Module 5: Mechanism of Reproduction

Hey guys and welcome to the HSC Biology Podcast. My name is Mr. Kalehler and I'm going to be running you through the core concepts in the HSC Biology syllabus. So, stay tuned and enjoy! Thanks for that Rick. Well, we might as well get started, hey? Let's get into it. Module number five, Heredity is where we begin. And it's always important to look at that inquiry question before each topic. So, this one is "How does reproduction ensure the continuity of a species?" And you can think about it like every point underneath that I'm going to go through, answers that question. So, this certainly could be an extended response or a nine mark question in the exam. That's a good way to think about the inquiry questions. Could you put together a nine mark answer? And I guess, as I just said before, the key points I'm about to talk about are the ways in which you would answer that question. So, underneath the inquiry question are the key points? And the first key point is explaining mechanisms of reproduction that ensure the continuity of a species by analyzing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to animals, advantages and of external and internal fertilization, plants, asexual and sexual reproduction, fungi, budding and spores, bacteria, binary fission, and protests, binary fission, and budding as well. So, let me look at the key points for the syllabus. It's really important to take into account the way in which they have used plurals throughout, because you often will get a question in the exam that will have an S at the end or asks for examples. And that's where it's important to make sure that you are giving or remembering examples when they ask you to. So, the first one says explain the mechanisms. I guess there's your first dot point to look at, and then it goes on and talks about asexual methods and methods of reproduction in a variety of organisms. So, you can see in that first dot point there is a lot of, I guess, specific content that is to do with more than one individual or animal. So, we're going to break the key points down there and have a look at what they mean. And I guess we can start at what the mechanisms are for reproduction, so sexual and asexual reproduction. So, sexual reproduction, great place to start. Probably shouldn't have put that in there, but let's go through the key concepts there, which pretty much are the fact that two individuals are involved, and it is the combination of gametes. Those are the sex cells for the individual animals. The combination of those gametes will create usually a unique individual, which will increase the chance of survival. So, we will be talking about those gametes a bit later when we go through myosis, but for now just remember the fact that sexual reproduction usually involves two individuals, and it is the combination of gametes. All right, let's talk about asexual reproduction now. I'll tell you why. Cause I'm all alone, there's no one here beside me. Yes, thank you for that donkey. We are with asexual reproduction. There is only one organism that's going to be involved, and they are going to be genetically identical to their parent, because the DNA they receive will be a copy of the parent DNA. And some examples of that are budding in binary vision that we are going to go through now. Now there is one other mechanism I suppose we could talk about here, which is Parthenogenesis, which is pretty cool. It's where an organism that doesn't usually give birth asexually is able to produce an offspring without the use of a mate. And so there are random examples in the animal kingdom where this can occur, and one that was more recent was a stingray, I believe, that gave birth in a tank full of only female stingrays, and it managed to give birth. So it can happen, but it is pretty rare. Obviously another sort of facet evolution, which increases the chance of survival. So a pretty cool one there. All right, now we are going to take a look at the advantages and disadvantages of sexual and asexual reproduction. I will survive over as long as I know how clever I know I feel like. Yes, I think that's a good place to start, Gloria, with the advantages of sexual reproduction, they do include the higher likelihood of survival for the offspring. And that is because they are being nurtured in a womb, they are being carried around and being cared for and supported with hormones and nutrition from the parent. So another advantage of sexual reproduction would be increasing variation, which is due to the combination of the gametes and crossing over, which we learn about a bit later. And also the fact that they are protected from predators. So I usually like to give at least three examples for each of the key points, that way you kind of cover your tracks if you're asked to give examples. Some of the disadvantages of sexual reproduction include the greater time and energy expenditure. So you're kind of going to go out there and find a mate or engage in courtship. Sometimes it's dangerous and so there can be issues with how to sort of achieve the goal. And obviously it requires two individuals, which compared to asexual reproduction is a disadvantage and they have to find each other as well. One of the advantages of asexual reproduction is that there is no need to find a mate, so they can just do it whenever population can increase rapidly, less time energy expenditure and there is a quick production time. Some of the disadvantages include of asexual reproduction include the fact that there is no variation. This is probably a really important point that will ask you to distinguish between, as you can see them doing potential crossover questions here with myosis and crossing over pun intended. And there are susceptibility to changes as well. So if there is a disease that affects the population, their DNA isn't varied enough for them to survive. So the pretty big issue considering evolution is usually benefited by these small changes that in a species that allow species to survive over time due to environmental changes. But the individuals that do produce asexually do have other mechanisms to help survive. For example, bacteria have a pretty high mutation rate, that helps them to change rapidly when there are environmental pressures as most of their DNA is coding DNA. Alright, so that brings us to the end of the advantages and disadvantages. And it's a good idea to kind of tabulate these key factors. So put them into a table if you can. And a good way to think about the table is each level should be able to be distinguishably different between them. So for instance, the number of organisms involved, so sexual to asexual one, the cell division, so how the cells are dividing. So sexually you need gametes involved and in asexually you don't, you can split by binary fission or a couple of other methods and we'll talk about in a minute. The different types of reproduction, the variation which is involved, the unit of reproduction, the time taken and the number of offspring as well. So all good points to consider when you are asked to potentially tabulate the difference between them. Alright, let's talk about the advantages and disadvantages of internal and external fertilization. So internal fertilization is fertilization that occurs inside the organism, which is conceiving the child or baby. And external fertilization is where the gametes meet outside the bodies. And they're usually in a, here's everybody's favorite word, moist environment, where the gametes are able to successfully combine and exchange genetic material. So with internal fertilization, there is a higher success rate because there is not that environmental pressure of stuff going everywhere. There's less danger involved as well if the individuals are able to fertilize successfully. It's safer for the offspring and there's fewer eggs that are needed, which is pretty important in conserving energy for all organisms. The disadvantages are that most internally producing organisms produce less offspring. So less viable offspring means that there is a less likely chance of the species surviving. And there's also actually less variation compared to external fertilization. So with less variation, there's still heaps of variation, there's crossing over from the gametes, there is the random mix of the sperm and egg cell. But when you talk about external fertilization, you've got to remember there's many more eggs than there are in internal fertilization. And so for that reason, there is less variation, but they are still very varied. With external fertilization, as I said before, this occurs outside the body usually in a wet environment. And a good example of this would be something like fish, frogs, coral, those sort of things produce offspring externally. And the advantages are that they produce more gametes, so that creates more variation. They are suited for an aquatic environment, so the gametes work well in an aquatic environment. There is less time and energy expended from the parents, so the parents are able to exchange material externally and not spend too much time waiting to see what happens. They kind of just, you know, go. Thanks for that, Wem. And then there is a wide dispersal offspring which increases survival rates. So because they make so many eggs and so many sperm and it just sort of, if you think about it in the ocean, it kind of goes everywhere. This isn't sounding too good. It obviously creates a large sort of area in which offspring can move to and hopefully survive in for the species. With the disadvantages, because there are two organisms required, it's still a form of sexual reproduction. The chances of the gametes meeting is less because if you think about it, they could be in different areas. There could be sort of a current that is moving things in the wrong direction, get their timing off. There are predators involved quite often as well. These are usually culmination events where there are multiple different animals that are in the area trying to take advantage of the large amount of food that is available. And there is no parental care, so that means again, the less likely offspring to survive. As I said before, we have the frogs, coral, fish that all produce externally and internally producing organisms include mammals and birds. Alright, that brings us to the end of the animal section. Now we're going to look at the ways in which plants can reproduce and they can reproduce both sexually and asexually. So with a plant, usually they're reproducing organisms of flower, or at least it's an easy way to understand their different organs. So with the female parts of the flower, it is hard to describe, but if you think about it in a very middle sort of sphere or circle, the ovary. And then inside that ovary is ovules, these are the eggs. And then on top of that is kind of like a, you can think of it like a long tube with a cap on the end. It's a good way to think about kind of like a pistol or a gun. And that's another name for it, the female parts is the pistol. And if we look at that part, you have the ovary down the bottom of the circle. And then the tube going up is the style, and then sitting on top is the stigma. And the stigma is very important. That's where the pollen has to land. So that's the female part of the flower. And there are both male and female parts on flowers. Some flowers only have one, some flowers only have the other, and some have both. Even if they have both some may open at different times, as in the different parts may sort of start at different times. So pollen may be produced at a different time to the stigma being ready to receive the pollen. And that is to minimize the idea of this variation problem, which can occur if they are self fertilizing. So self fertilization still does create unique offspring because it is a combination of the gametes of the plant or the sperm and the egg. But in this case, it's the pollen and the ovules. They still have undergone crossing over before meetings. So they're going to get a varied offspring, but obviously you want to increase variation to increase your chance of survival. Now the male part of the flower, you can think about it like long stringy bits that kind of hang off the side of the female part of the flower down at the ovary. And the filament is a long stringy filament. And on top of it, it's a little pad. And that pad is an anther. And that is where the pollen is produced. And the pollen can be lots of different types. But it's easy to think about it as like a light, dusty, really small fine grain that can easily be moved around. And the idea is for the plant to reproduce sexually, the pollen has to land on a stigma somewhere. And that pollen will then grow a tubule down into the ovary and deposit the DNA into the ovule. So that's the process of a plant reproducing sexually. And it is the combination of gametes. And in this case, they only need one individual. So there was a question in the HSC not long ago in one of the trial papers it might have been that asked you to sort of analyze whether or not it was sexual or asexual reproduction. It's still sexual reproduction because it is the combination of gametes. But it's certainly a blurred line because there is only one individual involved. But for the most part, plants want to reproduce with different plants. That is pollen landing on the stigma of a different flower, the same species. And as I said before, the pollen grows down deposits the DNA. And that swells up into a fruit. That fruit, not always a fruit, it can be multiple things, but it's always easier for me to think about it like a fruit. We'll swell up and inside that fruit will be seeds. And if an animal eats the fruit and then deposits the seeds somewhere else, that hopefully will create a tree which or plant which can survive and grow and be varied once again. And that is the basic structure of the flower. So with the ways in which fertilization can occur, pollen can be moved around by either bird or wind or insects or animals. And the idea is once again the overall success of the species. And that will occur if the pollen is able to land on a stigma somewhere and hopefully fertilize a plant. So that is sexual reproduction in plants. Let's talk about asexual reproduction in plants now. And with plants reproducing asexually they have a number of different mechanisms. So a good example is a modified stem called a runner. And these are ones that you probably have seen at the beach where you see grass that is sort of laid in these long strings across the beach. And every so once in a while there is a small tuft of grass attached to that long string. And that's the way in which it's growing across from place to place. And if one stem is to be separated, those little buds that are growing or those little sections that are growing along the way basically have the ability to grow into a new plant. So this creates an increased chance of survival and helps out with evolution. So that's a runner. And they are above ground. And a good example of that is spin effects grass. Another example that you can look at is where the root goes underground. So very very similar process. And rhizomes like ginger are a good example. They grow underground and they put up a bud or a new plant. So that continues along and they keep putting up new plants. Once again, if there is a disconnection from the original parent, they're able to continue growing into a new plant. We're the modified roots. We have a great example in potatoes. So potatoes. If you have ever looked in your pantry at home, those of you who cook, you may have noticed that the potatoes are starting to grow. They have little roots coming out of them. And that is because they have the ability to grow into a new plant as well. There is enough information and energy in them to begin to grow. They are kind of like giant seeds. You can almost think of them. But they do contain the full set of genetic information to grow into a new plant. And those potatoes are a form of chuba, is their name. There are other examples too, like upper mixes, which is a bit of a complicated one. Similar to pathogenesis or different type, I believe, of pathogenesis, where the plant is able to basically start the production of a new plant without the need for a seed. Spores as well as another complex one, where ferns are able to launch their haploid spores into the air, which hopefully land on the ground. They then go through a pretty complex process of joining together and then somehow reproducing sexually sort of later in their evolution or in their cycle. But again, it's quite complex the production of spores into a new fern. But again, a very successful way for a plant not having to worry about the sexual reproduction. All right, let's move on to another organism that can reproduce asexually, and that is fungi. And this might be a good time for me to tell my fungi jokes. Why did the mushroom go to the party? Because he was a fungi. I am so sorry. There's a second part of the joke as well, which I'll tell a bit later. All right, back to fungi. So with fungi, you have to keep in mind that they are a eukaryotic organism with the cell wall, which will be important to remember later when we do the stuff on infectious disease. But they have a pretty cool ability where they can reproduce using their haploid cells and they can all join together. So what they do is they use spores similar to the ferns I spoke about before and they launch them to different parts around the main body. Now the main body of the fungi is called the mycelium. And you can imagine that like the central nervous system or the brain of the fungi. And these spores land in lots of different locations around the mycelium and they start to grow these string-like fibers called hyphae. And they all connect back to this mycelium and they become part of that mycelium. So it's a really ingenious way to spread out over a large area and then use those hyphae to grow and connect back. And they are pretty cool, these little launches if you do want to check them out on YouTube. They can reproduce in a number of different ways as well. So budding, budding is a pretty simple one where an organism basically makes a little version of itself and that little version then drops off or stays connected and then keeps growing into a new organism. So it's a little bud of bud version and there are a few animals that can do it as well like hydros which is an organism that lives in the ocean. And they basically grow a tiny little version of themselves which sort of pops off and then is able to grow and function as a new organism. So again, another form of asexual reproduction. One other one we could talk about as well is fragmentation. And fragmentation is where a bit of the organism will break off and regrow into a new organism. So there is enough information in the part that is chopped off for it to grow into a new organism. And a good example apart from fungi planet area which is a worm that you can look at that are very simple. They have basically an eye that tells them to go away from near lights and into the darkness. And again, they are able to reproduce if they are separated or cut into pieces. Their fragments will grow into new species which is pretty cool. Alright, so that is asexual methods of reproduction in fungi. Alright, let's talk about bacteria now and bacteria also reproduce asexually. They are simple organisms. They are prokaryotic which means they have no membrane about organelles. They undergo a process called binary fission F I W S I O N and this process involves literally splitting pretty much down the middle and creating an identical copy. Now this process is pretty useful for scientists to exploit in making things like insulin via gene cloning and we do talk about that a bit later as well. So that is binary fission in bacteria. Alright, and finally let's talk about protests. Now these are pretty weird creatures. Protests are eukaryotic in nature. They look very similar to bacteria because they are unicellular. There is only one of them but they don't really have a cell wall but they do have those membrane bound organelles. And that is important to remember once again when we get down to the infectious disease topic because protozoans fit into the category of protests so you can see a crossover question potentially here. Now those protozoans or in this case we will just call them protests have the ability to use binary fission as well but they undergo the process of mitosis. So it's a bit different in bacteria. It doesn't undergo the complete PMAT prophase, metaphase, tila phase, segment that again we are going to go through a bit later. But the binary fission in the protests is a little bit more complex because there are organelles being replicated as well as the DNA and those are membrane bound organelles as well. As it divides it's going to become two new individuals and those individuals are going to be genetically identical. So once again decreasing the variability within a species but a very successful way of making a new copy. One main difference between them apart from the fact that there are eukaryotes and they use that mitosis process is that their division isn't always regular. In other words they can divide in different parts and make different shapes or they are asymmetrical sometimes you might hear. So a good example of that is plasmodium which as I said before fits into the category of an infectious pathogen and those pathogens have an amazing ability actually to do multiple things they can not only produce asexually via binary fission and that mitosis phase. They actually have the ability to reproduce sexually as well. So once again they can increase their variability and they actually do this in their entire life cycle between mosquitoes and humans. So malaria is the disease that is caused by plasmodium and that life cycle is very complex which involves them reproducing as I said asexually and sexually inside the human host and inside the mosquito they can reproduce sexually. So very complex and pretty unique creatures. All right well that brings us to the end of sort of dot point number one which is quite a large one we'll probably get a few more into the next podcast but I hope you guys enjoyed that for today and stay tuned for the next episode. See you later.