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Plant Life Cycles Alternate. Plants produce gametes , but their life cycle includes a few extra steps. Plants complete their life cycle by alternating between two phases . One phase involves a Diploid (2n) plant body that produces spores.

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plant life cycles alternate
Plant Life Cycles Alternate
  • Plants produce gametes, but their life cycle includes a few extra steps.
  • Plants complete their life cycle by alternating between two phases.
  • One phase involves a Diploid (2n) plant body that produces spores.
  • The other phase involves a Haploid (n) plant body that produces gametes.
  • This type of life cycle that alternates between diploid and haploid phases is called Alternation of Generation.
general overview of alternation of generation
General Overview of Alternation of Generation
  • The diploid phase begins with a fertilized egg (zygote).
  • This divides by mitosis and grows into a mature Sporophyte.
  • A mature sporophyte has cells that divide by meiosis to produce haploid spores.
  • A Spore marks the beginning of the Haploid phase of the plant life cycle.
  • A spore divides by mitosis and grows into a mature Gametophyte (gamete producing plant).
  • Specialized parts of a mature gametophyte produce gametes (sperm and egg).
  • When sperm meets egg, fertilization takes place and the cycle continues with a new sporophyte.
  • Why must gametophyte cells divide by mitosis?
life cycles in different plant groups
Life Cycles in Different Plant Groups
  • The sporophyte and gametophyte stages look different in nonvascular plants, vascular plants, and seed plants.
moss life cycle
Moss Life Cycle
  • The gametophyte stage is dominant.
  • The green carpet-like plants that you recognize as moss are gametophytes.
  • Moss sporophytes look like a brown stem topped with a tiny cup called a capsule.
  • These capsules contain spore producing sacs called. sporangia.
  • Male structures produce sperm with flagella and female structures produce eggs.
  • The sperm can get to the egg when water is present.
fern life cycle
Fern Life Cycle
  • The sporophyte is the dominant stage.
  • The plants that you recognize as ferns.
  • On the underside of a fern leaf (frond) you will see clusters of sporangia called sori.
  • Spores are released from the sori when they are mature.
  • If they land in a good spot, they develop into a gametophyte (prothallus)
  • The gametophyte anchors using rhizoids.
  • When water is present, male structures release sperm that swim towards the egg.
  • After fertilization, Fiddleheads form and slowly uncurl as they grow.
  • Eventually the sporophyte will grow into a new fern.
conifer life cycle
Conifer Life Cycle
  • The sporophyte is the dominant stage.
  • Seed plants produce two types of spores that develop into male and female gametophytes.
  • Gametophytes of seed plants are also microscopic.
  • Confers like Pine trees produce 2 different cones (male and female) .
  • Female cones are usually larger and more scaly than male cones.
  • Male spores develop into pollen and female spores develop into eggs.
  • Pollination occurs in a cone-bearing plant when a pollen grain reaches the small opening of an ovule.
  • A pollen tube will then form down to the egg.
  • If sperm fertilizes egg a zygote forms and grows into a new plant.
  • What is the difference between how seedless plants and seed plants disperse to new areas?
flowers
Flowers
  • Flower parts are arranged in layers.
  • Sepals are modified leaves that protect the developing flowers.
  • Petals are also modified leaves that are usually bright colors to attract animal pollinators.
    • Flowering plants that are not pollinated by animals usually have very small sepals and petals, or none at all.
flowers1
Flowers
  • Most flowers have both male and female structures.
  • A Stamen is the male structure of a flower.
    • It is made up of the filament (stalk) and the anther (produces pollen grains).
  • The Carpel (Pistil) is the female structure made up of three parts:
    • The Stigma is the sticky top that serves as the landing spot for pollen.
    • The Style is the tube connecting the stigma to the ovary.
    • The Ovary is found at the base of the flower and produces gametophytes.
  • What parts of conifers have functions similar to stamens?
pollination
Pollination
  • When a pollen grain reaches the stigma of the same plant species, pollination has occurred.
  • You can often tell how a flowering plant is pollinated by looking at its flowers.
  • Wind pollinators are usually small and produce large amounts of pollen.
  • Those that use insects, birds or other animals are specialized.
  • While drinking nectar, animals get pollen stuck to them and transport the pollen elsewhere.
  • Why is pollination more reliable by animals than by wind?
fertilization
Fertilization
  • The sporophyte is the dominant stage.
male gametophytes
Male Gametophytes
  • Anthers produce pollen grains.
  • Cell within the anthers divide by meiosis to produce four male spores.
  • Each spore divides by mitosis, producing two haploid cells.
  • The two cells together produce one pollen grain.
female gametophytes
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. (3 usually die)
  • The nucleus of the last spore grows, diving by mitosis three times (1 spore with 8 nuclei).
  • The end product is an embryo sac and an egg.
double fertilization
Double Fertilization
  • After pollination, one cell in the pollen grain grows into a pollen tube.
  • The tube grows to the ovule.
  • Two sperm travel down the pollen tube. (one fertilizes the egg).
  • The other sperm combines with the polar nuclei in the embryo sac and will become the endosperm.
    • The Endosperm is the food supply for the developing plant embryo.
  • Double Fertilization is the process in which one sperm fertilizes an egg and the other form a triploid cell.
  • Happen ONLY in flowering plants.
  • What is the function of each sperm during double fertilization?
seeds and fruit
Seeds and Fruit
  • At fertilization the ovule becomes a seed (contains an embryo and a nutritious endosperm in a seed coat).
  • While the seed develops, the surrounding ovary grows into a fruit.
  • Fruit is the mature ovary of a flowering plant.
    • Ex: Apples, watermelons, and cherries are fruits.
    • Sweet peppers, tomatoes, cucumbers, peanut shells are also considered “fruits”
  • Flowering plants that produce more seeds, produce larger fruits.
  • What is the major difference between seeds of flowering plants and seeds of cone-bearing plants?
seed dispersal
Seed Dispersal
  • Seed dispersal is important because a plant that grows right next to its parent may compete with it for space, sunlight, water and nutrients.
  • Fruits come in many shapes and sizes, each adapted to spread seed to new areas.
  • Fleshy fruits are designed to be eaten and digested with the seeds passing through the digestive system.
  • Some plants have burrs, which are designed to stick to fur.
  • Seeds dispersed by wind often have fruits that act like parachutes or wings.
  • Some plants grow by water and have seeds that float (like coconuts).
  • Why is it important for a fruit to ripen when its seeds are mature?
seeds grow
Seeds Grow
  • When a seed is released, it may be days, months, or years until the seeds begin to grow into new plants.
  • Dormancy
  • Dormancy is the period of time when the embryo has stopped growing.
  • This can take place for years, until conditions are right for growth.
  • Germination
  • During Germination, the embryo breaks out of the seed coat and being sto grow into a seedling.
  • Germination begins when the embryo starts to take up water.
  • As the embryo grows, the embryonic root (radicle) breaks through the cracks.
  • Germination continues until the plant can begin photosynthesis and make its own food.
  • Which emerges first from a seed, a root, or a shoot?
plants can reproduce asexually
Plants can Reproduce Asexually
  • Plants can reproduce sexually and asexually.
  • Sexual reproduction gives rise to genetic diversity.
  • Asexual reproduction allows a well-adapted plant to make many copies of itself.
  • Plants that can grow a new individual from a fragment of a stem, leaf, or root are reproducing by Regeneration.
    • Ex: prickly pear cactus have a jointed stem that looks like teardrop-shaped pads stuck together.
      • If one of these pads fall off it can take root and form a new plant.
plants can reproduce asexually1
Plants can Reproduce Asexually
  • Vegetative Reproduction is a type of asexual reproduction in which stems, leaves, or roots attached to the parent plant produce new individuals.
    • Ex: The Aspen Tree Forrest in Utah is actually 47,000 trunks growing from the roots of one parent plant.
  • Many plants have structures specifically designed for vegetative reproduction:
    • Stolons – Horizontal stems, also called runners.
    • Rhizomes – Horizontal underground stems.
    • Tubers – Large underground stem modified for storage.
      • Ex: the eyes of a potato can sprout new plants.
    • Bulbs – Bulbs are underground stems surrounded by modified leaves adapted for storage, covered with a papery skin.
  • What distinguishes regeneration from vegetative reproduction?
humans can also use vegetative propagation
Humans can also use Vegetative Propagation
  • Plant growers use a process called vegetative propagation to grow plants with desirable qualities, such as seedless fruits or tolerance to frost.
  • Many plants are created using cuttings from stems or leaves.
  • Fruit and nut trees growers usually use trees that have been produced by grafting, or joining vegetative structures from two or more plants together.
  • What is a benefit of producing houseplants through asexual reproduction?
plant hormones
Plant Hormones
  • A Hormone is a chemical messenger produced in one part of an organism that stimulates or suppresses the activity of cells in another part.
  • Hormones regulate many of the functions in cells.
  • Gibberellins
  • Plant hormones that produce dramatic increases in size.
  • Ethylene
  • A plant hormone that promotes ripening of fruits.
  • Cytokinins
  • A plant hormone that stimulate Cytokinesis (the final stage of cell division).
  • Auxins
  • Plant hormones involved in the lengthening of plants cells that promotes growth of new branches or stems.
  • The lengthening of cells caused by Auxins also controls some forms of Tropisms – the movement of plant to environmental stimulus.
  • If you started your own plant nursery, explain two way in which you could use different plant hormones to your advantage.
tropisms
Tropisms
  • There are 3 major types of Tropisms:
    • Phototropism,
    • Thigmotropism, and
    • Gravitropsim
tropisms1
Tropisms
  • Phototropism
  • Is the tendency of a plant to grow towards light.
  • Thigmotropism
  • The response of many plants towards touch.
  • Ex: Ivy and other vines wrap themselves around structures they come in contact with.
  • Gravitropism
  • The up and down growth of a plant in response to Gravity.
  • Downward growth (roots) show Positive gravitropism.
  • Upward growth (stems) show Negative gravitropism.
  • Rapid Response
  • Some plants have rapid response that have nothing to do with tropisms.
  • Ex: The mimosa quickly folds its leaves together a few second after being touched.
  • Ex: The Venus Flytrap quickly closes its leaves on prey.
  • Photoperiodism
  • A response in plants to the signals from the changing lengths of day and night throughout the year.
  • Ex: Leaves shedding in the fall.
  • What stimulus causes each of the following tropisms: phototropism, gravitropism, thigmotropism?