18 Sexual Reproduction

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18 Sexual Reproduction

  1. 2. Why sex? <ul><li>Sexual reproduction results in a greater diversity of individuals </li></ul>
  2. 3. Diversity <ul><li>This means that we, as a species, can adapt to an unfavourable environment </li></ul><ul><li>Some will die, but the strong ones will go on and produce strong babies </li></ul>
  3. 4. Diversity <ul><li>We will also be able to adapt and change with a changing environment </li></ul>
  4. 5. Plant sex <ul><li>Most plants are true hermaphrodites, which means that they have both male and female working sex organs </li></ul>
  5. 6. Reproduction in flowering plants <ul><li>Most flowering plants have flowers containing both male and female sexual organs. </li></ul><ul><li>A small number are monoecious (flowers only carry male or female sexual organs) </li></ul><ul><li>Some are dioecious (plant has single sex flowers of both genders) </li></ul>
  6. 7. Hermaphrodites <ul><li>Could this really be possible in animals? </li></ul>
  7. 8. Fertilization is not always internal! <ul><li>In many fish females will lay their eggs and the male will come and spray them with sperm </li></ul>
  8. 9. Reproduction in humans <ul><li>…um, when two people love each other very much … </li></ul><ul><li>…then a stork comes and drops off the baby </li></ul><ul><li>The End </li></ul>
  9. 10. Reproduction in humans
  10. 11. The male reproductive organs
  11. 12. The female reproductive organs
  12. 13. Puberty Males Females <ul><li>Development of sexual organs </li></ul><ul><li>Growth spurt </li></ul><ul><li>Increased muscle and bone mass </li></ul><ul><li>Hair growth </li></ul><ul><li>Voice breaks </li></ul><ul><li>Acne / odours </li></ul><ul><li>Development of sexual organs </li></ul><ul><li>Growth spurt </li></ul><ul><li>Breasts & buttocks grow, hips widen </li></ul><ul><li>Hair growth </li></ul><ul><li>Menstruation begins </li></ul>
  13. 14. Menstruation <ul><li>The shedding of the uterine lining (blood, mucous, cell debris) in preparation for the potential arrival of a fertilised egg </li></ul>
  14. 15. Now for the main attraction
  15. 16. Sexual intercourse <ul><li>When aroused the male’s penis becomes erect and the females vagina becomes lubricated. </li></ul><ul><li>When the male ejaculates, the sperm swim up the fallopian tubes until they encounter an egg. </li></ul>
  16. 17. Why is sex pleasurable? <ul><li>Evolutionarily speaking, sex is essential for the continuation of the species, but there is also a biological advantage: </li></ul><ul><li>The male orgasm is tied to the ejaculation of sperm. </li></ul><ul><li>The female orgasm causes the cervix to contract, thereby drawing in the sperm. </li></ul>
  17. 18. Fertilisation <ul><li>Once an egg is encountered the few hundred sperm that have made the distance surround it. </li></ul>
  18. 19. Fertilisation <ul><li>Once one sperm penetrates the egg, the surface changes and no more can enter </li></ul>
  19. 20. Development <ul><li>The egg travels a further 5 days down the fallopian tubes before embedding in the uterus wall. </li></ul>

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