Hi there, we are continuing with the angiosperms, and the two defining features of the angiosperms are flowers and fruits. So in this video we're going to move on to take a closer look at fruits. Fruits are really the same thing as flowers, they're just at a different point in development. So we talked last time about how the flower contains the carpal, and at the base of the carpal is the ovary where you will find ovules. Following fertilization, the ovules become the seeds, and the ovary around the ovule will develop into the fruit around the seeds.
So fruits, for the most part, are simply mature ovaries from the carpal of the flower. So we're going to take our ovary-ovule container and turn it into a fruit-seed container. So the fruit is derived mainly from the ovary wall.
A lot of the time the ovary wall has three layers to it which are called the exocarp, mesocarp, and endocarp in terms of outside to inside. And I'm just telling you those three layers so that you will be able to distinguish some of the different types of fruits that we're going to talk about. So the entire ovary wall usually will ripen into the fruit.
Inside the fruit you can find the seed containing the new sporophyte embryo. some food supply, which in the angiosperms is termed endosperm, and the seed coat around the outside. So we do have the seed contained within the fruit. Now what are the functions of fruit, and how are fruits beneficial to the angiosperms?
Come up with a couple of ideas. I want to take a closer look at some of the different types of fruits, and you will need this information for the lab as well as for lecture. Most fruits are going to be simple fruits.
Simple fruits develop from one ovary off of one flower. So one ovary, one flower, that's a simple fruit. The ovary could have multiple chambers to it or it could have all one chamber, but regardless it is one ovary from one flower.
There are a lot of different kinds of simple fruits. For example, follicles are simple fruits that are one ovary chamber which is dried out. and will burst to release the seeds.
We tend to think of fruits as being juicy tissue, but they can be dry as well, and follicles are an example of that. Pods are a simple fruit that has one ovary with one single chamber, and inside that carpal chamber are several seeds. So one chamber with several seeds, usually all attached on one side.
That would include legumes like peas. Droops are simple fruits where a portion of the ovary wall is hardened into a protective coat. So remember we said that the ovary wall has three layers to it, the exocarp, mesocarp, and endocarp. In a droop, the endocarp is hardened into a shell around the seed.
The mesocarp is the fleshy tissue, and then the skin would be the exocarp. Droops include stone fruits like peaches and cherries, anything with a pit in it. And looking at that, you might think that the pit is the seed itself, but it's not.
The pit is hardened ovary wall, the innermost layer of the ovary wall. And if you wanted to see the seed itself, you would have to actually cut open the pit to find it inside. So everything that you can see in this picture of the peach is actually ovary wall.
including that hardened inner layer with the seed inside. Acheans are a simple fruit where the entire ovary wall has been hardened into a protective structure. So not just the innermost layer, but all of the ovary wall is hardened into a protective shell.
That would include things like sunflower seeds, where the shell that you remove is the actual fruit and then the seed is found inside. Acheans are the most common kind of simple fruit. And a berry is a simple fruit where the ovary wall is fleshy and has a number of seeds contained within it, sort of suspended in the flesh.
Berries often have multiple chambers to the carpels, so if you think about the segments of an orange or the segments of a tomato, those are chambers, but you can see how all of the ovary wall is kind of soft and fleshy with seeds embedded in that flesh. The seeds will usually connect at the center. to a placenta, which holds the seeds suspended in that flesh.
Berries includes a lot of fruits that you don't think of as berries, like tomatoes and oranges and bananas. It doesn't include most of the things that you do call berries. So strawberries, raspberries, blackberries, none of those are actually real berries. If they're not real berries, what are they? They are in fact aggregate fruits.
Aggregate fruits are very different from simple fruits. Simple fruits are one ovary on one flower. Aggregate fruits are multiple ovaries from one flower.
So on the flower, it doesn't have only one ovary in the center. It has several ovaries, each of which will develop into its own fruit, all stuck together as an aggregate fruit. So for example, in a strawberry, at the center of the strawberry you can see there are multiple ovaries, and as the fruit ripens, each of those ovaries will develop into its own fruit, all fused together into the aggregate fruit. So for something like a raspberry or a blackberry, each of the little balls of the fruit is one individual ovary that all came from a single flower.
So the little balls are individual fruits that are really each representative of individual ovaries on a flower. Aggregate fruits, many ovaries from one flower. There are also multiple fruits.
Multiple fruits come from multiple flowers. So they are going to have many ovaries, but they're actually from separate flowers, not all from the same flower. This happens when the separate ovaries of the separate flowers will fuse together during maturation. A good example is a pineapple. Pineapples come from flowers termed inflorescences, which is when you have many flowers all grouped together on a stem.
And so this is what a pineapple looks like when it's a flower. You can see how each of these is in fact one individual flower with its own petals and its own floral structure. When the flowers mature into a fruit, they will all fuse together into the pineapple, which is a multiple fruit, and each of those segments of a pineapple is derived from one individual flower. So many flowers all fuse together. Another good example of a multiple fruit is figs, and figs actually have all of their flowers on the inside.
So they're kind of inside out. And each of the little balls that you see when you open up a fig is actually an individual flower. They are pollinated internally by tiny wasps that enter the fig and pollinate the flowers inside the fig and then leave. So many flowers all into one fruit, that's a multiple fruit. The final fruit type is accessory fruits.
Accessory fruits contain other parts of the flower besides the ovary. Simple fruits, aggregate fruits, and multiple fruits are all built from the ovary. It is usually the ovary that makes the fruit. Accessory fruits are going to include various other parts of the flower besides just the ovary.
Most commonly the receptacle, which is the central stalk of the flower. So in something like a simple fruit, you normally see the ovary sitting on top of the receptacle. In an accessory fruit, the ovary is lowered downwards into the receptacle, and as a result, when the ovary ripens into the fruit, the receptacle will also be included into the fruit. The best example of this is pommes, which includes things like apples and pears, and you can see how in the flower, the ovary is embedded down within the receptacle.
As a result, the fruit will contain a fair portion of receptacle. So when you cut open an apple or a pear and you see this line around the core, that line is actually the boundary of the ovary. So the core, the part that we do not eat, is the ovary containing the seeds.
And the soft, fleshy tissue outside of that that we eat is actually the receptacle. At the base of the apple or the pear, like on the little butt, you can see some little tiny leaf-looking structures. Those are actually the remnants of the other portions of the flower, the sepals and stamens and styles. So the part that we eat is receptacle and that makes it an accessory fruit. Another example of an accessory fruit is strawberries.
Strawberries, we already said, are aggregate fruits because they come from many ovaries on a single flower. Each of those ovaries develops into a little tiny individual fruit embedded in a large fleshy receptacle. So the red tissue that we eat in the strawberry is actually a receptacle, it's not ovary, and that makes it an accessory fruit. If you zoom in on what we tend to think of as seeds on the outside of the strawberry, you will actually find that each of those little tiny bumps on the outside of the strawberry is a tiny individual fruit.
And it is an aging fruit, like a sunflower seed. So in order to find the seed, you would actually have to cut open one of these tiny little fruits. So strawberries are aggregate fruits, they are accessory fruits, and they are aging fruits. What they are not is berries. So those are the different types of fruits.
Fruits are largely adapted for the function of dispersal. They're going to do the job of carrying the embryo away from the parent plant in some form, and so there are different ways in which fruits can be dispersed, and the structure and tissues of the fruit will be adapted to enable that dispersal. Why would you want to do this?
Why is it a good idea to disperse the seeds away from the parent plant? What do you think? Now you do want to make sure that the fruit is dispersed when the seed is mature and so there will be signals to help with identifying when the fruit is ready to disperse including things like the color of the fruit, its taste, the shape of the husk of the fruit. This is what we typically refer to as ripeness.
If the fruit is ripe, that is a signal that it is ready to be dispersed because the seed is sufficiently matured. There are lots of different methods that you can use for dispersal. One possibility is water. A great example of a water-dispersed fruit is palm trees. Palm trees produce coconuts, which they will drop down to the beach.
The coconut will then get washed out into the waves. Coconuts float. and that's going to allow them to get dispersed by water to a new beach where they will get washed up and then can germinate into a new palm tree. So the key feature for a water dispersed fruit is usually going to be floating. Another possibility is to use wind dispersal.
Wind dispersed fruits are often going to have structures to help them catch the wind, so propellers or umbrellas or something like that, and they will also be very lightweight so that they can get picked up by the wind and carried. So when you look at these you might be thinking that this is just the seed that you're seeing here, but in fact the seed is inside and this propeller blade is actually the fruit. It's a dry fruit that has been spread out into a lightweight surface to help catch the wind.
For a dandelion the little umbrellas that come off when you blow into a dandelion are actually the fruit itself. and each one of them carries a seed at its base. So you can see how wind dispersed fruits are adapted to help pick up the wind and allow them to carry the seed to a new location. But most fruits are going to be dispersed by animals. So besides just the flower, fruits are another place where angiosperms tend to have a close relationship with animals.
One possibility is for the fruit to be a hitchhiker on an animal. For example, these ones are burrs, which have little spikes on them that will attach to the fur of a passing animal, and then when the animal eventually kicks it off or chews it off, the fruit is in a new location so that the seed can germinate. A lot of fruits dispersed by animals will offer some kind of food to the animal in exchange for that dispersal service. Here you can see that this seed has a little nodule of fat on the end, which is the fruit and that will provide food for ants that will collect the seeds and carry them around and put them in their nests and disperse them to new locations.
A lot of animals will eat the entire fruit containing the seeds and the fruit will have signals to help the animal recognize when it is ready to be eaten, such as the color. Birds are very attracted to red, so a red fruit is often going to be eaten by a bird. When the bird eats the fruit, it will digest the ovary tissues of the fruit, but not actually the seeds themselves. It's not going to chew the seeds, it's not going to damage the seeds, and the seeds will end up passing through the digestive tract and getting defecated out a little bit later, which will put them in a new location. So if you have something like a bear that comes along and eats some berries, the bear will digest the sugars and carbohydrates in the fruit, and then a few hours later, will defecate out the seeds, which are now in a new location away from the parent plant and supplied with some fertilizer to potentially help them grow.
This is beneficial to both the animal disperser, which is getting a meal out of the equation, and the fruit itself because it is getting this dispersal service. A lot of the fruits that are dispersed by animals will not be consumed in their entirety. So for example, when a squirrel buries acorns, the acorns are the fruits, it's a dry fruit, and many of the acorns will not actually get eaten by the squirrel. It is collecting them and burying them as its food source, but it's not going to eat 100% of the acorns that it buries. It doesn't even eat a fraction of the acorns that it buries.
So all the rest of those acorns will be dispersed in a new location, buried underground in a perfect spot for them to hopefully germinate and continue growing. So I'm going to take a quick look at the angiosperm life cycle. We're going to be looking at this in more detail in our next lecture, so I'll just give you a general overview here. We will start with the sporophyte.
On the sporophyte, you will develop flowers made out of sporophylls. The carpal is the female portion of the flower made of a megasporophyll. At the base of the carpal is the ovary containing ovules. Inside the ovules is megasporangium. Inside the megasporangium are megasporocytes, which undergo meiosis to produce a megaspor.
The megaspor develops into a megagametophyte, which is also termed in the angiosperms the embryosac. In comparison to the gymnosperms, the megagametophyte will be further reduced. It was a couple of hundred cells in the gymnosperms For the angiosperms, it will be only seven cells. One of those is the egg.
So the megasporangium, megaspor, megagaminophyte egg is all inside the ovule, inside the ovary on the flower. Also on the flower are the stamens made of microsporophylls. At the top of the stamen is the anther, which contains microsporangium. Inside the microsporangium are microsporocytes, which undergo meiosis to make microspores coated in sporopalenin.
The microspor divides into the microgametophyte coated in sporopalenin, which is the pollen grain. Inside the microgametophyte are just two cells, the tube cell, which will produce the pollen tube, and the generative cell that will produce sperm. So you can see the gametophytes are still multicellular, but just barely. The female gametophyte is seven cells, and the male gametophyte is just two. The pollen will be released from the anther and land on the sticky stigma of a flower.
The pollen tube will then grow down the style and into the ovary, and deliver to the ovules two sperm for a special fertilization process called double fertilization. So we're going to use two sperm in double fertilization for the angiosperms. After fertilization, the ovule will develop into the seed and the ovary will develop into the fruit. So the seed contains the seed coat derived from the integument of the ovule, the food supply, which in angiosperms is a special structure called the endosperm, and then the new diploid sporophyte embryo. Around the seed, the ovary develops into the fruit.
The fruit is going to help with seed dispersal so that it can get to a new location and germinate into a new sporophyte. So that is the basics of the angiosperm life cycle, and you can see how the flowers are important for increasing dispersal of pollen, and then the fruits are important for increasing the dispersal of embryos. Okay, that's it for this video.