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Biology Chapter 4

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Biology chapter 4 : 4.1, 4.2
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  Biology Chapter 4: Reproduction and Growth Reproduction:  Production of new individuals of the same species for the continuation of the species. Types of reproduction: Sexual reproduction Asexual reproduction The production of new individuals involving sex cells or gametes  The production of new individuals without involving sex cells  Gametes are formed by meiotic division  The process relies entirely on mitotic division  Involves 2 individuals  Involves only one individual ( single parent )  New individual inherit genes from both  parents  New individuals get their genes from one  parent Occur in humans, other mammals, birds, reptiles, amphibians, fish, flowering plant Occurs in simple organism like  Amoeba sp.,  Paramecium sp., Hydra sp.  Produces offspring that are genetically different from their parents Ensure the survival of the species if the environmental conditions undergo changes constantly Produces offspring that are genetically identical from their parents Ensure the adaptations of the parent for survival are pass downed unchanged to the offspring Necessity for the formation of gametes: 1)   Formation of gametes happens in reproductive organs (gonads) 2)   Male gonads are known as testes and female gonads are known as ovaries 3)   Formation of gametes is through meiosis in which 46 chromosomes are halved to 23. 4)   During fertilisation, a fusion of a sperm and an ovum which has 23 chromosomes each produces a zygote with 46 chromosomes   The male reproductive system 1)   Testis:  produce both the male gametes (sperms) and male sex hormones. Has thousands of seminiferous tubules  inside. 2)   Scrotum:  hold the testes and located outside the main body cavity. Has lower temperature (2-3 C lower than normal temp) for development of healthy sperm. 3)   Epididymis:  Combination of thousands of seminiferous tubules coiled together outside the testis. Sperms are formed in the seminiferous tubules and mature within the epididymis. The functions is to store and mature the sperm. 4)   Vas deferens or sperm duct:  Connected to epididymis. Stores the sperm and transfer the sperm from the apididymis to the ejaculatory duct. The vas deferens leaves the scortum and enters the abdominal cavity 5)   The 2 sperm ducts are joined to urethra  which connects the urinary bladder  to the  penis. 6)   Seminal vesicles:  secrete a thick, clear fluid containing nutrients for the sperms 7)   Prostate gland:  secretes a milky white fluid that activates or increase the mobility of the sperm.  Spermatogenesis   1 2 3 4 5 1)   Primordial germ cells undergo mitosis to form many spermatogonia (spermatogomium) (2n) 2)   Each spermatogonium (2n) develops into primary spermatocytes 3)   Upon puberty, primary spermatocyte undergoes meiosis I and form 2 secondary spermatocyte (n)-haploid 4)   These spermatocytes undergo second meiosis and form 4 spermatids 5)   Spermatids differentiate to form spermatozoa (sperm cells) mitosis mitosis Cell growth Meiosis I Meiosis II differentiation  The female reproductive system 1)   Ovaries:  produce the female gametes (ova/ovum) and secrete female sex hormones; oestrogen an progesterone 2)   Fallopian tube : Move the ovum along. Has fimbriae which surround ovaries. 3)   Uterus : thick-walled, muscular organ that holds the developing embryo and foetus
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