Category Archive: Misconceptions

May 05

Adaptations evolve in populations

Pisum sativum (purple) [CC-BY-SA-3.0 Rasbak]

Organisms evolve adaptations to increase their fitness There are few ideas in science that explain as much of the natural world as does natural selection, but there are few ideas in science that are more frequently misunderstood. Often the misunderstandings are deliberate or disingenuous, but I’ve seen quotes like the one above even in undergraduate essays and …

Continue reading »

Aug 26

Statistical power

Fair coin simulation [CC-BY-SA-3.0 Steve Cook]

In a recent(ish) post, we saw that if a fair coin is flipped 30 times, the probability it will give us 10 or fewer heads is less than 5% (4.937% to be pointlessly precise). Fisher quantified this using the p value of a data set: the probability of obtaining data (or a test statistic based on those data) at …

Continue reading »

Oct 09

The Wason card problem

Wason cards [CC-BY-SA-3.0 Steve Cook]

The Wason card problem is a well-known psychological test that probes how people think about hypothesis testing. The version I use in one of my first-year lectures is shown below. I think the original version used letters and numbers, but I’m a biologist, so obviously I use pictures of dead pets instead of numbers. We …

Continue reading »

Aug 09

Enzymes provide alternative routes to product with a lower activation energy

Hydrogen peroxide decomposition [CC-BY-SA-3.0 Steve Cook]

An enzyme lowers the activation energy for a reaction Like a previous post, the problem here is not so much that this idea is flat-out wrong, but that it’s very prone to misinterpretation. Text-books often state that an enzyme, or any other catalyst, lowers the activation energy of a reaction. The activation energy for a reaction (written …

Continue reading »

May 01

The Michaelis-Menten model is not applicable to most enzymes in a cell

Sigmoidal kinetics [CC-BY-SA-3.0 Steve Cook]

Enzymes in cells can be modelled using the Michaelis-Menten model Enzymes can be, and often are, modelled by the Michaelis-Menten (well, Briggs-Haldane) model: v = vmax · [S] / (KM + [S]) Where: v is the velocity of the enzyme, which is the rate at which product accumulates vmax is the maximum velocity of the enzyme (i.e. …

Continue reading »

Apr 23

Metabolic pathways don’t really have end products

Metabolic pathways [CC-BY-SA-3.0 Zephyris from w]

The end product of glycolysis is pyruvate This, and equivalent statements about other metabolic pathways: The products of Krebs cycle are ATP/GTP, NADH and carbon dioxide are not exactly wrong, but they are easily over-interpreted in a way that leads to misunderstanding. They are also  easily swallowed as explanations without considering quite what ‘end product’ …

Continue reading »

Apr 09

Enzymes don’t necessarily increase the rate at which products are formed

An enzyme increases the rate of product formation What happens if you add the enzyme malate dehydrogenase to a mixture of of its substrates NAD and malate (both at 1 mM for the sake of argument)? A brief look on BRENDA indicates that the reaction malate dehydrogenase catalyses is: malate + NAD → oxaloacetate + …

Continue reading »

Apr 09

The product of succinate dehydrogenase is ubiquinol not reduced flavin

Succinate dehydrogenase [CC-BY-SA-3.0 Steve Cook, based on PDB 1NEK: Yankovskaya, V., Horsefield, R., Tornroth, S., Luna-Chavez, C., Miyoshi, H., Leger, C., Byrne, B., Cecchini, G., Iwata, S. (2003) Architecture of succinate dehydrogenase and reactive oxygen species generation. Science 299:700-704 doi: 10.1126/science.1079605]

Succinate dehydrogenase (SDH) produces reduced flavin (FADH2) as a product This misconception is so widespread, even the exam boards get it wrong. Page 41 of the Edexcel GCE specification for A-level biology (2008 onwards) states that students should be able to… Describe the role of the Krebs cycle in the complete oxidation of glucose and formation …

Continue reading »

Apr 09

Misconceptions in life sciences

Last month, I was involved in teaching on a life science communication course, some of the results of which you can see on Wikipedia. One of our guest speakers was Alom Shaha, who demonstrated the misconceptions students have about e.g. the forces acting on a ball in flight: A typical response demonstrates some common misconceptions, …

Continue reading »

Apr 08

Organism of the week #11 – Not even primitive

Psilotum nudum (Oxford Botanic Gardens) [CC-BY-SA-3.0 Steve Cook]

It’s not much to look at, but Psilotum nudum‘s naked fronds hold a cautionary tale for biologists: Psilotum looks a great deal like some of the earliest fossils of land plants. One of the earliest such fossils is Rhynia, the first specimens of which which were unearthed in Aberdeenshire around 1910, a mere 410 million years after they were …

Continue reading »

Older posts «