Angiosperm reproduction pp.535-539

A. Female Gametophyte Ovary contains 1 or more megasporangia = ovules Each ovule produces a megaspore mother cell (2n) Megaspore mother cell produces an embryo sac (n) by meiosis Embryo sac is made of 8 nuclei = female gametophyte 3 nuclei go to each end 2 nuclei go to the middle (= polar nuclei) One of the 3 nuclei at the end closest to the ovule’s opening enlarges & forms the egg nucleus

B. Male Gametophyte Anthers contain microsporangia = pollen chambers Each pollen chamber produces many microspore mother cells (2n) Microspore mother cells produce 4 microspores each by meiosis = pollen grains (n) The nucleus of the pollen grain divides to form 2 nuclei = a tube nucleus & a generative nucleus

Grass pollen Daisy pollen

C. Pollination = the transfer of pollen from anther to stigma There are two types of pollination: 1. Self pollination (same plant) 2. Cross pollination (different plants)

D. Fertilization Pollen grain lands on stigma Pollen grain grows pollen tube Generative nucleus divides to form 2 sperm nuclei When pollen tube reaches female gametophyte, sperm nuclei enter Both nuclei participate in double fertilization One sperm nucleus fuses with egg nucleus The other sperm nucleus fuses with the 2 polar nuclei to form a triploid (3n) endosperm (= food)