AP Biology class blog for discussing current research in Biology

Tag: pigments

Blueberries: Why They’re Blue


An article published on February 7th 2024 by ScienceNews identifies and reveals why blueberries are blue. Most people reading this article are probably wondering why this is such a big deal and how it relates to science. Spoiler, it does. The secret to a blueberries hue, or color, is in the structure of its wax coat. Many fruits such as grapes, plums, and blueberries have this waxy covering and researchers have identified that it is this waxy coat that makes these fruits appear blue to humans. 

Typically, blue is not a common color in nature and although there are some known blue fruits, few of them contain pigments of that shade. For example, blueberries contain large amounts of anthocyanin which is a skin pigment that should give each berry a dark red color, but structures in blueberries waxy outer layers work against anthocyanin creating their own blues. 

Rox Middleton, a physicist at the University of Bristol in England and Dresden University of Technology in Germany, conducted an experiment with the help of a few colleagues to better understand what is special about the berries waxy coverings. The group looked at a variety of fruits such as blueberries, Oregon grapes, and Plums under a scanning electron microscope to take a look at the finer details of blue-colored fruit skins. The resulting images revealed nano structures that reflect blue and ultraviolet light and cover up dark red anthocyanin pigments that are found underneath the waxy coating on blueberries skin. Furthermore, wax from the Oregon grapes became transparent when it was dissolved with chloroform

An article published on the same day through the University of Bristol provides another perspective on blueberries waxy coat. The article identifies that blueberries blue pigment can’t be extracted by squishing the berries because the pigment isn’t located in the juice that can be squeezed from the berry. The article then goes into further detail about the coating stating that it is an “ultra-thin colourant” around two microns thick that reflects UV light well which makes it appear blue as the coating is made up of miniature structures that scatter blue and UV light. 

A second article published by dole, helps explains the benefits of anthocyanin. The article states that anthocyanins bind to free radicals therefore protecting against some health disorders that can arise through oxidative processes such as cardiovascular disease and cancer. The pigment is also believed to have a positive effect on inflammation and high blood pressure as well as protecting the gut from bacteria by supporting the digestive system. 

To help further explain how pigments work and how we see certain colors, in AP Biology class, we learned that when a plant, for example, appears green, this is because that plant is absorbing all colors available except for green, which it reflects. This is why the rate of photosynthesis in plants is the worst in green light because the plant is unable to absorb the green light which contains the photons it requires to preform photosynthesis. Blueberries also reflect light, but it’s waxy coating instead reflects blue light which is why they appear blue to us. 

I believe that these new findings are very exciting as I personally didn’t realize that a waxy coating was responsible for blueberries blue appearance. I look forward to reading about more experiments like Middleton’s that help us further understand why certain fruits and vegetables appear the way they do, what do you think?

Guppy Love!

Tiger Guppy (domesticated)- CC licensed photo by Leonard Paguia

Guppies (those small, colorful freshwater fish that everyone loves to keep in their fish tanks) have been evolving in the wild for more than 500,000 years, yet one feature has remained constant over all that time. Research conducted by UCLA Biologists has shown that the orange spot found on the wild male guppy has remained not simply the same color, but the same hue of orange since near the beginning of this fish’s existence. The reason for all this effort? That particular shade of orange is the one that female guppies prefer. What is so fascinating about this to biologists is that it proves that evolution is not simply an organisms adaptations to be better suited to its environment.

The two pigments that, when combined, allow a male to have an orange-colored spot are carotenoids (taken in by the guppies through food) and drosopterins (synthesized by the guppies). A higher percentage of carotenoids would make a guppy’s spot appear more yellow, and a higher percentage of drosopterins would make the spot appear more red.

Now one would think that, in order to conserve energy and be able to function more efficiently, a male guppy that had an abundance of carotenoids in its diet would not waste energy on synthesizing drosopterins as it would not need them to have a brightly colored spot. Conversely, one would think that in order to maintain a bright and noticeable spot, a guppy that did not have a lot of carotenoids in its diet would synthesize more drosopterins. However, this is not the case.

As the type and availability of food for male guppies has varied as a result of both time and location (guppies are native to both trinidad and venezuela) they have evolved to match the levels of carotenoids and drosopterins to produce that orange that the females are so attracted to, even if it comes at a high energy cost, or the spot must be more dull to produce the correct shade.

Although we all understand that reproduction is the ultimate goal of all organisms, what these guppies have done over the past half a million years is still not evolution in the way that many of us think about it. What has happened with a great many organisms is that they adapt in ways that make it more easy for them to survive and then these traits become attractive to the opposite sex because their presence indicates that that individual will produce offspring that will also be better suited for its environment. Here, however, male guppies have striven to remain attractive to their mates even when this comes at a high energy cost for many. As a result, the females have not had to change their taste in mates, and the males have been forced to continue playing to their preferences, or risk not reproducing.

Can you think of any other organisms that have adapted to be attractive to mates even when it made them less suited for their environment?

For further reading on the actual experiment conducted by UCLA biologists click here


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