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Characteristics of Gymnosperms
- 1. Heterosporous. Micro and Megaspores.
- 2. Reduce gametophytes. Male - multinucleate pollen grains (from microspores). Female - small and retained in ovule of previous sporophyte generation (from megaspore).
- 3. Pollen grains - desiccation resistant and adapted for wind pollination.
- 4. Internal fertilization.
- 5. Embryonic sporophyte develops within gametophyte tissue which is protected by previous sporophyte generation (seed).
- 6. Advanced vascular tissue, tracheids (xylem) and phloem.
Gymnosperms ("naked seeds")
- Became free of the dependance of water by the development of internal fertilization via the pollen grain and the development of a seed.
- The seed contains a dormant embryo with a protective cover and special nutrient tissue.
- Reduce gametophytes; male is multinucleated pollen grain, and female is small and retained within the sporangium in the ovule of the sporophyte generation.
- Pollen grain is resistant and adapted to wind pollination.
- Pollen tube conveys the sperm nucleus to egg cell.
- Seed also packed with nutritive materials and can be dispersed away from the parent plant.
- Contain advanced vascular tissue; xylem for water and nutrients transport (xylem cells called tracheids), and phloem for photosynthetic products.
- Produce large amount of pollen that reach appropiate species by chance.
- Flower pollination is mediated by specific agents (insects, birds, and bats) in addition to water and wind.
- Pollination agents recive rewards of nectar and pollen. They provide placement of pollen on female structures that increas fertilization.
- It also enhances opportunity for cross-fertilization and increase genetic variation.
- Pollen grain: the male gametophyte.
- Embryo sac: the eight-nucleated remains of female gametophyte that provides nutrients for developing sporophyte embryo though a triploid endosperm tissue.
- Fruit: seed developed within the flower ovary, which matures into it, provides protection and enhances dispersal.
Advances of Angiosperms
- All gymnosperms are trees or shrubs with an investment in woody, persistent tissue and long life cycles.
- Flowering plants can be woody, but many are herbaceous with soft tissues that survive few years.
- Angiosperms have superior conducting tissues (xylem) and also large-diameter, open-ended vessels. Phloem cells, called sieve-tube members, provide more efficient transport of the products of photosynthesis.
Adaptations to the Land Environment
- Pollen grain; internal fertilization.
- Reduced female gametophyte.
- Ovule; seed.
- Advanced vascular tissue-tracheids.
- Pollen grain; internal fertilization.
- More reduced female gametophyte (embryo sac).
- Ovule; seed; carpal; fruit.
- Double fertilization.
- Flower with 1 or more carpels.
- Advance vascular tissue (tracheids, vessels).
- Herbaceous and woody habit.
Coniferophyta: pines, cone-bearing trees and shrubs like spruce and fir; contain cones for reproduction structures and have needle-like leaves.
Cycadophyta: have a palmlike appearance, found in tropical regiosn; cycads.
Gynkgophyta: ginkgos that have flat fan-shaped leaves, resistant to air pollution.
Gnetophyta: composed of gnetums, which are vines, Welwitschia, a rare desert plant with two long leaves, and mormon tea or Ephedra which is a desert shrubs
Pine Life Cycle
- All are wind-pollinated trees or shrubs bearing unisexual reproductive structures on different parts of same plant.
- Heterosporous: producing two kinds of spores.
- Microspores: male, develop into pollen which is produced in the microsporangium, when mature they are released into the air and conveyed by wind currents to female cone.
- Megaspores: female, retained within megasporangium and nourished by sporophyte parent plant.
- Pollen tubes: grow through the tissue of the megasporangium and sperm nucleus is released to fertilize the egg.
- Seed: dormant embryo embedded in nutrient tissue of female gametophyte and surrounded by hardened sporangium wall or seed coat.
Characteristics of Coniferophyta
Male cones: are ellongated and present only in spring producing pollen. Composed of radiating scales each containing two sacs called microsporangia
witin microsporangia divide by meiosis, each produces four haploid microspores
which develop into pollen grains
- Female cones: contain ovule (in megasporangium) on upper surface of scales that have dipoild megasporocytes inside that will produce megaspores.
- In the first year of ovulate, pollen sifts into the soft bracts (pollination) and the pollen tube begins to grow, digesting the tissues of the ovule.
- During second year it develops a multicellular female gametophyte with 2 archegonia where the egg will form.
- Fertilization occurs in the second year, when pollen tube releases a sperm nucleus into archegonium to form the zygote. Only one archegonia and zygote will develop into a seed.
- Development of embryo sporophyte takes another year. The outer tissues of the ovule will harden to form a seed coat.
Angiosperms ("vessel seed")
- Phylum Anthophyta
- Carpel: a unique characteristic of angiosperms that is a vessel in which ovules are enclosed. After fertilization, the ovule develops into a seed while the carperl matures into a fruit.
- Flowers: are composed of male and female reproductive structures surrounded by attractive or protective leaflike structures called perianth. It protects developing gametes and ensure pollination and fertilization.
- Plants attract pollinators to flower. Color, scent and shape are important. Nectar and pollen provide nutritive rewards for pollinators. Structure of flower provides landing platform, guidelines and mechanisms for pollen placement. Some are wind-pollinated which means they produce large amounts of pollen and are adapted to catch it in the wind.
- Internal double fertilization:
- 1 sperm nucleus + egg = zygote (2n)
- 1 sperm nucleus + 2 polar nuclei = endosperm (3n)
- Pedicel: stalk that support flower.
- Receptacle: tip of the pedicel where the flower parts attach.
- Sepal: outer whrol of bracts, which may be green, brown, or colored like the petals; may appear as small scales or be petal-like.
- Calyx: all the sepals collectively.
- Petal: colored, whorl of bracts located just inside the sepals.
- Corolla: all the petals collectively.
- Perianth: petals, sepals, receptacle and pedicel.
- Stamen: male, pollen-bearing structure, composed of filament and anther.
- Filament: thin stalk that supports the anther.
- Anther: pollen-producing structure.
- Carpel: female, composed of stigma, style and ovary; often pear-shaped and located in the center.
- Stigma: receptive tip of the carpel, often sticky or hairy, where pollen is placed.
- Style: tissue connecting stigma to ovary; pollen must grow through here to fertilize egg.
- Ovary: base of carpel, protects ovules inside, matures to form fruit.
- Plants have coevolved with a particular pollination agent.
- Flower pollinated by wind: inconspicuous sepals and petals, feathery stigma no odor.
- By hummingbird: red tubular flowers with little or no odor.
- By bat: white flowers that smell like fruit, strong pedicel and flower parts.
Angiosperm Life Cycle
- Pollination and Fertilization:
- When pollen grains are mature, the anthers split and the pollen is released. When pollen reaches stigma, it germinates to produce the pollen tube, which grows down the style and comes into contact with the opening to the ovule.
Double Fertilization: during this growth, one pollen nucleus divides into two sperm nuclei. One of them fuses with the egg to form zygote, and the other fuses with two polar nuclei to form a triploid endosperm, which will develop into a rich nutritive material for the support and development of the embryo.
Seed and Fruit Development
The zygote formed at fertilization undergoes rapid mitotic phyla, forming the embryo. The endosperm also divides, then the mature ovule forms a seed. At same time, the surrounding ovary and other floral tissues are forming the fruit.
Dispersal of Fruits
- Some dry fruits open when mature. Seeds from these might be dispersed by wind or gravity. Other dry fruits may be eaten by animals.
- Fleshy fruits don't open and they may be eaten.
Characteristics of Fruits
Archene: dry one-seeded fruit with ovary and seed fused.
Drupe: fleshy one-seeded fruit with a stony covering around the seed.
Berry: fleshy many-seeded fruit.
Structures of Seed plants
Pollen grains: Male gametophyte; transports sperm to egg without water, produced in large amounts with desiccation-resistant coat.
Microsporangium: Sterile jacket of cells protecting spore production (meiosis).
Flower: attracts pollinator to enhance efficiency of movement of pollen, increasing cross-fertilization and in some cases genetic variation.
Carpel: protects ovules and developing embryo plants.
Seed: can be dispersed to new areas, prepacked embryonic plant with nutritional resources and desiccation-resistant covering.
Fruit: enhances dispersal of seeds, protects seeds.
Endosperm: rich nutriet resource available ofr embryonic plant in developing seed.
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