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Chapter 7 - PowerPoint PPT Presentation

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Chapter 7

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  1. Chapter 7 Reproduction

  2. Reproduction: Making offspring • Reproduction refers to living organisms ability to produce offspring • Reproduction can be sexual or asexual • Asexual reproduction involves a single parent and produces clone offspring (genetically identical) • Sexual reproduction involves genetic contributions in the form of gametes (eg egg & sperm) from two parent sources

  3. A comparison of asexual/sexual reproduction

  4. Asexual Reproduction • Can occur via the following means: • Binary fission (prokaryotic organisms) • Splitting (single-celled eukaryotic organisms) • Spore formation (fungi) • Cloning (some animals) • Vegetative reproduction (plants)

  5. Prokaryotes: binary fission • Occurs in microbes such as bacteria • Binary = two • Fission = splitting • It is a simple, fast process • Steps are: • Replication of DNA • Attachment of DNA to plasma membrane • Lengthening of cell • Division of the cell into 2

  6. Eukaryotes: Asexual Repro Let’s split into two Budding to make more • Some single celled eukaryotes can reproduce by binary fission • This ‘binary fission’ is different to that performed by bacteria- it is done via the process of mitosis • Budding involves part of an organism ‘breaking away’ before developing into a new organism. (sea sponges)

  7. Eukaryotes: asexual repro Virgin birth in insects Asexual repro in plants • ‘parthenogenesis’ is also called virgin birth • Young are produced from unfertilised eggs • ‘vegetative reproduction’ can occur via: • Runners • Cuttings • Rhizomes (underground stems) • Suckers (shoot arising from an underground root)

  8. Sexual reproduction • Two parents make a genetic contribution to the offspring (egg or sperm) • Gametes produced by meiosis- have half the number of chromosomes of the organisms somatic cells • Humans • n = 23 = haploid = egg & sperm • 2n = 46 = diploid = somatic cells • Eggs produced in ovaries • Sperm produced in testis

  9. People and some animals have different sexes producing different gametes • However, it is common for organisms to be able to produce both types of gamete. Flowers (some) • Stamen produces pollen • Carpels produce eggs The garden snail ‘Hermaphrodite’ –has egg producing and sperm producing organs

  10. Getting gametes together • Fertilisation is the putting egg & sperm together to produce a zygote • External fertilisation is when this occurs outside the organism. When this occurs, large numbers of gametes are released (as it leaves a lot to chance) • Internal fertilisation occurs inside the organism (chance of gametes meeting is greater)

  11. Pollination in plants • Pollination is the transfer of pollen from the anther to the stigma. • Cross-pollination is when this is between 2 different plants • Self-pollination is when this occurs within the one plant (either the same flower or another flower on the same plant)

  12. Meiosis: making gametes • Process by which diploid (2n) cells produce haploid (n) cells • See pg 200

  13. Flowering plants: fertilisation • Sperm reaches egg to produce zygote • ‘spare’ sperm fuses with two polar nuclei to produce endosperm- this tissue is the food source for the zygote • Seeds contain both the zygote and the endosperm • Fruits are actually the ovary surrounding a seed.

  14. Questions • 1-3 pg 177 • 4-7 pg 186 • 15-18 pg 204 • Chapter review pg 211 Q 2, 3, 4, 9