Transcript Inquiry into Life, Eleventh Edition

Honors Biology
Chapter 10
Plant Reproduction
John Regan
Wendy Vermillion
Insert Ch opening photo
10-1
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10.1 Sexual reproduction in flowering
plants
• Alternation of generations
– Flowering plants have 2 multicellular stages in their life cycle
• Diploid sporophyte stage alternates with the haploid
gametophyte stage
• The sporophyte produces haploid spores by meiosis
– spores develop into gameotphytes
• The gametophyte produces gametes by mitosis
– after fertilization the cycle returns to the sporophyte
stage
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Alternation of generations in flowering
plants
• Fig 10.1
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Sexual reproduction in flowering plants cont’d.
• Overview of plant life cycle
– Flower- reproductive structure of angiosperms
– The diploid sporophyte is the predominant stage
• The sporophyte bears flowers; flowers produce 2 spore types
– Megaspore-develops into female gametophyte-embryo sac
– Microspore-develops into the male gametophyte-pollen grain
• Pollination-deposition of pollen onto female flower parts
– Pollen grain contains 2 sperm cells; pollen grain digests a tube
that the sperm swim through to reach the embryo sac
– Embryo sac contains an ovum; fertilization occurs and an
embryo develops
– Embryo sac develops into a seed which can be enclosed in a
fruit- aids dispersal
– When seed germinates a new sporophyte develops
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Sexual reproduction in flowering plants cont’d.
• Flowers
– Typical flower has 4 whorls of modified leaves attached to a
receptacle
1. Sepals-green leaflike structures that protect bud
2. Petals-attract pollinators
3. Stamens-male structures
– consist of anthers and filaments
4. Carpel-female structure
– consists of a stigma, style, and an ovary
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Anatomy of a flower
• Fig 10.2
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Sexual reproduction in flowering plants cont’d.
• Flowers, cont’d.
– A complete flower has all parts-petals, sepals, stamens, and carpels
flower can have a single carpel or multiple
• Each carpel contains the ovules
– Bisexual (perfect) flowers- have both stamens and carpels
– Unisexual (imperfect) flowers-have either stamens or carpels
• Dioecious plants- have either staminate or carpellate flowers on one
plant
• Monoecious plants- have both staminate and carpellate flowers on
the same plant
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Sexual reproduction in flowering plants cont’d.
• Production of the male gametophyte
– Microspores produced in anthers
– Microspore mother cell divides by meiosis to produce 4 haploid
microspores
– In each, the haploid nucleus divides mitotically and then an
unequal cytokinesis occurs
– the 2 cells are enclosed in a pollen grain; the larger is the tube
cell, the smaller is a sperm cell
– The sperm cell divides again to form 2 sperm
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Life cycle of a flowering plant
• Fig 10.5
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Sexual reproduction in flowering plants cont’d.
• Pollination
– Transfer of pollen from an anther to a receptive stigma of a
carpel
– Pollen grain contains 2 cells- generative cell, tube cell
• Tube cell grows into pollen tube
• Generative cell ÷ into 2 sperm cells
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Sexual reproduction in flowering plants cont’d.
• Production of the female gametophyte
– Embryo sac ÷3x into 8 nuclei as the functional nucleus divides 4
times by mitosis
– One small cell becomes the egg
– Double fertilization- one sperm fertilizes the egg and it becomes
the embryo(2n); the other fertilizes the central cell to form the
triploid (3n) endoderm
– Endosperm becomes the food source for the embryo inside the
seed
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Pollination
• Fig 10.6
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Development of a eudicot embryo
• Fig 10.7
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Growth and development cont’d.
• Development of the eudicot embryo, cont’d.
– Embryo changes from a ball of cells to a heart-shape
– Cotyledons-embryonic leaves appear
– Embryo next becomes torpedo-shaped, and the root tip and
shoot tip become visible
– Epicotyl-portion of embryo between the cotyledons that
contributes to shoot development
– Hypocotyl-portion below the cotyledons that contributes to stem
development
– Radicle-contributes to root development
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Growth and development cont’d.
• Monocots versus eudicots
– Eudicots have 2 cotyledons, monocots have one
– In monocots, the cotyledons do not store food
• cotyledon absorbs food from endosperm and passes it to the
embryo
• In eudicots the cotyledons store the nutrients the embryo uses
– Endosperm disappears as the cotyledons take up the nutrients
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Growth and development cont’d.
•
seed dispersal- the function of fruits is to disperse seeds
– seed dispersal
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Attach to fur of animals or clothing Ex: burrs
Passed in feces of bird or mammals Ex: berries
Dispersed when buried or stored by animals Ex: acorns
Wind-winged or plumed seeds Ex: maple seeds
Float-coconut
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Growth and development cont’d.
• Germination of seeds
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–
–
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Germinate in response to specific environmental conditions
Requires both inhibitor and stimulator substances
Mechanical stimuli also may be required in some
Uptake of water causes seed coat to burst
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Common garden bean seed structure
and germination
• Fig 10.9
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Growth and development cont’d.
• Eudicot versus monocot germination
– Eudicots
• Cotyledons shrivel and degrade
• Epicotyl produces immature leaves- plumule
• young shoot is hook-shaped as it emerges through the soil
– Monocots
• Cotyledon does not have a storage function
• Plumule and radicle are protected by sheaths called the coleoptile
and the coleorhiza respectively
• Plumule and radicle burst through the sheaths when germination
occurs
• Young shoot is straight, not hooked
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Corn kernal structure and germination
• Fig 10.10
10-20