Fungi - Online Tutor, Practice Problems & Exam Prep

Fungi - 1

Hi, In this video, we're going to talk about fungi, which include molds, mushrooms, yeasts, mildew, all that lovely stuff. Now, fungi are heterotrophic eukaryotes and they generally have a haploid nucleus. They tend to be the main decomposers in many ecosystems. And this is a very important feature of fungi that we're going to return to again and again. And here you can see a couple examples. We have morel mushrooms which are absolutely delicious type of mushroom. Here, these, Ammonium muscaria, these will kill you. Don't eat those. And of course, this is the most important mushroom, the power mushroom. Now, some fungi are mutualists and that basically means they exist in a relationship with another organism that benefits both of them. And this is another one of those really important properties of fungi and you'll see why momentarily. Now, fungi are essential to many land plants. You often think of these as being two completely separate organisms but the point that I'm going to try drive home to you is that most land plants would not be able to survive without fungi. And the reason is because of this mutualist relationship they share, this symbiosis they share. Now, a couple of examples of some fungi relationships, not the kinds that end in bad breakups, the good kinds are endophytes which are basically symbiotic fungi that live inside plants. They benefit the plants that they live in and the plants in which they live benefit them, and they lived happily ever after. That's not to say that things can, that things always work out well as we'll see soon. Now lichen are an especially cool example of a mutualist fungal relationship. It's a symbiotic association of fungus and algae or sometimes cyanobacteria. The main point being a unicellular organism that performs photo synthesis. Now in this example here, we see, in blue the fungal body. We'll learn more about what fungal bodies are made of momentarily, but for now just think of that as the body of the fungus, and it's wrapped around these algae. And essentially, these two organisms are going to help each other. I mean algae perform photosynthesis, right? Again, this could be cyanobacteria but for the sake of my example, I'm just going to talk about algae. So, algae perform photosynthesis meaning they're going to generate, organic compounds that the fungus can feed off of. In return, the fungus helps, secure water for the algae and also helps prevent it from drying out. There you can see a picture of some lichen right there. It's a little lichen clump. Lichen actually come in all different shapes and sizes. They have many different morphologies. Really cool organism. Now, the last thing I want to say is that some fungi are actually, or some fungi have symbiosis that are obligate. That is to say they exhibit obligate symbiosis, meaning they have to live in a symbiosis in order to survive. Now other fungi and many fungi in fact, are facultative. And if you recall these terms from when we talked about, cellular respiration, specifically aerobic respiration, You might recall that obligate means you have to and facultative means you can but it's not, necessary. So some fungi can have symbiosis but they don't necessarily need them in order to survive. They might just survive better with them. Now, said not all these relationships end well. Well, it turns out there are bunch of fungi that are parasites and they'll infect plants and animals. And when they infect animals, we call this mycosis. Now, fungi tend to be the main decomposers as I said and what's really important is they're able to digest plant material, specifically cellulose and lignin. You might remember, previously when we talked about lignin, we said it was a tough material and thinking way far back to when we first talked about cellulose, we actually talked about the fact that, cellulose cannot be digested. If you're curious as to this lesson, I'm referring to the lesson on carbohydrates in the biological molecules chapter. Now, cellulose can't be digested by animals. But fungi can digest cellulose. So they're actually a bunch of fungi that live in the guts of various animal species that help those animals digest plant material by breaking up the cellulose for them as well as the lignin for that matter. And what's so important about this is because plants take so much carbon out of the atmosphere, right? They take all that CO₂ that we animals put into the atmosphere. They take it out and they build it into their bodies, right? And if nothing is done about this, then that carbon just sits there and and eventually those plants, the carbon in those plants will turn to what we know as coal today. But fungi return this carbon to the carbon cycle. So they break down that non-digestible plant matter or what's non-digestible to many other organisms. They break it down and they return that carbon to the carbon cycle. And actually, we have a special term for fungi that feed on dead plant matter specifically. Right? If you're feeding on live plant matter, well, probably a parasite. Right? So fungi that feed on dead plant matter are called saprophytes. Now, here I just want to point out, this parasitic fungal infection. All these little tubular pink spaghetti strands, whatever you want to think of them as, branches they kind of look like. Those are part of the fungal body. And this, is animal tissue around it. So that is a fungal infection in an animal. And over here, we can actually see the, fungal bodies that are in the process of, decomposing or fungal bodies that will be part of organisms that are going to decompose plant matter and return carbon to the carbon cycle. Now before we turn the page, the last fungus I want to give a shout out to is yeast, my favorite fungus, the often overlooked fungus. However, it's a wonderful organism. It's a unicellular fungus and as you'll see most fungi, outside of yeast are multicellular, and it is the fungus that's responsible for leavened bread and beer. So we have been humans that is have been using yeast for an enormously long time. I mean it's hard to really say. I'd you know, I'm not an expert on anthropology but it's humans have incorporated yeast into our cooking processes and our brewing processes for a very, very long time and they're awesome organisms and they actually have many similarities to human cells which is why they're used, for a number of studies including genetic studies to learn more about humans. So go yeast. Yeast is awesome. And with that, let's turn the page.

Fungi - 2

Now fungi morphology is going to be a little strange, let's say, compared to what we've seen thus far. Fungal bodies are mostly made of what are called hyphae. These long filaments that are actually made up of 1 or sometimes many cells, and are surrounded by a kind of tube-shaped cell wall that will enclose all of them in a filament. You can see a microscopic image of hypha here. They are these filamentous strands you see. And we can see an artist's rendition of a hypha here. Each of these blocks actually represents individual cells and essentially, while the cells are technically independent, they do have pores between each other. And, these blockages or these divides in the cells, I should say, because they're not actually blockages, they allow passage between the cells. These divides are called septa. So here, this is a septum. That's going to be the singular form of the word. And, it's worth noting that these fungal cells, right, these hyphae, have a chitinous cell wall, which is actually a modified beta-glucose polymer. You might remember that beta-glucose is what is used to make cellulose, interestingly enough. Here however, these subunits have been modified with an amino acid-like group. And essentially, it, this polymer acts as a tough cell wall for the fungal cells. And it's actually also present in insect shells interestingly enough. And that's why when bugs die, their shells hang around and don't decompose or anything. Because there's really not a lot that digests chitin. It's a very tough resilient material. That's why, you know, you can keep, for example, an insect shell from a dead insect from, you know, a really long time ago. And also why, fungi tend to be or tend to have these resilient hardy cell walls. Now hypha refers to an individual filament and we use the term hyphae to refer to multiple hypha, so that's the plural form. The entirety of a fungus's hyphae is called the mycelium. So that's essentially the mass of the fungus, which is made up of all these interwoven hyphae that is called mycelium. So you might hear those terms used interchangeably from time to time, but just know that mycelium is the totality of the hyphae of a fungus. Say that 5 times. Now fungi, actually perform, what's called extracellular digestion. And essentially what they do is they release enzymes and absorb the nutrients, that the enzymes will break down compounds releasing nutrients and these nutrients get absorbed through, the fungal hyphae. Now it's worth noting that might sound really strange, but humans technically also perform extracellular digestion. Right? We put food into our gastrointestinal tract, and we release enzymes from cells, around the GI tract that break down our food and then those cells absorb the nutrients, as the food gets broken down. The difference really is that, we're doing this inside of our bodies whereas fungi, don't always, fungi don't usually do it like that. They will actually, or secrete these enzymes into the environment, break down the stuff, and then absorb it. So, not as weird as it sounds, but still different than the way humans do it. Now some parasitic fungi actually have these, special, hyphae called haustoria. And again, singular here is going to be haustorium; all these Latin words, I know. So a haustorium, that's going to be the singular form, and you can see them here. These are all plant cells and these dark bits that you see inserted into the plant cells; those are the haustoria. And you can tell because the fungus has been stained, this darker stain. So this band you see, that's the fungus and these nubs it's inserting into the plant cells, those are the haustoria. And this is what parasitic fungi are going to do to extract nutrients from plant cells. Now, with that in mind, fungi actually, generally, are really helpful to plants. Okay? So sometimes they're parasitic, always some bad apples in the bunch. Right? But, fungi are actually essential to many land plants, and they actually form this symbiotic association of hyphae and roots of vascular plants, obviously, because vascular plants are the only plants that have roots, and, as opposed to rhizoids, you might recall from plants. Now, this association of roots and fungi can be seen here in white, that is the, fungal body and the, little brown bits are roots. Basically, what you're looking at is, someone kind of like pulled a plant, flipped it upside down and brushed some of the dirt off the roots, and that's what we're looking at here. Now, there are actually two ways that these mycorrhizae can form. And notice that term mycorrhizae, right? Rhizae, that's referring to roots. Myco is referring to fungi. So we have fungal roots, basically. Now as I said, they're essentially, 2 different versions of mycorrhizae. This actually gets a little more complicated, you know, as I hope you realize by now we have to simplify things a little bit just to make it manageable to talk about and to paint some broad strokes pictures. But essentially you can have ectomycorrhizae, which form on the outside of plant cells, the extracellular surfaces. They don't penetrate into plant cells. And you can see an example of this right here. We have the artist's rendition in purple. These purple stringy bits, those are the fungi. And you can see that while they don't actually penetrate the plant cells, they will penetrate into the root of the plant and grow around the cells. And here you can see an image, an image of the ectomycorrhizae around a root. So we are, all this stringy stuff is the fungal body forming around the root. But it can also go the other way. Arbuscular fungi, which are sometimes referred to as endomycorrhizal, right, endo meaning internal. So, arbuscular fungi will actually penetrate into the cells in the roots of plants. However, in both instances, this is a beneficial relationship to the plants. Just 2 different strategies. So the main relationship here is that the fungi help the plants get certain nutrients and help them obtain water, and in return, the fungi are provided with nutrients by the plants. So with that, let's conclude this video, and I'll see you guys next time.