Published on January 28, 2014
Fertilisation Mammals & Flowering Plants Unit 2 Topic 3
• • • • Fertilisationthe fusion of gametes. Mammalian gametessperm & ovum Flowering plant gametespollen & egg The importance of reproduction in sexual reproduction: – it restores full competent (diploid number) of chromosomes (46 in humans); – it allows genetic variation.
Fertilisation in Mammals Stage Acrosome reaction Description of events • • Acrosome releases digestive enzymes when sperm head meets zona pellucida (jelly layer) of oocyte (egg cell before having gone through complete meiosis). Enzymes digest a channel in zona pellucida for sperm to burrow through to the cell surface membrane of oocyte. Membranes fuse • Cell surface membrane of sperm and oocyte fuse enabling haploid nucleus from sperm to enter cytoplasm of oocyte. Egg cell response (cortical reaction) • Special vesicles (cortical granules) move towards and fuse with cell surface membrane. They release their contents (by exocytosis)cause changes in surface layers of oocyte that stop other sperm from entering oocyte. • Meiosis restarted Fertilisation • The presence of the sperm nucleus in the cytoplasm of the oocyte causes the second division of meiosis to occur providing a haploid egg nucleus to fuse with haploid sperm nucleusforms an ovum (egg cell that has completed meiosis). • Chromosomes from the haploid sperm nucleus and from the haploid egg nucleus combine to restore the full complement of chromosomes, the diploid number.
Fertilisation in Flowering Plants Flowering plantsangiosperms Male gametepollen grain Female gameteembedded deep in ovary tissueovule • • • • • • • Pollen grain lands on surface of stigma of the flower during pollination. Molecules on surface of pollen grain and stigma interact. If they are of the same speciespollen grain begins to grow (germinate). Pollen tube begins to grow out from the tube cell of the pollen grain down the stylesecretes enzymes to digest style tissue and uses products to continue tube growth. During the growth and extension of the tube, the generative nucleus, behind the tube nucleus, divides by mitosis to produce 2 male haploid gametes. Pollen tube enters ovule through micropyle and penetrates the embryo sac wall. The tip of the tube bursts open, tube nucleus dies and what follows is called double fertilisation: – 1 male gamete fuses with female gamete nucleusdiploid zygote (2n) – 1 male gamete fuses with the two polar nucleitriploid primary endosperm nucleus (3n) – Immediately after fertilisation, the ovule is known as the seed.
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The footage gives a visual description of the process of fertilisation. ... Society of Biology; The Biologist Subscription; Fastpastpapers.com; KS3 Subjects.
Fertilisation revision notes and tests for GCSE Biology
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