Secondary Science Review Volume 23 Number 3 February 2013

Staying dry Insects in the rain The cover image shows a mosquito in an artificial rain shower. High-speed photography has revealed the strategies used by mosquitoes and other insects to survive when they are caught in a shower. See the article on pages 9-12. (Image courtesy of Tim Nowack.) Volume 23 Number 3 February 2013 Contents Fieldwork, labwork On pages 1-3 of this issue of Catalyst, a group of students 1 Speak to me, lichen from La Sainte Union Catholic School in north London Students of LSU School, London describe how they investigated the correlation between the lichen species growing on trees near their school and 4 Fracking: an energy revolution the level of atmospheric pollution. This study was part of Thomas Lewton the Silver Crest Award scheme, run by the British Science Association (http://www.britishscienceassociation.org/ 6 Memory myths crest), and their work drew on the OPAL project (http:// Lawrence Patihis, Ian W. Tingen, Elizabeth F. Loftus www.opalexplorenature.org). 9 Flying dry Laura Plant, an older student, had the chance to botanical David Sang fieldwork in the Amazon rainforest of Peru. She describes her work and shares some of her photographs on pages 13 Thermometry – a hot topic 20-22. Mike Follows While Biology provides plenty of opportunities for 16 Try this: Eating chocolate fieldwork, other secrets of nature have to be uncovered in the lab. On pages 9-12, we look at the work of a group Vicky Wong of scientists and engineers who wanted to know just how 17 Uncovering the magical world of signalling mosquitoes manage to survive outside in the rain. Suzy Moody 20 Adventures in the Amazon Laura Plant 22 Forest fieldwork Laura Plant Students: We have now created a website specially for you where you can browse hundreds of articles from past issues of Catalyst and find out how to subscribe. www.catalyststudent.org.uk

Editorial team David Sang Vicky Wong Gary Skinner Physics Chemistry Biology Brighton Didcot Halifax Published by the Gatsby Science Enhancement Programme Gatsby Technical Education Projects Editorial contact: The Peak 01273 562139 or [email protected] 5 Wilton Road London SW1V 1AP

Subscription information Catalyst is published four times each academic year, in October, December, February and April. A free copy of each issue is available by request to © 2013 Gatsby Technical Education Projects individuals who are professionally involved in 14-19 science teaching in the ISSN 0958-3629 (print) UK and who are registered with the National STEM Centre. Teachers should ISSN 2047-7430 (electronic) visit www.nationalstemcentre.org.uk to find out how to register. Design and Artwork: Pluma Design Individual annual subscriptions (4 issues) are available from Mindsets for £12.00. Bulk subscriptions are also available from Mindsets, ranging from The Catalyst archive £7.00 to £12.00 per subscription, depending on the number ordered. Over 300 articles from past issues of Catalyst are freely Visit www.mindsetsonline.co.uk/catalyst for further details, or email available in pdf format from the National STEM Centre [email protected]. (www.nationalstemcentre.org.uk/catalyst). Students of LSU School London

OSU Lichen Group. Speak to me, lichen How clean is the air?

e are students at La Sainte Union Catholic School in north London. Key words W For our Silver CREST Project, air pollution we explored the relationship between levels of lichen

the pollutant nitrogen dioxide (NO2) and the quadrat distribution of indicator lichens in the vicinity of identification our school. Lichens are indicators of changes in air quality; tolerant species replace those sensitive to a given pollutant. This effect is observed across urban and rural Britain, especially in regions where oxidised and reduced forms of nitrogen are

present. NO2 is the dominant air pollutant in urban areas, due to pollution from road traffic.

Therefore, measuring levels of NO2 can indicate the quality of our town air. What lichens can tell us Lichens are composed of two different organisms living symbiotically; fungus and alga. They absorb atmospheric moisture, rain water and minerals over their entire surface area. This makes them extremely sensitive to atmospheric pollution

(such as NO2) and therefore very good biological indicators of levels of atmospheric pollution. Lichens can be placed into three categories: Two lichen species: Parmelia sulcata is nitrogen- • Nitrogen-sensitive; found in clean, non-polluted sensitive, while Xanthoria parietina is nitrogen-tolerant. conditions We monitored NO2 pollution by placing NO2- • Intermediate; found in clean AND polluted diffusion tubes at different sites (see below) conditions and mapped the distribution of lichens on trees • Nitrogen-loving; found in conditions where levels at different locations along and either side of of nitrogen dioxide are particularly high. Highgate Road.

Catalyst February 2013 1 For a guide to Our hypotheses were: identifying lichens, • The concentration of pollutants would be see Identification highest along the main road (Highgate Road). on the OPAL • There would be a correlation between data from website: www. the NO2 diffusion tubes and lichen distribution. OPALexplorenature. • Information from the Camden Air Monitoring org. website showed us that air quality is poor in our

borough, Camden: in 90% of locations, NO2 levels exceed the Air Quality Standard. Method Learning to identify lichens: We started identifying Monitoring NO2 using diffusion tubes: NO2-diffusionlichens tubes on twigs (Gradko using International) keys. We then were surveyed placed intothe position with the open end at the bottom to prevent rainwatertrees on collection. the Heath NO with2 in the airhelp diffuses of lichen along experts the tube and is absorbed by a fluid on a grid in the lid. The concentration of NO2 was determined by Spectrophotometry. The tubes were replaced Patevery Wolseley three weeks and andHolger sent Thüsoff to beof analysed.the Natural History Museum. We kept lichen samples that were authenticated by Holger as our ‘reference herbarium’. Location of NO tubes and trees surveyed Surveying lichens in Hampstead Heath Making a ladder quadrat: We cut out a strip of 2

five 10 cm by 10 cm squares from thick plastic of a Monitoring NO2: NO2-diffusion tubes (Gradko bin-liner (see photograph). International) were placed into position with the open end at the bottom to prevent rainwater

collection. NO2 in the air diffuses along the tube and is absorbed by a fluid on a grid in the lid. The tubes were replaced every three weeks and sent

off to be analysed. The concentration of NO2 was determined by spectrophotometry. What we found

This graph shows the relationship of NO2 concentrations and the locations. Perhaps we should have used a bar chart because our independent variable is categoric, but line graphs made it easier to see trends. The values for the front of the school (the main road) were highest. The first set of data (10 March – 31 March 11) showed higher values than the rest. More people may have driven to work due to the cold weather, and there is less movement of air so the local

concentrations of the NO2 would remain high.

Surveying lichens in Hampstead Heath – note the ladder quadrats Then, for each tree: • We recorded tree species and girth at 1.50 m above ground. • We placed our plastic ladder quadrat on the north aspect of the trunk. • We recorded the presence of species of foliose and/or fruticose lichens (‘Macrolichens’) in each square. • We repeated on all compass points (N, E, S, W). In this way, the presence of lichen species in 20 squares was recorded for each trunk. To check reliability we moved to a new tree every 15 minutes. Each group surveyed the same three trees and This graph shows the nitrogen dioxide concentrations we then compared our results. When there was a at different locations from 10 March – 21 July 2011 discrepancy, we went back to the tree and rechecked. (corrected for blank readings); ppb = parts per billion 2

2 Catalyst February 2013 Macrolichen diversity The bar chart shows the correlation between the NO concentration and the pollution score (derived The table shows what we found when we looked for 2 from the lichen data). The pollution score was a correlation between the NO and lichen diversity. 2 minus 5 at the front of the school (on Highgate Nitrogen-loving lichens were found on all the trees Road) where the NO levels were highest, while the sampled, but a greater diversity of macrolichens 2 pollution score was minus 3 on Hampstead Heath including more ‘intermediate’ lichens, were found where the NO levels were the lowest. on the Heath. We might have expected a wider 2 Given more time, we could have measured NO diversity of lichens on the fruit trees in the Orchard 2 levels and surveyed trees on the back roads and as they are set back from the road. also deeper in Hampstead Heath away from the

NO Average number traffic. We could also have looked at lichens on 2 twigs because this would have provided more recent concentration of different history of lichen growth and air pollution. (ppb) lichens per tree Hampstead Heath 11.1 9.7 Orchard 14.1 4.0 Highgate Road 22.0 4.5

However several factors may have affected lichen results, e.g: • bark pH (related to tree species) • age of tree • proximity to sources of nitrogen (e.g. fertiliser) • immediate surroundings of tree (e.g. hedge) • shading of the orchard by the surrounding buildings. We then calculated a pollution score based on the Madeleine A., Mary D., Maureen L., Connie M., Isabel S., frequency of nitrogen-loving and nitrogen-sensitive Linnet M., Hannah R., and Siobhan P. were Year 10-11 pupils lichens. Nitrogen-sensitive species counted +1 as at La Sainte Union Catholic School in Highgate, London, at the they will not tolerate polluted air. Nitrogen-loving time of this research. Their project was exhibited at the Royal species counted -1 each as they grow in polluted air. Society’s annual Summer Science Exhibition.

Indicator lichens Total pollution score nitrogen-loving species nitrogen-sensitive species Location Xanthoria Xanthoria Xanthoria Physcia Physcia Evernia Flavoparmelia Parmelia ucrainica parietina polycarpa adscendens tenella prunastri caperata sulcata

Orchard -1 -1 -1 -1 -1 -1 -4

Highgate Road -1 -1 -1 -1 -1 -5

Hampstead Heath -1 -1 -1 -1 -1 -1 -1 -3

What are lichens? Lichens consist of at least two organisms How can we - a fungus and a photosynthesizing alga (a cyanobacterium) living together. In this amazing association both the fungus and the improve air quality? alga benefit. Small changes in our everyday behaviour can make big differences to • The alga provides food for itself and the quality of London’s environment. the fungus, using its chlorophyll for photosynthesis in the same way as green • Turn down the central heating when possible. plants do. The fungus does not have any • Install home energy efficiency measures e.g. loft, cavity wall insulation. chlorophyll. • Use public transport rather than the car wherever possible. • The fungus plays a vital role in providing a • Walk or cycle for short journeys, instead of using the car. physical structure to shelter the alga from • Use eco-driving techniques to reduce your fuel use. excess sunlight and in particular, water loss. • Also, the fungus absorbs water, nutrients Ensure your car is not wasting fuel, by regularly checking oil and and gases from the environment to share tyre levels. with the alga. • Avoid burning garden or domestic waste, especially in urban areas.

Catalyst February 2013 3 Thomas Lewton

Fracking: an energy revolution?

The UK’s first fracking n spring 2011 two minor earthquakes were contaminating drinking water. Dramatic images of site near Singleton in experienced in the Blackpool area of north tap water being set alight have given rise a large and Lancashire. vocal anti-fracking protest movement. All energy IEngland. The quakes had magnitudes 1.5 sources come with some risk to safety and to the and 2.3, strong enough to be detected by humans environment, but do those of fracking outweigh and even to make a few houses shake. Such the economic benefits? earthquakes are a regular occurrence in the UK, Fracking technology with roughly 20 detected by seismologists each Oil and gas are made from hydrocarbon year. But what makes the Blackpool earthquakes molecules, chains or rings of carbon atoms with hydrogen atoms attached. When burnt in air the different is that they are very likely to have been hydrocarbon reacts with oxygen to form carbon caused by a manmade activity: fracking. dioxide and water vapour. In the process a large amount of energy is released. We use this energy to Hydraulic fracturing, commonly known as power our cars, to produce electricity and to heat fracking, is the process of breaking up rocks deep our homes. underground using high-pressure water mixed with sand and chemicals. The process has been used for oil decades in the energy industry to free oil and gas trapped in rock formations. However, recently the gas technology has received a lot of attention for a new application in releasing natural gas from a type of sedimentary rock called shale. The impact has been most dramatic in the United States. Over the last five years natural gas production in the US has increased by a quarter. As a result the price of natural gas in the US has nuclear halved in only three years, making it a cheaper way coal hydro to produce electricity than coal. Yet questions have been raised over the other renewables environmental impact and safety of fracking technology. As well as the potential to cause Oil and gas account for over half of the energy earthquakes, some people believe that fracking is consumed around the world.

4 Catalyst February 2013 Shale gas has been used in a small way since the Environmental friend or foe? 19th century. There are huge reserves across the Although economically beneficial, some argue that world, yet most shale gas is trapped so tightly the development of shale gas may come at too inside the rock that, for a long time, it was too high a cost to the environment and to our health. costly to release it. George Mitchell, an American Fracking has probably caused minor earthquakes. businessman, experimented with fracking The tremors are too small to be a danger to technology when most believed shale gas to be a humans, but the same violent process of breaking pipe dream. apart rock formations could let fracking chemicals and natural gas seep into groundwater aquifers, from which we take our drinking water – see Box Chemicals for fracking. Another problem arises from the large amount Fissures of water needed to fracture shale rock. If shale Shale gas were produced in an area suffering a drought, it could take much needed water away from the already parched environment. But shale gas isn’t all bad news for the environment: when burned, natural gas produces far less carbon Gas flows out dioxide than an equivalent amount of oil or coal. As a result of switching power station fuel from coal to natural gas, carbon dioxide emissions in the US have decreased to their lowest level in 20 years. In Well the short term, the development of shale gas could

Gas flows out Water table help to reduce global carbon dioxide emissions, and so reduce the risk of climate change. Water, sand and chemicals injected into well

Shale

Hydraulic fracturing Fissures

Standard practice was to use high-pressure water to force open rock formations and release the natural gas. Adding sand to the mixture then kept the rock fractures open when the water pump was turned off. Mitchell’s innovation was to add chemicals to the water that enabled the fluid to be pumped into the well much faster and so fracture it more effectively. This refinement made it economical to Anti-fracking protesters fear that groundwater may become contaminated. extract natural gas from shale, providing a new source of cheap and abundant energy. A global revolution? Estimates of natural gas reserves have doubled Chemicals for fracking because of the newly developed technologies that can extract shale gas. Some seven quadrillion (a There are many different chemicals used in seven with 15 zeros following it) cubic feet of shale fracking. Some of the important types are: gas is now classified as ‘technically recoverable’. • acids to clean and initiate fissures Vast new reserves have been found across the • alcohols and guar gum to improve viscosity world, from China to Argentina to Poland. Even • friction reducers, such as polyacrylamide. the UK holds shale gas reserves worth around £1.5 trillion. In the UK, the Environment Agency must Before these reserves can be developed, the approve these chemicals before they are environmental and safety concerns of the public used. There have been protests that drinking will have to be allayed. But whether these reserves water supplies have been contaminated by are developed will depend on the tough decisions these chemicals. No one has yet provided societies must make about how to support our conclusive evidence that this can happen, future energy needs, and what the risks and rewards but the residents of fracking regions remain of each energy source are. understandably concerned. Thomas Lewton is a researcher on TV science programmes.

Catalyst February 2013 5 Lawrence Patihis Ian W. Tingen Elizabeth F. Loftus Memory Myths

emory is crucially important in There are different kinds of memory and each is Key words everything we do. Without memory very important. Memory for facts is important for memory students taking GCSE exams when they must recall we would not know who we are, names, dates or equations. Memory for emotions psychology M whom we love, where we come from or even how reminds us of how we felt on our first day in a new falsifiable theory to do simple tasks like get out of bed, brush our school, or when we shared a special moment with our family. Memory for events allows us to picture teeth or make tea. This is very clearly shown by the scene and recall the details of our last birthday the case of Clive Wearing who is unable to keep party. Memory for movement and coordination memories for more than thirty seconds. His diary, allows us to walk, talk and ride a bicycle. While it is clear that memory is essential in so many ways, for example, consists of multiple entries where he there are many myths about how memory works. records, time after time, having just woken up. In this article, we explore some of these fairytales and explain what modern psychological science has discovered about how memory really works. Myth 1: Memory works like a video recorder This idea would lead you to believe that all experience is recorded and we can then ‘play it back’ when we want to remember it. This idea became especially popular after the 1950s when brain surgeon Wilder Penfield was trying to treat epilepsy. In a quite shocking procedure, he electrically stimulated the brains of his patients before surgery and some reported vivid memory fragments coming back to

Clive Wearing suffered almost total loss of an ability to make memories after having viral encephalitis in 1985. He keeps a detailed diary of his thoughts. Wilder Penfield, Canadian neurosurgeon

6 Catalyst February 2013 them. Penfield made the mistake of thinking that Myth 3: Traumatic memories are this meant all experience is stored in the brain in the form in which it is to be retrieved. blocked out Over a century ago, the famous psychoanalyst What the Science says: Psychology experiments have Sigmund Freud suggested that traumatic shown that we store very little of what we actually experiences were repressed, which means they see, and these details fade with time. When we are blocked out immediately after the trauma so remember something, we put the memory together that they cannot be recalled at all. Freud thought (reconstruct it) out of the fragments we did manage traumatic memories were so painful that they are to store. Sometimes we fill in the gaps incorrectly - walled off from consciousness and that, years which leads us to the next myth. later, in a safe place, the blocked memories can be remembered in great detail. Myth 2: Memory can not be changed Many people think that memory of past events What the Science says: It is possible for people does not change, and therefore it is very reliable. to not think about a past event for a while and In a court of law, if a witness points a finger at a be reminded about it later. However, there is suspect and says, “That’s the thief, I remember no credible scientific evidence that traumatic that face!” most people assume the witness is memories can be completely walled away for many correct. Similarly, there is a widely held belief that years and then can come back in great detail much memory for our emotions remains the same, and later on. In fact, traumatic memories are usually is still completely accurate even many years later. remembered all too well. For example, people who have gone through terrifying events, such as war, What the Science says: Memory for both past often remember the trauma even when they do not events and emotions can actually be changed. want to. Highly emotional memories tend to be Many psychological studies show that misleading well remembered, but are not always remembered suggestions can completely change a memory. completely accurately. Distressing memories do Misleading suggestions can also plant entire events fade with time, although often more slowly than into a person’s mind. If your mother incorrectly non-emotional events. told you that, as a young child, you had caused You might ask: why would the brain evolve so that a scene by spilling a drink all over a relative at a memory is faulty? Memory errors are the result of a wedding, there is a real chance that you could flexible memory system, and that flexibility is usually develop a memory of this made-up event. beneficial. Changing past memories may improve Similarly, memory for our past emotions can future behavior and problem solving. It also makes change over time. How we remember our feelings 10 sense in terms of evolutionary adaptation that the years ago depends on how we are feeling today, and essence of traumatic events are well remembered also on how we now think about that past situation. to avoid situations like that in the future.

You are the witness Test yourself. This image was shown in a classic misinformation study in the1970s. It shows a car which, moments later, was involved in an accident. Study the photograph and remember the details. Your memory will be tested later in the article.

Catalyst February 2013 7 Why memory is important At the beginning of this article, we pointed out just how important memory is in everything we do. We know that memory does not record everything like a video recorder, that memory can be changed, and that terrifying events are usually remembered all too well. In light of this knowledge what could this mean for society? It is important in the legal system, the treatment of traumatized people and the way we all think about our lives. For example, this knowledge affects how we judge someone accused of a crime. If the police know how changeable memory can be, they can avoid giving leading suggestions to witnesses during questioning or when viewing an identity parade or lineup. Calvin Johnson’s book describes how he was wrongly identified as a rapist and spent 16 years in jail. DNA evidence eventually showed that his accuser’s memory was unreliable. How do we know the old myths are wrong? Over the last 100 years, the field of psychology has gradually become more scientific as it has moved 1 2 towards theories that can actually be tested (these are known as falsifiable theories). This approach has contributed, in part, to faster scientific progress in recent decades. Lawrence Patihis, Ian W. Tingen and Elizabeth F. Loftus are psychology researchers at the University of California, Irvine.

In the witness box 3 4 Think back to the old photo of the car on page 7. Don’t look back! An accident occurred just a few seconds later, and the police ask you this question: Can you remember if there was another car passing along the road as the car waited at the give-way sign? Think carefully. Was there another car? Think 5 6 back and recall as much detail as you can of the picture on page 7. Do you remember a stop sign A photo identity lineup (or parade) where all six faces or a give-way sign? are shown all at once. Not only is it important that the police do not use leading questions; research also If you pictured a give-way sign then your memory has been changed by suggestion suggests that memory is more accurate if the witness contained in the question. The image is taken is shown the series of photos one at a time rather than from a classic misinformation experiment all at once. (Photos: Lifespan Database of Adult Facial performed by Loftus et al. (1978). For a Stimuli; Minear & Park, 2004). detailed account of the research see also the book Eyewitness Testimony (Loftus, 1979). Just as important, police should be careful not to change the memory of a criminal suspect as this has led to false confessions in the past. Examples illustrating these problems can be found at the Look here! website of the Innocence Project (InnocenceProject. org), which documents heartbreaking stories of 60 Minutes episode Eyewitness: www. wrongful imprisonment. Knowing how traumatic cbsnews.com/video/watch/?id=5153451n memory really works can improve the treatment for A BBC interview with Elizabeth Loftus: those traumatized by war or abuse. Knowing that http://www.bbc.co.uk/programmes/ memory can change affects the fundamental way b00yhv36 we all look back at our own lives. Think about it.

8 Catalyst February 2013 David Flying dry Sang How mosquitoes survive the rain

o out in the rain and you get wet. It’s Photographing flies unpleasant, but you survive. Individual To find out how mosquitoes survive impacts with Key to pages 10-11 raindrops are small compared to a raindrops, a group of engineers from Georgia G Institute of Technology (USA) developed a system a human being so they can do little damage. which allowed them to photograph collisions c But imagine that you are a small, flying insect between water droplets and flying mosquitoes. b d such as a mosquito. A raindrop is much bigger Initially, they experimented with fake flies described as ‘mimics’. than you. How can you avoid being flattened? Figure 2 shows the apparatus. Water from jet a A mosquito tips its Some clever photography shows how it’s done. A passes through an infra-red beam (a light gate) wings to escape from B. This triggers the controller C and power supply under a raindrop. Physics for flies D which operates the solenoid E which pulls b A direct hit spells Picture a mosquito. Its mass is only 2 or 3 μg downwards, releasing the insect mimic F (the green danger. (micrograms). It likes living in damp places so it’s ball) made of expanded polystyrene (Styrofoam). c The raindrop breaks likely to be out in the rain. A high-speed camera films the impact. The over the mosquito. Now picture a raindrop. Its mass may be as photographs on pages 10-11 show what happens d A wet mosquito. much as 100 μg, 50 times that of the mosquito. when the apparatus was adapted so that a water It may be falling at 9 m/s. When a raindrop hits drop hit a flying mosquito. a mosquito, it’s like a double-decker bus hitting a human at top speed. If the mosquito is sitting on the ground, it’s likely to be crushed as the raindrop breaks up. But, if the mosquito is flying, the result is different.

V air 1 resistance

V 2

weight

a b

Figure 1 a As it falls, a raindrop soon reaches terminal velocity, a bit less than 10 m/s. This is when its weight is balanced by the force of air resistance. b When a large mass collides with a smaller, stationary mass, the large mass will slow very slightly. Some of its Figure 2 The apparatus used to film insect mimics as momentum has been transferred to the smaller mass. they are hit by water drops.

Catalyst February 2013 9 Tim Nowack/TimNowackPhotography.com Tim

10 Catalyst February 2013 www.catalyststudent.org.uk

A mosquito struck by a raindrop must avoid breaking the drop. Tim Nowack/TimNowackPhotography.com Tim

A mosquito flies Under impact among artificial The experimenters found two possible outcomes. raindrops. • A fly hit off-centre is tipped sideways but manages to shake off the drop. It does this within about one-hundredth of a second, before recovering its flight. • A direct hit causes the fly to fall with the drop, which remains intact. It may fall about 20 cm, so it is not advisable for flies to stay close to the ground. Staying dry If a raindrop hits a solid object, it usually splatters. What prevents this when it hits a mosquito? • Firstly, a mosquito’s mass is very small compared to that of a raindrop. The force of the raindrop on the mosquito is small, about the weight of a small feather. The mosquito is pushed so that it moves with the raindrop. • Secondly, a raindrop is held together by the force of surface tension. This is a result of the attractive forces which act between water molecules and which pull the drop into a roughly spherical shape. The force of the impact is not enough to break the drop. Scanning electron microscope images of water- • Thirdly, a mosquito is covered in water-repellent repellent hairs on the wing of a mosquito. hairs. These probably help it to pull itself free of a raindrop as they fall together. David Sang is Physics editor of Catalyst • A mosquito’s body is flexible with a tough exoskeleton. This allows it to survive the impact Look here! and cope with the sudden acceleration it This work was done by Andrew K. Dickerson, experiences – up to 300 times the acceleration Peter G. Shankles, Nihar M. Madhavan and due to gravity. David L. Hu. Follow the link to see their films So, provided a mosquito can avoid breaking the of mosquitoes in the rain and read their surface of a raindrop and thereby getting wet, it can published paper: http://dickerson.gatech. survive an impact. It must twist its body and wings edu/file/Mosquitoes_in_Rain.html so that it slips out from under the drop.

12 Catalyst February 2013 Mike Thermometry Follows ... a hot topic

Temperature and how we measure it is one of the Thermometer history most important and interesting areas of physics. The thermometer has been more of a development This is reflected in the huge number and variety than a single invention. Philo of Byzantium (280 - Key words 220 BC) was aware that air expands and contracts temperature of thermometers that have been developed. In with changes in temperature and described a this article, Mike Follows describes the surprising demonstration that was developed by Galileo thermometer to become his air thermometer or thermoscope range of thermometers available to scientists today. Kelvin scale in around 1600. This consisted of a glass bulb containing air with a long tube extending downward ideal gas any physical properties of materials into a container of wine or other coloured liquid (see depend on temperature. Our biochemical figure 2). Engraving a scale on the tube converted Mreactions work best at 37°C and we are the thermoscope into the first thermometer. in serious danger if our body temperature strays more than a couple of degrees either way. Being able to record the global mean surface temperature of the Earth is important in order to establish the magnitude of global warming. We have even found Air ways of working out how the temperature of the Earth has changed over the last half a million years as well as the temperature of distant stars and of Outer Space itself. Some definitions The temperature of a substance is a measure of the average kinetic energy of the constituent molecules – the faster the molecules are moving or vibrating, the hotter the body will feel. Temperature also tells you the direction that heat or thermal energy will flow; it flows down a thermal gradient from a hotter body to a colder body. In the process, the Wine hot body will lose thermal energy to the cold body. What is a thermometer? Figure 2 A thermoscope – as the air is heated, it expands and pushes the liquid The word thermometer comes from down the tube. On cooling, the air contracts the Greek thermos (meaning ‘hot’) and and atmospheric pressure pushes the liquid metron (‘measure’). Figure 1 shows a mercury-in-glass thermometer. As back up the tube. with most thermometers, it comprises The Galilean thermometer (Figure 3) was a thermometric substance that developed after Galileo’s death, based on changes in response to temperature principles that he developed. Each glass (mercury expands on being heated) bulb is partially filled with a coloured as well as a means of converting this liquid and has a metal disc, engraved physical change into a numerical value with the temperature, suspended from (the visible scale marked on the glass). it. The bulbs are adjusted by varying the mass of each metal disc so that they all have slightly different densities. When they are immersed in the column of liquid paraffin, they will float if they are less dense than the paraffin, and sink if Figure 1 A mercury-in-glass thermometer they are more dense. – as the mercury gets warmer, it expands Figure 3 A Galilean thermometer shows and rises up the tube. the temperature of its surroundings.

Catalyst February 2013 13 If the temperature rises, the paraffin expands temperature range from about minus 260 °C to and becomes less dense. One or more bulbs will 1000 °C. Driven by the voltage between the ends of now be too dense to float, and will sink. (The the metallic resistor, the free electrons drift along. density of each bulb is fixed because neither its However, increasing the temperature of the resistor mass nor volume changes with temperature.) The increases the vibration of the metal atoms. In turn, temperature is then shown by the metal disc on a this increases the number of collisions between the bulb which is free-floating in the gap. atoms and the electrons, slowing them down. This Galileo’s thermometer has the advantage that it is reduces the current – the resistance has increased. not affected by changes in air pressure in the way that Though the platinum resistance thermometer is his thermoscope was. The Galilean thermometer fairly reproducible, it is regarded as a secondary uses paraffin because the density of water changes thermometer as it needs to be calibrated against a very little in response to changes in temperature. primary thermometer. Ideal gases Glowing Many different thermometers followed but, Hot objects glow – they radiate light. We can use in 1780, Jacques Charles returned to the gas this to find out the temperatures of hot objects, thermometer. He showed that, for the same even distant stars and deepest space. increase in temperature, all gases exhibit the same When heated, the colour of metals pass through increase in volume. In a similar way, the pressure of red, orange and yellow. Eventually, they become a gas increases as it is heated if its volume is fixed white hot when all the colours of the visible – see figure 4. spectrum are emitted. They also glow more brightly because they are hotter and more thermal energy is emitted. Figure 5 shows how the spectrum of a hot object changes as it is heated. In this graph: • the x-axis shows the wavelength of the light • the y-axis shows the intensity of the light. You can see that, as the temperature increases, the peak in the graph gets higher – more energy is being radiated. At the same time, the peak moves to the left, to lower wavelengths which are more energetic.

Figure 4 Measurements of the pressure of a gas show that pressure increases linearly with temperature.

Notice that the graph in figure 4 can be extrapolated to zero pressure. The graph intersects the horizontal temperature axis close to minus 273.15 °C. This is absolute zero and so the absolute temperature scale was created. Sometimes called the Kelvin scale, it is regarded as the fundamental measure of temperature. The Celsius and Kelvin scales are related by the equation: K = °C + 273.15 Figure 5 The spectrum of light radiated by a hot object depends on its temperature. The peak wavelength Because the temperature can be calculated without λmax (in m) is related to temperature T (in K) by the any unknown quantities, thermometers based on equation λmax × T = 0.0029. an ideal gas are known as primary thermometers. We can use this to find the temperature of a Going electrical distant object such as a star. A telescope can be Gas thermometers are not very convenient or easy linked to a spectroscope that measures radiation to use so, in 1871, Sir William Siemens introduced intensity across the electromagnetic spectrum. the Platinum Resistance Thermometer. This is The star’s temperature can be deduced from the now widely used as a thermometer and covers the peak wavelength.

14 Catalyst February 2013 In 1964, Arno Penzias and Robert Wilson, two radio astronomers, accidentally discovered the The cricket as a thermometer cosmic background radiation, the afterglow of To many, the sound of chirping crickets is the Big Bang. From its spectrum, we now know its synonymous with summer. Only the males temperature to be 2.73 K – see figure 6. stridulate, which is the scientific term for chirping, and they do this to attract a female. Amos Dolbear noticed that the frequency of chirping of the narrow-winged tree cricket Oecanthus niveus depended on the prevailing air temperature and, in 1897, he published his law relating the temperature T to the number of chirps per minute N: T = 10 + (N - 40)/7 This is the equation of a straight-line graph. Why does the chirping frequency increase with temperature? Well, crickets are cold-blooded. As the temperature rises, it becomes easier Figure 6 The spectrum of cosmic background to reach the activation energy required for radiation, as measured by the COBE satellite. The line the chemical reactions that drive the muscle shows that it corresponds to a temperature of 2.728 K. contractions used to produce chirping, so they © Nick Strobel www.astronomynotes.com happen more often. Proxies We can work out the Earth’s past temperature and climate using proxy thermometers. Dendrochronology is probably the best known technique and uses the width of tree rings to infer past climate. Wide tree rings correspond to conditions that favour growth. We can go back almost half a million years using the ice cores that are being drilled out of the Antarctic ice at Lake Vostok. Apart from the measuring the concentration of greenhouse gases like methane, isotopes of oxygen can also be analysed. There are two important isotopes of oxygen, 16O and the heavier 18O. Water molecules with 16O atoms are lighter and evaporate more easily. Water with 18O atoms is heavier and is rained out more easily when the water vapour condenses. In a colder world, more of the heavier water is This graph shows that the rate of chirping of rained out before it reaches the poles so that polar the snowy tree cricket Oecanthus fultoni shows 18 ice has a smaller fraction of the O isotope. This the same pattern as Dolbear’s crickets as the can be used to infer past temperature – see figure 7. temperature increases. Published by Thomas J. Walker in the Annals of the Entomological Society of America in 1962.

Figure 7 Past temperature variations deduced from TJ Walker oxygen-isotope measurements of an Antarctic ice core. A male snowy tree cricket Ice formed 450 000 years ago was found at a depth of over 3 km. Mike Follows teaches Physics

Catalyst February 2013 15 Try This Eating chocolate

Cocoa pods growing on a tree in India hocolate is very popular. But what happens if you melt and re-harden it? What is going on? You added nothing to the chocolate so exactly the C same atoms are present as were there at the start. You will need: The way the atoms are arranged and the structure • 2 identical bars of chocolate – dairy milk works well. of the components have changed. In particular, • A warm place one of the ingredients of chocolate, cocoa butter, • A fridge can have many different structural forms which can easily be converted from one to another. The forms What you do have different melting points. Leave both bars of chocolate in their wrapping. When the chocolate is melted and put in the Keep one of the bars of chocolate at room fridge it usually changes to a form with a lower temperature. Melt the other one by putting it into a melting point than the original chocolate. This warm place such as on a radiator or in the hot sun. causes a change in the properties. In the original When it has fully melted, put it into the fridge to re- chocolate, the melting point is about the same as set. We will call this the melted chocolate although body temperature, 37°C. Melting is an exothermic it has re-hardened. process so tends to cool the mouth. The melted Remove it an hour or so before you want to do chocolate has a lower boiling point so no longer has the experiment and allow it to come up to room the cooling effect. It melts more quickly, however, temperature. which causes the flavour to be released faster.

Un-wrap both bars of chocolate. Try snapping Vicky Wong is Chemistry editor of Catalyst. each bar and then try eating chocolate from each. What do you notice? How are they different? It is probably best not to read ‘What you may find’ until you have tried tasting it. You may need to repeat the taste tests a few

times to make sure!

less smooth than the normal chocolate. normal the than smooth less

The melted chocolate often seems ‘grainier’ and and ‘grainier’ seems often chocolate melted The

The normal chocolate seems to cool the mouth. mouth. the cool to seems chocolate normal The

chocolate seems to have a more intense flavour. flavour. intense more a have to seems chocolate

do this – it is much softer. Sometimes the melted melted the Sometimes softer. much is it – this do

‘snap’. The melted chocolate does not normally normally not does chocolate melted The ‘snap’.

a distinctive noise when you break it. This is called called is This it. break you when noise distinctive a

You may notice that the normal chocolate makes makes chocolate normal the that notice may You What you may find may you What Cocoa butter is a fat, extracted from seeds in the cocoa bean.

16 Catalyst February 2013 Suzy Moody

Uncovering the magical world of signalling The Nobel Prize for Chemistry 2012

magine you are lying in bed. Your heart is the human body require signals to be released, beating. Gradually you wake, open your detected by a receptor in the right place and an Key words appropriate response to be mounted. For example, eyes and realise it is light outside. You get hormone I hormones can be released into the blood stream up and start the day. but, if there is no receptor to detect the hormone receptor level changing, there will be no response. crystallography All these things we tend to take for granted in Scientists have discovered many different life: heart beats; sleep; being able to see; being signalling molecules, among them names may Nobel prize able to move at will. Yet all these functions of be familiar such as adrenaline, dopamine and

Catalyst February 2013 17 serotonin. Adrenaline is part of the complex Nobel Prize system that moderates your heart beat and blood pressure. When you are scared or nervous, you feel your heart pounding. That is the body sensing and responding to an increase in adrenaline. Dopamine Spsmiler is a neurotransmitter, a signal that is detected by receptors on brain cells. Problems with regulating dopamine can lead to Parkinson’s Disease and are also thought to be the underlying cause of many mental illnesses. Drug design What is interesting about these examples (and many others) is that we have used our knowledge of the signal and what it does to create drugs that mimic or inhibit their action, thereby offering treatment for many different conditions. We have done this without actually knowing the nature of the receptor that the signal or the drug will bind to. To put that in context, it is thought that over half of the medicines we use bind to these receptors that we assume are present but which nobody has yet found. Robert Lefkowitz and Brian Kobilka, winners of the For example, in every Intensive Care Unit in every Nobel Prize for Chemistry 2012 hospital in Britain, many patients’ survival depends So what has all of this got to do with the Nobel on being given infusions of adrenaline. This is Prize for Chemistry? The 2012 prize has recently because when the body is extremely sick or injured been awarded to two American scientists, Robert it is likely to have a very low blood pressure. This Lefkowitz and Brian Kobilka. is dangerous as it stops oxygen getting to all the The prize was awarded for ‘studies of G protein- essential parts of the body like the brain, heart and coupled receptors’ or GPCRs. These two scientists kidneys. Giving artificial adrenaline can help the have led the way to finding those elusive receptors, body maintain a good blood pressure and ensure and trying to characterise them as much as that all the vital organs get as much oxygen as they possible, to advance our understanding of how our bodies work and how we can medicate them when things go wrong. In the 1980s, Lefkowitz started work on receptors which he describes as ‘gateways’ to the cells for all the hormones and signal transmitters. He radiolabelled hormones so he could visualise how they get through the cell membrane. It became apparent that the hormone would bind to a specific receptor (GPCR) in the membrane. The GPCR then activates a specific protein inside the cell, and a response to the signal is made. Over 1000 different receptors have now been identified. Patients in intensive care are often given adrenaline. They are known to mediate the senses (sight, taste need. Yet the receptor that adrenaline binds to was and smell), pain tolerance, glucose metabolism unknown for many years. and a huge variety of other physiological responses. Mental illnesses such as manic depression and The first receptor to be characterised by schizophrenia are caused by problems in signalling Lefkowitz and his colleagues was an adrenergic in the brain. As mentioned above, dopamine is a receptor – the receptor responsible for detecting neurotransmitter signal that passes between brain adrenaline and noradrenaline. They rapidly found cells. When dopamine activity is excessive, the several other receptors, and it became clear that Radiolabelling uses brain cells are over-stimulated and the person is they all shared great similarity. The receptors molecules containing unable to think coherently or behave rationally. make up a protein family, with specific amino radioactive These debilitating conditions can be treated with acid sequences common to all. Over time, the isotopes. These can drugs. Dopamine as a signal must have a receptor GPCR family have been described in more detail. be detected and on the surface of brain cells that it binds to. Anti- They are large proteins which sit in the membrane followed as their psychotic drugs bind to the same receptor, and (thereby having contact with the outside and inside radiation makes block dopamine binding. The amazing thing is of the cell simultaneously). The proteins all have a them stand out from that the drugs were found to be effective before we long stretch of amino acids that winds back and other molecules. knew what the dopamine receptor looked like. forward through the membrane seven times.

18 Catalyst February 2013 This is the kind of model that can be generated from X-ray crystallography. The blue is the protein, the curly tubes are common structures (called motifs) and give the protein its 3D shape. This is a protein that complexes with haem groups; this is shown in red. The crystal of this protein was grown by the author, and the X-ray haem crystallography was by Bin Zhao at Vanderbilt University, USA. It was published this year in Int J Mol Sci.

Protein structures These properties of GPCRs make them very difficult to work with. Crystallisation is the best way to characterise the structure of any protein, but this requires the protein to be isolated in high quantity and purity. GPCRs rely on the membrane How X-ray crystallography works: the beam of X-rays is of the cell to keep all the 7-fold structure intact, diffracted by the regular array of protein molecules in and removing them from the membrane can easily result in the protein falling apart. GPCRs, like many the crystal; the crystal structure can be deduced from membrane proteins, were found to be unstable in the pattern of the diffracted beams. solution. This again makes any manipulation or Kobilka and Lefkowitz fully deserve their Nobel characterisation very difficult. Prize for Chemistry. They recognised the need for One of the junior scientists who worked with identifying and understanding these receptors and Lefkowitz during the 1980s was Brian Kobilka. the vital role they play in maintaining homeostasis. He was involved in the work on adrenergic When asked what kept him going on such a receptors, and when he set up his own lab in difficult challenge, Kobilka’s response is typical of 1989 he continued working on GPCRs. Kobilka many passionate scientists. ‘I just wanted to know was particularly interested in producing GPCRs how they work.’ in sufficient quantity and purity that he could use them for X-ray crystallography to determine their Suzy Moody is a microbiologist who investigates signalling structure. As mentioned above, these processes in bacteria. were fraught with difficulty. Kobilka used DNA sequencing (devised by fellow Nobel prize winner Fred Sanger) to identify and Look here! clone the genes coding for GPCRs. This allowed The official Nobel Prize website description the protein to be produced in insect cells, using the of Lefkowitz and Kobilka’s work: http:// cell membranes to keep the protein intact until it tinyurl.com/8q7psvo could be coaxed out without becoming unstable. Find out about the work of two important It took over 20 years of lab work for him to have British crystallographers: Rosalind Franklin big enough crystals of pure GPCR protein that and Dorothy Hodgkin. crystallography could be used to solve the 3D Search the Catalyst archive for earlier articles structure of the receptor. This work has improved about Nobel prize winners in the Sciences: understanding of how signals and receptors work www.catalyststudent.org.uk and means drugs can now be designed to target specific receptors.

Catalyst February 2013 19 Laura Plant

Adventures in the Amazon The Amazon flows aura Plant describes the time she spent in harvesting, the cutting of lianas that are attached from Peru into Brazil. the Amazon rainforest in northern Peru to multiple trees to prevent other trees being pulled down, only cutting down trees that are bigger than on a project researching the impacts of a certain size, and the creation of conservation and Key words L forestry on the plants and animals that live there. regeneration areas. A company that does all these rainforest things can be certified by the Forest Stewardship Timber has many uses – in building, paper-making Council (FSC). forestry and as an energy resource. Bbut demand for wood sustainability is increasingly rapidly. How can we ensure that this resource is available for long into the future? This conservation is the principle of sustainable use, and it is vital in conserving forests and their plant and animal communities for future generations. Forest management In tropical regions, large areas of rainforests have been untouched for centuries. This means that many rare and unique plants and animals have become specialized to live only in these habitats, making rainforests highly biodiverse. This biodiversity is threatened when rainforests are cut Cut timber is marked with the logo of the Forest down to supply wood. For example, mahogany has Stewardship Council to show that it has been become very rare due to over-harvesting. harvested responsibly. The practice of Sustainable Forest Management (SFM) aims to harvest wood from forests in ways However, any type of logging disturbance could that cause minimal damage to the surrounding have a lasting negative impact on a forest. The area and allows sufficient time for the trees to re- sustainable forestry company GreenGold Forestry grow before they are harvested again. This involves: (GGF) wanted to find out how big this impact is in only harvesting on average one tree per hectare, a their concession in the Peruvian Amazon and they long rotation time (around 20 years) before re- asked me to help them find out.

20 Catalyst February 2013 Assessing the impact species of hummingbirds and monkeys, as well as a herd of stampeding huangana (wild boar). The Our project had two aspects. Firstly, we wanted plants were formidable, with their dense canopy to know how the felling of a single large tree effectively blocking out the sky from our view, would affect the growth of the surrounding trees and their aggressive or prickly defence systems and vegetation. Would the large space that has making them a danger to anyone who tyripped and been created in the canopy allow more light into grabbed them for support. the usually shaded undergrowth and cause faster growth? Or would damage caused by tractors and Potential results logging machinery to the area slow the growth of the surrounding vegetation? To assess this we decided Since rainforest trees grow slowly, our research will to establish permanent 20 m x 20 m plots in the need a few more years of data collection before rainforest containing a tree of commercial interest. growth rates can be obtained and a comparison Half of the plots will have the tree harvested, the made between our logged and unlogged plots. other half will be kept as controls with no harvesting Results from similar studies have shown that an and all will be monitored over the next 5 years. All intermediate amount of disturbance can increase the trees in the plots were tagged with metal discs growth rate and diversity of vegetation. This is and their size and species recorded so they can be thought to be due to the following reasons: re-measured in years to come. 1. When there is little disturbance, one or two well- Our second aspect was to look at the how adapted tree species tend to dominate the area animals are affected by the disturbance to their and the canopy is so thick that little light gets habitat. How long does it take for them to return through to allow regeneration on the forest floor. to the logged area or do they never return at all? 2. When there is too much disturbance (as in Finding mammals in the rainforest is no easy task clear-felling), few trees are able to grow at all and sightings are usually rare; however, where there and important seed-dispersing animals have are mammals, there is mammal dung and where been lost from the area. After the land has been there is dung, there will be dung beetles. This meant abandoned, a few colonizer species will be able that we could use the diversity of dung beetles as to start the process of secondary succession. a measure of the diversity of mammals in the area. 3. At an intermediate level of disturbance, caused We needed bait for this and the obvious bait is naturally by heavy storms, a lot of different dung. Luckily, we found a small zoo in Iquitos where, niches are opened up that a wide diversity of after much laughter, the zoo-keeper allowed us to species can occupy. For example, light gaps in remove dung from the cages of a variety of jungle the canopy or the exposure of new soil. mammals including monkeys, pumas and jaguars.

Logs can be stored in the river to prevent insect damage.

Collecting jaguar dung at the zoo Sustainable logging practices attempt to have an intermediate disturbance effect on the forest, Carrying out the project avoiding irreversible damage to the forest and Armed with thick wellies, mosquito repellent perhaps actually increasing biodiversity. and machetes to cut a path through the dense This project was an amazing opportunity for rainforest, we set off. A four-day boat ride up the me to see how data is collected in the field and Amazon river took us to the area of rainforest the challenges faced by scientists as they try to owned by the logging company where we camped understand how a complicated system like a for the next three weeks. rainforest works. I hope that more research in this Days were spent carrying equipment, setting up area will show people how vulnerable the rainforest plots and collecting data. The near 100% humidity is to human influence and how important it is that makes it so warm that even the ‘shower’- a plastic we harvest resources from this beautiful ecosystem tub to pour water over yourself while perched on in a sustainable way. You can see some of a plank of wood across a stream, felt like luxury! Laura Plant is a graduate student at the University of Laura’s pictures on The wildlife was truly incredible. We saw many Cambridge studying for an MPhil in Environmental Policy. the back page.

Catalyst February 2013 21 Forest fieldwork Her photos revealsome of thedifficulties of working inthisenvironment. Laura Plantspent three weeks intheAmazon rainforest of Peru.

Laura working in the rainforest

A forestry worker with a baby huangana or

white-lipped peccary

You wouldn’t want to hug this tree! this hug to want wouldn’t You

trees difficult. trees

make measuring measuring make Buttress roots roots Buttress

A dung beetle trap with bait – in one trap we caught a tarantula!

Birds such as the scarlet macaw are important seed dispersers in the rainforest. large fractionofthe rainforest coversa landmass ofSouth

The Amazon America.

Barun Patro