Lesson video

Hello, and welcome to this lesson from the unit Reproduction in Humans.

And the title of today's lesson is Gametes and Fertilization in Sexual Reproduction.

And what we're gonna be looking at today is what sexual reproduction actually is and how genetic information is passed from parents to offspring and what that means for the amount of genetic information that both parents and offspring have.

And we're gonna be looking at how the offspring develops from an early fertilized egg cell on into a baby as part of the human life cycle.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to describe the role of gametes and fertilization in sexual reproduction.

And we've got quite a few key terms for you today in today's lesson.

So we've got gametes, sperm cell, egg cell, fertilization and embryo.

So I'm gonna put the definitions up, so you might want to copy these down or you might just want to read through them, but we will be taking our time over each of these during today's lesson.

So pause the video if you want to copy them down.

Okay, so our lesson today is going to be in three parts.

So the first part is sexual reproduction, so that is a definition of what sexual reproduction is and how it happens in humans.

The next section of the lesson is about how the genetic material is passed on from parents to their offspring in chromosomes and what numbers of chromosomes each will have.

And finally, after sexual reproduction has taken place, how that fertilized egg cell can develop into an embryo and on into a baby as part of a human lifecycle.

So let's get started with the first part of today's lesson, which is sexual reproduction.

So humans reproduce using sexual reproduction.

Some organisms don't use sexual reproduction.

That's why we're making it quite clear here what sexual reproduction is.

You may have learned about some of those organisms in primary school that can make copies of themself, but it certainly will come up in later units.

So in sexual reproduction, we have a male and a female human.

And when they reproduce, they make the first stage of their offspring, so the first development stage of their offspring, which is called a zygote.

And a zygote is a fertilized egg cell and it is the offspring of both parents.

Now, the reason it's the offspring of both parents is because they both pass DNA on to form that zygote, and then that zygote goes on to grow to form a baby, which is the offspring of both parents.

So the DNA from each parent, the way that they are able to pass that on during reproduction is in sex cells.

Now, sex cells has a scientific word, and that is gametes, so the gametes are the sex cells of an organism.

Now, in humans, we have egg cells, which females produce, and in males, we have sperm cells.

So those are the gametes of a human, egg cells and sperm cells, and they carry the DNA from the parent to the offspring.

Now, the way that they do this is because you want the offspring to have a full set of DNA, each gamete carries half of the genetic information that make the offspring, so the cell will carry half and the sperm cell will carry half.

The genetic information is coded in DNA.

So the half of the DNA that each of those gametes have is stored as DNA.

Now, that DNA is a long chemical molecule, which is packaged into chromosomes, and they are stored within the nucleus.

So you can see from these images here, we've got an egg cell and a sperm cell and we can see their nuclei.

Now, nuclei is just the plural of nucleus, so if I use that word, that's what it means.

And inside those, you can see these packages.

Now, those are chromosomes.

Now, if you could zoom in and look really closely at what a chromosome is, it is just lots of DNA wound up in a funny shaped bundle, so that's what a chromosome is.

Okay, so those are the packages of the DNA that the egg cell and the sperm cell can carry to form the new offspring.

So time for a quick check because there's quite a few key terms in those first few slides.

So if you can match up these key terms with the correct definition.

So our key terms are sperm cell, egg cell, gametes, chromosome, and zygote.

So match them up, pause the video, and we'll see how you've got on.

Okay, let's see how you've got on with that then.

So sperm cell is the male gamete an egg cell is the female gamete.

Gametes are the sex cells, chromosomes are packaged DNA stored in the nucleus, and the zygote is the fertilized egg cell.

All right, time for a quick practice.

Now, in this practice task, we're going to be doing a confidence grid.

So for each of the statements below, I want you to decide whether you think they're correct or incorrect.

Now, if you're sure about your answer, then you're going to put it into the first column or the last column.

because that's I'm sure I'm correct or I'm sure I'm incorrect.

However, if you think you're correct, okay, put your ticks in the middle two boxes, which is I think it's correct or I think it's incorrect, and then repeat that for each of the statements.

So when you're finished, okay, we'll come back and we'll have a look at what you've done, so but for now, let's just pause the video.

Okay then, so the gametes are the sex cells, so this is correct, they are the sex cells.

And the sperm and egg cells are needed for human reproduction, that is correct.

And a sperm cell carries all the genetic information of the parents, that is incorrect, it carries half, okay?

And a zygote carries half of the genetic information, this is incorrect, the zygote carries all of the genetic information for the offspring because it receives half from each parent, so half from each gamete.

Okay, so if you've got those right then well done.

So it's now time for us to move on to the second part of our lesson, which is looking at the chromosome numbers between parents and offspring.

So human sperm and egg cells meet in the fallopian tubes.

So this is a picture of the female reproductive organs, and these are the fallopian tubes.

Now, there are two of them, eggs are only released from either one of the ovaries each month.

So a sperm would only meet an egg in one of the fallopian tubes each month.

The sperm in that fallopian tube would enter the egg cell.

So here is like zooming in on the fallopian tube there, and you can see the sperm meeting the egg and the sperm moving inside the egg, so just one sperm, and that is called fertilization.

So when the nucleus of the sperm cell fuses with the nucleus of the egg cell, this process is called fertilization.

So we can see we've got our two gametes here, and our gametes have got 23 chromosomes each, so that's those packages of DNA.

And they're in their nuclei, now nuclei is just the pleural of nucleus.

Once they fuse, once those nuclei fuse, we call it a zygote.

So you can see once the sperm cell enters the egg, it actually loses its tail and the nucleus that it's got with its chromosomes will fuse with the nucleus that's already inside the egg cell, and then we get a new nucleus.

And the new nucleus in the zygote will have 46 chromosomes, so it's received 23 chromosomes from each parent.

So let's do a quick check.

So is this true or false?

And once you've decided, choose which of the statements best justifies the answer.

So fertilization occurs in the uterus of the female reproductive system.

Do you think that's true or false?

And once you've decided which of these statements supports your answer, is it that the sperm cell and the egg cell fuse in the uterus to form a zygote where development continues or is it that the sperm cell and the egg cell fuse in the fallopian tubes to form a zygote, which then moves to the uterus?

So if you want to pause the video while you make your choice, and then we'll come back and see how you've got on.

Okay, let's see how you got on then.

So fertilization occurs in the uterus of the female reproductive system.

This is false.

And the statement that justifies that is that the sperm cell and the egg cell actually fuse in the fallopian tubes to form a zygote, which then moves on to the uterus.

So let's move on our learning about chromosome number.

So there are two copies of each chromosome in the nucleus of the zygote, one copy from each of the parents' gametes.

Now, in this picture, you can see that there's only four pairs of chromosomes drawn, and that's because it would just get a little bit busy on the slide here if we tried to draw 23 pairs.

But in a human, there are actually 23 pairs in the nuclei of all cells.

And there is in the nucleus of the zygote, which is the first stage of development of human offspring.

And the reason they're in pairs is because one has come from the mum and one has come from the dad, so one has come from the sperm cell and one has come from the egg cell.

Now, different organisms, different species have different numbers of chromosomes.

Now, the number of chromosomes is not related to how complicated the species is, it's to do with how their DNA is packaged for the number of packages of DNA that they have.

But offspring always have the same number of chromosomes as their parents.

So here's an example.

So we've got a horse, and a horse has, an adult horse has 64 chromosomes in all of its nuclei.

And a baby horse, called a foal, has 64 chromosomes also.

However, the gametes of organisms always have half of the number of chromosomes.

So in the gametes of a horse, the sperm and the egg cells, they will have 32 chromosomes each because that is half of the whole number.

So let's have a quick check.

So what I would like you to do is match the organism to the number of chromosomes in its gamete.

Okay, so we've got a spotted seal, a clownfish, a corn and a sparrow, and they've got the number of chromosomes that they have in their nuclei of their body cells listed there, so just match it to the number of chromosomes in the gamete and then check back.

So if you pause the video now.

Okay, shall we see how you got on with that then?

So a spotted co has 32 chromosomes in its body cells, which means it's gats will have half of that, which is 16.

And then a clownfish has 24, so therefore its gametes will have 12.

And then corn has 20, so its gametes will have 10.

And a sparrow has loads, got 76, and therefore its gametes will have 38.

So well done if you've got those right.

So time for our practice now.

So Andeep and Alex are discussing the chromosome numbers in humans and their offspring.

And Andeep says, "Adults and babies have 46 chromosomes.

Zygotes have 23 as they have not yet grown into a baby.

" And Alex says, Adults, babies and zygotes all have 46 chromosomes and gametes have 23 each.

" So first of all, what I'd like you to do is decide which of these pupils has the correct understanding.

And then I would like you to write a description of the changing chromosome number, so how it changes, but using labeled diagrams to show that you understand.

So if you can pause the video while you do this and then come back and we'll see how you've got on.

Okay then, so the pupil who had the correct understanding hopefully you got was Alex.

Now, it might have taken you a little bit of time to do your drawings, but here's your first one, your adult humans, and they have 46 chromosomes each in their body cells.

And then we've got their gametes, the sperm cell and the sex cells, and they have half the genetic material so they have 23 chromosomes.

And then we've got the nuclei of those gametes will fuse to form the zygote, and that has got 46 chromosomes.

And then we've got the fact that that zygote will then grow into a baby and the baby will also have 46 chromosomes.

So hopefully you got those numbers correct with some good descriptions, and it's time to move on to the third part of our lesson.

And the third part of our lesson today is embryo development.

A zygote is the offspring of two parents, it is the first stage in the lifecycle of a living organism.

And the gametes had 23 chromosomes each, so when they'd fused together, the nuclei of the zygote contains 46 chromosomes.

That is a full set of chromosomes ready for the lifecycle to begin.

You can see that that takes place after fertilization in the fallopian tube.

So the lifecycle continues because what then happens is that that fertilized egg, that zygote will make copies of itself and it will divide.

And then all the new cells that it produces will also have 46 chromosomes.

And as it divides, then we call that zygote an embryo, and it moves down the fallopian tube towards the uterus.

And as it does, it continues to make copies of those cells, which each have 46 chromosomes.

So here is an image of a embryo down a microscope.

Now, you can see it's got at least four cells that have divided there, but there might be some that we can't see around the back.

So it's always nice to see a real picture of something so that we can see how similar the diagram is.

So the zygote, as it continues to make new cells, those cells are gonna start to take on different jobs.

And when they start to take on different jobs, it means that a fetus is developed and the fetus grows inside the uterus.

And over time, that fetus will grow and grow until it forms a baby that is ready to be born, and the fetus is called a baby after birth.

So let's have a quick check then.

So starting with the earliest, put these stages of embryo development in order.

So pause the video, then we'll check back after.

Okay, so let's put these in the correct order.

So the first one is the zygote, and then we move to the embryo, and then the fetus, and then finally a baby.

So if you got that right, well done.

So let's move on to a practice task.

So Lucas has drawn a lifecycle of humans, but he's included some details of embryo development in it.

So he is got gametes and fetus, child, adolescents and adults.

He's missed off some of the stages and he's not labeled those arrows.

So what I would like you to do is to draw a correct lifecycle of a human, including those stages of embryo development, and also to label the arrows with reproduction and growth.

So when you've done that, you can come back and we'll have a look at how you've got on.

Okay, so you should have a life cycle that looks like this.

So we've got zygote, then embryo, then fetus, then baby, and then we have child, adolescent, adult.

And then for the arrows to be labeled, now just to make it so it didn't look too busy, I've done a little key and colored those arrows in.

So reproduction is between the adult and the zygote, and then every stage after that is growth, so it's making new cells.

So if you got that right, then well done.

So that brings us to the end of today's lesson, and here is our summary.

So our lesson was on Gametes and Fertilization in Sexual Reproduction.

So sperm cells and egg cells are the sex cells of humans.

These are called gametes.

Humans produced through sexual reproduction, which involves each gamete passing half of the parents' genetic information to the offspring.

The DNA from the parents is packaged in chromosomes.

Each human gamete contains 23 chromosomes.

Fertilization occurs when gametes join to form a zygote.

The zygote is the first stage in the growth of offspring, and it has a full set of chromosomes, which is 46 in humans.

The zygote then divides to form a ball of cells called an embryo, which then grows to form a fetus and then on into a baby.

So well done for your work in today's lesson, and hopefully we will see you again soon.