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Plant Life Cycles -All plants alternate between two phases in their life cycles. Alternation of generations • Sporophyte (diploid) – Begins when sperm fertilizes egg (zygote) – Diploid zygote divides by mitosis to create a mature sporophyte – Meiosis produces haploid cells called spores – Haploid spores released Alternation of generations • Gametophyte (haploid) – Begins with spores created by meiosis – Spore grows into gametophyte • Male gametophyte creates sperms • Female gametophyte creates eggs – Sperm & egg create diploid zygote (process repeats) Group 1: Seedless, nonvascular plants ex: moss • Nonvascular plants have a dominant gametophyte phase. – moss gametophytes look like green carpet – moss sporophytes shoot up as stalklike structures sporophyte (2n) capsule spores (1n) gametophyte (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 .. . sporophyte gametophyte 4) Sporophyte will create and release haploid spores 5) Spores land and grow into new gametophytes 6) The process repeats gametophyte ground Plant Life Cycle Comparisons Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, GAMETOPHYTE carpet-like plant that produces specialized gametes Fern More familiar, leafy plant with clusters of spore producing sacs (sori) Haploid plant body SPOROPHYTE (prothallus) is size of a finger nail, produces both male and female parts 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 SPOROPHYTE Group 2: Seedless, Vascular Plants • Ex: Ferns Ferns • Seedless, vascular plants – Vascular: allows taller growth • Rhizoids: underground stems draw nutrients • Fronds: leaves uncurl – sporangia on underside • Sori: clusters of sporangia Fern Life Cycle • Sporophyte phase – Dominant stage – Sporangia produces haploid spores – Spores released into air • Gametophyte phase – Spore grows into prothallus • Archegonium: produces female egg • Antheridium: produces male sperm – Sperm swims to egg – Zygote begins sporophyte stage See appendix B in your text book 1) Sporophyte creates and releases haploid spores . . . . Adult Sporophyte (diploid) 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 . Plant Life Cycle Comparisons Plant type Sporophyte Gametophyte Dominant? Moss Stalk with cup (capsule) at tip, which is where spores are produced. More familiar, GAMETOPHYTE carpet-like plant that produces specialized gametes Fern More familiar, leafy plant (fronds)with clusters of spore producing sacs (sori) Haploid plant body SPOROPHYTE (prothallus) is size of a finger nail, produces both male and female parts 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 SPOROPHYTE
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