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Flowers and reproduction (Sexual reproduction (The plant life cycle…
Flowers and reproduction
Sexual reproduction
Gametophytes
Microgametophyte
Mitosis occur producing large vegetative cells and small generative cells which divide and form 2 sperm cells
Microgametophyte is protected and nourished by style tissue
Microspore develops into microgametophyte
Megagametophyte
Nucleus undergo 3 mitotic divisions, producing 2,4 and 8 haploid nuclei all in a single
Multi-nucleated mega-gametophyte is called embryo sac
Within the ovule the surviving megaspore develops into a megagametophyte
Fertilization
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Fertilization in flowering plants happens
through a process called pollination.
After fertilization occurs, each ovule develops into a seed
Syngamy of sperm and egg involve plasmogamy and karyogamy
four steps: pollination, germination, penetration of the ovule, and fertilization
When both sperm nuclei undergoes fertilization it is called double fertilization
Flower structure
Stamen
Composed of filament and anther (2n)
collectively called androecium, Male part
Anther opens an release pollen
Petal
Flat, thin and usually with attractive colors
Attracts insects for pollination
carpel
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Stigma, style and ovary are present
Constitute gynoecium, located at the highest level, female part
Flowrers can have 0-many carpel
Sepal
Sepals are the lowermost and outermost part
Thickest, toughest and waxiest part that support petals
Embryo and seed development
Environmental conditions affecting seed germination include; water, oxygen, temperature and light
The embryo is developed from the zygote and the seed coat from the integuments of the ovule.
distinct phases of seed germination occur: water imbibition; lag phase; and radicle emergence.
A seed is an embryonic plant enclosed in a protective outer covering
The plant life cycle
Germination happens inside the seed, and with just the right combination of soil, water, and sunlight
Diploid adult produce haploid sex cells called gametes
Major stages of the flower life cycle are the seed, germination, growth, reproduction, pollination, and seed spreading
Gametes fuse with other gametes called syngamy or fertilization
Fruit development
The formation of fruit is controlled by certain hormones like auxins, cytokinins, gibberellins
Development varies with the nature of carpel and the nature of mature fruit.
Development of the ovary and the initiation of the cell division, predominant feature and cell expansion
As the ovule develops into a seed, the ovary matures into a fruit.
Inflorescences and pollination
Racemose and Cymose are the types of inflorescences
Inflorescences are complex structures with many functions
Inflorescence is a group of flowers arranged on a floral axis
During flower and fruit development they provide nutrients to the developing flowers and fruits.
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There may be dozens or even hundreds of flowers in an inflorescence
Asexual reproduction
In some species, plantlets are formed where flowers are expected
A grove of aspens that covers several acres in Utah has been discovered to be a single plant
Individual part became self sufficient by establishing adventitious roots
Cacti is a good example for fragmentation
Fragmentation is one of the common asexual reproduction
Fruit type and seed dispersal
Classification of fruit types
Dry fruit
Indehiscent fruits
Dehiscent fruits
Fleshy fruit
Pome
Drupe, pepo
Berry
Compound fruits
Aggregate fruits
Multiple fruits
True fruit and accessory fruits
True fruits include cherries, plums, and peaches
Accessory fruits are strawberry, pineapple, common fig, and mulberry
Development from other parts of the female gametophyte and are known as accessory fruits
Apple develops from inferior ovary and the bulk of fruit is enlarged base of sepal and petals
fruits develop from the ovary and are known as true fruits
Flower structure and cross pollination
Monoecious and Dioecious species
Monoecious describes a single plant that bears both male and female flowers
Dioecious plants: Poplar, willow, ash, mulberry, holly, juniper, pepper trees, red maple,
Dioecious is a plant group that includes distinct male and female plants
Monoecious plants are birch, hazelnut, oak, pine, spruce, corn, and squashes
Cross pollination
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Resulting seeds will have characteristics of both varieties and is a new variety
diversity in the species, as the genetic information of different plants are combined
Cross pollination is when one plant pollinates a plant of another variety
Animal pollinated flower
Evolution of animals have dramatic impact on evolution of plants
Petal color attracts animals, its pigmentation, fragrance and the sweetness helps to attract different animals
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Bees, butterflies, moths, flies, and hummingbirds are most important for pollination
Ovary position
When the flower is hypogynous, the ovary is said to be superior
one that is attached to the stem below where the other flower parts are attached is an inferior ovary
Ovary is a part of the female reproductive organ of the flower or gynoecium.
Wind pollinated flower
Large production of pollen grains.
Anther is well exposed.
Flowers are not attractive and scent emitting.
Feathery and sticky stigma.
Flowers do not possess nectar.
