Plant Life Cycles

Plant Evolution• Descendants from green

algae (~450mya)

– Contain cellulose in cell walls

– Contain chlorophyll

– Starch stored

• Land Plants Must Overcome

– Drying out

– Gas exchange

– Nutrient transport system

– Support

Land adaptations• Cuticle: Waxy coating

prevents water loss• Stomata: pores that

open/close to permit gas exchange

• Roots & Stems: support• Vascular system: tissue

that transports nutrients– Nutrients & water go up

plant– Sugars go down the

plant

General Plant Life Cycle• Alternation of

generations• Gametophyte

(haploid)– Begins with spores

created by meiosis– Mature

gametophyte grows by mitosis

– Male & female organs

– Sperm & egg created

General Plant Life Cycle• Sporophyte

(diploid)– Begins when

sperm fertilizes egg (zygote)

– Zygote divide by mitosis to create a mature sporophyte

– Meiosis produces haploid cells

Mosses• Nonvascular,

seedless• Grow low to ground

to retain moisture• Lack true leaves

– Leaf-like structures only 1 cell thick

• Rhizoids anchor into soil

• Early inhabitant of new ecosystems (succession)

Moss Life Cycle• Gametophyte phase– Dominant stage

– Carpet of moss growing near ground

• Archegonium: produces female egg

• Antheridium: produces male sperm

– Sperm swims through water to fertilize egg

• Sporophyte phase– Stalk grows up from

the gametophyte

– Sporangia houses haploid spores

– Spores land and new gametophyte grows

Ferns

• Seedless, vascular plants– Vascular: allows taller growth

• Rhizoids: underground stems draw nutrients• Fronds: leaves uncurl

– sporangia on underside• Sori: 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

Conifers• Seed advantages

– Don’t depend on water

– Protects & nourishes embryo

– Allow plants to grow in new locations

• Conifers: woody cone houses seeds– Male cones: produce

pollen– Female cones:

produce egg

• Pines, redwoods, spruce, cedar

Conifer Life Cycle• Sporophyte phase

– Cones grow on tree– Female cones

• Megaspores inside archegonia (gametophyte)

– Male cones• Microspores (gametophyte)

released from antheridia• sticks to archegonium• Pollen tube grows from

pollen• Sperm travels down pollen

tube (zygote/seed created)• Sporophyte stage restarts

male

female

Flowers• Reproductive

structure of flowering plants

• Sepals– outer ring of leaves– protection

• Petals– Inner ring of leaves – Brightly colored to

attract pollinators• Open petals & sepals

reveal male and female structures

Flowers • Female Carpal– Inner most part– Ovary: within the

base (female gametophyte)

– Style: long stalk– Stigma: sticky

tip, collects pollen

• Male Stamen– Surrounds carpal– Filaments: long

stalks– Anther: produces

pollen (male gametophyte)

• 1) Flower matures and opens

• 2) Microspores (male gametophytes) created in the anthers

In the Anthers

• Meiosis makes 4 microspores

• In each microspore

– Nucleus splits in two

– 1 nucleus: forms pollen tube

– 1 nucleus: splits again to make 2 more nuclei

• 1 nucleus: fertilizes the egg

• 1 nucleus: fuses to make endosperm

• 3) Microspores continue to develop

• 4) Ovaries divide by meiosis to create megaspore

In the Ovules• Meiosis makes 4

megaspores (only 1 survives)

• In megaspore– Mitosis creates 8 nuclei– 1 nucleus: egg cell– 2 nuclei: form embryo

sac– 5 nuclei: disintegrate

Microspore lands on stigma

• 5 & 6) Pollen tube grows from pollen– Two sperm nuclei follow down the pollen tube

• 7) Double fertilization:– 1 sperm nuclei fuses w/ egg (zygote created)

– 1 sperm nuclei fuses w/ the embryo sac (endosperm created)

• 8) Ovule hardens to form seed

Seed germinates

Fruit Production

• In the seed– Embryo– Endosperm

• Surrounding ovary grows into a fruit

• Fruit attracts animals to eat and spread the seeds Fruit seeds in fox droppings

End of the Semester!