I mean welcome back to three size lessons.com okay by the end of this video you should be able to describe the importance of mitosis you should then be able to describe the stages of the cell cycle involving mitosis we've already seen that both plant and animal cells contain a nucleus and I'm showing you that here in the nucleus we find chromosomes and they're made of the molecule DNA so this cell contains four chromosomes now one key fact is that body cells contain two of each chromosome in other words they're paired in this cell we can see a pair of long chromosomes here and also a pair of short chromosomes here human body cells contain 23 pairs of chromosomes now I should point out that certain cells called gametes have got chromosomes which are not paired and we're going to look at that in a later video so I'm showing you a close-up of a pair of chromosomes here and that brings us to a second key point chromosomes carry a large number of genes and these determined many of our features these chromosomes only have four genes but most human chromosomes contain hundreds now animals and plants contain a very large number of cells so that means that cells have to be able to divide that's called the cell cycle cells can divide by either mitosis or meiosis we'd be looking at meiosis in a later video in this video were looking at mitosis now the cell cycle including mitosis consists of three main stages and you need to learn these in the first stage of the cell cycle the DNA replicates to form two copies of each chromosome I'm showing that here as you can see the chromosome and the copy remain attached the cell also grows and it copies its internal structures such as mitochondria and ribosomes in the second stage of the cell cycle mitosis takes place one set of chromosomes is pulled to each end of the cell the nucleus also divided in the final stage of the cell cycle the cytoplasm and the cell membrane divide to form two identical cells so as you can see at the start we had one cell which had two pairs of chromosomes and at the end we've got two identical cells again each with two pairs of chromosomes now in certain textbooks you might see lots of different stages of mitosis however the AQ exams you've only required to know the stages I'm showing you in this video I'm going to finish now by looking at the functions of mitosis remember that mitosis copies one cell into two firstly mitosis is essential for growth and development of multicellular organisms multicellular organisms have got more than one cell and plants and animals are good examples of multicellular organisms secondly mitosis takes place when an organism repairs itself for example when a broken bone heals and lastly mitosis happens during asexual reproduction and we're going to be looking at that in a later video film you'll find plenty of questions on the cell cycle and mitosis in my revision workbook and you can get that by clicking on the link above okay so hopefully now you should be able to describe the importance of mitosis you should then be able to describe the stages as the cell cycle involving mitosis [Music]