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

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

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

– 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.

22.1 Plant Life Cycles

• The sporophyte is the dominant phase for seed plants.

22.1 Plant Life Cycles

• sepal

Flowers contain reproductive organs protected by specialized leaves.

• Sepals and petals are modified leaves.– Sepals are outermost

layer that protectsdeveloping flower

22.1 Plant Life Cycles

– Petals can help to attract animal pollinators

• petal

22.1 Plant Life Cycles

• A stamen is the male structure of the flower.

– anther produces pollen grains – filament supports the anther

• stamen

• filament• anther

22.1 Plant Life Cycles

• carpel • style

• stigma

• ovary

• The innermost layer of a flower is the female carpel.

– stigma is sticky tip – style is tube leading from stigma to ovary – ovary produces female gametophyte

22.1 Plant Life Cycles

Flowering plants can be pollinated by wind or animals.

• Flowering plants pollinated when pollen grains land on stigma.

• Wind pollinated flowers have small flowers and large amounts of pollen.

22.1 Plant Life Cycles

• Animal pollinated flowers have larger flowers and less pollen.

• pollen grains

– many flowering plants pollinated by animal pollinators

– pollination occurs as animal feeds from flower to flower– animal pollination more efficient than wind pollination

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

22.1 Plant Life Cycles

– four female spores produced in ovule by meiosis – one spore develops into female gametophyte – female gametophyte contains seven cells – one cell has two nuclei, or polar nuclei – one cell will develop into an egg

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

22.1 Plant Life Cycles

• Pollination occurs when a pollen grain lands on a stigma.

• pollen tube• pollen tube

• sperm• sperm

• stigma• stigma

– one cell from pollen grain forms pollen tube– other cell forms two sperm that travel down tube

22.1 Plant Life Cycles

• Flowering plants go through the process of double fertilization.

• female• gametophyte

• ovule

• egg

• sperm

• polar nuclei

22.1 Plant Life Cycles

• endosperm

• seed coat

• embryo

– one sperm fertilizes the egg

– other sperm unites with polar nuclei, forming endosperm

– endosperm provides food supply for embryo

• Flowering plants go through the process of double fertilization.

22.1 Plant Life Cycles

• Each ovule becomes a seed.• The surrounding ovary grows into a fruit.

22.1 Plant Life Cycles

Animals, wind, and water can spread seeds.

• Seeds dispersed by animals can have nutritious fruits or fruits that cling.

•

22.1 Plant Life Cycles

• Seeds dispersed by wind can have wing- or parachute-like fruits.

• Cypselae

• Double samaras

22.1 Plant Life Cycles

Seeds begin to grow when environmental conditions are favorable.• Seed dormancy is a state in which the embryo has stopped

growing. – Dormancy may end

when conditions are favorable.

– While dormant, embryo can withstand extreme conditions.

22.1 Plant Life Cycles

• Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat– embryonic root, radicle, is first to emerge– water activates enzymes that help send sugars to

embryo

22.1 Plant Life Cycles

• Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat– embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to

embryo– embryonic shoot, plumule, emerges next

22.1 Plant Life Cycles

• Germination begins the growth of an embryo into a seedling. – water causes seed to swell and crack coat– embryonic root, radicle, is first to emerge – water activates enzymes that help send sugars to

embryo– embryonic shoot, plumule, emerges next

– leaves emerge last

22.1 Plant Life Cycles

• Once photosynthesis begins, the plant is called a seedling.

22.1 Plant Life Cycles

Plants can reproduce asexually with stems, leaves, or roots. • Asexual reproduction allows a plant to make copies of itself.• Regeneration is one type of asexual reproduction.

– plants grow a new individual from fragment of parent – occurs when piece of a stem, leaf, or root falls off parent

plant

22.1 Plant Life Cycles

– stems, leaves, or roots attached to parent plant produce new individuals

– specific adaptations include stolons, rhizomes, and tubers

• Vegetative reproduction is another type of asexual reproduction.

22.1 Plant Life Cycles

Humans can produce plants with desirable traits using vegetative structures. • Vegetative propagation takes advantage of plants’ ability to

reproduce asexually. • Humans use one plant with desirable traits to produce

many individuals.

– grafting joins the parts of two plants together to form

a hybrid plant

– cutting of leaves or stems may grow new roots