Angiosperm & Gymnosperm

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  • Seedless plants depend on water through which sperm swim to fertilize an egg
  • Seed plants do not depend on water
  • Seed plants produce pollen which can be carried by the wind or on the body of an animal pollinator, such as a bee
  • Pollination - happens when pollen meets female reproductive parts of the same plant species
  • Each pollen grain has a cell that will divide to form sperm
  • The ability to reproduce without free-standing water allows many seed plants to live in drier climates
  • A seed consists of a protective coat that contains a plant embryo and a food supply
  • A seed can survive for many months or years in a dormant state
  • Wind, water, or animals often carry seeds far from the plant that produced them and will only begin to develop until it reaches a suitable environment
  • Seeded plants evolved about 360 million years ago
  • Gymnosperm - a seed plant whose seeds are not enclosed in fruit
  • Angiosperm - seed plant that has seeds enclosed in some type of fruit
  • Most gymnosperms are cone-bearing and evergreen
  • A woody cone is the reproductive structure of most gymnosperms
  • Pollen is produced in male cones, while eggs are produced in female cones
  • Seeds are developed on the scales of female cones, which protect fertilized eggs
  • Three living phyla of gymnosperms: cycads (phylum Cycadophyta), Ginkgo biloba (phylum Ginkgophyta), and conifers (phylum Coniferophyta)
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Cycads
Cycads
  • Look like palm trees with large cones
  • Huge forests of cycads grew during the Mesozoic era, 248 - 65 million years ago
  • These plants provided food for dinosaurs
  • Today, they grow in tropical areas in the Americas, Asia, Africa, and Australia
  • Are endangered species because of their slow growth and loss of habitat in these tropical areas
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Ginkgo
Ginkgo
  • Abundant while dinosaurs lived
  • Only one species lives today, the Ginkgo biloba, which are native to China
  • Today, it is grown around the world in gardens, and used in urban landscaping
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Conifers
Conifers
  • The most diverse and common gymnosperms alive today
  • Pines, redwood, spruce, cedar, fir, and juniper all belong to this phylum
  • Conifers supply most of the timber used for paper, cardboard, housing lumber, and plywood
  • They grow quickly and large tree farms help produce enough wood to meet demand
  • Conifers are well adapted to high altitudes, sloping hillsides, and poor soil
  • These characteristics allow conifers to thrive in mountainous regions
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Reproductive System of a Flowering Plant
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Fruit


Flowering Plants
  • Angiosperms belong to a phylum of their own and are commonly called flowering plants
  • Flower - reproductive structure of flowering plants
  • Flowers protect a plant’s gametes and fertilized eggs
  • Fruit - the mature ovary of a flower which surrounds and protects the seed/seeds
  • Fruit can take the form of a peach, the wings attached to a maple seed, or the fluff surrounding dandelion seeds
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Life Cycle
Flowers and Pollination
  • Flowers allow for more efficient pollination than occurs in most gymnosperms, which rely on wind for pollination
  • As an animal or insect that feeds from the flower, it gets pollen on itself and then moves to another flower for more food which then some of the pollen brushes off onto the new flower
  • Flowering plants pollinated by animals don’t need to produce as much pollen as do plants that rely on the wind to randomly transfer their pollen

Fruits and Seed Dispersal
  • As animals digest the fruit tissues but not the seeds, the seeds pass through the animal which are deposited along with the supply of fecal fertilizer that is helpful during germinating
  • Others take the form of burrs that cling to passing wildlife, or fibers that help spread seeds by wind

Botanists classify flowering plants into two groups based on seed type
  • There are at lease 250,000 identified flowering plant species
  • The three gymnosperm phyla have a total of 720 species
  • Botanists classify flowering plants into two groups based on two basic kinds of seed: seeds with one or two cotyledons
  • Cotyledon - an embryonic leaf inside a seed
  • As an embryo develops into a seedling, the seed leaf of some species remains inside the seed coat, and in others the cotyledons break out of the seed and turn green

Monocots
  • Flowering plants whose embryos have one seed leaf are called monocotyledons (monocots)
  • Have parallel veins in long, narrow leaves, such as those of an iris or lily
  • Their flower parts usually occur in multiples of three and bundles of vascular tissue are scattered throughout the stem
  • The cereal plants we depend on--corn, wheat, rice-- are monocots
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Monocots & Dicots
Dicots
  • Dicotyledons are flowering plants whose embryos have two seed leaves
  • Dicots have leaves with netlike veins, the flower parts usually occur in multiples of four or five, and bundles of vascular tissue are arranged in rings
  • Most deciduous trees, which lose their leaves in the fall, are dicots

Herbaceous or Woody Stems
  • Wood - a fibrous material made up of dead cells that are part of the vascular system of some plants
  • High concentrations of lignin and cellulose make the cell walls of these cells thick and stuff
  • Some flowering plants develop woody stems, while others do not
  • Plants that do not produce wood, such as cucumbers, cacti, and marigolds, are called herbaceous plants

Three Types of Lifespans
  • Annual - Flowering plants that mature from seeds, produce flowers, and die in one year
  • Corn and lettuce are common annuals
  • Biennial - Flowering plants that take two years to complete their life cycle
  • During the first year, a biennial produces a short stem, leaves that grow close to the ground, and underground food reserves
  • During the second year, these reserves are used to produce a taller stem, leaves, flowers, and seeds
  • Perennial - Any flowering plant that lives for more than two years
  • Most woody plants, including trees, are perennials

Plant life cycles alternate between producing spores and gametes
  • Alternation of generations - Plant life cycles alternate between a sporophyte phase, which produces spores, and a gametophyte stage, which produces gametes
  • Sporophyte - a zygote divides by mitosis and grows into a spore-producing plant
  • A mature sporophyte has specialized cells that divide by meiosis to produce haploid spores
  • Cell division by meiosis reduces the number of chromosomes in a cell by one-half
  • Gametophyte - a spore divides by mitosis and grows into a mature gamete-producing plant
  • Specialized parts of a mature gametophyte produce gametes--sperm and eggs-- through mitosis
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Life Cycle of Nonvascular Plants: Moss
  • Nonvascular plants are the only plants in which the gametophyte phase is dominant
  • Moss sporophytes are stalklike structures that grow up from the gametophyte
  • The capsule at the tip of the moss sporophyte contains spore-producing sacs called sporangia, which opens and releases them when the spores mature
  • Spores allow seedless plants to disperse to new areas
  • Each male structure produces hundreds of sperm with whiplike flagella, and each female structure produces a single egg
  • When water is present, sperm will swim toward an egg
  • Once a sperm fertilizes an egg, the sporophyte phase begins once again
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Life Cycle of Fern
Life Cycle of Seedless Vascular Plants: Ferns
  • The sporophyte is the dominant phase for all vascular plants, including seedless vascular plants such as ferns
  • Fern gametophyte are often called a prothallus
  • The prothallus anchors itself to the soil with tiny threadlike structures called rhizoids
  • The prothallus contains special reproductive structures that produce sperm and eggs
  • When a sperm fertilizes an egg, a zygote forms on the prothallus, which eventually rots away
  • The mature sporophyte is the familiar fern plant
  • Newly forming fronds are called fiddleheads, and they slowly uncurl as they grow
  • The sporophyte will produce spores on the underside of each front and the cycle will begin again
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Life Cycle of Seed Plants: Conifers
  • Cone bearing plants have male and female cones
  • Female cones are more scaly than the male cones
  • Each scale of a female pine cone has two ovules that produce spores
  • One spore in each ovule can develop into a microscopic female gametophyte, and the rest will die
  • Male spores are produced inside of male cones, the spores develop into pollen grains which are very tiny male gametophytes of seed plants
  • Pollination occurs in a cone-bearing plant when a pollen grain reaches the small opening of an ovule
  • After pollination, eggs are produced inside the ovule and a pollen tube begins to grow from the pollen grain towards an egg
  • Two perm also develop inside the pollen grain during this time
  • These sperm travel down the pollen tube toward the egg, the sperm of the seed plants do not have a flagella, since they do not need to swim through water to reach an egg
  • One sperm may fertilize an egg, forming a zygote, which will develop into an embryo
  • Once the seeds are mature, the scales open up and release them and then the life cycle begins again with a new sporophyte

Flowers contain reproductive organs protected by specialized leaves
  • Sepals - modified leaves that protect the developing flower
  • Petals - the layer just inside of the sepals
  • Their bright colors often help to attract animal pollinators
  • Some species have flowers with only male or female structures, but the flowers of most species have both
  • Stamen - male structure of a flower
  • Each stamen has a stalk called a filament that supports an anther
  • Anthers produce pollen grains(male gametophytes)
  • Carpel - the innermost layer of a flower that is made up of the female structure called carpel
  • Most flowers have several carpels fused together, forming a structure called a pistil

Production of Male Gametophytes
  • Anthers produce pollen grains, which are the male gametophytes of seed plants
  • Cells within the anthers divide by meiosis to produce four male spores
  • Each spore divides again, by mitosis, producing two haploid cells
  • These two cells form a single pollen grain
  • Wind-pollinated plants have light, fine pollen grains that can be carried far by the wind

Production of Female Gametophytes
  • One female gametophyte can form in each ovule of a flower’s ovary
  • One cell in the ovule divides by meiosis to produce four female spores
  • In more flowering plants, three of these spores die
  • The nucleus of the last spore grows, dividing by mitosis three times, resulting in one spore with eight nuclei
  • Membranes grow between the nuclei to form seven cells, and together these seven cells make up the female gametophyte, which is sometimes called an embryo sac
  • One large, central cell has two haploid nuclei, called polar nuclei
  • One of the other cells develops into an egg

Double Fertilization
  • After pollination, one cell in the pollen grain grows into a pollen tube
  • The tube extends down towards the ovule
  • The other cell in the pollen grain divides by mitosis, producing two sperm
  • Both sperm travels down the pollen tube, one sperm fertilizes the egg, the other sperm combines with the polar nuclei in the embryo sac
  • This cell has a triploid nucleus and will become the endosperm, a food supply for the developing plant embryo
  • Double fertilization only happens in flowering plants and gives them an advantage over cone-bearing plants
  • Cone-bearing plants produce a food supply for each egg before fertilization
  • If the egg of a flowering plant is not fertilized, the plant does not waste energy making an unneeded food supply

Seeds and Fruit
  • At fertilization, the next sporophyte generation begins, the ovule becomes a seed which contains an embryo and a nutritious endosperm enclosed by a protective seed coat
  • Using the nutrients provided by the endosperm, the embryo develops one or two cotyledons, or seed leaves
  • Cotyledons sometimes provide nourishment for the new plant before it can begin producing its own food through photosynthesis
  • While the seed develops, the surrounding ovary grows into a fruit
  • Flowering plants that produce many seeds within one ovary have larger fruit

Dormancy
  • When a seed is dormant, the embryo has stopped growing
  • For some plant species, proper temperature, moisture, oxygen, and light levels are enough to end dormancy
  • Other plant species have seeds that stay dormant even during good growing conditions
  • Strawberry seeds remain dormant until their seed coats are weakened in the digestive tract of an animals. This way the seeds are not carried far from the parent plant but they are also deposited with their own batch of fertilizer
  • Other seeds have waterproof seed coats that can only be cracked by winter ice. Then, in the spring, the embryo can begin to grow with less chance of freezing than if it had begun to grow in the fall
  • Seed dormancy allows the next generating of plants to grow under favorable conditions

Germination
  • During germination, the embryo breaks out of the seed coat and begins to grow into a seedling
  • Begins when the embryo starts to take up water. Water causes the seed to swell and crack the seed coat
  • As the embryo grows, the embryonic root called a radicle, breaks through the cracks
  • A young shoot called the plumule eventually breaks through the surface of the soil
  • In most monocots, the cotyledon stays underground while the shoot grows upwards
  • Some species of dicots have cotyledons that stay below ground, but the cotyledons of other dicots emerge above ground with the growing shoot
  • When leaves emerge from the shoot, they begin to make food through photosynthesis
  • Once the photosynthesis begins, the young plant is called a seedling