9.4 Reproduction in plants

Paradigm shift—more than 85% of the world’s 250,000 species of flowering plant depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species.

Albert Einstein is claimed to have said: “If the bee disappears from the surface of the earth, man would have no more than four years to live.” (Quote Investigator). While it appears he did not actually ever say this, it is a remarkably prescient observation about the role that pollinators play in continuing the survival of plants.

While wind, water and explosive propulsion do work for some flowering species, the majority rely on animal pollinators. The co-evolution of pollinators with the plants they pollinate means that, in many cases, species may be pollinated by only a select few animals.  Should the animals decline in population, so will the plants.

A recent example in New Zealand reminds us of this (Biello). The endemic flowering shrub Rhabdothamnus solandri, or New Zealand gloxinia, relies primarily on the bellbird (Anothornis melanura) and stitchbird (Notiomystis cincta) to pollinate its flowers.  These birds have long beaks and tongues to access the long, tubular flowers of the shrub.  However, the bellbird and stitchbird have recently become extinct on New Zealand’s North island. To investigate this impact on the flower, researchers conducted a study on three smaller offshore islands, where the birds were still present. The results were alarming – in the absence of the two birds on the North island, just 22% of of flowers produced fruit and had only 37 seeds per flower. This compares to the the islands that still have the birds, where they produced 232 seeds per flower and 58% produced fruit. In order to save this flower, we must also save the birds.


New Zealand Gloxinia – Rhabdothamnus solandri. 


A paradigm shift represents a radical change in thinking based on new evidence.  Understanding that protecting birds, for example, will also protect plants, is an important change in thinking from purely looking at the conservation of single species. Conservation methods that focus on ecosystems as a holistic unit reflect our increased understanding of the way animals and plants in particular are inter-related.


Biello, David. “For Want Of A Pollinator, A Flower May Be Lost–Or A Forest”. Scientific American. N. p., 2016. Web. 13 Oct. 2016.

“If The Bee Disappeared Off The Face Of The Earth, Man Would Only Have Four Years Left To Live | Quote Investigator”. Quoteinvestigator.com. N. p., 2013. Web. 13 Oct. 2016.

“T.E.R:R.A.I.N – Taranaki Educational Resource: Research, Analysis And Information Network – Rhabdothamnus Solandri (Taurepo) “. Terrain.net.nz. N. p., 2016. Web. 14 Oct. 2016.


8.3 Photosynthesis

Developments in scientific research follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation.

At the beginning of the 20th-century, the scientific understanding of photosynthesis was centred on the combination of Carbon Dioxide with chlorophyll to produce formaldehyde as an intermediate before being converted to a carbohydrate (Benson). This view predominated up to the discovery of radioactive Carbon-14 by Kamen and Benson in 1940 (Benson).

In 1945, C14 became readily available to researchers in the US. A young researcher in California, Melvin Calvin, was told by a senior scientist at the University of California-Berkley that he should start to do something interesting with it. So began a research focus that led to the Nobel Prize in Chemistry in 1961 “for his research on the carbon dioxide assimilation in plants” (“Melvin Calvin-Facts”).

The shape of the apparatus Calvin used led to it being called the “lollipop” experiment. The central “lollipop” contained a suspension of algae, to which was introduced the radioactive carbon.  Periodically, a sample of the algae was released into the tube below (the stick of the lollipop) where it was immediately killed by a solution of alcohol.  The compounds could then be analysed through chromatography.  By using the radioactively labelling isotope of carbon, it was possible to trace the path the isotope took and by analysing the intermediate compounds the researchers were able to determine what happened to the carbon – where was it absorbed and what was it used for? The series of experiments helped identify the sequence of carbon compounds produced in the Calvin Cycle and also disproved the idea that chlorophyl fixes carbon.

Lollipop PS
The “Lollipop” apparatus (The Bancroft Library)

These experiments were carried out be many individuals over a period of nearly 15 years and in some ways it seems unfair that Calvin tends to receive all the credit (as well as a solo Nobel Prize). A personal report by Andrew Benson (available here) gives a good idea of the collaborative nature of this process.


Benson, A. Following the path of carbon in photosynthesis: a personal story. Photosynthesis Research. 73: 29–49, 2002. Web. April 20, 2016.

Calvin, Melvin. “The Path of Carbon in Photosynthesis.” Nobel Lectures, 1964, pp. 618–644., http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1961/calvin-lecture.pdf. Web. 30, Jan. 2018

“Calvin’s Lollipop Experiment.” The Bancroft Library, The University of Berkeley, California, bancroft.berkeley.edu/Exhibits/Biotech/Images/3-9lg.jpg. Web. Jan 30, 2018.

“Melvin Calvin – Facts”. Nobelprize.org. Nobel Media AB 2014. Web. 19 Apr 2016.


A.6 Ethology

Testing a hypothesis—experiments to test hypotheses on the migratory behaviour of blackcaps have been carried out.

Male blackcap warbler (Bird fieldguide)

In the 1950s, blackcap warblers (Sylvia atricapilla), a small European songbird, began to be observed wintering in Great Britain, instead of North Africa. These observations led to the formation of hypotheses regarding blackcap migratory behaviour: were the changes due to inherited (innate) factors, was it a response to the environment or did the birds simply lose the ability to migrate normally?

To test these hypotheses, it was necessary to use experimental methods, as fieldwork would have been unfeasible.  The birds were kept in specially designed cages that could register if birds began to become restless during the migratory season and then what direction they tried to orient towards.

The results showed that the offspring of birds that migrated to Britain oriented consistently in a NW direction, despite being raised in isolation from their parents. Follow-up genetic analysis showed a strong heritability for this trait in both British wintering blackcaps and those from other parts of Europe.  The authors were led to suggest that:

“Under moderate selection intensities and environmental conditions similar to those presented in this study, the southern German blackcap population could evolve into a short-distance migrant in 10-20 generations.” (Berthold and Pulido; p311)

These results represent rapid evolutionary changes in behaviour- it is worth considering what selection pressures are working to promote these changes.  Can you relate this back to the Evolution/Natural Selection topics (5.1/5.2)?


Berthold, P and Pulido, F. Heritability of Migratory Activity in a Natural Bird Population.
Proc. R. Soc. Lond. B. 257. 1994. 311-315. Web. Mar 15, 2016. Full text available: at https://www.researchgate.net/profile/Francisco_Pulido/publication/216768532_Heritability_of_migratory_activity_in_a_natural_bird_population/links/0fcfd50c5c5adc29c9000000.pdf

Berthold, P. et al. Rapid microevolution of migratory behaviour in a wild bird species. Nature. 360.  1992. Web. Mar 15, 2016.

“Identify A Blackcap, Sylvia Atricapilla”. Birdfieldguide.co.uk. N. p., 2016. Web. 15 Mar. 2016.

11.1 Antibody production and vaccination

Consider ethical implications of research—Jenner tested his vaccine for smallpox on a child.

The story of Edward Jenner is a fascinating one and he played a key early role in the development of vaccines. The PBS Series “Rx for Survival” has a nice little dramatisation on his vaccine research in Episode 1: Disease Warriors (9m 13s – 12m 01s), though the whole episode is worth watching.

Jenner had noticed that milk-maids contracted cow pox, a non-fatal disease from cows, in the course of their work.  While this might make them ill for a time, they rarely ever caught the much more dangerous relative of cow pox, small pox. To test his theory, he inoculated a farm boy with pus from a milk-maid’s cow-pox pustules; the boy was unwell for a few days but made a full recovery. Jenner then exposed him to live small pox virus and he survived.

The ethical issues seem clear, but on reflection may not be so cut-and-dried.  Under modern medical standards, it is considered unethical to expose patients to live, virulent strains of a pathogen in order to test the efficacy of a vaccine. Such experiments would also not be done on children as young as eight. It is also likely that Jenner never received informed consent for the experiment as well.

However, there is a good case to be made that Jenner was merely following the ethical standards of the day, and that in fact, inoculation of this sort was relatively common in rural England (Abc). Given the very real danger of contracting the fatal small pox, it might be argued that the possibility of protection from the disease was sufficient motivation.  We can also link to TOK here and think about the challenges of applying modern ethical standards to past events, particularly where the context is so very different to today.  This link is a very nice ethical discussion of this, including a hypothetical hearing before an ethics review board (Davies).

It was not without controversy at the time, however, with the anti-vaccination movement already forming its arguments.  The famous cartoon below shows their misplaced fears:

The Cow Pock – 1802 (Wilson and Marcuse)


Abc. Ockham’s Razor: Defending Edward Jenner, 2015. Web. 15 Dec. 2015.

Bioethicscourse.info,. “Jenner On Trial: Introduction”. N. p., 2015. Web. 15 Dec. 2015.

Davies, H. “Ethical Reflections On Edward Jenner’s Experimental Treatment”. Journal of Medical Ethics 33.3 (2007): 174-176. Web. 15 Dec. 2015.

Wilson, Christopher B., and Edgar K. Marcuse. “Vaccine Safety–Vaccine Benefits:Science And The Public’s Perception”. Nat Rev Immunol. 1.2 (2001): 160-165. Web. 15 Dec. 2015.

7.2 Transcription and Gene Expression

Looking for patterns, trends and discrepancies—there is mounting evidence that the environment can trigger heritable changes in epigenetic factors.

This is highly topical given some recent events in the science news. But firstly, for a primer on epigenetics, check out Sci Show for their episode on Epigenetics.

Epigenetics is essentially “…genetic control by factors other than an individual’s DNA sequence.” (Simmons). These factors are thus important in the switching on or off of particular genes. While this happens throughout life, particularly during embryonic development, it is the growing body of evidence of environmental influence during adulthood that is particularly exciting.

A recent study investigating the genomes of obese men and obese men before and after bariatric surgery detected epigenetic effects coded in men’s sperm (Donkin et al.).  The environmental factors of obesity, as well as recovery from obesity, seem to effect the genes coded in the sperm, thus influencing the genome of future offspring. These genes seem to be linked to appetite control, providing intriguing insights into how obesity may become genetic and not just environmental.

If the environment affects genes and these changes are passed on to offspring, rather than the genes you were born with and inherited from your parents, then there are some very interesting possibilities that emerge for evolution.   As one scientist commented, this is a “…provocative start to asking some really interesting questions,” (Simmons).  Consider some of these yourself – it makes you rethink topic 5!


Donkin, Ida et al. ‘Obesity And Bariatric Surgery Drive Epigenetic Variation Of Spermatozoa In Humans’. Cell Metabolism (2015): -. Web. 10 Dec. 2015.

Simmons, D. (2008) Epigenetic influence and disease. Nature Education 1(1):6

Zusi, K. ‘Obesity Alters Sperm Epigenome | The Scientist Magazine®’. The Scientist. N. p., 2015. Web. 9 Dec. 2015.

3.3 Meiosis, 10.1 Gene Linkage and 10.2 Inheritance

Making careful observations—meiosis was discovered by microscope examination of dividing germ-line cells. (3.3 – Core)

Making careful observations—careful observation and record keeping turned up anomalous data that Mendel’s law of independent assortment could not account for. Thomas Hunt Morgan developed the notion of linked genes to account for the anomalies.  (10.1 – AHL)

Looking for patterns, trends and discrepancies—Mendel used observations of the natural world to find and explain patterns and trends. Since then, scientists have looked for discrepancies and asked questions based on further observations to show exceptions to the rules. For example, Morgan discovered non-Mendelian ratios in his experiments with Drosophila. (10.2 – AHL)

Both core and HL topics on meiosis focus on the importance of making observations and accurately interpreting them.  The HL NOS, with its references to Morgan, illustrates how this process helps expand and redefine our understanding of biology. Morgan is an interesting character and worth spending some class time on.

When Mendel’s genetic studies were rediscovered, scientists set about replicating and confirming them. However, one group (William Bateson, Edith Rebecca Saunders, and Reginald Punnett, he of the eponymous square) persistently found phenotypic ratios that were far more common than could be predicted based on Mendelian inheritance patterns. Examining pea plants during a dihybrid cross (link to AHL Topic 10.2), they received statistically significant deviations from the predicted, as seen below:

Characteristics of the F2 Generation (Bateson et al., 1905)
Characteristics of the F2 Generation (Bateson et al., 1905)

They surmised that the alleles must be coupled somehow, but could not explain how.  Enter Professor Thomas Hunt Morgan.  Five years later, 1910, he was experimenting on fruit flies, Drosophila melanogaster, and found a white-eyed male in one of his studies (fruit flies normally have red eyes). Further experimentation found that instead of an expected 1:1:1:1 ratio of red-eyed females, red-eyed males, white-eyed males, and white-eyed females, he observed the following phenotypes in his F2 generation: 2,459 red-eyed females, 1,011 red-eyed males and 782 white-eyed males. The lack of white-eyed females led him to hypothesise that the gene must be linked to the sex factor.  This later led to the concept of gene linkage: genes on the same chromosome do not assort independently.

Columbia University Fly Room - note bunches of bananas! © 2013 The American Philosophical Society
Columbia University Fly Room – note bunches of bananas!
© 2013 The American Philosophical Society

This was groundbreaking – it meant that genes were concrete, real objects that could be located on chromosomes  and their inheritance and behaviour mapped, predicted and analysed. Interestingly enough, Morgan had initially rejected the idea that genes were located on chromosomes, believing that data generated through passive observation could not be trusted; another instance of scientists having to reject old ideas in favour of new and compelling evidence. Morgan would go on to win the Nobel Prize in Physiology or Medicine  “for his discoveries concerning the role played by the chromosome in heredity” (Nobelprize.org; 2014).

We will discussing a lot more about Prof. Morgan in our next unit, Inheritance.

Extra: One of the prescribed TOK Essay Titles for May 2015 was: “There are only two ways in which humankind can produce knowledge: through passive observation or through active experiment.” To what extent do you agree with this statement?  You could consider drafting a short response using Morgan as a specific example.


Lobo, I. & Shaw, K. (2008) Discovery and types of genetic linkage. Nature Education 1(1):139. Web. 17 Mar 2015.

Miko, I. (2008) Thomas Hunt Morgan and sex linkage. Nature Education 1(1):143. Web. 17 Mar 2015.

“The Nobel Prize in Physiology or Medicine 1933”. Nobelprize.org. Nobel Media AB 2014. Web. 17 Mar 2015.


Bateson, W., et al. (1905) Characteristics of the F2 Generation. Reports to the Evolution Committee of the Royal Society. Nature Education. Web. 17 Mar 2015.

n.a. (1913). Columbia University Fly Room. The American Philosophical SocietyNature Education. Web. 17 Mar 2015.

7.3 Translation

Developments in scientific research follow improvements in computing—the use of computers has enabled scientists to make advances in bioinformatics applications such as locating genes within genomes and identifying conserved sequences.

Bioinformatics is the application of computer science to molecular biology, allowing the creation of massive databases of molecular information (proteins, genes, DNA sequences etc.) You might remember from our Crash Course video on replication that one cell contains genetic information equivalent to a stack of single A4 pages nearly 100m high! It is only the advent of powerful (and affordable) computers over the last 25 years that has enabled the collection and synthesis of genetic information on a large scale.

To explore this topic, we will be performing a BLAST search using resources from the European Molecular Biology Lab (EMBL).  We will be searching for information about the Protein PAX6 through a series of databases on the web.  The activity we are doing can be found through the EMBL’s education section, the European Learning Laboratory for Life Sciences.