Module 7: Pathogen Classifications

Biology, biology, biology. Welcome back to another episode of the HSC Biology Podcast. We are halfway through the syllabus guys, which is very exciting, up to module 7 infectious disease, and our enquiry question for today is how are diseases transmitted, and the dot point itself is described by a variety of infectious diseases caused by pathogens including microorganisms, macro organisms and noncellular pathogens, and collect primary and secondary source data, and information relating to disease transmission, including and the one we're focusing on today is classifying different pathogens that cause disease implants and animals. So, before we get into the content stuff, it's very important that we go through a couple definitions first. So, what is an infectious disease? It is a disease that can be transmitted from person to person, and is caused by a pathogen. A pathogen is an infective agent or organism that can cause the disease. So, examples that you might know of are bacteria and viruses, but there are more, and that's what this dot point is all about, it's about classifying the different pathogens. So, I usually start at the smallest of the pathogens and then go to the largest. And the reason I do that is because previous HSC questions have been asked to analyze and put into size order the different pathogens. The new syllabus is a bit different obviously, but classification would be involving size order, so there's no reason not to still use this as a guide. And so, where we start is with the preons and the preons are a really interesting pathogen, because they're not living. They're simply just misfolded proteins. Now, we've talked a lot about proteins on this podcast. There, you know, bunches of amino acids all combined in a particular way. Well, a preon is a particular type of protein that is misfolded in such a way that it causes other proteins to misfold in the same way. So, it's kind of like a cascade effect. If you have one of these preons, it obviously can attach to another one and then those two can attach to more and the process goes on. Now, these preons will usually affect proteins in the brain, which is the most unfortunate part. And we'll talk about the diseases that it causes in a minute. But these are, if we were to classify them, these are classified as non-living, which is part of the dot point and non-cellular, which is really important. So, they're extremely small, like very tiny, down in the nanometer range. And that means that, you know, they're one of the smallest things that can cause disease. So, preons definitely the smallest. And one of the more interesting ones, because they're just proteins. They have the ability to cause some of the worst conditions. So, with this dot point, it does mention specifically that you need plant and animal examples. So, you should be really getting more than one. But with preons, it's a bit tricky. There's not many, or as far as I could find, or any preon conditions. There is one that I found that is lack of preon. It acts like a preon and not necessarily in plants, but the protein itself behaves like a preon. And it's pronounced, forgive me for this, lumine depadence, dependence, lumine dependence. And it's involved in responding to daylight and controlling flower time and things like that. But when it's inserted into yeast, it causes the proteins to clump together and causes misfolding of other proteins, just like a preon would. But that's the only plant example I've got for preons. It's probably not good to use that as a reference, or even use it at all, because it's not really going to be that valid. But something interesting. With the animal example, it certainly is much more prevalent in animals, obviously. And one that you may have heard of is mad cow disease, where, again, the proteins clump together and cause neurological disorders in humans. If they eat the infected meat of an individual, or in some cases, there are tribes that used to eat the brains of their ancestors. They can get conditions, again, like mad cow disease. But in humans, we call it Croitsfeld Yakovs disease. And another disease, the one of eating brains called kuru, which you can look up and check out. But they are horrible diseases, because they just lead to a gradual, you know, neurodegeneration, which isn't very nice. So they're the diseases for each one. But yeah, the key points, non-living, non-cellular, very small, very deadly, found in the brain, usually, and disease would be the Croitsfeld Yakovs in humans or mad cow disease. Alright, we're moving on now to viruses and very relevant at the moment, obviously. And this is where it's good to use some drawings and diagrams. In fact, it's good to use drawings and diagrams for all of the pathogens. So at our school, we use a set of many white boards. And if you guys don't or haven't used white boards in your teaching, I found it to be the most useful thing that we've probably ever used in a classroom. So we have a class set in each of our rooms. And whenever we do an activity like looking at structures and functions, every student can get out there, many whiteboard. We just keep them at the front of the class, and we have a set of whiteboard markers they use. So drawing these diagrams and using all the features to label them in class is wonderful. And then you just rub them out at the end of the lesson, and they all go back. So if you do want to look at getting some many whiteboards, I definitely recommend them. So the next size-order pathogen is a virus. And again, this is very relevant at the moment. Now with viruses, there's really lots to know. And they have asked a few questions about viruses in the HSC. So I'll go through it in a bit of detail and try and be as specific as I can about why it's important you pay attention to the way things can be worded. So the first thing is a virus. There are so many different types of viruses. There's viruses that have protein codes. There's ones that have envelopes and non-envelopes. There's ones that are string-like. There's ones that are circular. There's ones that look kind of like little bugs, bacteria, phages. So we have so many different versions of a virus that this, to me, is a great HSC skills question because if you understand what a virus is made of, regardless of how it is presented, it's made of the same basic components. And that's what we'll go through today. So the easiest virus to look at probably would be something like a flu virus from the coronavirus family. And the most common way you'll see it presented is a protein code around the outside with these projecting fibers as well. And so this protein code is, you know, as we said before, just like the pre-hands are made of, it's just made of a bunch of proteins. And that's all it is. That's the outside code. Now the little projecting fibers that come out are used as keys or as mechanisms to get past our cell defenses. So this is where it gets really cool. And there's an awesome documentary. I think it's called the BBC, our secret universe, the hidden life of the cell. And that will be on the Facebook page if you want to check it out. Now these projecting fibers that allow entry into the cell are obviously very useful because our defenses have been developed to detect these things. More importantly on the inside of the virus is the mechanisms it uses to attack. And that is either DNA or RNA. It's very important to remember that it has either because when you're asked about viruses, some viruses use different attack mechanisms. So if it's a DNA virus and you can have double-stranded DNA and you can have single-stranded DNA in a virus. So you could have either. When it gets into your body and into your cells, a DNA virus needs to get the DNA into the nucleus in order to make just like we normally do proteins using the mRNA that it produces. So DNA viruses really need the mechanisms inside our nucleus. Now an RNA virus does not need that. An RNA virus is going to put a string of mRNA into our cells and that RNA is going to be translated once again into a protein. And those proteins will be put together and form the new virus. So inside a virus, you can have DNA or RNA. It can be double-stranded or it can be single-stranded. Just keep in mind that the basic structure is a protein coat with DNA or RNA on the inside. They are the second smallest in terms of pathogens and they use our cells mechanisms in order to make more of themselves. So they have no ability to self-replicate. They're non-living and they are non-cellular. Now one of the coolest things about a virus is that it behaves like it has a purpose. It wants to get inside our cells. And again, I've spoken about this on previous podcasts. A virus is part of the evolutionary cycle of all living things. Without viruses, we don't become more complex. And they evolve with us at the same time. And that creates variation in a population which allows us to survive and reproduce. The other example I spoke about is a bacteria phase. And they do look like little spiders. And these guys don't use a protein coat in the same way. They still have a protein coat around the outside. But they actually inject their DNA or RNA directly into bacteria. So these are phages or bacteria phages. And they kill billions of bacteria every day in the battle for supremacy in viruses and bacteria. It's an ongoing thing. Again, I think the HSC last year did ask a question about a virus entering a cell and you had to analyze what kind of pathogen it was and how it was functioning. So it was quite complex. With the enveloping and non-involoping, that's really about whether or not it has the ability to get past our cell membrane. So this is probably overly complex and not really needed. But the way that a virus can get into our cell is by using the envelope that is around the outside to combine with our cell membrane and then make its way inside the cell and then deposit that DNA or RNA. An example of a plant virus is the lettuce mosaic virus, the lettuce mosaic virus, and an example of a virus that can affect humans is influenza, HIV/AIDS, and of course the ones the kids will refer to the most is coronavirus. Now why not always mention here because it's useful as an example and really good as a skill is Ebola. Ebola is a particular type of virus. It is string-like and it looks very similar to a worm. It's from the Filoviridae genus I think. But it's good because when you look it up, it looks like something that we'll study a bit later a macro parasite. And if you saw a diagram of a labeled Ebola virus, it has the same structure as the protein, coat, and DNA or RNA on the inside that I just spoke about. But it would be an excellent skill to see how students adapt to understanding that a virus, although it looks the same as a worm or a parasite, it might not be because of the structure that it's got. So it's non-cellular but it certainly looks like a cell. So check out the Ebola virus because it is a particular type that might be different to what the kids are used to looking at. All right, moving on now. The next one in size order is the prokaryotes or the bacteria. Now bacteria are into the living pathogens. These are the most simple form of a living thing, pro coming first. And a prokaryote, hopefully as you know by now, has no membrane bound organelles. Now this is the distinguishing factor that differentiates it from the other pathogens that are cellular. So if you understand that it's a prokaryote, it has no membrane bound organelles. It is the only pathogen type that we study that has that particular combination. Now one other main feature is that it usually has a cell wall and usually has a flagellum. I say usually because there are examples of bacteria that do not have a cell wall. So just be careful. Again, the HSC will put things in there to get you to apply your knowledge. So you could show your kids a bacteria that does not have a cell wall. And then they would have to analyze the fact that, oh look, it's a prokaryote, it has no membrane bound organelles. It might have flagella. What is it? Which of the pathogens is it going to be? And because it's a prokaryote, they should hopefully know that it is a bacteria. These are smaller than human cells. And I say that because it has been a question where they get you to analyze the size of a pathogen, these are usually quite small in size, but can range from about 0.5 to 10 micrometers. So really telling you the numbers on the podcast isn't going to be that useful. You should have a table set up with all this information in there to differentiate between the pathogens. So an example of a disease caused by bacteria in plants is blight of beans. I really just like that name so I put it in there. Blight of beans sounds pretty cool. And an example of an animal disease is salmonella. So most kids would have heard of salmonella and you can kind of go into a bit more detail if you'd like about what the disease is and how the bacteria works and what it looks like. But I won't go into that today. But that's it for prokaryotes. All right, moving on now and we're going to go into two cellular pathogens that look very similar but have different features. So the fungi and the proto zones. These can both range in size and sometimes cross over. So just be aware that sometimes there can be smaller or larger versions of this. This is where classifying them may be a bit more difficult. And the HSC might try and give you something with a bit more information to help you classify these. So it's unlikely they'll give you fungi and proto zones together because they are quite similar and can overlap in size. So with the fungi, they have a cell wall. So we've already spoken about bacteria and bacteria have a cell wall as well, usually. So fungi have a cell wall. So it doesn't differentiate them. It's not separately classifying them. The main difference between fungi and bacteria is that fungi are youkaryotes. So I always say to my students, you are a youkaryote. You are complex. So fungi is complex. It is youkaryotic and therefore it has membrane bound organelles. So when you're looking at a labeled diagram of fungi, you should be seeing the organelles particularly like the nucleus or the mitochondria and things like that. Now we studied fungi earlier in the year as well and they can reproduce asexually using spores. So the production of spores is unique to fungi as well. And those spores have again membrane bound organelles in order to produce more copies of the original plant. For the most part, that's about the only thing that separates it from the other pathogens. And this is where again, it can be ambiguous between fungi, protozoans and bacteria at times. So you've got to know the intricacies of each one. With a plant disease, a plant disease caused by fungi is myrtle rust. And myrtle rust is a good one because I bring it up later in the syllabus. It is a condition that affects eucalyptus trees. And that's great because we talk about Australian plants and how it affects them and you can even use examples. So myrtle rust is a good one to use for plant pathogens that are fungi. And for examples of animal diseases, we have athletes foot or tinier. And again, another good one to talk about because you know, you can kind of scare the kids and talk about the fact that you get it in in showers and things like that when you're on camps or whatever. So it's a good idea to get them to bring thongs. So they're the conditions for fungi. All right, moving on to protozoans and protozoans are super weird and kind of cool, but also kind of scary. They are eucaryotic as well. They are complex, but they have no cell wall. So the most common question I have seen in the HSC is comparing protozoans with bacteria. And the reason is they look very similar. And this is where student's ability to perceive and analyze different models is really important. How similar is a protozoan to a bacteria? Well, the main similarity that we find is usually the fact that it just has a flagellum. So it looks like a bacteria because it's got a little tail, but that doesn't mean that it's a bacteria. It's eucaryotic again. So it's complex. It's larger than a bacteria. It is a complex organism that can be from one to 500 micro meters. So I know that personally using some pond water that we've analyzed at school that we've seen some amoeba. And they've been so large that we've seen them actually with our eye. Now this is where it kind of almost breaches into the macro parasites, but they're still considered microscopic. So the main difference is here we have a protozoan that has a cell membrane only, no cell wall cell membrane only. It's eucaryotic, meaning it's complex and has membrane bound organelles. And it usually has a flagellum or a tail. Not always, but it usually has at least drawn in diagrams. Some conditions caused by protozoans. For plant conditions, I found one called a flowem necrosis disease that you can check out, flowem necrosis disease. And that's caused by a parasite called phytomonas, leptovasaurum. Now that sounds a lot like a Harry Potter spell. Okay. And the other disease we can look at in animals is malaria. And those of you who have used the past HSC would know that malaria used to be in there in quite a bit of detail. So there's lots of information out there about malaria. And I always give my kids this quicker run down of how malaria kind of works. The protozoan that causes malaria has a very intricate life cycle where it can produce sexually, it can reproduce asexually. And it goes from a mosquito into our blood cells, and it just keeps going in this cycle. So the malaria life cycle is actually quite complicated, but a really good example to show a flow chart that might require some skills to analyze. So a good example there in malaria. The final one is macroparasites. And macroparasites are those large enough to be observed with the human eye. And we have two main types. We have endoparasites, they live inside the body, and we have ectoparasites, and they live outside the body. So endoparasites might be things like worms and ectoparasites might be things like ticks. They are complex and they are multicellular. Now that brings me to the next classification with multicellular organisms. This is where we can reintroduce fungi, because fungi can be both single-celled and multicelled. So this is where the distinguishing factors I was talking about before can create confusion among students. When you describe fungi and you show diagrams of fungi, you look at a single cell and you analyze the fact that it's eukaryotic and has a cell wall. But sometimes it is combined to form a multicelled organism, like mushrooms and things like that. But mainly we talk about disease causing types. But it can be a multicelled organism. So just be aware of that that the definition of multicelled can cross over here with macro parasites and fungi. Now a condition that can be caused in plants could be root knot, and that's caused by a worm or a nematode. And in humans, we have a condition called elephant tyassus. And if you want to look that up, it's pretty full on for the kids to see, but I find that it helps them remember it. And that's where a parasitic worm causes really significant swelling of the body part that it gets infected in. So if you look it up, that's elephant tyassus, like spelt like elephant, but then IASIS. It is a significant enlargement of usually the legs, but again, it helps students to remember that this parasite, macro parasite can cause a significant condition, elephant tyassus, and that causes swelling and enlargement of particular limbs. All right, that brings us to the end of the classification of different pathogens. Now, as I said before, it's really a good idea to get all of these different things I've spoken about into a table. So is it living? Is it cellular? How big is it? Does it have a cell wall? Does it have a cell membrane? Is it prokaryotic? Is it eukaryotic? Is it multicelled? Is it single-celled? What diseases do they cause in plants and in animals? And obviously, all those things together will give you a really good picture of everything that a pathogen, every single way a pathogen can be classified. Now, once you've finished all those things, it's a really good idea to use something called a dichotomous key. And a dichotomous key is where you're separating each of the levels of your key by a particular factor. So you might start with the heading pathogens, for instance. And then you put a little line and then you put living or non-living. And the line separates into two things. And the living and non-living sides can then maybe go into cellular and non-cellular. And then they can look at living inside the body, outside the body. They could be microscopic, macroscopic, proteins, protein, prokaryotic, eukaryotic, you get the idea. They want to make a classification chart or a key that they can then see how each one can be classified. And when you do this with the students, they can each come up with their own key. And then you can look at how they're classified based on those keys. So it's a really good way to teach classification. And it's something that we used to do in a lot more detail in previous HSCs. The last thing that you could probably look at would be whether or not things can be observed with different microscopes. So viruses and prions are things that are going to need an electron microscope. And when we get into bacteria, protozoans, and fungi, we need light microscopes. And then we have the macroparasites that can be seen with the eye. And obviously can be analyzed under each of the microscopes. Apart from that, there are a number of HSC questions you can check out on this. And each of the HSC questions, in fact, I will upload a copy of those HSC questions to the Facebook page for you to check out. So please come on over to the Facebook page to see those HSC questions. Apart from that, guys, I hope you've enjoyed today's episode. And I will see next time on the podcast. Have a good day. Bye. And make sure you check out stemreactor.com.au. If you want to get biotechnology at your school, and it's really useful if you do like extension science or anything like that. So make sure you check out stemreactor.com.au. Thanks. Bye.