 In this video let's try to answer the question how are fruits and seeds formed? Like other videos in this unit, let's begin with the flower which houses the male and female reproductive structures in plants. As part of the male reproductive structure, the anther produces pollen grains which we know contain a larger vegetative cell and a smaller generative cell. So when the anther bursts open the pollen grains are released and the pollen grains come and land on the stigma part of the female reproductive structure. But it is within the ovary, specifically inside these lobe-like structures called the ovules where the female gamete is present. So somehow the male gametes have to reach the ovules so that they can fuse with the female gametes. Well, the vegetative cell solves that problem by forming the long pollen tube. Now as the pollen tube is formed, the generative cell divides and forms two male gametes which then travel down the pollen tube and reach the ovules. So what happens when they reach the ovules? For that, let's first take a look at how an ovule looks like. So this is how a typical ovule looks like. Now I have not marked all the parts of the ovule, just the parts that are important for this video. You have the micropile which serves as an opening for the pollen tube to reach inside the ovule. The embryosac is the actual structure that contains the female gamete. It is immediately surrounded by the new cellus which provides nutrition to the developing embryosac. Beyond the new cellus the embryosac is covered by two protective layers called the outer and inner integuments. And inside the embryosac it looks something like this. So you have two synergists which are located on the micropiler end of the embryosac. And within the synergists there are filiform apparatus. Now these filiform apparatus have finger leg projections and the function of the filiform apparatus and synergists is to guide the pollen tube so that it can reach inside the embryosac. Below the synergists is the actual female gamete which is called the egg cell and it is haploid. Below the egg cell are two polar nuclei. Now these are haploid as well but they are written as N plus N because they are two separate nuclei and they are not diploid. At the opposite end of the synergists are three antipodal cells. So now that the pollen tube has finally entered the embryosac the gametes also reach inside the embryosac. One of the gametes fuses with the egg cell and forms the diploid zygote. And this process is called syngamete. What about the other male gamete? The other male gamete comes and fuses with the two polar nuclei here to give rise to the primary endosperm nucleus. And this primary endosperm nucleus is as you can guess triploid because there are three haploid nuclei that are fusing together. So this primary endosperm nucleus is triploid and the formation of this PEN which it can also be written as PEN is called triple fusion because it involves the fusion of three haploid nuclei. So inside the embryosac two events are taking place one syngamete and one triple fusion because of this because there are two fertilizations or two fusion processes happening this entire process is called double fertilization. So what happens after this double fertilization? What does the embryosac look like after this? Well after fertilization has occurred the embryosac looks something like this. Notice how that I have not drawn the synergists or the antipodal cells. Well that's because the antipodal cells and the synergists degenerate or degrade after zygote formation has occurred because they have served their purpose. So once the zygote and the PEN formation has occurred the PEN first begins to develop. That's because the main role of this primary endosperm nucleus is to provide nutrition to the developing zygote. So before the zygote can develop into an embryo which is the future plant it needs a lot of energy needs a lot of nutrition. To give that the primary endosperm nucleus begins to divide rapidly. So notice how I am just drawing nuclear division and not drawing cellular division. Well that's because nuclear division is not immediately followed by cellular division. Once enough nuclei have been formed the nuclei that have been pushed to the sides or the periphery begin to undergo cell wall formation. So this part of the endosperm is called cellular endosperm while the nuclei inside that are not covered by cell wall they are called nuclear endosperm. So in plants like peas and groundnut this endosperm is completely consumed as the embryo develops. But in cases like coconut the endosperm is persistent even after embryo development has occurred. In fact the white kernel that you see in coconuts is nothing but the cellular endosperm and the water that we drink the coconut water is nothing but the nuclear endosperm. So this endosperm is persistent in cases like wheat and maize as well. So once the endosperm has finished developing it's time for the embryo to begin to grow and that process is called embryogenesis because genesis means formation and embryo refers to the developing embryo. So let's talk about embryogenesis in a typical dicot plant. Now remember dicot plants are plants that have two cortilidins. So initially the zygote begins to divide and forms a globular embryo. And this globular embryo gives rise to the heart shaped embryo. Now these two lobes of the heart shaped embryo then give rise to the two cortilidins in the mature embryo. Now the part of the embryo from which the root develops or the root tip is formed is called the radical. And the part of the embryo from which the stem or the shoot develops or the stem tip is formed is called the plumule. And these two together make up the embryonal axis. So in a typical dicot embryo the embryo is made up of the embryonal axis and the cortilidins. Let's come back to our original question. How is a seed formed? So when we take a look at a seed like in the seeds of mango and grapes do we see the embryo as such? Do we see the radical, the plumule? No, right. We see a hard tough seed. We can say that the seeds are the final product of fertilization in plants. But then how exactly are the seeds formed? Remember how we spoke about the inner and outer integuments of the ovules? Well, the seed is nothing but the embryo, the plumule and the radical and the cortilidins covered by a seed coat. And the seed coat is nothing but the hardened inner and outer integuments. So the embryo is enclosed within the seed along with it is the cortilidins. So this is how a typical dicot seed looks like. So when you look at a seed like in the case of grapes or mango, this is what you actually see, the hardened structure outside. Inside it is the embryo and the two cortilidins. So when seeds are formed the endosperm may be completely consumed like I mentioned in the cases of pea and groundnut. Such plants are called non-albuminous plant. In plants like wheat and maize as the seeds are being produced some endosperm still remains after the seed has fully developed. Such plants are called albuminous plant. In plants like pepper even the new cellus is persistent even after the seed has finished developing. Remember how new cellus is the structure that provides nutrition to the embryo sap. In such cases the new cellus is called perisperm. So does this answer our question how a seed is formed? Yes, fertilization results in the formation of the zygote which then develops into the embryo which is enclosed within the seed. But what about the fruit? How is that formed? Well if we say that the zygote gives rise to the seed we can say that the seeds are formed from the ovules right. Well if the ovules give rise to the seeds it is the ovaries that give rise to the fruits. So when seed formation is occurring the ovary begins to swell and it forms the fleshy part or the fleshy fruit in many fruits. So the ovary gives rise to the fruit while the ovule gives rise to the embryos or the seeds. So the walls of the ovary begins to harden and forms the pericarp which is the wall of the fruit like the wall of the grape that you see here. So the pericarp is made up of three layers the inner endocarp, the middle mesocarp and the external exocarp. So now I have written something called a true fruit here with an example of grape. What does a true fruit mean? Does that mean that there are false fruits? Absolutely. If only the ovary contributes to the formation of the fruit such fruits are called true fruits and mango, grapes are all true fruits. So why this occurs is while the fruit and seed formation is occurring the other parts of the flower like the thalamus begin to fall off but in cases like apple they don't fully fall off but actually contribute to the formation of the fruit along with the ovary. So such fruits in which apart from the ovary other structures of the flower are involved in fruit formation they are called false fruits. So this answers our question how the fruit is formed. So the ovules give rise to the seeds while the ovary gives rise to the fruit. Next time you eat a fruit try to figure out if it is a true fruit or a false fruit. Play a true or false game with your fruit.