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KEY CONCEPT All plants alternate between two phases in their life cycles.
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Plant life cycles alternate between producing spores and gametes.
A two-phase life cycle is called alternation of generations. haploid phase diploid phase alternates between the two fertilization meiosis SPOROPHYTE PHASE GAMETOPHYTE
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The spore-producing plant is the mature sporophyte.
sporophyte phase is diploid begins with fertilized egg spores produced through meiosis The gamete-producing plant is the mature gametophyte. gametophyte phase is haploid begins with spore gametes produced through mitosis fertilization meiosis SPOROPHYTE PHASE GAMETOPHYTE
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Life cycle phases look different among various plant groups.
Nonvascular plants have a dominant gametophyte phase. moss gametophytes look like green carpet moss sporophytes shoot up as stalklike structures sporophyte (2n) gametophyte (1n) capsule spores (1n)
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1) Moss gametophytes grow near the ground (haploid stage)
2) Through water, sperm from the male gametophyte will swim to the female gametophyte to create a diploid zygote 3) Diploid sporophyte will grow from the gametophyte where the zygote is located 4) Sporophyte will create and release haploid spores . . . . . sporophyte gametophyte
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5) Spores land and grow into new gametophytes 6) The process repeats
. . . . . ground gametophyte
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Plant Life Cycle Comparisons
Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, carpet-like plant that produces specialized gametes GAMETOPHYTE Fern More familiar, leafy plant with clusters of spore producing sacs (sori) Haploid plant body (prothallus) is size of a finger nail, produces both male and female parts SPOROPHYTE Conifer More familiar- like pine trees, produces male and female cones that produce spores Pollen grains are male gametophytes sperm, female gameotphytes are microscopic eggs
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The sporophyte is the dominant phase for seedless vascular plants.
Fern spores form in sacs, sori, on underside of mature sporophytes (fronds). sporophyte (2n) sori
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A fern gametophyte, or prothallus, produces sperm and eggs.
gametophyte (1n)) rhizoid A zygote forms on the prothallus, growing into the sporophyte.
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. . . . 1) Sporophyte creates and releases haploid spores ground Adult
Sporophyte (diploid) ground
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2) Spores land in the soil
. . . . ground
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3) From the haploid spores, a prothallus (haploid gametophyte) grows in the soil
-- Rhizoids anchor Let’s zoom in ground
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4) Sperm swim through water from the antheridium to the archegonia
Let’s zoom back out
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5) Diploid sporophyte (fiddlehead) grows from the prothallus
-- prothallus eventually dies ground
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6) Fiddlehead uncurls into fronds of ferns.
7) Cycle repeats -- Sporangia creates spores to be released . . . . ground
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Plant Life Cycle Comparisons
Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, carpet-like plant that produces specialized gametes GAMETOPHYTE Fern More familiar, leafy plant with clusters of spore producing sacs (sori) Haploid plant body (prothallus) is size of a finger nail, produces both male and female parts SPOROPHYTE Conifer More familiar- like pine trees, produces male and female cones that produce spores Pollen grains are male gametophytes sperm, female gameotphytes are microscopic eggs
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Gymnosperm Life Cycle
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The sporophyte is the dominant phase for seed plants.
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1) Male and female seed cones grow in adult sporophytes
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2) Pollen grains released from the male seed cones
2) Pollen grains released from the male seed cones -- Pollen is the male gametophyte Let’s zoom into the female seed cone
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3) Pollen grain sticks to the female ovule
4) Pollen tube grows from the male spore 5) Two nuclei transfer into female spore - one fertilizes the egg 6) Diploid embryo develops (sporophyte stage restarts)
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7) After seeds harden, the cone reopens and the seeds are released
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8) Seed will land ground
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9) Seedling grows into (sporophyte)…the cycle repeats
ground
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Plant Life Cycle Comparisons
Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, carpet-like plant that produces specialized gametes GAMETOPHYTE Fern More familiar, leafy plant with clusters of spore producing sacs (sori) Haploid plant body (prothallus) is size of a finger nail, produces both male and female parts SPOROPHYTE Conifer More familiar- like pine trees, produces male and female cones that produce spores Pollen grains are male gametophytes sperm, female gameotphytes are microscopic eggs
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22.2 Flower Life Cycle Angiosperm Life Cycle
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Flowering plants are pollinated when pollen grains land on stigma
22.2 Flower Life Cycle Flowering plants are pollinated when pollen grains land on stigma Wind pollinated flowers- small flowers and large amounts of pollen. Animal pollinated flowers- larger flowers and less pollen (more efficient). many flowering plants pollinated by animal pollinators
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Fertilization takes place within the flower.
22.2 Flower Life Cycle Fertilization takes place within the flower. Male gametophytes, or pollen grains, are produced in the anthers. male spores produced in anthers by meiosis each spore divides by mitosis to form two haploid cells two cells form a single pollen grain pollen grain stamen anther
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22.2 Flower Life Cycle One female gametophyte can form in each ovule of a flower’s ovary. Many cells can be made in the ovule one cell becomes the egg one cell becomes 2 polar nuclei the rest die Polar nuclei (2n)
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22.2 Flower Life Cycle 1. Pollen grains are released
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22.2 Flower Life Cycle 2. Pollen grains land on the stigma (pollination)
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22.2 Flower Life Cycle 3. Pollen tube grows and 2 nuclei transfer into the ovule . . Let’s zoom in…
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22.2 Flower Life Cycle 3. Flowering plants go through the process of double fertilization. female gametophyte ovule egg sperm polar nuclei Double Fertilization 1 sperm fuse with the polar nuclei = triploid (3n) endosperm 1 sperm fuse with the egg = zygote
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22.2 Flower Life Cycle 4. Each ovule becomes a seed.
endosperm seed coat embryo 4. Each ovule becomes a seed. Endosperm provides food supply for embryo The surrounding ovary grows into a fruit.
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5. Seeds get dispersed 6. Seed germinates, and the cycle starts over ground
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Plant Life Cycle Comparisons
22.2 Flower Life Cycle Plant Life Cycle Comparisons Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, carpet-like plant that produces specialized gametes GAMETOPHYTE Fern More familiar, leafy plant with clusters of spore producing sacs (sori) Haploid plant body (prothallus) is size of a finger nail, produces both male and female parts SPOROPHYTE Conifer (gymnosperm) More familiar- like pine trees, produces male and female cones that produce spores Pollen grains are male gametophytes sperm, female gameotphytes are microscopic eggs Flower (angiosperm) More familiar- apple tree, peach tree, zucchini, berries, etc. Contain flowers that produce male and female spores Pollen grains are male gametophytes 2 haploid cells = pollen tube + sperm, Female gametophyte in ovule egg + 2 polar nuclei
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