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Chapter 49 - Bio Notes CHAPTER 49 Asexual Reproduction...

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Bio Notes February 24, 2009 CHAPTER 49 Asexual Reproduction Single parent o Genes of offspring identical to parent’s (except for mutations) Benefits Energy efficient Successful in stable environment No searching for mate Genetic stability Budding Small parts of the parents body grows, detaches Hydra o Part of body grows outwards separates and develops into new individual o E.g. flatworms and annelids o Fragmentation Parents body breaks into pieces Each piece can develop new animal Sea stars Parthenogenesis Sexual Reproduction Fusion of two gametes o Egg is large non motile o Sperm is small and motile o Fusion leads to zygote External Fertilization o Mating partners release eggs and sperm into water simultaneously Frogs Internal Fertilization o Male delivers sperm into females body o Fusion inside body Humans Hermaphroditisim Single individual produces both eggs and sperm o E.g. tapeworm, earthworm, tunicates o Typically individuals come together to swap sperm and egg Male Reproductive System Testis, epididymis, and spermatic cord: o Testes show arrangement of seminifourous tubules Testes 1
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o Contained in the scrotum Testes + scrotal sac= scrotal sac Paired male gonads Serves as a cooling unit maintaining sperm below body temperature (35 degree C) Connected to pelvic cavity by inguinal canals: Straining can cause loop of intestine into scrotum (inguinal hernia) Contain seminifourous tubules Hollow tubes where spermatogenesis (sperm production) takes place o Spermatogonia (undifferentiated cells in the walls of the tubules) Seminifourous Tubules (Fig 49-4 o Interstitial cells (Leydig Cells) Lie between the seminiferous tubules in the testes and secrete testosterone o Sertoli Cells Ring the fluid-filled lumen of the seminiferous tubule Produce signaling molecules and fluid that nourishes sperm cells Phagocytes sperm’s cytoplasm which is discarded during development Tied together by tight junctions which prevent harmful substances from entering tubule Sperm Structure o Fig 49-6 o Head of the sperm consists of the nucleus and a cap (Acrosome) Acrosome differentiates from the Golgi complex; contains enzymes that help the sperm penetrate the egg o Mitochondria in the midpiece provide flagellum (microtubule formation 9+2) with energy Spermatogenesis o In seminiferous tubules of testes Spermatogonia divide by mitosis: some differentiate and become primary spermatocytes, which undergo meiosis Gametes are haploid First meiotic division produces two secondary spermatocytes Second meiotic division: each secondary spermatocyte produces two spermatids Spermatids are haploid Each differentiate (you get 4) Conducting Ducts o Sperm moves from seminiferous tubules to another coiled tube, the epididymis Sperm maturation and storage o Ejaculation of sperm
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Via vas deferens To ejaculatory duct
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