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Sexual Reproduction in Flowering Plants. What are flowering plants?. -The flowering plants, also known as angiosperms are seed-producing plants.
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Sexual Reproduction in Flowering Plants What are flowering plants? -The flowering plants, also known as angiosperms are seed-producing plants. -The characteristics of angiosperms includehaving flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Formation of male and female gametes in flowering plants - Male and female gametes are produced in flowers Gametes Female Male Egg Cell (1) Polar Nuclei (2) Pollen Grain
Male and Female Structures in a Flower Sticky Join stigma to ovary Carry Ovules Place where pollen grains are produced
The Formation of embryo sac in the ovule • Ovary • is the part of the pistil which holds the ovule(s) • Above the ovary is the style and the stigma, which is where the pollen lands and germinates to grow down through the style to the ovary • - A fruit is the ripened ovary or ovaries Ovule - The egg. A small structure in a seed plant that contains the embryo sac and develops into a seed after fertilization
Embryo Sac • A large cell that develops in the ovule of flowering plants. • It contains a large number of nuclei derived by division of the megaspore nucleus. • At the micropyle end is the egg nucleus and two synergids; at the opposite end are nuclei that will become the antipodals and in the centre are two polar nuclei which fuse to become the primary endosperm nucleus.
Review the formation of female gametes in a flower E.S.M cell (2n) 3 1 Forms 4 (n) megaspores, 3 die 3 antipodal cells 2 2 synergid cells 1 egg cell 4 5 The nucleus of the functional megaspore
Pollination and the formation of pollen tube Pollination A process in which ripe pollen from an anther are transferred to a stigma Fertlisation Fertilisation starts when pollen grains land on stigma Formation of pollen tube The formation of pollen tube is stimulated by the sugar on the stigma. The pollen grain on the stigma will germinate and form pollen tube, grow into style towards ovule.
Sugar on stigma stimulates pollen grain to germinate The pollen grain forms a tube known as ; POLLEN TUBE The generative nucleus divide by mitosis forming 2 GAMETE NUCLEI
The pollen tube grows into the style towards the ovule 2 male gamete nuclei The tube nucleus lead the 2 male gamete nuclei down the pollen tube
The pollen reaches the ovary The pollen tube penetrates the ovule through the micropyle Micropyle
The pollen tube penetrates the ovule through the micropyle The tube nucleus disintegrates giving a clear passage for 2 male gamete nuclei disintegrate
2 male nuclei 1 male nucleus 1 male nucleus Fuse with egg cell Fuse with 2 polar nuclei + 1 male nucleus Diploid Zygote (2n) Triploid Nucleus(3n) + 1 male nucleus Embryo Endosperm
The outer layer loses its moisture *Protects the embryo and endosperm* Ovule seed Embryo (2n) *protects the seeds and may function to disperse them Ovary develops Fruit Triploid Nucleus (3n) *provides nourishment to the developing embryo* *a nutrient-rich tissue
Fertilisation in Flowering Plants is called “Double Fertilisation”. The process that takes place in ovule occurs twice 1st : The fertlisation of egg cell and 1 male gamete nucleus to form a diploid zygote 2nd : The fertlisation of 1 male gamete and 2 polar nuclei s to form a triploid nucleus
The importance of Double Fertilsation for the Survival of Flowering Plants Give rise to endosperm -Endosperm formed when 2 polar nuclei are fertilised by 1 male gamete nucleus -Endosperm is a nutritive cell, it stores food in form of starch and protein as well as fat -After a fertlisation in an ovule, there are 1 embryo and 1 triploid nucleus (which later develops into endosperm). It means each embryo has its own temporary food store in the endosperm -Therefore, each embryo in each ovule feeds on its own stored food in endosperm for survival -Food stored in endosperm enable embryo lives longer when the conditions are unfavourable
