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
• KEY CONCEPT Reproduction of flowering plants takes place within flowers.
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
• KEY CONCEPT Seeds disperse and begin to grow when conditions are favorable.
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
• KEY CONCEPT Plants can produce genetic clones of themselves through asexual reproduction.
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
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