co43 - CHAPTER 43 REPRODUCTION Chapter Outline 43.1 How...

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43 R EPRODUCTION Chapter Outline 43.1 How Animals Reproduce A. There are two patterns of reproduction. 1. Asexual –only one parent is involved. 2. Sexual –two parents are involved. B. Asexual Reproduction 1. Some animals usually reproduce asexually but most use a combination of sexual and asexual. 2. Hydra undergo budding ; a new individual arises as an outgrowth (bud) of a parent. 3. Obelia polyps produce a medusa by budding; the medusa the produces eggs and sperm. 4. Flatworms can constrict and pinch off. 5. Fragmentation followed by regeneration is seen among sponges and echinoderms. 6. Parthenogenesis is found among some insects, worms, fish, lizards and some other animals; the egg develops without fertilization. 7. In honeybees, the queen can decide to fertilize or not fertilize the eggs, producing diploid female workers or haploid male drones. C. Sexual Reproduction 1. In sexual reproduction , the egg of one parent is fertilized by the sperm of the other. 2. Hermaphroditic organisms possess both male and female organs. a. A pair of earthworms cross-fertilize each other. b. Sex reversal involves the changing of sex; a male wrass (a reef fish) has a harem but if the male dies, the largest female becomes a male. 3. Gonads are organs specialized to produce gametes . a. Sponges are an exception since their collar cells give rise to sperm and eggs. b. Hydras produce only temporary gonads in the fall when sexual reproduction occurs. c. Animals in other phyla have permanent gonads. 4. There are two types of gonads: testes produce sperm and ovaries produce eggs. 5. Eggs and sperm cells derive from germ cells that specialize early for this development. 6. Other cells in the gonads support and nourish the developing gametes or produce hormones for reproduction. 7. Accessory organs form ducts and storage areas that aid in bringing gametes together. 8. Sexually-reproducing animals have various methods to ensure that the gametes find each other. a. Aquatic animals that practice external fertilization must synchronize egg release. b. The lunar cycle is one trigger that cues animals by tides. c. Hundreds of thousands of palolo worms rise to the surface to release eggs during a 2–4 hour period. 9. Copulation is sexual union to facilitate the reception of sperm by a female. a. The penis is a male copulatory organ typical of terrestrial males; it deposits sperm into the female’s vagina. b. Aquatic animals have other types of copulatory organs or employ other strategies for delivering sperm: 1) Lobsters and crayfish have modified swimmerets. 2) Cuttlefish and octopuses use an arm. 3) Sharks have a modified pelvic fin to pass packets of sperm to the female shark. c.
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co43 - CHAPTER 43 REPRODUCTION Chapter Outline 43.1 How...

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