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.

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

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.

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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GCSE

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A Level Biology

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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.

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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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Tissue Fluid

As blood flows through capillaries within tissues, some of the plasma leaks out through gaps between the cells in the wall of the capillary, and seeps into the spaces between the cells of the tissues. This leaked plasma is known as tissue fluid.

Tissue fluid is almost identical in composition to blood plasma. However, it contains far fewer plasma proteins as most are simply too big to pass through the tiny holes in the capillary endothelium. Red blood cells are also too big so tissue fluid does not contain these, but some white blood cells can squeeze through and move freely between the tissue cells.

The tissue fluid leaves the capillaries under high pressure at the arterial end of capillary beds. In order to demonstrate this I use the following:

  • Five or six small balloons
  • Permanent marker pen
  • Large glass bowl
  • Glass jug
  • Water
  • Yellow food-colouring
  • Red beads
  • Rice
  • Pestle and mortar
  • Sieve

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Use the permanent marker pen to draw nuclei on the balloons and then place them into the glass bowl. The balloons represent the tissue cells. Fill the glass jug with water and add a drop or two of yellow food colouring (blood plasma). Throw in some red beads (red blood cells) and rice (plasma proteins) – grind up the rice in the pestle and mortar beforehand so that you have different sized fragments.

Pour the ‘blood’ through the sieve, highlighting that the holes in the sieve represent the tiny gaps in the capillary wall. I like to pour it from a great height so that it sprays everywhere (showing that the blood is under high pressure) and covers the cells below. Highlight that none of the red blood cells have passed through the holes and nor have most of the plasma proteins (the students should see some of the smaller bits of rice floating about in the tissue fluid but most will remain trapped in the sieve).

 

Lego Telomeres

telomeres

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.

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’).