The Science of Everything Podcast - Episode 99: Plant Reproduction and Fruit

Episode Date: January 6, 2020

A discussion of the method of reproduction of flowering plants, including an overview of the structure and function of the different components of the flower, pollination, double fertilisation, and seed formation, dispersal, and germination. I also discuss the different types of fruit and vegetables and how the different components of the plant relate to the parts that we consume. I conclude with a brief overview of non-edible plant products, including fibres, resin, and sap. Recommended prerequisite is Episode 97: Plant Structure and Function.

You're listening to The Science of Everything podcast episode 99, plant reproduction and fruit. I'm your host, James Fodal. So, first of all, I must apologize to all of my listeners out there for not uploading an episode in such a long time. I had anticipated that I would have more time over the course of 2018 to produce some episodes. But, alas, you know, the best laid plans of mice and men, as they say, However, there are exciting new developments for the podcast in the works, and coming up soon, we will have episode 100, which is going to be a special 100th episode of the podcast. In that show, I'm going to talk more about the future of the podcast and how I'm going to make some changes so that I can get more content out to you guys. So look forward to that.

That will be coming out probably within a week or two. I'm going to try to stick to a more regular schedule for 2020. So, as I said, stay tuned to next week or next time for more information about that. But this episode, we're going to do the follow-up to the episode 97, plant structure and function. And so I recommend listening to that first, as this content will make more sense. In this show, then, we're going to talk about the reproduction systems of plants, focusing on flowering plants or angiosperms. I'm going to talk about the alteration of generations,

the reproductive anatomy of plants focusing on the flower, of course, and I'll talk about pollination, seeds, fruits, and seed dispersal and the development of new plant organisms. And then we'll finish off with a bit of a discussion about different types of fruit and how the reproductive components and functions of fruit relate to the culinary fruits and different types of fruits and also vegetables that we consume. and I'll also talk a little bit about a few other types of products that are derived from plants.

So, that's enough of the introduction. Let's get started by talking about a very important concept, which is the alteration of generations. So this is a critical concept to understand for understanding, well, not just plant reproduction, actually, but the reproduction of many different types of organisms in different forms of life. So the concept of the alteration of generations is a little bit hard to understand because it doesn't occur in humans, or indeed it doesn't occur in any mammals. And so it's not something that we're familiar with.

So in humans, you may recall, as I said, indeed in other mammals as well, the life cycle consists of a multicellular organism, an adult or even a child. The mature multicellular organism, an adult, produces gametes, which are the sex cells. So these are sperm cells for males and eggs for females. And these are called gametes because they only have a single copy. of the genetic material of that organism. So that's often written, if you've seen it as a lowercase n. A gamete is also called a haploid cell, because it only has, as I said before, one copy of the genetic material.

So that means a single copy of each of the 23 chromosomes. Now, most of the cells in our bodies contain two copies of each chromosome. But the point is that gametes are different because they only have one copy of each. and in humans and other mammals, the only gamete cells are sperm cells in males and eggs if they're females. They're produced and stored in special reproductive tissues. And they only exist in single cellular form. During reproduction, the egg and the sperm come together and fertilization occurs, producing the zygote, which is a diploid cell again, because by bringing together two cells each of which has a single copy of the genetic material,

and combining them into a new cell which forms then a single cell that has, again, two copies of all the genetic material. So that's how it works in mammals, including humans. In flowering plants, however, it's different because there are structures that contain gametes that are multicellular. So that's the key concept to understand behind the idea of alteration of generation, that there are multicellular structures composed of gametes. So again, these don't exist in humans or mammals, but they do exist in any other types of organisms, including flowering plants. So the idea of the alternation part of the name is that over the life cycle of, well, actually multiple organisms of a given species, there's an alternation occurring between the multicellular gametophyte, which is a haploid organism,

and the multicellular sporophyte, which is an organism containing diploid cells, each of which has two copies of all the chromosomes. So that's often written as a 2 and a lowercase end, so N and 2N, N for haploid and 2N for diploid. That's the basic idea of alternation of generations, and in some cases, the haploid gamutophytes can exist as independent organisms during part of their life cycle, and then at some point there'll be a combination of gametes from, effectively, male and female organisms, which then form the diploid sparatophyte,

and then that exists for a certain period of time as part of its life cycle, and then it produces what are called spores, which then give rise to the new gamutophytes, and so the cycle continues. So it alternates from the sporophyte to the gametophyte, from the two-end diploid to the one-end haploid, and so forth. So this concept is important to understanding the reproductive anatomy of angiosperm,

so that's flowering plants, which is what we're now going to discuss. So to do so, we're going to focus on the flower, and I'm going to talk about just kind of a generic simplified flower rather than any particular species because there's a lot of variation in the specifics, but the general story is more or less the same. So what's called a perfect flower has two main types of structures called starmons and carpels. Now, just to avoid confusion, sometimes you'll see the word pistol written in a diagram or wherever. Technically, pistols consist of one or more carpels, and I'm just going to talk about carpels from here on in. But some plants have, you know, basically multiple carpels and then taken together,

those are called pistols. But I'm not going to work too much about that. I don't want to complicate the story more than it already is. So let's just talk about the starmen and carples. So a perfect flower has both of these. So what do these structures look like? Well, basically, if you picture a flower, you know, you've got the petals and there's kind of the leave bits at the bottom that hold everything together. So those leave bits at the bottom are called sepals that just like modified leaves. They just sort of give structure and protect everything. Okay. And then there's the petals. They're also modified leaves. They're often, but not always brightly colored.

Their purpose is to attract pollinators, which we'll talk about later. But, okay, so we've got the petals, we've got the sepals, and of course there's the stalk. But the key reproductive components of the flower are, as I said, the starman and carpal. So let's talk about those. The starmen, and there's usually multiple of these, basically they look like buds on a wire. So the wire bit is called the filament and the sort of bud bit or the protuberance at the end is called the anther.

And so these kind of stick out from the center of the flower. And they look a bit like whiskers, except they've got the anther on the end. So it's a little bit like a whisker with like a marshmallow on the end, if you want to think of it that way. Hopefully you can visualize what I'm talking about because you've seen a flower before.

Again, not all flowers have these, but these are the starmen. So the starment are the male reproductive organs or components of a flower. How that works, we'll come back to, but just remember the starmen, which is like your marshmallow on a whisker, that's the male bit. The female bit, that those are the carpels, these consist of the stigma, which is like a kind of a platform on top, the style, which is like a kind of a stalk structure holding it up, and then a bulb at the base, which is the ovary of the flower. So generally the carpal is going to be kind of more at the center of the flower, and it consists of like a bowl, which is the over either style holding up the stigma, which is a bit like a platform, and it just kind of stands up there. And then surrounding it, kind of branching and poking out are the starmins.

So, as I said, a perfect flower has both starmins and carpels, and so it can be described as bisexual or hermaphroditic. But some types of flowers have only starmins, and so they're male, some have only carpels. carpals are only female, and some have both. So they're bisexual. Terms Staminate is sometimes used, which means it only has functional estarmines, and so it's a male. Carpolate has only function in carpals, and so it's a female flower. Yet another term, just to throw in a bit more jargon into the mix, is monoecious and dioecious. So humans are diacious, meaning that male and female reproductive organs are only found on separate organisms. so there's the male and the female organisms

and they're separate from each other. Monetious is the term used to describe species which have staminate and carpellate flowers on the same plant. And so monoecious species can self-fertilize for flowers on the same plant, whereas dioecious species can't. They need two different plants

in order for fertilization to occur. So the purpose of these reproductive structures, of the starmons and the carpels, is to produce spores. A spore is just a fairly generic term for, it's like a unit of sexual or asexual, but in this case it's a unit of sexual reproduction. And it's generally adapted for dispersal and for survival over periods of time. So think of a seed. A seed is a good example of a spore, although that's only one type of spore. So just to understand the basic idea, the purpose of the reproductive components or organs of the flower, starmans and carpals, is to produce spores.

Now, there's male spores, and there's female spores. Of course, the male spores are produced in the starmen and the females in the carpels. So let's talk a bit about that. Because of the difference between the male and female reproductive units, the male reproductive units are called microspores. They're smaller, and megaspores are the female reproductive units. So microspores are the ones produced in the starmen, specifically in the anther. Remember, that's like the marshmallow bit at the end of the filament.

And microspores go on to form a single pollen grain. And a pollen grain consists of two important types of cells in the microspore forming the pollen. So there's the vegetative cell and the generative cell. So the vegetative cell is kind of like a supportive cell. The generative cell, that's the haploid cell. That actually splits and forms two sperm cells. And we'll come back to what those mean in a moment. But a pollen grain is produced from the microspore, and that is produced by the anther component of the starment, so that's the male reproductive component.

Now, the megaspore is produced inside the ovary, or specifically an ovule, which is like a little component or part of the compartment within the ovary. Like the ovary is composed of multiple ovules, and in each of those ovules will be produced megaspores. and that gradually develops inside the ovule into the embryosac, which is the female gametophyte. So that's the female reproductive spore. So in flowering plants, the embryo sac consists of seven cells in eight nuclei, and there's two key important cells that we need to understand in the embryo sac there. One of the cells is called the egg cell. That's the actual haploid cell component, and there's another cell called the central cell.

That's actually a diploid cell, so it's got two copies of the geneticature, but that's not super important. So we'll come back to these two cells because they do different things. There's also two... All right, so at this point, I've described the difference between the starmins and the carpels, starments being the male reproductive components of a flower, carpels being the female reproductive components. Flowers can have one or both of these, and the purpose of the starmen is to produce microspores, which turn into pollen grains.

Pollen grain consists of the vegetative cells, which are support cells, and also two sperm cells. And I'll explain why there are two in a moment. The carpels, which is the female component, consists of the platform, the stigma, and then the style and the ovary. The ovary has multiple ovules in it.

Each of the ovules is producing megaspores, which turns into the female gamutified, consisting of the embryosac and the egg inside that. So how then are the sperm cells brought into contact with the egg cell, which is, of course, fertilization. That has to occur for the new generation to be brought about, you know, for reproduction to actually occur. So how does that actually happen? In mammals, the egg cell and sperm cells are brought in direct contact into each other through the process of sexual intercourse and then the sperm cells migrating

up the fallopian tubes and basically coming into direct contact with the egg cell or with one egg cell. That doesn't happen in plant cells, obviously because plants are not motile, so they can't kind of move to each other. So how does this work? Well, the key thing that has to happen is for fertilization to occur is that at least one pollen grain must find its way onto the stigma of the same species of plant, and this is called pollination. So pollination is the process in which a mature pollen grain goes from being on the anther, which is where it was produced, and through whatever means, lands on the stigma, which is like the top platform bit of the carpal of a flower of the same species.

Now remember, some plants have perfect flowers, which means that they have both starmins and carols, and they can self-fertilize, or at least potentially, I should say, they can self-fertilize, because in some species there's physical or other mechanisms to prevent self-fertilization, but at least some perfect flowers are able to self-fertilize,

which means that the pollen grains produced and the starmen can just directly fall onto the stigma of the carpels of the same flower, and that's obviously very simple, because they're literally physically right next to each other or very close to each other. But in many species, that doesn't happen, either because there are mechanisms to prevent self-fertilization or self-pollination, or because the species doesn't have perfect flowers. It's a unisexual flower, which is either Starmin-8, so only Starmin-8, or Carpull-A-only carpals. In either of those cases, what's going to be necessary is for pollens produced in the

Starmine of one flower to move to the stigma of another flower, possibly a different flower on the same plant, or indeed a flower on a different plant entirely. Again, that depends on the species. So how does that happen? How does it get there? Well, there's many ways that pollination can occur. Many plants rely solely on wind, which, because pollen grains are small, they'll be picked up in the wind and blown around. But many other plants also take advantage of organisms, like insects and birds. So the basic idea is that the pollen grain has special structures on the surface so that it will adhere to different parts of the body surface of the vector organism, insect or a bird, including the face, legs, mouth parts, hair, feathers, or wherever else,

depending on the animal in question. And then the pollen grain will move with the organism from one flower to another, and some of them detach, and then find themselves on the stigma of a flower of the same species. Obviously, this is a very messy process, because whether you're carried by the wind or a bee or a bird or whatever else, most of the pollen grains are going to be spread hither and yon all over the place, falling on the ground, blowing into water, carried off by the insect back to its hive or whatever else, even if they do get to another flower, it may be the wrong species, or it may just not reach the stigma. So there's going to be a low hit rate.

But pollen grains are smaller, fairly easy to produce, and so that's why plants produce a lot of them, and at least some of them make it onto the stigma of a plant of the same species. And when that happens, pollination has occurred, which then allows for fertilization to occur. So after a pollen grain grain falls on the stigma, a pollen tube grows down the style. Remember the style is like the stalk bit holding up the stigma and connecting it to the ovary. So a pollen tube grows down the style and eventually reaches the ovary and discharges the two sperm that were carried by the pollen into the embryo sac of the ovule. So they've literally moved down the pollen tube, the sperm cells move down the pollen tube,

and are carried to the mature female gametophile, which is sitting in the ovule. So that's somewhat like how fertilization occurs in mammals. One of the big differences being that in mammals, nothing has to grow, the cells just move to each other. But the overall idea is kind of similar. Now, one thing you might have been wondering is if many plants rely on insects or birds or other organisms as pollen vectors, why would these organisms bother to go from one flower to another and spread the pollen? There has to be something in it for them. And the answer is there is. This is an example of mutualism, where different organisms each produce something or engage in some behavior that's beneficial for the other.

So what flowers do is they provide two different things. They provide nectar, which is a good source of energy. Basically, it's just like sugars. And they also provide pollen, which is a source of protein. So there's protein. in the pollen grains. Bees will be interested in both of those as sources of nutrients, and so they'll travel from flower-at-flower connecting pollen and nectar, and depositing pollen grains as they do so onto other flowers, thereby pollinating them. So the flowers have to provide that source of energy to attract the insects. They also have to show the insects, or birds or whatever, where they are, and that's largely what the petals are for, the purpose of the bright coloration and the fancy patterns.

is so that they're easy to spot, which helps the insects and other pollinating organisms to find them. Obviously, if they can't find you, they're not going to pollinate you, and you won't reproduce, and you die off. So it's in the flower's interest to produce the nice colours and patterns, also smells, which can help attract organisms, and the nutrients that attracts the pollinators. And it's in the interest of the pollinator to travel from flower to flower, because they've got these great nutrients that are available there. So this is an example of mutualism. It's a mutually beneficial arrangement. So, coming back to the fertilization process, however,

I mentioned that the mature pollen grain contains two sperm cells, which is different to humans, where the sperm cells are just separate from each other, and that both of these sperm cells need to travel down the tube, down the stigma to the ovule, and fertilize at the same time, or more or less the same time. And this is called double fertilization. Now, this is necessary because what has...

happens is that there are two cells that need to be fertilized. The egg cell, which I mentioned, that's the haploid cell. That's what will actually form the new organism. And then the central cell, which I mentioned before, it's actually the largest and kind of most important, in some sense, cell in the mature female gametophy. Remember I said there's only seven cells there, so the central cell is one of those. It's actually already a diploid cell, so it becomes a triploid cell, meaning that it's got two copies of the genome. It's fertilized by one of the sperm cells, and so it picks up a third copy.

It then undergoes cell division, so it breaks up further. But once this central cell is fertilized, it becomes what's called the endosperm. And that's basically a source of nutrition and energy that will go into the seed and provide a source of nutrients for the plant when it's going to grow later on. So the purpose of double fertilization,

ensuring that both are fertilized and the fact that the whole process will stop if only one of them is fertilized ensures that there's no wastage because if say only the zygote sorry if only the egg cell is fertilized to produce the zygote well that's great the zygote can develop but there's no nutrients for it

and it won't be able to produce a proper seed and therefore it's a waste of time or vice versa if you fertilize the central cell to form the endosperm but then the egg cell doesn't get fertilized well you'll have the energy the nutrition but nothing to actually, nothing that's actually going to use that.

And so, again, it's a waste. So double fertilization, having two sperm cells that fertilized together is a kind of insurance policy to make sure that there's no wastage of resources. Okay, so we've now explained the basic process by which the pollen, grain, and the female grammatophyte are produced and how fertilization occurs after pollination.

Now we need to explain how seeds fit into this. I've mentioned a seed, but what is the seed, and what does it do? We all know what a seed is, right? It's this little hard thing that you plant in the soil, and if you water it and give it sun, grows into a new plant. And of course, that's correct. What we've been describing, this process of production of the gametes and pollination leading to fertilization, this is all how seeds are formed. So what happens when the following double fertilization, the zygote is formed and the endosperm is formed, and they begin to divide up to a certain point. like it becomes an embryo, is it undergoes cell division, and the endosperm grows and acquires nutrients.

But after a certain point, that growth stops. So the embryo ends up surrounded by the nutritive endosperm, at least in most types of flowers. But at some point the embryo stops growing and dehydrates, so it loses much of its water, and it enters a period of dormancy. So it then becomes surrounded by a dry seed coat, which surrounds everything, the embryo and the endosperm. protects the embryo and stops it from being hydrated before it's ready. Before this process of, before dormancy occurs, the zygo usually divides, as I said, it forms a plant embryo, and the plant embryo usually has three main components. So basically there are seed leaves, a shoot apex, and a root apex. So there's the merri stems, the cells ready to form seeds, to form a shoot,

and to form roots. And that's really all it needs. Once it's got those, and it's got the nutritive endosperm, it's ready to stop, dehydrate, and enter dormancy. And once it's got that and the dry seed coatings around it, it's a mature seed. It's ready to go. So that's what the seed is. It's like it's literally a little plant that's got all the key components that it needs. It's got nutrients to get it started, and it's got the protective covering, and it's good to go. And seeds can last a very long time. I think the record is 2,000 years old. Seeds were excavated, and I don't remember where exactly, archaeological sites and have been grown. successfully that are thousands of years old, and that can probably last longer than that.

That's just the longest we know of. So, again, there's nothing like this in mammals. You can't have like a baby that grows into an embryo and then becomes dormant for hundreds of years. It doesn't work like that. So that's a big difference, obviously, between plant and mammal reproduction. What happens to the seed? So this has all been happening inside the plant ovary, right? Remember that the female comedified that was formed from the megaspore in one of the ovules in the ovary, which is part of the carpal in the flour, and so all this happens in there as well. So what then happens to the seed, how does it get out of the ovary and then go and form its own plant? Well, usually after fertilization or after a particular season in the year,

that the flower structure will degenerate because it's been fertilized. It doesn't need the petals and everything else anymore, and the fertilized eggs grow into seeds, and there might be just one seed or multiple seeds on a flower depending on the plant. There's a lot of variation with that respect. But in most cases, a fruit is produced. So a fruit is a seed-bearing structure found in flowering plants, and it's formed from the ovary after flowering. It's at this point we need to talk about the concept of fruit

and what the word means in the context of botany compared to in the context of a culinary or everyday usage. So from a botanical point of view, the fruit is a fleshy substance that contains seeds, or contains one or more seeds, it may just contain one or it may contain indeed thousands of seeds. It's a fleshy substance containing one or more seeds that's produced from the ovary of flour. So the flower, or the ovary of a flower, basically grows and turns into the fleshy substance that we think of as the fruit. So fruit is the

former ovary tissue of a flower, and fruits always contain, at least naturally, they always contain at least one seed. That's the purpose of a fruit to contain the seeds. The basic idea is plants produce fruit in order to attract, generally animals or birds, to consume those fruits, go off somewhere else, and excrete out the seed, which then falls into the soil and can grow into a new plant. Not all farrowing plants reproduce that way, but that's a very common strategy, and that's the purpose for which fruits are produced. They produce to attract animals to eat them, so as to facilitate the spread of seeds. because you don't want all the seeds just dumped at the base of a plant. I mean, it's true some plants reproduce like that, but generally it's better to spread them over a wider area,

so they'll have access to new resources, and they won't all be crowding out in the same space. Now, it must be said that when we think of fruits, we think of very generally quite juicy, fleshy substances, and these are almost always, have been selectively bred over hundreds or thousands of years. natural fruits, although they are fleshy and animals will eat them, they're not nearly as fleshy and tasty and sweet as the fruits that we have developed for human consumption, because we've basically

seen, oh, you know, this is a good thing. Let's take the plants that have the sweetest and the juiciest fruit, and we'll plant those, and then we'll take the fruits of that that are the juiciest and fleshiest and so forth, and do that over hundreds of years in the amount of with very substantially increased size of fruit and greater sweetness and so forth. So these have been selectively bred. So naturally, they don't look at that there's not that much sweetness and there's not that much a fleshy substance to the fruit. Now, that's what a fruit is in a botanical context.

In common language, which is more of the culinary use of fruit, it just means any fleshy seed-associated structure of a plant. And usually it's something that can be eaten raw. So we're talking apples, bananas, grapes, lemons, oranges, and strawberries and so forth. Now, botanically, a fruit also includes many structures that we wouldn't think of as fruits, including bead pods, corn kernels, tomatoes and wheat grains. So many grains are actually fruit. They're just not as fleshy and sweet, but they still produce from the tissue of the plant ovary, and they surround seeds. So it's a fruit, same with bean pods.

So the concept of a fruit in a botanical sense is really just defined in terms of what structure of a plant it derives from and what it's kind of evolutionary purposes. Whereas in a culinary sense, it's more like things that you can eat raw and that are kind of soft and tasty, either sweet or sour, but generally not, something like wheat grains, which by themselves don't have that much taste. So just bear in mind that the difference there. So that's why people say, well, technically a tomato is a fruit. Well, it's unclear what's meant by that. I'm technically a corn kernel or a wheat grain is a fruit as well, but we don't normally think of it that way. In everyday speech and in a culinary sense, we distinguish fruit. fruits from vegetables. So a vegetable doesn't really have any particular botanical meaning.

In an everyday sense, it usually refers to parts of a plant that are edible, that are not fruits. Now, this is interesting because many things that we would call a culinary vegetable are actually fruits. So examples of this include most legumes of beans, peanuts and peas, the tomato, as was mentioned, but also cucumbers and pumpkin, and even some spices like chili pepper. These are all technically fruits. botanically speaking, because remember, botanically speaking, it's all about, does it derive from the outer tissue of the ovary of the flower? If so, it's a fruit. And it doesn't matter what it tastes like or what it looks like, because they can look very different. As I've said, anything from a corn kernel to a banana is actually a fruit in a botanical sense. So now I want to talk

a little bit more about seed germination, well, see dispersional and germination. And then we're going to discuss, to finish us out, some of the different types of fruits and vegetables and also other plant products. So let's then discuss how seed germination works. So as I mentioned, plants are not motile, they can't move around to sort of decide where they're going to germinate. So they rely on vectors like animals or the wind or sometimes the ocean in order to disperse their seeds. Note that this is different from pollen dispersion. which requires transporting the mature pollen grains from usually flowers in one plant to flowers in another plant, so that pollination and then fertilization can occur.

This occurs after pollination, and once the mature seed has been formed, and the purpose of this is to transport the seeds to an environment in which they will have greater access to resources, rather than just sort of dumping them all in the same location. So once seed dispersal has occurred, the seed ultimately falls on the ground somewhere, and if it lands in an appropriate environment in which there's sufficient sunlight and water and so forth, then seed germination may occur.

So seed germination is a complicated process that depends on a wide range of internal and external factors. So as I mentioned, these include the temperature, water, oxygen, and light requirements, which vary by species, obviously. and it also has, there's a dependency on the time of year, so many species have a germination delay built in that receive signals based on the temperature. For example, there's many types of seeds that require a cold period,

which then ends and it warms up again before they will germinate, so they require a winter to pass. Exact details of that vary from species to species. That's essentially built into the genome, and there's complicated by a chemical, mechanisms that mediate that. So once the full set of external and internal conditions is met, then germination will occur.

And the first stage to this is called imbiation, or imbibition, in which the seed absorbs water. So remember I said that the embryo dries out in the stage prior to the final formation of the seed. So this essentially shuts down the continued growth of the plant. well, in the imbubition stage, that is reversed, and so the seed absorbs water once again. This causes it to expand, rupture its seed coat, so they're protecting on the outside, and then growth commences. So the first part to emerge is called the radical. That's the embryonic root. Remember that I mentioned that the seed embryo consists of basically the embryonic root, stem, and leave components.

So the first two emerges the root, which emerges from the seed, and then form. a root system, and then shortly thereafter the chute breaks out through the surface of the soil. The exact way that that happens differs a bit by species to species, but the basic idea is that the root comes out, begins to form a root system, and then the chute breaks through the soil. Embryonic leaves spread out and then begin to grow into a foliage system, and so you get the plant beginning to grow. Now, not all plants engage in sexual reproduction. Some plants have the ability to engage in vegetative propagation, which involves taking pieces of the plant

and placing them somewhere else and regrowing them into a new plant. Vegetative propagation involves basically taking small pieces of a plant and placing them in a different location, or sometimes grafting them onto another plant. So that's a horticultural technique, which is obviously only possible really artificially, and then they can grow into a new. new plant. The reason this is possible is because many types of plant tissues contain meristemic cells

that are capable of continued differentiation forming new tissues. Humans don't have this, or mammals don't have this capability, because we don't have the requisite types of stem cells. So in adult humans, we do have different types of stem cells that are capable of producing, continuously dividing to produce new tissues, but they are not of the sufficient generality to produce the range of cells necessary to grow a new organism. Those are only present in human embryos, hence embryonic stem cells are capable of producing a wider variety of tissues. So humans can't reproduce in this way, but many types of plants can. This vegetative propagation is used in agriculture a lot. Cutting is one of the most common methods used. Basically, you just literally cut off a piece of the parent plant,

you remove it, place it in a suitable environment, it grows into a new plant. Grafting is a variation of this, as I mentioned, where you graft on a piece of one plant onto another, and it's often used as a way of sort of combining different plant varieties to produce commercially desirable product. One example of a type of plant that can be produced or reproduced through vegetative propagation of potatoes, so you probably know that you can take a potato, and plant it in the ground, or indeed you can cut up a potato, and as long as it contains, as long as the piece that you've cut up contains basically the nodes that have the meritemic cells

necessary, you can plant, you can plant that in the soil, and it can grow into a whole new potato plant. And this is the case for many different types of plants as well, and exactly what parts of it you require depend on, obviously, the species of plant in question. So those types of plants often normally reproduce sexually, so the potato plant, for example, it's a flowering plant, it produces in the way that has been discussed in this episode, but it can also reproduce vegetatively. The difference in vegetative propagation is that it'll always produce a clone of the original plant because, well, it's basically just like a new version of the same plant. There's no recombination of genetic material, which happens in the process of sexual reproduction.

And so there are evolutionary issues with that because you don't have the diversity of new genetic materials. So there's the possibility of accumulating recessive genes that might have diseases or or other issues for the plant. But in a controlled agricultural environment, that problem can be mediated. Although there are people who are worried about the decline in genetic variation in the world's crops, but that's a discussion for another time. So let's move on then to talk about plant products and different types of fruits. So I mentioned before that botanically speaking, that the fruit is just the material derived from the ovary of a flower after fertilization has occurred. The thing that we would think of as the fruit is the generally fleshy tissue.

That's called the pericarp. It consists of different layers, the endocarp, mesocarp, and exocarp. Exocarp's kind of like the skin of the fruit, if you like. Mizo carp, that's generally what we'd think of as the fleshy part of the fruit. Endocarp is kind of like the inner layer that's. surrounds the seed. The seed inside the fruit, as I mentioned, consists of the embryo itself, which is basically the new plant, the dried out embryo, endosperm, which is a source of nutrients for the embryos and it germinates, and a seed coat, which is just a hard cover and keeping it dry

and protecting the seed. So all of that together is a fruit. Although, as I mentioned, the part that we think of is the fruit is actually the pericarp, and then there's the seed inside that. But there are many different types of fruits, and I'm going to just talk through them now and try to explain a little bit of the difference between them and which parts of the fruit that we think of correspond to the different botanical components. So to begin, a multiple fruit is formed from the ovaries of many different flower to which combine together in a single mass. So an example of this is the pineapple and figs. So if you look at a pineapple, it looks like it has this of compartmental structure on the outside. And that is because it is composed of multiple fruits,

which then sort of fused together. So that's a multiple fruit. Now there's a different thing, which is called an aggregate fruit. This is a fruit that contains seeds from different ovaries of a single flower, which then join up to form a complete fruit. So the difference here is whether there is multiple ovaries combining together to form a single mass. which is really multiple fruits that it just sort of fused together. Or in the case of an aggregate fruit, there's multiple seeds from different ovaries, which then form a single fruit. It's a subtle difference, but it is botanically distinct.

Examples of aggregate fruits include blackberries and raspberries. So you think about a blackberry, and there's all those little, I guess, spheres on it that make up the single mass. Each of those contain seeds from different ovaries of single flower, which have then fused together. So kind of similar to multiple fruit, but as I said, a little bit different. Then there are legumes, which are also called pods. Now, these form from dry ovary structures in plants of a particular family. I don't know how to pronounce the name, Faber Se or something. Sorry, my Latin isn't very good.

So again, these are technically, at least botanically speaking, fruits. The difference being that the ovary structure is dry, so it's not. fleshy, like many other types of fruits. So this includes clover, peas, beans, chickpeas, lentils, soybeans, and peanuts. Peanuts, yes, they are actually a fruit because they are formed from the ovaries and containing seeds of flowers. So legumes are botanically speaking fruits because of how they're formed, but because of the dry ovary, they do form sort of their own separate type of fruit. Next on the list we have poems. In poems, the pericarp is, actually not the main part of the fruit. That is the fleshy, most edible part that we think of as sort of the fruit bit.

In poems, the main edible part is actually formed from even more exterior regions, formed from the floral cup, so essentially extensions of the stem, if you like, or other parts of the tissue of the plant that are not part of the ovary itself. They actually then, after fertilization, form the most important fleshy part of the fruit. and then there's the ovaries which form the pericup inside of that and then the seed inside of that. So the most commonly known examples of foams are apples and pears. And so the main part that you eat in an apple is actually not even formed from the ovary. It's formed from, as I said, the floral carp surrounding the ovary. The pericarp is sort of the outer bits of the core that you may or may not eat.

And then the actual seeds inside the core are the seeds of the plant. So this is another example of the fact that the part that we think of is the fruity bit, which part of the plant this corresponds to varies a lot depending on the species. Moving on to droops, these are fruits in which the outy fleshy part surrounds a single shell, which is called the pit or the stone, which is derived from the ovary wall. So in the case of droops, the inner seed is contained within a hardened shell, which is what we call the stone or the pit inside the fruit. And the part that we eat is formed from only the outer two layers of the pericups,

so the mesocarp and the exocarp. A good example of droop is a peach. So if you think of a peach, there's the outer sort of skin layer. That's the exocarp. Then the main fleshy bit is the mesocarp. Then there's the pit or the stone in the middle. And that's a hard outer layer of the endocarp, which is, again, all of that is formed from the ovary.

And inside that is the actual seed part. containing the endospoem embryo and then the seed coat. So the main difference between droops and poems is that, in the case of a poem, the fleshy part is actually the main part of the fleshy bit that we eat is formed from bits external to the ovary, whereas in the case of a droop, it's formed from ovary tissue itself. Examples of droops, in addition to peaches, include coffee, interestingly, mangoes, olives, coconuts, cashew, almonds, apricot.

cherries, nectarines, and plums, so a wide range of... You may be surprised to learn that a coconut is actually a fruit. In the case of a coconut, the outer, well, the sort of nut part is formed from the ovary tissue. So the exocarp, mesocarp, and endocarp, the outer layer, the fibrous husk, and the hard shell, those are all formed from the ovary tissue. The coconuty part, the actual coconut grains, are formed from the endosperm. So that's the nutritious material that the seed uses of following germination. Moving on to berries.

So berries are a fleshy fruit that does not have a stone produced from a single flower containing one ovary. So this is sort of a very straightforward type of fruit in the sense that it doesn't have multiple fruits and doesn't have multiple ovaries. It's just one flower, one ovary. So grapes are an example of this as well as avocados, pumpkin, watermelon, blueberries, cucumbers, cucumbers, tomatoes, tomatoes, eggplants, plants, bananas and kiwi fruit. So a single ovary can have multiple ovules and therefore multiple seeds in it, but there's no large stone berry. It's just the outer tissue is formed from the, so the endocarp, exocarp, and the mesocarp that forms the sort of fleshy part of it, mostly the mesocarp, and then there's the seeds or pips inside that, and there'll be multiple

of those corresponding to multiple ovules in the single ovary. So berries are a fairly simple form of fruit to understand. Moving on, nuts are fruits composed of a hard, inedible shell that does not release its internal seed, and which itself is usually edible. So nuts are kind of a bit more defined in terms of a culinary sense, because there's the idea that you can eat a nut, and the edible part being the internal seed rather than the hard shell that surrounds it. Now, the interesting thing is that most of the things that we think of as nuts are not,

tannically speaking, actually nuts. So true nuts include hazelnuts, chestnuts, and acorns. They have a hard out of shell, which is formed from the ovary-derived material, forming the pericarp. That's usually inedible, and you have to remove that in order to get to the seed, which is edible, and that's also hard and dry as the seed is. Now, many things that we call nuts aren't actually nuts, so these include almonds, cashews, peccans, peanuts, walnuts. None of these are actually botanically speaking nuts. mostly there the seeds of droops or legumes.

The difference there being that the seed part is what we think of as the nut. But botanically speaking, a nut actually includes the whole fruit. So it's the outer pericarp and then the seed inside it. If you take off the pericarp, what you've got left is a seed, not a whole fruit. And so it's not a nut, because a nut is a fruit. A fruit includes the pericup and the seed inside it. You can't just take out the seed and call it a nut, because then it's not a whole fruit anymore. It's part of a...

A coconut is also not a nut, because although it has kind of a hard outer layer, it's still relatively fleshy compared to the very hard outer layer of things like hazelnuts and acorns. Also, there's an important component of a nut in that, naturally, the hard end will show, does not release the internal seed. It just germinates with it. Now, there's another type of fruit called a capsule. capsule is basically like a nut, except that it opens automatically to release its internal seed during the process of germination. This includes Brazil nuts and horse chestnuts. So that's another

distinction between the nuts and the capsules. Now, another type of botanical fruit is called charyopsis, or the class is called charyopsis. And this is a simple dry fruit in which the pericab is completely fused to the seed coat, meaning that the fruit and the seed are effectively the same thing. You can barely even distinguish the pericarp from the seed coat, that they just look the same. And so most cereal grains like wheat, barley, fall into this category. So looking at a seed grain in a bit more detail, so there's the embryo part, which is like the baby plant, which we've discussed. Then there's the end of sperm, which provides energy for the embryo, and then that's all surrounded by the seed coat, which protects it. Adhering to that is the pericarp, which is, again,

basically the same thing in this case as the seed coat. It's not technically the same thing, because they are derived from different tissues, but they're really indistinguishable and just form two layers that are directly fused to each other in the case of grains. So that's what distinguishes grains from nuts, really, is the fact that in a nut you do have a distinct hard outer shell, whereas in the seed grain, it's basically they just fuse together completely. Now, this leads to an interesting question about the difference between white grains, so white flour, white rice, and so forth, and whole grain variations.

of those. Whole grain are more basically traditional formulations of the corresponding foods and they're formed by processing all of the seed or all of the fruit, if you want to think of it that way, of the grain, including the outer

what's called the bran that is composed of the surrounding seed coat as well as the pericarp which fuses to that. Internal to that is the what's called the germ that's just the seed embered embryo, and the endosperm, which is the nutritious material that provides the nutrients for the growing

embryo when the seed is germinating. So these three main components, the germ, the endosperm, and the bran are all processed and form part of the flour used to produce the bread or the pasture or whatever else in whole grain foods or whole grains. In more processed grains, so white rice, white bread, and so forth, the bran and the germ are removed, and so only the endosperm remains. And the endosperm contains a much higher percentage of carbohydrates, and also some proteins, and basically no fat and very little fiber, and so that's why it is not as tough, and it's sort of a bit easier to eat, and generally regarded as kind of tastier. The bran and also the germ, but especially the bran, are much higher in fiber, so they're

tougher, more fibrous material, and they have higher proportionate. protein content, also higher fat content. They do contain a range of other nutrients as well that are not present in the endosperm, as well as higher concentrations of iron. So whole grain foods are generally regarded as healthier, at least for most people, because they do contain more fiber, more protein and high concentrations of other vitamins that are, particularly vitamin B, that are relatively lacking in many people's diets, at least in today's day and age. So at least that illustrates how an understanding of the anatomy of a plant can help you to understand what the actual difference is between whole grain and white grain breads and pastures and so forth.

The last type of fruit that we're going to talk about is called an Akeen. So this is a simple dry fruit, which is very similar, or it appears very similar to cereal grains, but the surrounding pericarp is small and also dry like an cereal grain, but they don't directly adhere to each other. So there are distinct layers. It's a fairly subtle distinction. The reason that I mentioned at Keynes is because strawberries are probably the most well-known example of these, and strawberries are actually an aggregate fruit, which means those little spot things that you see on the surface of a strawberry, which you might think are seeds, are actually fruits. So each of those is actually formed from a different ovary on the same plant.

So the tissue that you see is ovary tissue, and inside that. that is the seed. The fleshy part, the red fleshy part that we actually eat, is what's called accessory tissue, which just means it's tissue that's not actually part of the ovary. It's from exterior tissue. So that, remember, that was the case for poems as well, like an apple, except the difference in a strawberry is that there are many individual fruits contained in the whole berry thing that we would regard as a fruit. Strawberries are very poorly named because they're not berries. A berry is produced, as I mentioned before, from a single flower and one ovary, whereas the strawberry actually is produced from many different ovaries, each of which produces one of the little

achines, which is a single fruit embedded in the aggregate. Okay, so now you know a bit more about the different types of fruits and how they relate to the different anatomical components of the flower. The important point to note here is that the parts that we actually eat are highly variable. Sometimes it's the endosperm that we mostly eat. Sometimes it's the inner part of the pericarp. It might be the endocarp. Sometimes it's the outer, the mesocarp or the exocarp. And sometimes it's accessory tissue. So it's external to that again. So the part that we eat of the fruit, the main part that we're interested in, varies greatly, depending on what species we're talking about what type of fruit it is. Now, just around this outer bit, I wanted to talk a little bit about different types of vegetables. So the word vegetable originally just referred to any plat,

and that's related to the term vegetation. These days in culinary and just sort of everyday language, we usually use the word vegetable to talk about edible plant parts that are not otherwise categorized as nuts, grains, or fruits. So, as I mentioned, nuts and grains are actually all types of fruits, but we don't normally think of them as fruits because they're not sort of fleshy and sweet or sour. That's the difference between the botanical and the culinary conceptions of fruit.

And so vegetables in a broad sense would include fruits, but normally as sort of a vegetable is anything that you can eat that comes from a plant that's not a fruit or grains or nuts. And so aside from those types of fruits, normally the tissue that we eat in things that we think of as vegetables comes from the stems, the leaves, or the roots of plants. Also, there are sometimes special storage structures called tubers, which are either part of the roots or the stems, but they're sort of. sort of specialized stem or root structures. So in terms of those different components, the stems of a plant. So onions are examples of plants where we eat the stems, although you might think of onions as sort of bulb. It's actually just sort of a bulb that forms in the stem.

And so we're actually eating the stem of the plant. Leaves, while that's lettuce, cabbage, spinach, bocchoy, Brussels, sprout. All those cases, we're eating the leaves of the plant. Roots. So parsnip, carrot, beech, root, and turnip. We're eating the roots of the plant in that case. tubers, so modified storage structures, potatoes, yam sweet potato, cassava, and fruits, which we think of as vegetables, but actually fruits, that's pumpkin, tomato, cucumber,

eggplant, pepper, and all the different types of beans, as well as nuts and grains as well. There are some very interesting examples, particularly the species of Brassica, which is a single species of plant, but has different cultivars or varieties that have been specifically bread in order to accentuate particular parts of it. So, for example, Brussels Sprout is a type of brassica that has been grown for eating the leaves. But then there are other cultivars of brassica such as cauliflower, so that's actually the same species as Brussels sprouts. And there we eat the merry stem, so part of the stem essentially, but the sort of the growing portion. Then there's broccoli, which is also the same species,

and there we eat the stem and the flowers. And of course, there are many other. other varieties of brassikas as well. So kale, different types of cabbage, are all forms of brassica, and different parts of it have been selectively grown so that they suit some particular person's idea of taste, and therefore that part of the plant accentuated. So it's fascinating how much variation is possible, even within the same species in terms of which parts of the plant we think of as the edible part. Now, to finish off, I just wanted to speak briefly about some other plant products that are used in what part of the plants they derive from. So many fibers are derived from plants. So a fiber is just a natural or synthetic substance that's long.

That's really the only defining characteristics. So here we're talking about natural fibers. So flax is a plant whose stem fibers are used to make plant fiber. That's also called flax. So flax can refer to the fiber or the plant. So linen and bedsheets tablecloths and undergarments are typically made from flax. Then there's cotton, so that's a plant that has fluffy white fibers surrounding the seeds, so they help to protect and aid in their dispersal, but those

fibers are harvested to make cotton fabrics. So there the fiber is derived not from the stem, but from parts surrounding the seeds produced from the flowers. Then there's jute, which is a coarse fiber that's used to make like Heshencloth, and hemp, which is another plant that is used to make fibers to make things like rope and canvas. So all of these types of products are made from

different fibers, from different plants. Then there are also plant liquid products, including resin, latex and sap. So these are all very distinctive parts of the plant, and I'll talk about how they differ. So resin is highly viscous or even sometimes a solid substance that's excreted by plants in response to injuries from insects or herbivores or otherwise. So resins have typically been used varnishes or adhesives. Other types of resins have been used as odiferous substances, so like frankincense and turpentine. Gum resins contain essential oils. So, myr is an example of that. You've probably heard of. Some are used for therapeutic purposes. Some are used for food. Some are used for incense. Amber is a type of fossilized resin that's used as a gemstone. That's what we see in

Jurassic Park, if you recall. He's got the cane that has the fossilized mosquito inside the amber. So the point is all of these different types of resins are derived from different types of plants and use for different purposes. But in all cases, resin is the substance that plants excrete in response to injuries. Now, then there's latex, which is a dispersion of small polymer particles in water that's found in some types of flowering plants and it uses a defense against insects. So natural rubber is made from latex, and it's probably the main form of latex that is known. you extract that by making a hole in the bark and draining off the latex in a process called tapping. It's different from resin because it's not highly viscous, and it's not produced in response to injuries. It's really a defense mechanism.

The final type of liquid product is sap. So sap is very different from resin or latex. It's a fluid that's transported in the xylem cells, which I discussed in the previous episode. These are basically vessel components that transport water, and the function of sap is also totally different. Its function is nutritional rather than defensive. So pretty much all plants have sap, so any plants that have xylem cells, that'll also have sap, as opposed to resin, which is only excreted by certain types of plants. Maple syrup is made from the xylem sap of maple plants. So that concludes our discussion of plant products and also of plant reproduction.

So before we finish out the episode, I'll just give a very brief recap of the basic idea that the main idea that I wanted to get across in this episode, which is that all of these different products, well, except for, I guess, the fibres and the liquid products, but all the rest of them relate directly to plant reproduction and to the different parts of the generic plant flower. So remember, there are perfect flowers that have both the male and the female components, and then there are some flowers that only have one or the other.

Some plants have flowers that have both. Some plants have some flowers. that have one and some flowers that have the other on the same plant, and then some species will have different plants, some that are male and some that are female. The Starman is the male component, reproductive component of flowers. It consists of like, that's the whiskers with the bulbs on the end. That produces microspores, which then divide to produce pollen grains, which then are dispersed in pollination and have to land on the stigma, which is the sort of platform forming the top of the pistol, which is the female part of the flower, and consists of the stigma, the style, which is like a store, and the ovary, which contains the ovules. Once the pollen lands on the stigma,

pollen tube grows down the style and releases two sperm cells, which then enter the ovule and fertilize, in a process called double fertilization, fertilize both the egg and the central cell, which forms the endosperm and metabolic support, and the egg cell forms the zygote, which then grows into the embryo. The embryo and the endosperm are enclosed in a hard shell, which is called the seed coat.

Once the process of embryogenesis has completed, the seed dries out and forms a seed, which is then dispersed by generally organisms eating the fruit and then defecating, or sometimes it's just by wind or other abiotic factors. After seed dispersal, when the seed finds the right environment, the seed will germinate, producing first the embryonic root and then a stem and then the leaves and then the plant grows from that. Different types of fruits are produced by different types of plants and basically they depend on which part of the plant we're eating. Whether it's the ovary tissue itself, which is actually what defines the fruit, or whether it's actually the endosperm or the seed coat, as in the case of grains,

or whether in some types of fruits it's actually tissues that are exterior to the embryo form, basically formed from different parts of the plant stem, as is the case in certain types of fruits, or whether it's just the seed itself, stripping out the Adelaia, in the case of nuts, it varies a lot depending on the type of fruit. Botanically, almost all of the things that we call fruits, many things that we call vegetables, and basically all nuts are all technically types of fruits, although in terms of culinary speech, there's much less clear exactly what fits into water, and it's mainly determined by which things we like to eat with other things.

So, hopefully this episode has given you a greater insight into how plants reproduce and how they produce fruit and how those different fruits and other components relate to the components of plants that we like to eat or use to make fibers and so forth. So that brings us to an end. If you enjoyed this episode, please subscribe to the show, give it a like, give the podcast page a like on Facebook. You can find it as the Science of Everything podcast. Also, as I mentioned at the start, stay tuned.

There'll be a new episode released quite soon, the 100th episode. In that episode, I'm going to talk a lot more about the future of the show and many exciting ideas that I have to get more content out to you guys. If you'd like to send any questions, feedback or suggestions, my email address is Fods12 at gmail.com. That's F-O-D-S-1-2 at gmail.com. Until then, have a great time, and I'll talk to you next time.