This page contains a number of scientifically incorrect statements, but I am most concerned about your misleading characterisation of phosphorus as a 'safe' material.
Scientific errors
Your site claims that
"phosphorus…has the ability to absorb and store surrounding light"
"the ability to absorb and store surrounding light…works similar to the natural process of photosynthesis"
"Phosphorus glow absorbs and stores surrounding light. When it is dark, the stored light is slowly released in the form of a glow"
"Glow in the Dark products contain phosphorus…it needs to be exposed to light before it can work"
"Radium glow produces light on its own through a chemical process."
All of these claims are mistaken.
1. Luminescent materials do not store light. Light cannot be stored, it is a form of electromagnetic radiation. (In LASERS light is contained within a cavity by reflecting it back and forth by mirrors, but phosphorus is not able to do anything like this.) When the radiation is absorbed by a photoluminescent material the radiation ceases to exist. Because the molecules of the absorbing material are excited into a higher energy state, new electromagnetic radiation (light) may later be emitted – but it is not light that has been stored. (The energy transferred to the luminescent material by the radiation may be considered as stored: but not the light).
2. The process of photosynthesis does not involve "the ability to absorb and store surrounding light" – absorb, yes, but the light is not stored – it ceases to exist once absorbed.
3. Materials which absorb energy from radiation, and then release it slowly ('glow') are called phosphorescent. This does not (only) occur 'when it is dark', but from immediately after irradiation. (The process occurs regardless of whether it is dark enough to observe.)
4. Phosphorus is not itself a phosphorescent material. The glow seen around white phosphorus is due to a chemical reaction with oxygen in the air. Not only does this not store any light, but, also, it does not need light to initiate.
5. Radium does NOT produce light through a chemical process. Radium is radioactive. It undergoes radioactive decay (due to a change in the atomic nucleus). This is NOT considered a chemical process.
Now I turn to what I consider a more serous problem with your site.
Potentially dangerous misinformation
The more serious matter concerns your claim that to be selling products containing 'non toxic' phosphorus:
"Glow in the Dark products contain phosphorus (a non toxic substance) which has the ability to absorb and store surrounding light…"
"Phosphorus is non toxic and safe for general use."
"Phosphorus is a natural mineral found in the human body. Phosphorus Glow in the dark products is perfectly safe for everyday use"
"Many get confused and associate all green glow products to be radioactive. This is not true. Phosphorus glow is non toxic and non radioactive."
You may wonder why I think this matters enough to contact you.
It is very misleading to suggest to people reading the site (which could include children who might well be interested in glow-in-the-dark toys) that phosphorus is harmless, and this is completely wrong.
Phosphorus is not found as a natural mineral, as it is much too reactive to be found native (that is, as phosphorus) on earth – although many minerals are compounds of phosphorus (and thus do NOT share its chemical properties), and so sources of the element for use in agriculture etc. The human body does contain compounds of phosphorus, notably in the bones, but again there is no phosphorus (the substance phosphorus) in the human body – if you introduced some it would very quickly react. Sources of phosphorus are important in the diet, but it would be very unwise to try to eat phosphorus itself.
Phosphorus can be obtained in different forms (this is called allotropy where the same element can have different molecular structures – like graphite and diamond both being pure forms – allotropes -of carbon). Some allotropes of phosphorus are not especially dangerous. However, the form which glows is white (or yellow) phosphorus, and this is a very hazardous material.
So, handling phosphorus is dangerous and needs special precautions. (If you really did use phosphorus in your products, I imagine you would know that?) Here is some information from authoritative websites
"Ingestion of elemental white or yellow phosphorus typically causes severe vomiting and diarrhea [diarrhoea], which are both described as "smoking," "luminescent," and having a garlic-like odor. Other signs and symptoms of severe poisoning might include dysrhythmias, coma, hypotension, and death. Contact with skin might cause severe burns within minutes to hours…"
"White phosphorus is extremely toxic to humans, while other forms of phosphorus are much less toxic. Acute (short-term) oral exposure to high levels of white phosphorus in humans is characterised by three stages: the first stage consists of gastrointestinal effects; the second stage is symptom-free and lasts about two days; the third stage consists of a rapid decline in condition with gastrointestinal effects, plus severe effects on the kidneys, liver, cardiovascular system, and central nervous system (CNS). Inhalation exposure has resulted in respiratory tract irritation and coughing in humans. Chronic (long-term) exposure to white phosphorus in humans results in necrosis of the jaw, termed "phossy jaw."
Please feel free to check on this information for yourself.
However, I recommend you change the information on your website. In particular, please stop suggesting that phosphorus is a safe, non-toxic material, when the form of phosphorus which glows is highly toxic. I trust that now this has been brought to your attention, you will appreciate that it would be highly irresponsible for you to continue to advertise your products using misleading information about a hazardous substance.
stars are born, start young, live, sometimes living alone but sometimes not, sometimes have complicated lives, have lifetimes, reach the end of their lives, and die, so, becoming dead, eventually long dead; and, indeed, there are generations of stars with life cycles
One of the themes I keep coming back to here is the challenge of communicating abstract scientific ideas. Presenting science in formal technical language will fail to engage most general audiences, and will not support developing understanding if the listener/reader cannot make good sense of the presentation. But, if we oversimplify, or rely on figures of speech (such as metaphors) in place of formal treatments of concepts, then – even if the audience does engage and make sense of the presentation – audience members will be left with a deficient account.
Does that matter? Well, often a level of understanding that provides some insight into the science is far better than the impression that science is so far detached from everyday experience that it is not for most people.
And the context matters.
Public engagement with science versus science education
In the case of a scientist asked to give a public talk, or being interviewed for news media, there seems a sensible compromise. If people come away from the presentation thinking they have heard about something interesting, that seems in some way relevant to them, and that they understood the scientist's key messages, then this is a win – even if it is only a shift to an over-simplified account, or an understanding in terms of a loose analogy. (Perhaps some people will want to learn more – but, even if not, surely this meets some useful success criterion?)
In this regard science teachers have a more difficult job to do. 1 The teacher is not usually considered successful just because the learners think they have understood teaching, but rather only when the learners can demonstrate that what they have learnt matches a specified account set out as target knowledge in the curriculum. This certainly does not mean a teacher cannot (or should not) use simplification and figures of speech and so forth – this is often essential – but rather that such such moves can usually only be seen as starting points in moving learners onto temporary 'stepping stones' towards creditable knowledge that will eventually lead to test responses that will be marked correct.
An episode of 'In Our Time' on 'The Death of Stars' "The image above is of the supernova remnant Cassiopeia A, approximately 10,000 light years away, from a once massive star that died in a supernova explosion that was first seen from Earth in 1690"
The Death of Stars
With this in mind, I was fascinated by an episode of the BBC's radio show, 'In Our Time' which took as its theme the death of stars. Clearly, this falls in the category of scientists presenting to a general public audience, not formal teaching, and that needs to be borne in mind as I discuss (and perhaps even gently 'deconstruct') some aspects of the presentation from the perspective of a science educator.
The show was broadcast some months ago, but I made a note to revisit it because I felt it was so rich in material for discussion, and I've just re-listened. I thought this was a fascinating programme, and I think it is well worth a listen, as the programme description suggests:
"Melvyn Bragg and guests discuss the abrupt transformation of stars after shining brightly for millions or billions of years, once they lack the fuel to counter the force of gravity. Those like our own star, the Sun, become red giants, expanding outwards and consuming nearby planets, only to collapse into dense white dwarves. The massive stars, up to fifty times the mass of the Sun, burst into supernovas, visible from Earth in daytime, and become incredibly dense neutron stars or black holes. In these moments of collapse, the intense heat and pressure can create all the known elements to form gases and dust which may eventually combine to form new stars, new planets and, as on Earth, new life."
I was especially impressed by the Astronomer Royal, Professor Martin Rees (and not just because he is a Cambridge colleague) who at several points emphasised that what was being presented was current understanding, based on our present theories, with the implication that this was open to being revisited in the light (sic) of new evidence. This made a refreshing contrast to the common tendency in some popular science programmes to present science as 'proven' and so 'certain' knowledge. That tendency is an easy simplification that distorts both the nature and excitement of science.
Presenter Melvyn Bragg's other guests were Carolin Crawford (Emeritus Member of the Institute of Astronomy, and Emeritus Fellow of Emmanuel College, University of Cambridge) and Mark Sullivan (Professor of Astrophysics at the University of Southampton).
Public science communication as making the unfamiliar familiar
Science communicators, whether professional journalists or scientists popularising their work, face similar challenges to science teachers in getting across often complex and abstract ideas; and, like them, need to make the unfamiliar familiar. Science teachers are taught about how they need to connect new material with the learners' prior knowledge and experiences if it is to make sense to the students. But successful broadcasters and popularisers also know they need to do this, using such tactics as simplification, modelling, metaphor and simile, analogy, teleology, anthropomorphism and narrative.
There were quite a few examples of the speakers seeking to make abstract ideas accessible to listeners in such ways in this programme. However, perhaps the most common trope was one set up by the episode title, and one which could very easily slip under radar (so to speak). In this piece I examine the seemingly ubiquitous metaphor (if, indeed, it is to be considered a metaphor!) of stars being alive; in a sequel I discuss some of the wide range of other figures of speech adopted in this one science programme.
Science: making the familiar, unfamiliar?
If when working as a teacher I saw a major part of my work as making the unfamiliar familiar to learners, in my research there was a sense in which I needed to make the familiar unfamiliar. Often, the researcher needs to focus afresh on the commonly 'taken-for-granted' and to start to enquire into it as if one does not already know about it. That is, one needs to problematise the common-place. (This reflects a process sometimes referred to as 'bracketing'.)
To give one obvious example. Why do some students do well in science tests and others less well? Obviously, because some learners are better science students than others! (Clearly in some sense this is true – but is it just a tautology? 2) But one clearly needs to dig into this truism in more detail to uncover any insights that would actually be useful in supporting students and improving teaching!
The same approach applies in science. We do not settle for tautologies such as fire burns because fire is the process of burning, or acids are corrosive because acids are the category of substances which corrode; nor what are in effect indirect disguised tautologies such as heavy objects fall because they are largely composed of the element earth, where earth is the element whose natural place is at the centre of the world. (If that seems a silly example, it was the widely accepted wisdom for many centuries. Of course, today, we do not recognise 'earth' as a chemical element.)
I mention this, because I would like to invite readers to share with me in making the familiar unfamiliar here – otherwise you could easily miss my point.
"so much in the Universe, and much of our understanding of it, depends on changes in stars as they die after millions or billions of stable years"
Tag line for 'the Death of Stars'
The lives of stars
The episode opens with
"Hello. Across the universe, stars have been dying for millions of years…
Melvyn Bragg introducing the episode
The programme was about the death of stars – which directly implies stars die, and, so, also suggests that – before dying – they live. And there were plenty of references in the programme to reinforce this notion. Carolin Crawford suggested,
"So, essentially, a star's life, it can exist as a star, for as long as it has enough fuel at the right temperature at the right density in the core of the star to stall the gravitational collapse. And it is when it runs out of its fuel at the core, that's when you reach the end of its lifetime and we start going through the death processes."
Prof. Carolin Crawford talking on 'In Our Time'
Not only only do stars have lives, but some have much longer lives than others,
"…more massive stars can … build quite heavy elements at their cores through their lifetimes. And … they actually have shorter lifetimes – it is counter-intuitive, but they have to chomp through their fuel supply so furiously that they exhaust it more rapidly. So, the mass of the star dictates what happens in the core, what you create in the core, and it also determines the lifetime of the star."
"The mass of the star…determines the lifetime of the star…. our sun…we reckon it is about halfway through its lifetime, so stars like the sun have lifetimes of 10 billions years or so…"
Prof. Carolin Crawford talking on 'In Our Time'
This was not some idiosyncratic way that Professor Crawford had of discussing stars, as Melvyn's other guests also used this language. Here are some examples I noted:
"this is a dead, dense star" (Martin Rees)
"the lifetime of a stable star, we can infer the … life cycles of stars" (Martin Rees)
"stars which lived and died before our solar system formed…stars which have more complicated lives" (Martin Rees)
"those old stars" (Martin Rees)
"earlier generations of massive stars which had lived and died …those long dead stars" (Martin Rees)
"it is an old dead star" (Mark Sullivan)
"our sun…lives by itself in space. But most stars in the universe don't live by themselves…" (Mark Sullivan)
"two stars orbiting each other…are probably born with different masses" (Mark Sullivan)
"when [stars] die" (Mark Sullivan)
"when [galaxies] were very young" (Martin Rees)
"stars that reach the end point of their lives" (Carolin Crawford )
"a star that's younger" (Martin Rees)
So, in the language of astronomy, stars are born, start young, live; sometimes living alone but sometimes not, sometimes have complicated lives; have lifetimes, reach the end of their lives, and die, so, becoming dead, eventually long dead; and, indeed, there are generations of stars with life cycles.
The processes that support a star's luminosity come to an end: but does the star therefore die?
(Cover art for the Royal Philharmonic Orchestra's recording of David Bedford's composition Star's End. Photographer: Monique Froese)
Are stars really alive?
Presumably, the use of such terms in this context must have originally been metaphorical. Life (and so death) has a complex but well-established and much-discussed meaning in science. Living organisms have certain necessary characteristics – nutrition, (inherent) movement, irritability/sensitivity, growth, reproduction, respiration, and excretion, or some variation on such a list. Stars do not meet this criterion. 3 Living organisms maintain a level of complex organisation by making use of energy stores that allow them to decrease entropy internally at the cost of entropy increase elsewhere.
Animals and decomposers (such as fungi) take in material that can be processed to support their metabolism and then the 'lower quality' products are eliminated. Photosynthetic organisms such as green plants have similar metabolic processes, but preface these by using the energy 'in' sunlight to first facilitate endothermic reactions that allow them to build up the material used later for their mortal imperative of working against the tendencies of entropy. Put simply, plants synthesise sugar (from carbon dioxide and water) that they can distribute to all their cells to support the rest of the metabolism (a complication that is a common source of alternative conceptions {misconceptions} to learners 4).
By contrast, generally speaking, during their 'lifetimes', stars only gain and lose marginal amounts of material (compared with a 70 kg human being that might well consume a tonne of food each year) – and do not have any quality control mechanism that would lead to them taking in what is more useful and expelling what is not.
As far as life on earth is concerned, virtually all of that complex organisation of living things depends upon the sun as a source of energy, and relies on the process by which the sun increases the universe's entropy by radiating energy from a relatively compact source into the diffuse vastness of space. 4 In other words, if anything, a star like our sun better reflects a dead being such as a felled tree or a zebra hunted down by a lion, providing a source of concentrated energy for other organisms feeding on its mortal remains!
Are the lives and deaths of stars simply pedagogical devices?
So, are stars really alive? Or is this just one example of the kind of rhetorical device I referred to above being adopted to help make the abstract unfamiliar becomes familiar? Is it the use of a familiar trope employed simply to aid in the communication of difficult ideas? Is this just a metaphor? That is,
Do stars actually die, or…
are they only figuratively alive and, so, only suffer (sic) a metaphorical death?
I do not think the examples I quote above represent a concerted targeted strategy by Professors Crawford, Rees and Sullivan to work with a common teaching metaphor for the sake of Melvyn and his listeners: but rather the actual language commonly used in the field. That is, the life cycles and lifetimes of stars have entered into the technical lexicon of the the science. If so, then stars do actually live and die, at least in terms of what those words now mean in the discipline of astronomy.
Gustav Strömberg referred to "the whole lifetime of a star" in a paper in the The Astrophysical Journal as long ago as 1927. He did not feel the need to explain the term so presumably it was already in use – or considered obvious. Kip Thorne published a paper in 1965 about 'Gravitational Collapse and the Death of a Star". In the first paragraph he pointed out that
"The time required for a star to consume its nuclear fuel is so long (many billions of years in most cases) that only a few stars die in our galaxy per century; and the evolution of a star from the end point of thermonuclear burning to its final dead state is so rapid that its death throes are observable for only a few years."
Thorne, 1965, p.1671
Again, the terminology die/death/dead is used without introduction or explanation.
He went on to refer to
deaths of stars
different types of death
final resting states
before shifting to what a layperson would recognise as a more specialist, technical, lexicon (zero point kinetic energy; Compton wavelength of an electron; neutron-rich nuclei; photodistintegration; gravitational potential energy; degenerate Fermi gas; lambda hyperons; the general relativity equation of hydrostatic equilibrium; etc.), before reiterating that he had been offering
"the story of the death of a star as predicted by a combination of nuclear theory, elementary particle theory, and general relativity"
Thorne, 1965, p.1678
So, this was a narrative, but one intended to be fit for a professional scientific audience. It seems the lives and deaths of stars have been part of the technical vocabulary of astronomers for a long time now.
When did scientists imbue stars with life?
Modern astronomy is quite distinct from astrology, but like other sciences astronomy developed from earlier traditions and at one time astronomy and astrology were not so discrete (an astronomical 'star' such as Johannes Kepler was happy to prepare horoscopes for paying customers) and mythological and religious aspects of thinking about the 'heavens' were not so well compartmentalised from what we would today consider as properly the realm of the scientific.
In Egyptian religion, Ra was both a creative force and identified with the sun. Mythology is full of origin stories explaining how the stars had been cast there after various misadventures on earth (the Greek myths but also in other traditions such as those of the indigenous North American and Australian peoples 5) and we still refer to examples such as the seven sisters and Orion with the sword hanging in his belt. The planets were associated with different gods – Venus (goddess of love), Mars (the god of war), Mercury (the messenger of the gods), and so on.6 It was traditional to refer to some heavenly bodies as gendered: Luna is she, Sol is he, Venus is she, and so on. This usage is sometimes found in scientific writing on astronomy.
Yet this type of poetic license seems unlikely to explain the language of the life cycles of stars, even if there are parallels between scientific and poetic or spiritual accounts,
Stars are celestial objects having their own life cycles. Stars are born, grow up, mature and eventually die. …The author employs inductive and deductive analysis of the verses of the Quran and the Hadith texts related with the life and death of stars. The results show that the life and death of the stars from Islamic and Modern astronomy has some similarities and differences.
Wahab, 2015
After all, the heavenly host of mythology comprised of immortals, if sometimes starting out as mortals subsequently given a kind of immorality by the Gods when being made into stars. Indeed the classical tradition supported by interpretation of Christian orthodoxy was that unlike the mundane things of earth, the heavens were not subject to change and decay – anything from the moon outwards was perfect and unchanging. (This notion was held onto by some long after it was established that comets with their varying paths were not atmospheric phenomena – indeed well into the twentieth century some young earth creationists were still insisting in the perfect, unchanging nature of the heavens. 7)
So, presumably, we need to look elsewhere to find how science adopted life cycles for stars.
A natural metaphor?
Earlier in this piece I asked readers to bear with me, and to join with me in making the familiar unfamiliar, to 'bracket' the familiar notion that we say starts are born, live and later die, and to problematise it. In one scientific sense stars cannot die – as they were never alive. Yet, I accept this seems a pretty natural metaphor to use. Or, at least, it seems a natural metaphor to those who are used to hearing and reading it. A science teacher may be familiar with the trope of stars being born, living, and dying – but how might a young learner, new to astronomical ideas, make sense of what was meant?
Now, there is a candidate project for anyone looking for a topic for a student research assignment: how would people who have never previously been exposed to this metaphor respond to the kinds of references I've discussed above? I would genuinely like to know what 'naive' people would make of this 8 – would they just 'get' the references immediately (appreciate in what sense stars are born, live, and die); or, would it seem a bizarre way of talking about stars? Given how readily people accept and take up anthropomorphic references to molecules and viruses and electrons and so forth, I find the question intriguing.
Even if for the disciplinary experts the language of living stars and their life cycles has become a 'dead metaphor 'and is now taken (i.e., taken for granted) as technical terminology – the novice learner, or lay member of the public listening to a radio show, still has to make sense of what it means to say a star is born, or is alive, or is nearing the end of its life, or is dead.
The critical feature discussed by Professors Crawford, Rees and Sullivan concerns an equilibrium that allow a star to exist in a balance between the gravitational attraction of its component matter and the pressure generated through its nuclear reactions.
A star forms when material comes together under its mutual gravitational attraction – and as the material becomes denser it gets hotter. Eventually a sufficient density and temperature is reached such that there is 'ignition' – not in the sense of chemical combustion, but self-sustaining nuclear processes occur, generating heat. This point of ignition is the 'birth' of the star.
Fusion processes continue as long as there is sufficient fissionable material, the 'fuel' that 'feeds' the nuclear 'furnace' (initially hydrogen, but depending on the mass of the star there can be a series of reactions with products from one stage undergoing further fusion to form even heavier elements). The life time of the star is the length of time that such processes continue.
Eventually there will not be sufficient 'fuel' to maintain the level of 'burning' that is needed to allow the ball of material to avoid ('resist') gravitational collapse. There are various specific scenarios, but this is the 'death' of the star. It may be a supernova offering very visible 'death throes'.
The core that is left after this collapse is a 'dead' star, even if it is hot enough to continue being detectable for some time (just as it takes time for the body of a homeothermic animal that dies to cool to the ambient temperature).
It seems then that there is a kind of analogy at work here.
Organisms are alive as long as they continue to metabolise sufficiently in order to maintain their organisation in the face of the entropic tendency towards disintegration and dispersal.
Stars are alive as long as they exhibit sufficient fusion processes to maintain them as balls of material that have much greater volumes, and lower densities than the gravitational forces on their component particles would otherwise lead to.
It is clearly an imperfect analogy.
Organisms base metabolism on a through-put of material to process (and in a sense 'harvest' energy sources).
Stars do acquire new materials and eject some, but this is largely incidental and it is essentially the mass of fissionable material that originally comes together to initiate fusion which is 'harvested' as the energy source.
Organisms may die if they cannot access external food sources, but some die of built-in senescence and others (those that reproduce by dividing) are effectively immortal.
We (humans) die because the amazing self-constructing and self-repairing abilities of our bodies are not perfect, and somatic cells cannot divide indefinitely to replace no longer viable cells.
Stars 'die' because they run out of their inherent 'fuel'.
Stars die when the hydrogen that came together to form them has substantially been processed.
One person's dead star is another person's living metaphor
So, do stars die? Yes, because astronomers (the experts on stars) say they do, and it seems they are not simply talking down to the rest of us. The birth and death of stars seems to be based on an analogy: an analogy which is implicit in some of the detailed discussion of star life cycles. However, through the habitual use of this analogy, terms such as the birth, lifetimes, and death of stars have been adopted into mainstream astronomical discourse as unmarked (taken-for-granted) language such that to the uninitiated they are experienced as metaphors.
And these perspectival metaphors 9 become extended to describe stars that are considered young, old, dying, long dead, and so forth. These terms are used so readily, and so often without a perceived need for qualification or explanation, that we might consider them 'dead' metaphors within astronomical discourse – terms of metaphorical origin but now so habitually used that they have come to be literal (stars are born, they do have lifetimes, they do die). Yet for the uninitiated they are still 'living' metaphors, in the sense that the non-expert needs to work out what it means when a star is said to live or die.
There is a well recognised distinction between live and dead metaphors. But here we have dead-to-the-specialists metaphors that would surely seem to be non-literal to the uninitiated. These terms are not explained by experts as they are taken by them as literal, but they cannot be understood literally by the novice, for whom they are still metaphors requiring interpretation. That is, they are perspectival metaphors – zombie words that may seem alive or dead (as figures of speech) according to audience, and so may be treated as dead in professional discourse, but may need to be made undead when used in communicating to the public.
Strömberg, G. (1927). The Motions of Giant M Stars. The Astrophysical Journal, 65, 238.
Thorne, K. S. (1965). Gravitational Collapse and the Death of a Star. Science, 150(3704), 1671-1679. http://www.jstor.org.ezp.lib.cam.ac.uk/stable/1717408
Wahab, R. A. (2015). Life and death of stars: an analysis from Islamic and modern astronomy perspectives. International Proceedings of Economics Development and Research, 83, 89.
Notes
1 In this regard, but not in all regards. As I have suggested here before, the teacher usually has two advantages:
a) generally, a class has a limited spread in terms of the audience background: even a mixed ability class is usually from a single school year (grade level) whereas the public presentation may be addressing a mixed audience of all ages and levels of education.
b) usually a teacher knows the class, and so knows something about their starting points, and their interests
2 Some students do well in science tests and others less well.
If we say this is because
some learners are better science students than others
and settle for defining better science students as those who achieve good results in formal science tests (that is tests as currently administered, based on the present curriculum, taught in our usual way)
then we are simply 'explaining' the explicandum (i.e., some students do better on science tests that others) by a rephrasing of what is to be explained (some students are better science students: that is, they perform well in science tests!)
3 Criterion (singular) as a living organism has to satisfy the entries in the list collectively. Each entry is of itself a necessary, but not sufficient, condition.
4 A simple misunderstanding is that animals respire but plants photosynthesise.
In a plant in a steady state, the rates of build-up and break down of sugars would be balanced. However, plants must photosynthesise more than they respire overall in order to to grow and ultimately to allow consumers to make use of them as food. (This needs to be seen at a system level – the plant is clearly not in any inherent sense photosynthesising to provide food for other organisms, but has evolved to be a suitable nutrition source as it transpires [no pun intended] that increases the fitness of plants within the wider ecosystem.)
A more subtle alternative conception is that plants photosynthesise during the day when they are illuminated by sunlight (fair enough) and then use the sugar produced to respire at night when the sun is not available as a source of energy. See, for example, 'Plants mainly respire at night because they are photosynthesising during the day'.
Actually cellular processes require continuous respiration (as even in the daytime sunlight cannot directly power cellular metabolism, only facilitate photosynthesis to produce the glucose that that can be oxidised in respiration).
Schematic reflection of the balance between how photosynthesis generates resources to allow respiration – typically a plant produces tissues that feed other organisms. The area above the line represents energy from sunlight doing work in synthesising more complex substances. The area below the lines represents work done when the oxidation of those more complex substances provides the energy source for building and maintaining an organism's complex organisation of structure and processes (homoestasis).
5Museum Victoria offers a pdf that can be downloaded and copied by teachers to teach about how "How the southern night sky is seen by the Boorong clan from north-west Victoria":
'Stories in the Stars – the night sky of the Boorong people' shows the constellations as recognised by this group, the names they were given, and the stories of the people and creatures represented.
(This is largely based on the nineteenth century reports made by William Edward Stanbridge of information given by Boorong informants – see 'Was the stellar burp really a sneeze?')
The illustration shown here is of 'Kulkunbulla' – a constellation that is considered in the U.K. to be only part of the constellation known here as Orion. (Constellations are not actual star groupings, but only what observers have perceived as stars seeming to be grouped together in the sky – the Boorong's mooting of constellations is no more right or wrong than that suggested in any other culture.)
6 The tradition was continued into modern times with the discovery of the planets that came to be named Neptune and Uranus after the Gods of the sea and sky respectively.
7 Creationism, per se, is simply the perspective or belief that the world (i.e., Universe) was created by some creator (God) and so creationism as such is not necessarily in conflict with scientific accounts. The theory of the big bang posits that time, space and matter had a beginning with an uncertain cause which could be seen as God (although some theorists such as Professor Roger Penrose develop theories which posit a sequence of universes that each give rise to the next and that could have infinite extent).
Young earth creationists, however, not only believe in a creator God (i.e., they are creationists), but one who created the World no more than about 10 thousand years ago (the earth is young!), rather than over 13 billion years ago. This is clearly highly inconsistent with a wide range of scientific findings and thinking. If the Young Earth Creationists are right, then either
a lot of very strongly evidenced science is very, very wrong
some natural laws (e.g. radioactive decay rates) that now seem fixed must have changed very substantially since the creation
the creator God went to a lot of trouble to set up the natural world to present a highly misleading account of its past history
8 I am not using the term naive here in a discourteous or demeaning way, but in a technical sense of someone who is meeting something for the first time.
9 That is, terms that will appear as metaphors from the perspective of the uninitiated, but now seem literal terms from the perspective of the specialist. We cannot simply say they are or are not metaphors, without asking 'for whom?'
Photosynthesis illuminating a plant? (Image by OpenClipart-Vectors from Pixabay)
Analogies, metaphors and similes are used in communication to help make the unfamiliar familiar by suggesting that some novel idea or phenomena being introduced is in some ways like something the reader/listener is already familiar with. Analogies, metaphors and similes are commonly used in science teaching, and also in science writing and journalism.
An analogy maps out similarities in structure between two phenomena or concepts. This example, from a radio programme, compared the COVID pandemic with photosynthesis.
"So, what we were particularly aiming to do, was to understand the collision between a range of different political economic factors of a pre-2020 world, and how they were sort of reassembled and deployed to cope with something which was without question unprecedented.
We used this metaphor of photosynthesis because if you think about photosynthesis in relation to plants, the sun both lights things up but at the same time it feeds them and helps them to grow, and I think one of the things the pandemic has done for social scientists is to serve both as a kind of illumination of things that previously maybe critical political economists and heterodox scholars were pointing to but now became very visible to the mainstream media and to mainstream politics. But at the same time it also accentuated and deepened some of those tendencies such as our reliance on various digital platforms, certain gender dynamics of work in the household, these sort of things that became acute and undeniable and potentially politicised over the course of 20230, 2021."
Prof. Will Davies, talking on 'Thinking Allowed' 1
Will Davies, Professor in Political Economy at Goldsmiths, University of London was talking to sociologist Prof. Laurie Taylor who presents the BBC programme 'Thinking Aloud' as part of an episode called 'Covid and change'
A scientific idea used as analogue
Prof. Davies refers to using "this metaphor of photosynthesis". However he goes on to suggest how the two things he is comparing are structurally similar – the pandemic has shone a light on social issues at the same time as providing the conditions for them to become more extreme, akin to how light both illuminates plants and changes them. A metaphor is an implicit comparison where the reader/listener is left to interpret the comparison, but a metaphor or simile that is explicitly developed to explain the comparison can become an analogy.
Often science concepts are introduced by analogy to more familiar everyday ideas, objects or events. Here, however, a scientific concept, photosynthesis is used as the analogue – the source used to explain something novel. Prof. Davies assumes listeners will be familiar enough with this science concept for it to helpful in introducing his research.
Mischaracterising photosynthesis?
A science teacher might not like the notion that the sun feeds plants – indeed if a student suggested this in a science class it would likely be judged as an alternative conception. In photosynthesis, carbon dioxide (from the atmosphere) and water (usually absorbed from the soil) provide the starting materials, and the glucose that is produced (along with oxygen) enables other processes – such as growth which relies on other substances also being absorbed from the soil. (So-called 'plant foods', which would be better characterised as plant nutritional supplements, contain sources of elements such as nitrogen, phosphorus and potassium). Light is necessary for photosynthesis, but the sunlight is not best considered 'food'.
One might also argue that Prof. Davies has misidentified the source for his analogy, and perhaps he should rather have suggested sunlight as the source metaphor for his comparison as sunlight both illuminates plants and enables them to grow. Photosynthesis takes place inside chloroplasts within a plant's tissues, and does not illuminate the plant. However, Prof. Davies' expertise is in political economy, not natural science, and it was good to see a social scientist looking to use a scientific idea to explain his research.
Plants mainly respire at night because they are photosynthesising during the day
Keith S. Taber
Image by Konevi from Pixabay
Mandy was a participant in the Understanding Science Project. When I spoke to her in Y10 (i.e. when she was c.14 year old) she told me that photosynthesis was one of the topics she was studying in science. So I asked her about photosynthesis. She suggested that "respiration produces energy, but photosynthesis produces glucose which produces energy". (See 'How plants get their food to grow and make energy'). She told me that she respired to get energy.
How do you get your energy then?
We respire.
Is that different then [from photosynthesis]?
Yeah.
So what's respire then, what do you do when you respire?
We use oxygen to, and glucose to release energy.
Do plants respire?
Yes.
So when do you respire, when you are going to go for a run or something, is that when you respire, when you need the energy?
No, you are respiring all the time.
… What about plants? Do they respire all the time?
They mainly do it at night.
Why's that?
'cause they're photosynthesising during the day, cause they need the light.
I was not clear why Mandy thought that plants should respire less when they were photosynthesising.
So why do you need to respire all the time?
'cause you're making energy and you need energy to do everything.
So are you respiring at the same rate all the time, do you think?
No.
So sometimes more than others?
Yeah.
So when might you need to respire more?
When you are doing exercise. Running around a lot.
So are there time when you do not need to respire as much?
Yeah.
So when might you not need to respire very much?
When you 're sleeping or just sitting watching tele [television].
…Do you have to respire at all during the night – you are not doing anything are you?
You need a little bit of energy.
What for?
Erm, I don't [indistinct], well I suppose it's just to keep everything, cause if you did not have energy then your heart would not beat, and you need it to keep breathing, and your heart pumping.
Mandy recognised the need for people to respire continuously, although she associated this with functioning at the organism level (breathing, blood circulation) and did not seem to be thinking about cellular level metabolism.
Why do plants need to respire? What do they use it, the energy for?
Erm, to grow, and to fix cells that are – broken.
Oh right, like repair damage?
Yeah.
So, do you think they are like us then, that they sort of sleep sometimes and don't need to respire as much, or?
Not as much, I don't know. I don't know.
Do you think a plant sleeps, a tree has a good sleep?
No.
So when do you think plants need to respire the most, or do you think they respire the same all the time?
They respire more at night, because – they do it then instead of in the day because they do photosynthesis during the day, but they still respire a little bit.
So is it difficult to try and do both at the same time?
Probably.
Or just maybe they are too busy photosynthesising to do much respiration?
Yeah, erm, I don't know.
Not sure?
No.
Mandy was not offering any specific reason why a plant should need to respire less at night (and did not seem to have previously thought about this), but simply seemed to assume that when the plant was photosynthesising a lot it would only respire "a little bit". This seemed to be an intuition rather than a considered proposition. It was almost as if she implicitly assumed that the plant would be fully occupied photosynthesising, and so would put respiration 'on the back burner'.
It seemed Mandy's understanding of the roles of photosynthesis and respiration at that point in her learning was limited by not fully seeing how energy was involved in the two processes (i.e., respiration produces energy, but photosynthesis produces glucose which produces energy), and because she was not considering the need for respiration to support ongoing basic cell functions.
Respiration produces energy, but photosynthesis produces glucose which produces energy
Keith S. Taber
Image by Frauke Riether from Pixabay
Mandy was a participant in the Understanding Science Project. When I spoke to her in Y10 (i.e. when she was c.14 year old) she told me that photosynthesis was one of the topics she was studying in science. So I asked her about photosynthesis:
So, photosynthesis. If I knew nothing at all about photosynthesis, how would you explain that to me?
It's how plants get their food to grow and – stuff, and make energy
So how do they make their energy, then?
Well, they make glucose, which has energy in it.
How does the energy get in the glucose?
Erm, I don't know.
It's just there is it?
Yeah, it's just stored energy
I was particularly interested to see if Mandy understood about the role of photosynthesis in plant nutrition and energy metabolism.
Why do you think it is called photosynthesis, because that's a kind of complicated name?
Isn't photo, something to do with light, and they use light to – get the energy.
So how do they do that then?
In the plant they've got chlorophyll which absorbs the light, hm, that sort of thing.
What does it do once it absorbs the light?
Erm.
Does that mean it shines brightly?
No, I , erm – I don't know
Mandy explained that the chlorophyll was in the cells, especially in the plant's leaves. But I was not very clear on whether she had a good understanding of photosynthesis in terms of energy.
Do you make your food?
Not the way plants do.
…
So where does the energy come from in your food then?
It's stored energy.
How did it get in to the food? How was it stored there?
Erm.
[c. 2s pause]
I don't know.
At this point it seemed Mandy was not connecting the energy 'in' food either directly or indirectly with photosynthesis.
Okay. What kind of thing do you like to eat?
Erm, pasta.
Do you think there is any energy value in pasta? Any energy stored in the pasta?
Has lots of carbohydrates, which is energy.
…
So do you think there is energy within the carbohydrate then?
Yeah.
Stored energy.
Yeah.
So how do you think that got there, who stored it?
(laughs) I don't know.
Again, the impression was that Mandy was not linking the energy value of food with photosynthesis. The reference to carbohydrates being energy seemed (given the wider context of the interview) to be imprecise use of language, rather than a genuine alternative conception.
So do you go to like the Co-op and buy a packet of pasta. Or mum does I expect?
Yeah.
Yeah. So do you think, sort of, the Co-op are sort of putting energy in the other end, before they send it down to the shop?
No, it comes from 'cause pasta's made from like flour, and that comes from wheat, and then that uses photosynthesis.
Now it seemed that it was quite clear to Mandy that photosynthesis was responsible for the energy stored in the pasta. It was not clear why she had not suggested this before, but it seemed she could make the connection between the food people eat and photosynthesis. Perhaps (it seems quite likely) she had previously been aware of this and it initially did not 'come to mind', and then at some point during this sequences of questions there was a 'bringing to mind' of the link. Alternatively, it may have been a new insight reached when challenged to respond to the interview questions.
So you don't need to photosynthesise to get energy?
No.
No, how do you get your energy then?
We respire.
Is that different then?
Yeah.
So what's respire then, what do you do when you respire?
We use oxygen to, and glucose to release energy.
Do plants respire?
Yes.
So when do you respire, when you are going to go for a run or something, is that when you respire, when you need the energy?
No, you are respiring all the time.
Mandy suggested that plants mainly respire at night because they are photosynthesising during the day. (Read 'Plants mainly respire at night'.)
So is there any relationship do you think between photosynthesis and respiration?
Erm respiration uses oxygen – and glucose and it produces er carbon dioxide and water, whereas photosynthesis uses carbon dioxide and water, and produces oxygen and glucose.
So it's quite a, quite a strong relationship then?
Yeah.
Yeah, and did you say that energy was involved in that somewhere?
Yeah, in respiration, they produce energy.
What about in photosynthesis, does that produce energy?
That produces glucose, which produces the energy.
I see, so there is no energy involved in the photosynthesis equation, but there is in the glucose?
Yeah.
Respiration does not 'produce' energy of course, but if it had the question about whether photosynthesis also produced energy might have been expected to elicit a response about photosynthesis 'using' energy or something similar, to give the kind of symmetry that would be consistent with conservation of energy (a process and its reverse can not both 'produce' energy). 'Produce' energy might have meant 'release' energy in which case it might be expected the reverse process should 'capture' or 'store' it.
Mandy appreciated the relationship between photosynthetic and respiration in terms of substances, but had an asymmetric notion of how energy was involved.
Mandy appeared to be having difficult appreciating the symmetrical arrangement between photosynthesis and respiration because she was not clear how energy was transformed in photosynthesis and respiration. Although she seemed to have the components of the scientific narrative, she did not seem to fully appreciate how the absorption of light was in effect 'capturing' energy that could be 'stored' in glucose till needed. At this stage in her learning she seemed to have grasped quite a lot of the relevant ideas, but not quite integrated them all coherently.
Amy was a participant in the Understanding Science Project. Amy was a Y10 (14-15 year old) student who had separate lessons in biology, chemistry and physics. When I spoke to her, she told me that in biology she was studying respiration which she suggested was "converting glucose and oxygen into energy…through anaerobic respiration and aerobic respiration". This involved "converting glucose into energy, glucose and oxygen into energy and either carbon dioxide and lactic acid, or just carbon dioxide. Something like that".
In physics lessons she had been studying the topic of electricity, and she recognised that energy was an idea which appeared in both topics:
The work in physics on electricity and the work in biology on respiration, is there any connection there?
Well, in respiration energy is produced, and in physics energy is stored in a battery or a power supply and that then travels round – the circuit.
When I spoke to her again, some weeks later, Amy repeated that respiration was "converting oxygen and glucose into energy and carbon dioxide". She told me that this was important "because it produces energy which like in humans your body needs, well in anything, your body needs and to grow and move and things like that". She also told me that trees were "living and they need to produce energy and when they photosynthesise they produce like energy anyway" but that she obtained energy "through food which is then broken down and converted into energy".
It is a basic principle in science, that energy cannot be created or destroyed. (Since Einstein, is has become clear that strictly matter can be considered as if a form of energy, and interconversion can take place, for example in nuclear processes, but this effect is negligible in normal chemical systems.) What Amy took away from her biology classes, though, was that energy could be produced in respiration and photosynthesis, and that indeed glucose and energy were converted into energy in respiration (i.e., an alternative conception). Amy did not seem to be applying the principle of energy conservation here – although it transpired (see here) that she had recently studied this in her physics lessons.
