Reproduction in Flowering Plants Objective: Describe the reproductive organs of the plant Explain how the female and male gametes are formed. Explain the process of sexual reproduction in angiosperms Describe the structure and function of seeds

9Ad Parts of an angiosperm 2

Sexual Reproduction in Angiosperms How do plants get to new areas? Seeds Plants reproduce sexually The products of this sexual reproduction are seeds. These seeds are contained inside an ovary. Which develops into a fruit in angiosperms. Seeds have two functions Protect and nourish the embryo inside Carry that embryo to a new location

Reproductive Parts Male reproductive organs (stamen): Anther: produces pollen grains Filament: supports anther above female reproductive organs Female reproductive organs (carpel): Stigma: sticky landing site for pollen grains Style: tube that leads down to ovary Ovary: contains ovules that develop into seeds

Before Pollination(Microgametogenesis) Meiosis begins when flower is a bud 1. Microsporogenesis: a process by which the diploid microsporocyte (pollen mother cell) undergoes a meiotic division to produce haploid microspores  Microsporogenesis occurs in the stamens  Microspores develop thick cell walls to prevent desiccation 3. Microgametogenesis: development of the male gametophyte  Mitotic division of the haploid microspore forms a two-celled microgametophyte; a vegetative cell and a generative cell - wall layers are added to the microspore wall during this time (forming pollen grains) and the microspore is still within the anther 4. Anther ruptures releasing the pollen grains 5. Generative cell undergoes mitosis to form two sperm cells; therefore, there are now 3 haploid cells in the pollen (1 vegetative cell, and 2 sperm cells)

Reproductive Mechanisms 9Ad Reproductive Mechanisms Pollen (male gamete) from one plant lands on the stigma of another plant. This is called pollination. pollen stigma 6

Methods of Pollination Natural Reproduction Pollination in angiosperms can happen by wind or animals. Animals can transfer pollen (bees) from one plant to the other. They are called pollinators Pollen can be blown from one plant to another. Wind dispersal

Megagametogenesis Ovary contains one or more developing ovules each containing one ore more diploid megasporocytes (egg mother cells) 1. Megasporocyte undergoes meiosis producing one functional haploid megaspore and three abortive megaspores that are reabsorbed 2. Functional megaspore becomes the developing megagametophyte 3. Three mitotic divisions (no cytokinesis) produce an eight-nucleate megagametophyte (embryo sac) 4. Cytokinesis and migration follows 5. Three of the nuclei migrate to the micropyle end, undergo cytokinesis, and form a central egg and two flanking synergid cells 6. The flower bud opens

From Pollen to Ovary pollen tube ovary containing ovule A pollen tube grows through the style, where it receives water and nutrients for growth After germination of the pollen grain, the vegetative cell becomes the pollen tube cell The nucleus of the pollen tube cell is at the tip of the pollen tube and the two small sperm cells follow behind The pollen tube goes through micropyle into the megagametophyte micropyle pollen tube style ovary containing ovule megagametophyte 9

Reproduction the two sperm cells and tube nucleus are released into one synergid cell this synergid cell transfers one sperm to the egg, then it ruptures and releases the second sperm into the central cell sperm cell nucleus fuses with the egg nucleus to form the zygote the other sperm cell nucleus fuses with the two central nuclei (polar nuclei) to form a triploid - "double fertilization" the triploid nucleus undergoes mitotic divisions to produce the endosperm (nutrient tissue for the developing embryo) the diploid zygote undergoes mitotic divisions to form the embryo

Fertilization pollen tube with pollen grain nucleus ovule egg cell 9Ad Fertilization The two sperm cells and tube nucleus are released into one synergid cell. This synergid cell transfers one sperm to the egg, then it ruptures and releases the second sperm into the central cell pollen tube with pollen grain nucleus ovule Embryo grows inside the ovule. egg cell 11

Sperm cell nucleus fuses with the egg nucleus to form the zygote The other sperm cell nucleus fuses with the two central nuclei (polar nuclei) to form a triploid - "double fertilization" The triploid nucleus undergoes mitotic divisions to produce the endosperm (nutrient tissue for the developing embryo) The diploid zygote divisions to form the embryo https://www.youtube.com/watch?v=bUjVHUf4d1I

Zygote to Embryo The zygote will grow through the process of mitosis to form an embryo (The ovule is now called a seed and is covered by a protective seed coat.) seed seed coat food supply (cotyledon) embryo

Fruit Formation Some plants produce fruit containing seeds. Fruit: Mature ovary Tissue surrounding the embryo develops into fruit. When the fruit is fully developed it drops off the plant, or is carried away by an animal. When fruit decomposes it releases the seed and germination can occur.

Germination A seed requires moisture (water) to germinate. Then as the embryo grows, the root and shoot break through the seed coat. Nutrients stored in the cotyledon provide nourishment and support early development

Germination Once germination (growth and development of new plant) begins there are several other structures that become visible. Cotyledons: seed leaves (supply food to embryo and perform photosynthesis for developing plant) Coleoptile: shoot (or stem where it first appears) of corn Radical: young root Epicotyl: stem above cotyledons Hypocotyl: stem below cotyledons http://www.youtube.com/watch?v=pB4ASdELBbQ

Asexual Reproduction in Plants… The stem is the most common organ used in asexual reproduction. Results in genetically identical offspring Requires less energy Results in less diversity, but diversity may not be energy efficient or necessary.

Examples… Plants such as the grasses produce underground stems called rhizomes.  Grow through the soil periodically producing adventitious roots and a new above ground shoot. 

Some plants, like strawberry plants grow stems that produce few, if any, leaves.  Stems sprout adventitious roots down into the soil, and new above ground shoots. 

Plantlets… Duckweed miniature plants on the edge of their leaves.  These drop off and develop into mature plants.  Reproduces almost entirely by this method. 

Plenary.. What is the function of the flower? Explain the what double fertilization means to a plant. What is a seed? What basic condition is required for a seed to germinate? Describe two methods of pollination.

Your Task Read 592 – 594 (Asexual Reproduction) #1-7 Read 595 – 602 (Sexual Reproduction) # 1-10