’s it is only small and once full, it is a one out, one in policy even if there are lots of people waiting downstairs.

Havanna’s models the facilitated diffusion of large, polar molecules (‘big names’) via carrier proteins (‘the doormen actually accompany you up in the elevator’). Again, facilitated diffusion is passive (‘free to enter’) and net movement continues until equilibrium is reached (‘once full, it is a one out, one in policy’).

The Oxford Club

doormen

You have to pay to get into The Oxford Club, an exclusive members club downtown. There are doormen and they are extremely fussy about who they let in. It is a very strange place though as it is always busy inside but you rarely see people outside waiting to get in.

The Oxford Club represents active transport. It requires energy (‘you have to pay to get into the Oxford Club’) and carrier proteins (‘doormen’). Active transport involves the accumulation of ions against a concentration gradient (‘it is always busy inside but you rarely see people outside waiting to get in’). 

Jack’s

Jack’s is free and tends to be full of the particularly lively people who were turned away from Luigi’s. There is a doorman but he just politely holds the door open and in you go. It does tend to fill up quickly though and once full, the policy is strictly one out, one in only.

Jack’s models facilitated diffusion through channel proteins (‘just politely holds the door open and in you go’). Facilitated diffusion is passive (‘free’) and net movement continues until dynamic equilibrium is reached (‘once full, the policy is strictly one out, one in only’).

The Penalty Spot

The Penalty Spot is free but only open to supporters of the local football team after a match. There are lots of entrances but you can only get through if you present your season ticket (it is very selective). Away fans certainly can not get in. By the way, did you know that the nickname of the local team is the H2Os because they play in blue?

The Penalty Spot represents the net movement of water molecules by osmosis (‘only open to supporters of the local football team’). Water moves from a region of higher water potential to a region of lower water potential (‘open to supporters of the local football team after a match’), through a partially permeable membrane (‘you can only get through if you present your season ticket’). 

 

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.

LEGO and M&M Half-Life

The half-life of a radioactive substance is the time it takes for the number of parent nuclei in a sample to halve, or for the count rate from the original substance to fall to half its initial level. Half-life is random and it is impossible to know which individual parent nucleus will be the next to decay. LEGO and M&Ms can be used to model this random decay while also negating the need for students to handle radioactive materials.

M&Ms

791px-Plain-M&Ms-Pile

Students start with 100 M&Ms (other sweets can be used so long as there are two distinct sides e.g. Skittles) and tip them into a tray. Record the number of M&Ms which have landed face-up (these represent parent nuclei which have decayed). Remove these ‘decayed’ nuclei and tip the remaining M&Ms into a second tray. Once again count the ones that have ‘decayed’ and repeat until all of the M&Ms have gone. Use the data to plot a half-life curve.

LEGO

Lego_Color_Bricks

Students throw 60 2×2 LEGO bricks into a tray and remove all of the bricks that land studs-up (these represent parent nuclei which have decayed). Stack these bricks together to show the activity i.e. the number of decays per throw. Throw the remaining LEGO bricks and again remove those that have ‘decayed.’ Stack these into a second column and place this next to the first to quite literally build an activity vs. throws bar chart. Repeat until all of the LEGO bricks have gone.

 

Oreo Plate Tectonics and Moon Phases

A couple of nice activities using Oreo cookies (or in my case, cheaper alternatives).

Plate tectonics

Explain that the upper cookie is the lithosphere, the creamy filling is the asthenosphere, and the lower cookie is the lower mantle. Begin by simulating the motion of the rigid lithosphere plate over the softer asthenosphere by sliding the upper cookie over the cream. Then break the top cookie in half and simulate a divergent plate boundary by sliding the two cookie halves apart.

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Push one cookie half under the other to make a convergent plate boundary.

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Finally, simulate a transform plate boundary by sliding the two cookie halves past one another. Students should feel and hear that the two ‘plates’ do not glide smoothly past one another (thus modelling the earthquakes that occur at transform fault lines such as San Andreas).

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Moon phases

Simply remove the top cookie to reveal the creamy filling beneath. Scrape away and shape the cream to show the phases of the moon. Students should draw the relative location of the Earth and label the phases. Great as a revision tool or plenary.

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