Reproduction in Flowering Plants

Reproduction is the process by which new individuals of a species are produced; transferring genetic information from one generation to another to ensure the continuation of the species.
Types of Reproduction:
- Asexual reproduction
- Sexual reproduction

Microsporangium: A chamber in the anther where pollen is produced.
Microsporocyte (Microspore Mother Cell): A diploid cell that undergoes meiosis to produce four haploid microspores.
Microspore: A small haploid spore that develops into a pollen grain (male gametophyte).
Tetrad: A group of four haploid microspores.
Pollen grain: Male gametophyte containing two cells: a generative cell and a tube cell, encased by two layers:
- Exine: The outer wall, secretes chemicals for compatibility.
- Intine: The inner wall, secretes chemicals for digesting stigma tissue.
Generative cell: A cell within a pollen grain responsible for producing two non-motile sperm cells via mitosis.
Tube cell: A cell within a pollen grain that produces the pollen tube, which extends down the style towards the ovary to deliver the sperm cells.

Synergid cells: Two short-lived haploid cells in the embryo sac, closely associated with the egg cell.

The pollen grain is enclosed by two walls: the thick outer exine and the thin inner intine.
The pollen grain is an immature male gametophyte containing two cells, a generative cell and a tube cell.
When the pollen grain lands on a compatible stigma, the generative nucleus divides by mitosis to produce two sperm nuclei (male gametes).
The tube cell nucleus produces the pollen tube which grows down the style towards the ovary.
The pollen grain is now a mature male gametophyte, ready to deliver sperm cells for fertilization.

Occurs inside the ovary, involving meiosis and mitosis to produce the egg cell.
Meiosis:
- Diploid megaspore mother cell divides meiotically to produce four haploid megaspores.
Mitosis:
- Only one of the four megaspores survives, and undergoes three mitotic divisions to produce eight nuclei.
- These eight nuclei reorganize to form the embryo sac with seven cells:
  - Egg cell
  - Two synergid cells
  - Three antipodal cells
  - Central cell with two polar nuclei

Fertilization occurs when a sperm nucleus from the pollen tube fuses with the egg cell in the ovule, forming a zygote.
The zygote undergoes mitosis and cell division to form the embryo.
The other sperm nucleus fuses with the two polar nuclei in the central cell to form the endosperm, which provides nutrition for the developing embryo.

Begins after fertilization.
The zygote divides repeatedly in a process called cleavage, forming a hollow ball of cells called a blastocyst.
The blastocyst implants in the uterine wall.
The fluid-filled cavity of the blastocyst is called the blastocoel.
The outer layer of cells, known as the trophoblast, will later form the chorion and contribute to the placenta.
The inner cell mass cluster of cells gives rise to the embryo.

Gastrulation: The formation of the gastrula through cell movements, producing three germ layers: the ectoderm, mesoderm, and endoderm.
Four extraembryonic membranes also form: chorion, amnion, yolk sac, and allantois.

The process by which the three germ layers differentiate and develop into specific organs of the body.
Begins during week 3 of development.
Ectoderm: Forms the nervous system, epidermis of the skin, and sensory organs.
Mesoderm: Develops into muscles, bones, cartilage, heart, circulatory system, kidneys, and reproductive system.
Endoderm: Creates the innermost lining of the intestine, digestive organs (pancreas & liver), and urinary bladder.
Early organogenesis:
- Neurulation (formation of brain & spinal cord)
- Notochord development
Fetal period: Weeks 9-birth (continued growth and development).
Somites: Segmented blocks of mesoderm that develop into vertebrae, muscles, and ribs.
At the end of organogenesis, all organ systems are formed, and the embryo is now called a fetus.