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Nature of Science 5.2: Natural Selection

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5.2 NATURAL SELECTION: NATURE OF SCIENCE

Use theories to explain natural phenomena – the theory of evolution by natural selection can explain the development of antibiotic resistance in bacteria.


No question that bacterial resistance to antibiotics is a global, medical issue of priority significance. Over the counter purchase of antibiotics, without a prescription and indeed, often without any evidence of a bacterial infection, has simply brought the issue ahead by some years.

The evolutionary, natural selection part of it is easy enough to explain and understand with a couple of simple images.antibiotic_resistance-anatural-selection_140211

A combination of a-sexually reproducing bacteria, quickly mutating genes and carrying those mutations on their little ring of DNA or on a plasmid, from which genes can ‘jump’ to other bacterial species, largely explains why the development of resistance is so rapid. Yes, it is an awesome example of natural selection at work. An ‘in-your-face’ example.

Here are a bunch of related media articles which you might like to read if the topic interests you enough.

And finally, Simon Underhill on his super Blog devoted to the Nature of Science does a really fine job on this topic:  https://natureofscienceib.wordpress.com/2016/12/11/5-2-natural-selection/

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NoS – Improved techniques lead to advances in understanding: Genetic adaptations to living at altitude in Tibet

The fascinating research outlined and linked below has been made possible by the ease with which geneticists can now look at the human genome. It shows how major improvements in scientific techniques help propel significant advances in knowledge and understanding. This is a repeating Nature of Science theme in the new IB syllabus in Biology.

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We live at high altitude here in Ecuador and are accustomed to going over 4,000 metres when we visit the sierra or even drive over the Eastern cordillera on our way to the Amazon jungle. Our bodies can become acclimatised to the thin air after a few weeks and months. The long-term inhabitants of the sierra of the Andes have physiological and anatomical adaptations that enable them to survive happily at these extreme altitudes, where air pressure can be a third lower than at sea level, thus making it so hard to obtain the oxygen they require. The phenotypic adaptations are the result of a small number of genetic differences between the people of the sierra and those who live lower.

Interestingly the people of the Tibetan Plateau, also living well above 4,000 metres, show significantly different physiological, anatomical and genotypic differences to their compatriots lower down the mountains. That raises interesting questions and takes us into the realm of human ancestry and evolution. The BBC article linked here describes research which suggests that the people of the Tibetan Plateau have unique genes which demonstrate origins, some 50-30,000 years ago, from early human ancestors called the Denisovans. Foot and hand prints found on the Tibetan Plateau a long time ago have always puzzled scientists and the general acceptance was that they were evidence of human occupation which coincided with the advent of an agricultural economy 5,000 to 3,000 years ago. It can now be proposed that early habitation of the high Tibetan Plateau began long before an agricultural economy appeared.

http://www.bbc.com/future/story/20170227-how-tibetans-survive-life-on-the-roof-of-the-world

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NoS 3.2 Chromosomes

3.2 Chromosomes

Developments in research follow improvements in techniques – autoradiography was used to establish the length of DNA molecules in prokaryotes

The focus here is to show how advances in scientific techniques, in this case, autoradiography, help move scientific knowledge and understanding ahead.

Autoradiography has a long history, well over a 100 years, and was at first instrumental in the discover of radioactivity. Since then, advances in the technique have added huge scope to what scientists can find out.

Radiography is the visualisation of the pattern of distribution of radiation. In general, the radiation consists of X-rays, gamma (g ) or beta (b ) rays, and the recording medium is a photographic film. For classical X-rays, the specimen to be examined is placed between the source of radiation and the film, and the absorption and scattering of radiation by the specimen produces its image on the film. In contrast, in autoradiography the specimen itself is the source of the radiation, which originates from radioactive material incorporated into it. The recording medium which makes visible the resultant image is usually, though not always, photographic emulsion.

Autoradiography has contributed a great deal to a better understanding of the carbon pathway in photosynthesis, sugar translocation in plant stems, oxidative respiration, mitosis and cell reproduuction, and chromosome structure.


(NoS) AUTORADIOGRAPHY AND THE LENGTH OF DNA

John Cairns, a British biochemist, developed what is now known as the ‘Cairns Technique’, which significantly helped move forward an understanding of DNA:  https://www.youtube.com/watch?v=UHnxiF6qzhI

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Essential idea 3.1 Genes

3.1 Genes

Every living organism inherits a blueprint for life from its parents

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Nothing very threatening here! As long as we agree to reject spontaneous generation and creationism as theories to explain from where organisms come, then we are left with the idea that all organisms have ‘parents’ and it is the parents who pass on to their offspring a design framework or a bank of codes which enable the offspring to grow and develop according to a common family plan.

Within this idea we can then talk about DNA, chromosomes numbers, genes, alleles and loci, genomes, genotypes and phenotypes, mitosis and meiosis, and asexual and sexual reproduction.

All quite straightforward!

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NoS: The kidney and osmoregulation 11.3 (HL)

Nature of Science in 11.3 (HL): Kidney and osmoregulation

Curiosity about particular phenomena – investigations were carried out to determine how desert animals prevent water loss in their wastes.

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This is a link to Simon Underhill’s NoS Blog, where the osmoregulatory control in desert rats, is described so nicely. Understanding this should help greatly in an understanding of how the kidneys and especially the loops of Henlé function, as well as contribute to properly grasping the NoS context.  https://natureofscienceib.wordpress.com/2017/02/09/11-3-the-kidney-and-osmoregulation/

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The Essential idea 6.6 Hormones, homeostasis and reproduction

Hormones are used when signals need to be widely distributed.


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This one is perhaps not a very demanding idea to grasp, but it does drive home the differences between responses made by the nervous system and responses made by the endocrine system.

Hormones:

  • are chemicals
  • are secreted by endocrine glands
  • are carried in the blood (and other body fluids)
  • often target many different cells, tissues and organs in different parts of the bidy
  • usually work in the long-term
  • generate an irreversible response
  • cannot be stored and so must be synthesised and secreted when needed

The way hormonal responses happen is very different from the way in which neural responses happen.

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Nature of Science 6.6: Hormones, homeostasis and reproduction

Developments in scientific research follow improvements in apparatus – William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented 17 years after his death.


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William Harvey’s story is a good read! After training at Cambridge and in Italy, he fortuitously (he chose his wife well!) became royal physician to King James I and afterwards to King Charles I. Both took an interest in his investigations and his work on the human circulation, and supported his many, many dissections by providing him with deer which they had hunted down in the royal parks and forests.

He gained fame for the results of his investigations which showed that blood flowed in a continuous circulation in the mammalian body, with the heart as its pump and valves in the veins preventing back-flow. His fellow scientists generally accepted Harvey’s work, which is perhaps one of the first examples of science moving forward as a result of experimentation, rather than as a result of unproven theories. Prior to Harvey’s publication, bloodletting was all the rage amongst physicians and the medical profession, and many non-scientists continued to want to believe this way, despite Harvey’s evidence.

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William Harvey and Embryology

In addition to his research into blood and the circulation, William Harvey (1578-1657) was one of the first to study embryology (the study of reproduction in its earliest stages) by observing the development of the chick in the egg. Harvey was the first to suggest that humans and other mammals reproduced via the fertilisation of an egg by sperm. It took a further two centuries before a mammalian egg was finally observed, but nonetheless Harvey’s theory won credibility during his lifetime, partly because of his fame and standing in the scientific world.

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He performed many dissections of mammal embryos at various stages of formation. From these experiments Harvey was able to formulate a new theory of animal generation, emphasizing the primacy of the egg rather than sperm. Prior to Harvey’s work, it was thought that the male sperm was the primary source of new life, and that the egg was simply an empty home, provided for the sperm to develop.

Harvey was hampered in  his research into embryology by a lack of a microscope, which was not invented until some 17 years after his death. With a microscope, he would have been able to substantiate many of his perfectly correct ideas.


Follow this link for more about William Harvey and embryology: https://embryo.asu.edu/pages/william-harvey-1578-1657

And this link for a brief summary about Harvey and his work into the circulation of blood:  http://www.bbc.co.uk/history/historic_figures/harvey_william.shtml

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