1. Ch Plant Life Cycles

2. Alternation of Generation
Plants complete their lif cycle by alternating between two phases
Phase 1: diploid plantbody that produces spores ……. Two copies of chromosomes (2n)
Phase 2: haploid plant body that produces gametes….. One copy of each chromosome (n)
Alternates between diploid and haploid phases

3. Alternation of Generation
Diploid phase: begins with a fertilized egg…. Zygote
Zygote: divides by mitosis and grows into a mature sporophyte (2n)
Sporophyte: spore producing plant that has specialized cells that divide by meiosis to produce haploid spores (n)

4. Sporophyte
Sporophyte: divides by meiosis to produce haploid spores (n)
Cell division by meiosis reduces chromosomes by ½… 2n to n

5. Meiosis

6. Gametophyte
Spores mark the beginning of the haploid phase on the plants life cycle (n)
Spores divide by mitosis and grow into mature Gametophytes
Mature gametophytes produce gametes (sperm and eggs) by mitosis
Sperm and egg meet….. Fertilization takes place
Cycle continues with a new sporophyte

8. Life cycles Non-vascular plants Seedless vascular plants Seed plants
Different plant groups have their own version of alternation of generation
Sporophyte and gametophyte generations are different for:
Non-vascular plants
Seedless vascular plants
Seed plants

9. Nonvascular plants: Moss
Nonvascular: only plant where the ganetophyte phase is dominant
Green leaf-like structures are the gametophyte generation
Stalk like structures with capsule: sporophyte generation

10. Moss Capsule: contains spore-producing sac: sporangia
When the spores are mature: capsule opens and spores disperse
If spore land in a favorable spot: it will grow into a gametophyte
Moss gametophyte produce gametes in special reproductive structures
Male structure: produces 100’s of sperm
Female structure: produce a single egg
When water is present: sperm swim toward an egg and join: Fertilization
After fertilization, the sporophyte phase begins again

12. Seedless Vascular plants: ferns
Sporophyte is the dominant phase for all vascular plants
The fern structure that is recognizable: sporophyte phase
Sori: sporangia (spore producing sacs) are on the underside of the leaf
Sori look like brown dots on the ferns fronds (leaves)
Once mature, spores are released and develop into a gametophyte

13. Ferns Prothallus: fern gametophyte
Small plant body that anchors itself to the soil by rhizoids
Prothallus contain special reproductive structures that produce: sperm and eggs
When water present: sperm is released and swim toward an egg
When fertilization occurs (egg & sperm join): zygote forms
Zygote grows above the prothallus: turns into the sporophyte
Fiddleheads: newly forming fronds
Once mature, the sporophyte will produce sori and the cycle continues

15. Seed Plants: Conifer’s life cycle
Sporophyte is the familiar form of seed plants
Seed plants produce 2 types of spores: develop into male and female
gametophytes
Seed plants gametophytes are microscopic
Pine tree: typical conifer sporophyte
Produce two kinds of cones: male cone and female cone
Female cone: each scale has 2 ovules that produce spores. One will
develop into a microscopic female gametophyte, & one dies
Male cones: produce pollen grains which are tiny male gametophytes

17. Conifers Male cones release clouds of pollen in the spring
Pollen lands and sticks to a female cone
Pollination occurs when pollen reaches the small opening of an ovule
After pollination, eggs are produced in the ovule and a pollen tube begins to grow from the pollen grain toward the egg
In pine species, it takes one year for the pollen tube to reach the egg
Two sperm develop in the pollen grain and travel down the tube to the egg
Sperm of seed plants do not have flagella
One sperm fertilizes an egg, forming a zygote, then develops into an embryo
Once mature, the scale opens and the seed is released: sporophyte pine seedling