22.1 Plant Life Cycles

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

22.1 Plant 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

fertilizationfertilization

meiosismeiosis

SPOROPHYTE PHASE

GAMETOPHYTE PHASE

22.1 Plant Life Cycles

– sporophyte phase is diploid – begins with fertilized egg – spores produced through

meiosis

• The gamete-producing plant is the mature gametophyte.

• The spore-producing plant is the mature sporophyte.

– gametophyte phase is haploid– begins with spore – gametes produced through

mitosis

fertilizationfertilization

meiosismeiosis

SPOROPHYTE PHASE

GAMETOPHYTE PHASE

22.1 Plant Life Cycles

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)sporophyte (2n)

gametophyte (1n)gametophyte (1n)

capsule

spores (1n)

22.1 Plant Life Cycles

•gametophyte

•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

22.1 Plant Life Cycles •5) Spores land and grow into new gametophytes

•.

•ground•gametophyte

•6) The process repeats

22.1 Plant Life Cycles

Plant Life Cycle ComparisonsPlant 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

SPOROPHYTE

22.1 Plant Life Cycles

sporophyte (2n)sporophyte (2n)

sori

• The sporophyte is the dominant phase for seedless vascular plants. – Fern spores form in sacs, sori, on underside of mature

sporophytes (fronds).

22.1 Plant Life Cycles

– A fern gametophyte, or prothallus, produces sperm and eggs.

gametophyte (1n))gametophyte (1n))

rhizoid

– A zygote forms on the prothallus, growing into the sporophyte.

22.1 Plant Life Cycles

•Adult

•Sporophyte

(diploid)

•.

•.•.

•.

•1) Sporophyte creates and releases haploid spores

•ground

22.1 Plant Life Cycles •.•.

•.

•.

•ground

•2) Spores land in the soil

22.1 Plant Life Cycles

•ground

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

22.1 Plant Life Cycles •4) Sperm swim through water from the antheridium to the archegonia•Let’s zoom back out

22.1 Plant Life Cycles

•ground

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

22.1 Plant Life Cycles •6) Fiddlehead uncurls into fronds of ferns.

•ground

•7) Cycle repeats• -- Sporangia creates spores to be released

•.

•.

•.•.

22.1 Plant Life Cycles

Plant Life Cycle ComparisonsPlant 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

SPOROPHYTE

22.1 Plant Life Cycles

Gymnosperm Life Cycle

22.1 Plant Life Cycles

• The sporophyte is the dominant phase for seed plants.

22.1 Plant Life Cycles 1) Male and female seed cones grow in adult sporophytes

22.1 Plant Life Cycles •2) Pollen grains released from the male seed cones-- Pollen is the male gametophyte

•Let’s zoom into the female seed cone

22.1 Plant Life Cycles

•3) Pollen grain sticks to the female ovule

•5) Two nuclei transfer into female spore- one fertilizes the egg

•4) Pollen tube grows from the male spore

•6) Diploid embryo develops (sporophyte stage restarts)

22.1 Plant Life Cycles •7) After seeds harden, the cone reopens and the seeds are released

22.1 Plant Life Cycles •8) Seed will land

•ground

22.1 Plant Life Cycles •9) Seedling grows into (sporophyte)…the cycle repeats

•ground

22.1 Plant Life Cycles

Plant Life Cycle ComparisonsPlant 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

SPOROPHYTE

22.1 Plant Life Cycles

Angiosperm Life Cycle

22.2 Flower Life Cycle

22.1 Plant Life Cycles

• 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

Flowering plants are pollinated when pollen grains land on stigma

22.2 Flower Life Cycle

22.1 Plant Life Cycles

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 twohaploid cells

– two cells form asingle pollen grain

•pollen grain

antherstamen

22.2 Flower Life Cycle

22.1 Plant Life Cycles

• One female gametophyte can form in each ovule of a flower’s ovary.

o 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)

22.2 Flower Life Cycle

22.1 Plant Life Cycles

1. Pollen grains are released

22.2 Flower Life Cycle

22.1 Plant Life Cycles

2. Pollen grains land on the stigma (pollination)

22.2 Flower Life Cycle

22.1 Plant Life Cycles

..

3. Pollen tube grows and 2 nuclei transfer into the ovule

Let’s zoom in…

22.2 Flower Life Cycle

22.1 Plant Life Cycles

3. Flowering plants go through the process of double fertilization. female

gametophyte

ovule

egg

sperm

polar nuclei

• 1 sperm fuse with the polar nuclei = triploid (3n) endosperm• 1 sperm fuse with the egg = zygote

22.2 Flower Life Cycle

Double Fertilization

22.1 Plant Life Cycles

•endosperm

•seed coat

•embryo

• Endosperm provides food supply for embryo

4. Each ovule becomes a seed.

• The surrounding ovary grows into a fruit.

22.2 Flower Life Cycle

22.1 Plant Life Cycles

5. Seeds get dispersed

6. Seed germinates, and the cycle starts over

ground

22.1 Plant Life Cycles

Plant Life Cycle ComparisonsPlant 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

SPOROPHYTE

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

SPOROPHYTE

22.2 Flower Life Cycle