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Cell Division

Cell Division. Part 2. Starter. 1. What do the letters below summarise about mitosis? IPMAT 2. What is cytokinesis ? 3. Which enzyme is needed in DNA replication first - helicase or DNA polymerase? 4. How are two new strands of DNA made from one original strand?. Learning Objectives.

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Cell Division

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  1. Cell Division Part 2

  2. Starter 1. What do the letters below summarise about mitosis? • IPMAT 2. What is cytokinesis? 3. Which enzyme is needed in DNA replication first - helicase or DNA polymerase? 4. How are two new strands of DNA made from one original strand?

  3. Learning Objectives • Learn about the role of egg and sperm cells. • Learn about the events that take place during fertilisation. • Learn how these gametes are made by meiosis.

  4. Success Criteria • Remember that sexual reproduction results in a zygote with unique genes (E-D). • Describe and explain the adaptations that sperm and eggs have for reproduction (C) • Explain what the word ‘haploid’ means (B-A) • Explain the importance of halving the number of chromosomes during meiosis (A-A*)

  5. Why do you think men need to produce so many sperm cells? How many cells did the maturing sperm cell divide into? How does this differ from mitosis? How many chromosomes do you think there are in sperm and eggs cells? Why?

  6. In order to make one of these… You need… & one of these… one of these.

  7. Gametes & Fertilisation • The words and definitions below are jumbled up. • Rewrite them in your books so that they match: Reproduction that involves making unique offspring FERTILISATION GAMETE Male gametes (sex cells) SEXUAL REPRODUCTION Cells with half the number of chromosomes compared to normal body cells The process in which sperm and egg meet each other SPERM

  8. Sexual Reproduction • Egg cells and sperm cells are also known as: Sex Cells or Gametes • Gametes have half the number of chromosomes in their nucleus. In sexual reproduction, a sperm cells fertilises an egg cell to form a ZYGOTE. Many sperm are released by a male, but only one will make it into the egg.

  9. cytoplasm cytoplasm nucleus nucleus cytoplasm Sperm and Egg cells though, have 23 chromosomes each. We call these cells HAPLOID Normal human body cells contain 46 chromosomes. We call these cells DIPLOID nucleus

  10. Fertilisation • When the gametes meet, the sperm cell will penetrate the egg cell. • Its nucleus will fuse with the nucleus of the egg cell. • This fusion of sperm and egg is known as fertilisation. • It results in the zygote, which will then develop into a fully grown baby. • In humans, the development takes 9 months. The Zygote: This cell is the result of fertilisation. It has a full set of unique DNA 46 zygote 23 23 Sperm nucleus Egg Cell nucleus

  11. A Sperm Cell The acrosome contains enzymes which digest the egg cell membrane. The neck contains many mitochondria to provide energy for the tail. The nucleus contains the chromosomes Tail allows the sperm cell to move towards an egg cell Now complete Worksheet 2

  12. Meiosis • Meiosis is a special type of cell division that produces the gametes. • It happens only in: • A cell with the normal number of chromosomes (46), divides into four cells. • These four cells contain half the number of chomosomes. The Ovaries If you’re a girl. The Testis If you’re a boy. Make sure you remember what diploid and haploid mean.

  13. Meiosis These two cells divide themselves, to form four cells with half the chromosomes. Normal Body Cell 46 46 23 46 23 The body cell divides into 2 cells with the same chromosome number. The four cells are modified into the final gametes. Sperm in Testis or Egg Cells in Ovaries. 23 23

  14. Questions • Why do new-born babies have their own unique set of genes? • Where in the human body does meiosis take place? • If sperm and eggs were diploid, not haploid, how many chromosomes would the zygote have? • What is the function of the acrosome of a sperm?

  15. Meiosis in Detail • Read the bottom half of page 25 of the new student textbook. • Watch the animation on the next slide. • Then answer the two questions on Worksheet 3.

  16. Summary Contains enzymes to breakdown egg membrane • Explain why sperm cells have an acrosome. • Which type of cell division produces gametes? • In humans, body cells contain two pairs of 23 chromosomes – 46 in total. What name do we give to a cell that contains a pair of each chromosome? • Cells produced by meiosis have only one of each chromosome. What name do we use to describe a cell with one of each chromosome. • Describe how a zygote forms. Meiosis Diploid Haploid First division – homologous pairs separate; half go to one pole and the other half to the other pole, (which reduces the number of chromosomes). Second division – chromosomes split as in mitosis .

  17. Look at the table below. Discuss with the person next to you, what needs to be added to complete it. Then raise your hands to share with the class.

  18. Homework • Meiosis involves two different divisions. Describe what happens to the chromosomes in each division and explain how this changes the number of chromosomes in the new cells.

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