The structure of the ovule, and how one megaspore becomes the 7-celled, 8-nucleate embryo sac.
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Structure of the pistil and the internal anatomy of an ovule.
The gynoecium represents the female reproductive part of the flower, consisting of the pistil. Each pistil has three parts: the stigma (landing pad for pollen), style (elongated stalk), and ovary (basal bulged part).
Pistils can be syncarpous (fused together) or apocarpous (free).
Diagram of an anatropous ovule.
(a) A dissected flower of Hibiscus showing pistil (other floral parts have been removed)
(b) Multicarpellary, syncarpous pistil of Papaver
(c) A multicarpellary, apocarpous gynoecium of Michelia;
(d) A diagrammatic view of a typical anatropous ovule - with Hilum, Funicle, Micropyle, Micropylar pole, Outer integument, Inner integument, Nucellus, Embryo sac, and Chalazal pole
How a single megaspore becomes a 7-celled, 8-nucleate structure.
The process starts with a single large cell in the nucellus called the Megaspore Mother Cell (MMC).
The MMC undergoes meiosis to produce four megaspores. In most flowering plants, three degenerate and only one remains functional.
Distribution of the 7 cells and 8 nuclei inside the embryo sac.
(a) Parts of the ovule showing a large megaspore mother cell, a dyad and a tetrad of megaspores.
(b) 2, 4, and 8-nucleate stages of embryo sac and a mature embryo sac;
(c) A diagrammatic representation of the mature embryo sac.
Match the cells of the embryo sac to their locations and features.
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