2. Alternation of generations
Sporophyte
Dominant in flowering plants
Bears flowers – reproductive structure
Diploid or 2n
Produces haploid microspores and megaspores by meiosis
Gametophyte
Haploid or 1n
Produces gametes
Microspore undergoes mitosis and become a pollen grain, a male
gametophyte
Megaspore undergoes mitosis to become embryo sac, a female
gametophyte
Upon fertilization, the cycle returns to the 2n sporophyte
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3. Plant Reproduction, cont.
Once a sperm fertilizes an egg, the zygote becomes an embryo,
still within an ovule
Ovule develops into a seed, which contains the embryo and
stored food surrounded by a seed coat
Ovary becomes a fruit, which aids in dispersing the seeds
When a seed germinates, a new sporophyte emerges and,
through mitosis and growth, becomes a mature organism
Sexual life cycle of flowering plants is adapted to land
24-3
8. Figure 24.1D A corn plant is monoecious (flowers that are only male or only female
a. The staminate flowers produce pollen that is carried by wind to
b. the carpellate flowers, where ears of corn develop. 24-8
9. Figure 24B
Butterflies, birds, and bats are adapted for acquiring nectar from certain flowers.
Flowers that attract beetles produce much pollen and those that attract flies have
24-9
the smell of rotting flesh
10. Sexual reproduction involves
1. Production of pollen grains (male gametophytes) in
the anthers of stamens
2. Production of an embryo sac (female gametophyte)
in an ovule located within the ovary of a carpel
Pollination
Pollen transferred from anther to stigma so an egg
within female gametophyte is fertilized
Most angiosperms use animals to carry out
pollination
24-10
15. Double fertilization is unique in angiosperms
Results in not only a zygote but also a food source for
the developing zygote
Endosperm – nutritive tissue developing embryonic
sporophyte uses as energy source
Mature seed contains
Embryo – will develop into the plant
Stored food – endosperm
Seed coat – develops from ovule wall for protection
24-15
17. 24.4 The ovary becomes a fruit, which
assists in sporophyte dispersal
Fruit = a ripened ovary
Protects and helps disperse the plant
(“marketing for the seeds”)
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18. 24.4 The ovary becomes a fruit, which
assists in sporophyte dispersal
Fleshy Versus Dry Fruits
Dry fruits
Exs: peas, maples
Fleshy fruits
Exs: apples, strawberries, tomatoes, corn
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21. Simple Versus Aggregate & Multiple Fruits
Simple fruits are derived from the simple ovary of a
single carpel Exs: grapes, tomatoes
Accessory fruits form from other flower parts in
addition to ovary Exs: strawberry, apple
Aggregate and multiple fruits are examples of
compound fruits derived from several individual
ovaries
Strawberry – aggregate fruit, each ovary becomes a one-
seeded fruit called an achene
Pineapple – a multiple fruit derived from many individual
flowers, each with its own carpel
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25. Germination – seeds form into a seedling
Doesn’t usually take place until there is sufficient
water, warmth, and oxygen to sustain growth
For seeds, dormancy is the time during which no
growth occurs, even though conditions may be
favorable for growth
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29. 24.6 Plants have various ways of
reproducing asexually
Also called vegetative reproduction
Type of cloning – offspring exactly like parent
Plants can grow from axillary buds of above or
below ground stems
Rhizome – underground horizontal stem (iris, many
grasses)
Tuber – enlarged portion of rhizome (potato)
Corm – bulbous underground stems (onion)
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32. 24.7 Cloning of plants in tissue
culture assists agriculture
Tissue culture
Growth of a tissue in an artificial liquid or on agar
3 methods
Somatic embryogenesis – technique that uses hormones to
cause plant tissues to generate small masses of cells
Meristem tissue culture – many new shoot tips from a single
shoot tip
Anther tissue culture – produces haploid plantlets or
chromosomal doubling chemically induced
24-32
37. Connecting the Concepts:
Chapter 24
Life, as we know it, would not be possible without
vascular plants
Although we now live in an industrialized society, we are
still dependent on plants and have put them to many
more uses
We grow plants for food, shelter, beauty and substances for
industry
Half of all pharmaceutical drugs have their origin in plants
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