KEY CONCEPT All plants alternate between two phases in their life cycles.

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

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

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)

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

5) Spores land and grow into new gametophytes 6) The process repeats . . . . . ground gametophyte

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

A fern gametophyte, or prothallus, produces sperm and eggs. gametophyte (1n)) rhizoid A zygote forms on the prothallus, growing into the sporophyte.

. . . . 1) Sporophyte creates and releases haploid spores ground Adult Sporophyte (diploid) ground

2) Spores land in the soil . . . . ground

3) From the haploid spores, a prothallus (haploid gametophyte) grows in the soil -- Rhizoids anchor Let’s zoom in ground

4) Sperm swim through water from the antheridium to the archegonia Let’s zoom back out

5) Diploid sporophyte (fiddlehead) grows from the prothallus -- prothallus eventually dies ground

6) Fiddlehead uncurls into fronds of ferns. 7) Cycle repeats -- Sporangia creates spores to be released . . . . ground

The sporophyte is the dominant phase for seed plants. pine trees are typical seed plant sporophytes female spores produced in female cones male spores produced in male cones male spores develop into pollen grains, the male gametophytes female spores develop into female gametophytes that produce eggs sperm from pollen travel down pollen tube toward egg fertilized egg develops into embryo ovule develops into protective pine seed

The sporophyte is the dominant phase for seed plants.

1) Male and female seed cones grow in adult sporophytes

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

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)

7) After seeds harden, the cone reopens and the seeds are released

8) Seed will land ground

9) Seedling grows into (sporophyte)…the cycle repeats ground