01:119:115 Lecture Notes - Lecture 8: Double Fertilization, Endosperm, Zygote

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Gymnosperm life cycle: (cid:862)(cid:374)aked(cid:863) seeds i(cid:374) (cid:272)o(cid:374)es (strobili, most are conifers, male and female cones, male cone holds microsporagium, female cone holds megasporangium. Microsporocytes 2n undergo meiosis -> microspores (n) Meanwhile megasporocyte undergoes meiosis -> haploid cell is megaspore (female gametophyte) Fertilization -> more than 1 year later. Cycadophyta most endangered of all planta. Angiosperm life cycle female gametophyte: ovary has ovules, ovule = megasporagium, megasporocyte undergoes meiosis, produces 4 haploid megaspores, 3 megaspores disintegrate, 1 functional megaspore undergoes 3 mitotic divisions 1->2->4->8 haploid nuclei. Male gametophyte is in the flower, anther contains microsporangia: microsporocytes (2n) -> produce microspores (n) Male gametophyte = 2 cells (in a pollen grain: tube cell (n) grows a tube, generative cell (n) divides and forms 2 sperm. Pollination anther to stigma (cross-pollination for diversity: pollen lands on stigma, tube grows from tube cell, penetrates through micropyle into ovary, two sperm cells travel to female gametophyte (embryo sac)

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