You can't tell by looking at your favorite edible mushroom (or just any mushroom if you hate mushrooms), but a fungus is actually a closer relative to you than it is to a plant.
How we know that? Fungi don't exactly have feet or eyes or heads or anything that we have.
That's because there's more to a mushroom than meets the eye. We're constantly changing the tree of life, changing our minds about who's related to what and when the species diverged from an ancestor. We regularly cut off tree branches and twigs and superglue them to an alternate location. Molecular biology, understanding cells on the teeniest tiniest level, comes a long way in helping us make those connections.
Historically, molecular biology has been used to figure out what species are related to each other through DNA sequencing, as well as verify a baby's daddy.
rRNA sequencing has also been a popular tool used to cut up and reconfigure the tree of life in prokaryotes. rRNA is the type of RNA that makes up ribosomes, the little machinery that performs translation. All cells have ribosomes—both prokaryotic and eukaryotic. But the rRNA that makes up these ribosomes is different. Prokaryotes contain a small rRNA known as 16s rRNA, and it's been sequenced in bacteria like crazy. By sequencing these rRNAs, we can look at how similar they are between organisms on a genetic level.
Currently, scientists are starting to sequence the eukaryotic version of this rRNA (called 18s rRNA due to its larger size). While these sequencing methods haven't exactly shaken many tree branches yet, it has a lot of potential as a method that could tell us a lot more about the differences and similarities between different organisms. We know that fungi are more like us than plants, because we do things like make our own food and don't do things like photosynthesize. Additionally, fungi and some animals share the molecule chitin, which no plant contains. These are good lines of evidence, but not totally fool-proof. Sequencing our rRNA could be the icing-like proof on this cake and solidify the similarities between you and the World's 10 Most Amazing Mushrooms.
Picture this. You're driving on a highway with the top down on your convertible, the wind blowing at your hair. When suddenly—you hear a tiny alarm. Whoops! You forgot to fill up the tank again.
Ah well. You pull up to the "gas" station, unscrew your gas cap, and fill up your car with clean, green algal biofuel. Breathe in the sweet smell of a renewable resource and forget the noxious smell of gasoline.
This isn't quite reality, but it's not too far off from the dreams of scientists that are developing ways to extract oil from algae and turn it into fuels such as biodiesel, biogasoline, and even jet fuel (Leavin' on a jet plane is a lot easier when you're being nice to the Earth). Algae are fairly simple to grow, requiring sunlight and water, and produce an environmentally friendly source of energy—no climate change-inducing fossil fuels.
So what's stopping your local gas station from stocking algae byproducts? The main hurdle isn't making these fuels. That's been done. It's how to make these fuels affordably and in mass quantity. Algae need lots of light to perform photosynthesis, and a lot of water to live in. In addition, the perfect nutrient conditions have yet to be established for maximal yield of the green stuff. After growing the algae, the oil must be extracted and then refined and processed into different types. Science needs to figure out how to make this feasible and profitable.
We're probably a good 20-30 years away from seeing this reality, but both the government and private companies have a stake in the venture. The US Department of Energy, for example, is funding grants for projects that aim at turning these little green guys into gas.
Algae have also been touted as the solution to rising climate temperatures caused by an increase in carbon dioxide emissions. Since algae use carbon dioxide to perform photosynthesis, they can be used to suck the excess carbon dioxide right out of the air. You might ask yourself why we can't just use plants for this process. Well, we can. But, algae are smaller, and they don't take up land resources to grow. You could grow them in a big tub o' water.
Why spend so much money on fancy schmancy expensive equipment to measure air quality when you can figure it out for free using lichens?
What's a lichen, you ask? Some lichens are extremely cool examples of eukaryotic symbiosis, where two organisms mutually benefit from each other in perfect harmony. Lichens are two separate organisms, such as photosynthetic algae and fungus, working together. The fungi makes a nice pad for the algae to live in, and the algae pays the fungi back for the sweet living arrangement by providing food (specifically, with carbohydrates the algae make from photosynthesis). As a combo, these two are like peanut butter and jelly.
Lichens put up shop in a range of habitats. Neither organism has roots or a vascular system like plants do, which gives them the freedom to grow on surfaces like rocks and trees. But, without roots and shoots to transport food from the ground, they have to take up nutrients from the air around them.
An example of lichens growing merrily on a rock. Image from here.
Without roots, lichens get the nutrients they need from absorbing the atmosphere around them. Not only do they absorb yummy nutrients from the air, they also absorb the gross stuff, too. This means lichens can be used as indicators of air quality. They are super sensitive to changes in the environment. They can be used to map out microclimates in different areas of the world and map out itty-bitty individual areas of slightly different temperature, moisture, and chemical stressors. Lichens essentially can sense environmental stress before the rest of us know what's coming by absorbing small amounts from the air.
Lichens can therefore replace all the fancy shmancy expensive equipment used to measure air quality. Case in point: lichens were used to tell scientists about air-borne toxins following the Chernobyl Nuclear Power plant meltdown back in 1986. Lichens accumulate more radioactivity than most other organisms by sucking it out of the air. Scientists were then use lichen for use as a relevant indicator of radioactive contamination in different areas resulting from the catastrophe.
So, next time you're wondering what's going on in the world, just ask a lichen, "What's up?"