Are there edible non-photosynthetic plants

Why are so few foods blue?

While @ AliceD's answer is a great simple demonstration of the lack of blue in our natural world, there is likely a more nuanced / technical reason.

Short answer

Blue light was the most available wavelength of light for early plants growing underwater, which likely led to the initial development of chlorophyll-mediated photosystems that can still be seen in modern plants. Blue light is the most available and energetic light that continues to reach plants, and therefore plants have no reason not to continue using this abundant high-energy light for photosynthesis.

Different pigments absorb different wavelengths of light, so plants ideally contain pigments that can absorb the best available light. This is the case because both chlorophyll a as well as b mainly absorb blue light. (The absorption of red light likely developed as soon as plants moved on land due to their higher efficiency.)

Pigments appear as the color that Not is absorbed (i.e. they appear as the wavelength (s) of light that they reflect). Since blue pigments would reflect most of the light that modern plants rely on for their chlorophyll-mediated photosystems, blue pigments remain rare in plants.

  • Photosynthetic organisms would not remain competitive if they did not absorb the readily available, high-energy blue light, and so evolution has likely very rarely favored the formation (or propogaiton) of blue pigments.

Atmospheric transmission

As this page from Humboldt State University shows, blue and green light travel better than almost all other light wavelengths through the atmosphere to the earth's surface:

Transmission is when electromagnetic energy is able to travel through the atmosphere and reach the surface. Visible light goes largely through the atmosphere.

This means that blue and green light the best available Are wavelengths of light.

  • Note that blue / green is followed closely by the rest of the visible spectrum and the NIR (near infrared).

  • Also note that a large part of the ultraviolet is largely absorbed by atmospheric gases (mainly ozone) and therefore poorly transmitted.

Wave properties

It is important to understand that (by U. Wisconsin):

More energetic waves have shorter wavelengths, while less energetic waves have longer wavelengths.

Consequently blue light (which is the best available wavelength with the highest energy of light) appears to be the optimal wavelength of light for photosynthesis .

  • Note that UV light is available though is more energetic and can drive photosynthesis, but often something to is high in energy and can damage cells. Therefore, it is often best for organisms to reflect UV rays.

  • Further information on the physics behind light energy can be found here.

photosynthesis

Photosynthetic organisms contain pigments (typically heme / porphyrin-based chlorophylls and various carotenoids) that absorb light energy. Basically, the energy of a photon of light brings an absorbing pigment into a state of higher energy (than excited state ), and then the pigment releases this unstable energy to return to its basic state - this excess energy drives the biochemical reactions involved in photosynthesis. More details can be found here.

Here are two sample graphs (from here and here) showing the absorption spectrum of typical plant pigments:

As you can see, Plants have evolved into pigments that mainly emit blue light (followed by red light) absorb . These pigments reflect green light and therefore appear green.

  • The presence of blue pigments (i.e. those the a lot of blue light reflect ) would stand in direct contrast to these photosynthetic measures. Consequently remain blue pigments in photosynthetic organisms, which are mainly powered by chlorophyll-driven photosystems , Rare .

However, a number of sources (e.g. Mae et al. 2000, Brins et al. 2000 and here) suggest that while plants absorb more blue light than other wavelengths, the most efficient photosynthesis does not occur with blue light. Instead, red light leads to the highest photosynthetic efficiency.

  • One of the reasons they (in this case, Brins et al.) Found was that xanthophylls diverted the excess energy associated with blue light, causing a decrease in the rate of photosynthesis of blue light.

  • This NIH page suggests that high energy light isn't even required for plants:

    Chlorophyll a also absorbs light at discrete wavelengths less than 680 nm (see Figure 16-37b). Such absorption brings the molecule into one of several higher excited states that exist within 10-12 Seconds (1 picosecond, ps) decay into the first excited state P *, with the additional energy being lost as heat. The photochemical charge separation takes place only from the first excited state of the reaction center chlorophyll a, P *. This means that the quantum yield - the amount of photosynthesis per absorbed photon - is the same for all wavelengths of visible light shorter than 680 nm.

However, all of this can be for free as there is abundant sunlight available to plants. Again from the NIH side:

Even at the maximum light intensity of photosynthetic organisms (tropical midday sun, 1.2 × 10 20 Photons / m2 / s) is absorbed by every chlorophyll a des Reaction center about one photon per second, which is not enough to support photosynthesis sufficiently for the needs of the plant. To increase the efficiency of photosynthesis, especially at more typical light intensities, organisms use additional light-absorbing pigments.

In other words, plants are not completely photosynthetically efficient and typically do not use all of the light available to them. From Wikipedia:

Photosynthesis increases linearly with light intensity at low intensity, but this is no longer the case at higher intensity (see photosynthesis-irradiance curve). The rate no longer increases above about 10,000 lux or ~ 100 watts / square meter. Therefore, most plants can only use ~ 10% of the total sunlight intensity at noon.

So in summary:

  • Blue and green light are the best available wavelengths of light.
  • Blue light is the most energetic of the highly available wavelengths of light
  • Plant pigments mostly absorb blue light
  • BUT plants don't necessarily need the high energy of blue light for efficient photosynthesis.

So what's up? ...

evolution

Given all of this, the question still remains: why absorb mainly blue light and not green light?

The answer, while still somewhat presumptuous, is likely due to the ready availability of early plants. Early plants, like all life, developed underwater.

It turns out that just like the variability of the transmittance of different wavelengths of light through the atmosphere, certain wavelengths of light are more capable of penetrating deeper water depths. Blue light usually travels deeper than any other visible wavelength of light. Hence, the earliest plants would have evolved to focus on absorbing this part of the EM spectrum.

However, you will find that green light also penetrates relatively deeply. The current understanding is that the earliest photosynthetic organisms were aquatic archaea and (based on modern examples of these ancient organisms) these archaea used bacteriorhopsin to absorb most of the green light.

Early plants grew among these purple bacteriorhopsin-producing bacteria and had to use every light they could get. As a result, the chlorophyll system in plants evolved to harness the light available to them. In other words, based on the deeper penetration ability of blue / green light and the loss of the availability of green light for pelagic bacteria Plants have a photosystem that mainly absorbs in the blue spectrum as this was the light that was most available to them .

Why didn't plants evolve to use green light after moving on land? As mentioned above, plants are terribly inefficient and cannot use all of the light available to them. As a result, there is likely to be no competitive advantage in developing a drastically different photosystem (i.e., incorporating green absorbing pigments). So the plants on earth continue to absorb blue light and reflect the green, and blue pigmentation continues to be uncommon in our world.

  • Plants likely evolved Anthocyanins (the pigments responsible for the red / blue / purple colors attributed to blueberries and violets) for reasons other than photosynthesis - e.g. B. attraction, UV protection or even protection against herbivores. You can find examples here, here and here.

So what about non-plant organisms?

According to Wikipedia:

  • Carotenoids are the most common group of pigments found in nature, including in animals.
  • Caroteno-protein complexes are responsible for the different colors (red, purple, blue, green, etc.)
  • Animals are unable to make their own carotenoids and therefore rely on plants for these pigments .

In other words, most of the pigments in non-plant organisms come either directly or biochemically from the diet of the organism. Without direct absorption of blue pigments, these chemicals are not available or biochemically expensive to produce (see crustacyanin). As a result, blue pigments are also uncommon in animals.

Although AliceD's sources point this out, we still don't fully understand why animals stop producing blue pigments.

the forest ecologist

@ Jamesqf Yes exactly. See my point (and related links) on anthrocyanins. However, this is an explanation for Why we have blue foods: p. The rest of my answer is about why we are likely to run out of blue pigments in organisms!

J. Manuel

I did not understand exactly where you are something say about it. Why are so few foods blue?

Race of lightness in orbit

@ J.Manuel: Our food consists of animals and plants. This answer is a great explanation for why animals and plants are not blue. What more do you want?

Race of lightness in orbit

@ J.Manuel: And why do you think that is? That's right - because animals and plants don't tend to be blue! In the end, it all comes back to that.

the forest ecologist

@Nikana plants evolved in conditions of mostly blue light, causing them to develop photosystems that use a pigment that absorbs primarily blue light. Once they went ashore, there was plenty (often too much) of high-energy blue light (and other wavelengths of light as well) to ever have to develop new pigments to become more competitive. Even if plants were to add new pigment, they would likely not evolve to add more blue pigment b / c, which would decrease their ability to photosynthesize using their current chlorophyll-mediated photosystem.