Angiosperms - Cycle 3 Flashcards
Methods of Pollination: Abiotic Pollination
- Among abiotically pollinated species, 98% rely on wind and 2% on water.
- Since their reproductive success does not depend on attracting pollinators, there has been no selective pressure favoring colorful or scented flowers.
- Wind circulates but water ends so that’s why it relies on wind more
Methods of Pollination: Biotic Pollination
- Most angiosperm species depend on insects, birds, or other animal pollinators to transfer pollen directly from one flower to another
- Pollination by: flies, bees, birds, bats, and moth/butterfly
Coevolution
- The joint evolution of two interacting species, each in response to selection imposed by the other, is called coevolution.
- Ex: Some species have fused flower petals that form long, tubelike, structures bearing nectaries tucked deep inside.
Parts of the Flower: Petals
Attract pollinators
Parts of the Flower: Sepals
Protect the bud as the flower develops
Parts of the Flower: Carpels
The female portion
Parts of the Flower: Stamens
The male portion
Parts of the Flower: Stamens, Anther
Houses pollen grains
Parts of the Flower: Stamens, Filament
Supports the anther
Parts of the Flower: Carpel, Stigma
Recieves the pollen
Parts of the Flower: Carpel, Style
Pathway for pollen
Parts of the Flower: Carpel, Ovary
Structure that will become fruit
Parts of the Flower: Carpel, Ovule
Structure that will become seed
Complete Flower
Possess sepals, petals, stamens, and carpels
Incomplete Flower
Lack one or more of these components
Perfect Flower
Posses both stamens and carpels.
Imperfect Flower
Posses either stamens (staminate) or carpels (carpelate) but not both.
Forms of Pollination: Self-Pollination
The pollination of a flower by pollen from the same flower or from another flower on the same plant
Forms of Pollination: Cross-Pollination
Occurs when pollen grains are transferred to a flower from a different plant.
Alternation of Generations
- Describes the life cycle of a plant as it alternates between a sexual phase and an asexual phase
- The sporophyte produces flowers. Inside the flower, diploid cells undergo meiosis to produce haploid microspores and megaspores. These cells, in turn, develop into the gametophytes that produce sperm and egg by mitosis.
Alternation of Generations Types: Sporophyte Generation
- Non-sexual stage in plants
- Plants grow and develop to form flowers
- The flowers produce reproductive cells called spores
Sporophyte Generation Types of Spores: Microspores
may become the male gametophyte
Sporophyte Generation Types of Spores: Megaspores
may become the female gametophyte
Alternation of Generations Types: Gametophyte Generation
- This is the sexual stage in plants.
- Development of sperm cells from male gametophyte (pollen grains)
- Development of egg cells from female gametophyte.
Sexual Reproduction
- In this life cycle, a diploid (2n) sporophyte alternates with a haploid (n) gametophyte
- The sporophyte (2n) produces haploid spores by meiosis. The spores develop into gametophytes.
- The gametophytes (n) produce gametes
Diploid
(2n) is a cell organism that has paired chromosomes, one from each parent
Haploid
(n) is a cell organism that contains a single set of chromosomes
Mitosis
- For growth and development
- Produces two diploid (2n) somatic cells that are genetically identical to each other.
Meiosis
Produces four haploid (n) gametes that are genetically unique from each other
Microspore Develops into Sperm
- Four microscopes are produced via meiosis. Each one becomes a pollen grain.
- A pollen grain at first consists of two cells
- The larger cell will eventually produce a pollen tube
- The smaller cell divides, either right away or later, to become two sperm
Megaspore Develops into Embryo Sack
- Four megaspores are produced via meiosis but only 1 survives
- The remaining cell divides 3 times through mitosis
- Embryo sac is developed containing seven celled containing a single egg cell
Eight-Nucleate, Seven Cell Female Gametophyte.
- From the 8 generated haploid cells:
- 2 haploid cells move in the middle and join forming a diploid cell
- 3 cells move at the end of the embryo sac and later disintegrates
- 3 cells move in the entry of embryo sac.
Sexual Reproduction: 1st Step
Inside the anther’s pollen sacs, diploid cells divide by meiosis to produce four haploid microspores
Sexual Reproduction: 2nd Step
Meanwhile, meiosis also occurs in the female flower parts. The diploid cell in megaspores initially produces 4 haploid cells. Three of these cells disintegrate leaving one large megaspore.
Sexual Reproduction: 3rd Step
In the anther of the flower, each of the four haploid microspores develops and forms pollen grains. Each of these pollen grains contain one large and one small cell. The large cell becomes the pollen tube, and the small cell eventually forms two-sperm nuclei.
Sexual Reproduction: 4th Step
In the embryo sac of the flower, the large haploid megaspore undergoes 3 mitotic divisions forming 8 cells. Eventually, 2 cells fuse together thus becoming one cell with two nucleus. Thus the result is a seven-celled structure.
Sexual Reproduction: 5th Step
After a pollen grain lands on the stigma, a pollen tube emrges. When the pollen tube reaches an ovule, it discharges its two sperm nuclei into the embryo sac.
Sexual Reproduction: 6th Step
One sperm fertilizes the egg cell and forms a diploid zygote which will later develop into an embryo.
Sexual Reproduction: 7th Step
The other sperm nucleus fuses with the embryo sac central cell’s two nuclei. The result is a triploid cell that will become a tissue called endosperm
Sexual Reproduction: 8th Step
Immediately after fertilization, the ovule contains an embryo sac with a diploid zygote and a triploid endosperm.
Sexual Reproduction: 9th Step
The ovule eventually develops into a seed: a plant embryo together with its stored food, surrounded by a seed coat.
Sexual Reproduction: 10th Step
The ovary grows rapidly to form the fruit.
Fruit
- Protection of seeds
- Fruits promote seed dispersal
Mechanisms of Seed Dispersal
To prosper, seeds must be widely dispersed. Plants use biotic dispersal agents as well as abiotic agents such as water and wind.
