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Biology
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2. 24–1 Reproduction With Cones and Flowers
Photo Credit: © Carl R. Sams II/Peter Arnold, Inc.
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3. Alternation of Generations
All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation.
Male and female gametes of a gametophyte plant join and form a zygote that begins the next sporophyte generation.
In some plants, the two stages of the life cycle are distinct, independent plants.
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4. Alternation of Generations
In seed plants, gametophytes are found within tissues of the sporophyte plant.
In gymnosperms, they are found inside cones.
In angiosperms, they are found inside flowers.
Cones and flowers represent two different methods of reproduction.
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5. Life Cycle of Gymnosperms
What are the reproductive structures of gymnosperms?
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6. Life Cycle of Gymnosperms
Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant.
Gymnosperms produce two types of cones: pollen cones and seed cones.
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7. Life Cycle of Gymnosperms
Pollen Cones and Seed Cones 
Pollen cones produce the male gametophytes, also called pollen grains.
Pollen cones
Pollen grain (N)
(male gametophytes)
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8. Life Cycle of Gymnosperms
Seed cones produce female gametophytes and are generally larger than pollen cones.
Female gametophytes develop in two ovules located near the base of each scale.
Seed cones
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9. Life Cycle of Gymnosperms
Within the ovules, meiosis produces haploid cells that grow and divide to produce female gametophytes.
Each gametophyte contains egg cells.
Female gametophyte and egg cells
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10. Life Cycle of Gymnosperms
Pollination
The gymnosperm life cycle typically takes two years to complete.
The cycle begins as male cones release pollen grains.
Pollen grains are carried by the wind and reach female cones.
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11. Life Cycle of Gymnosperms
Meiosis
This illustration shows the life cycle of a typical gymnosperm. A pine tree—the mature sporophyte—produces male and female cones. Male cones produce pollen, and female cones produce ovules located on cone scales. If an egg is fertilized by the sperm, it becomes a zygote that is nourished by the female cone. In time, the zygote develops into a new sporophyte plant.
Fertilization
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12. Life Cycle of Gymnosperms
Male Cones
Pollen cone
Pollen grain (N) (male gametophytes)
A pine tree—the mature sporophyte—produces male and female cones. Male cones produce pollen, and female cones produce ovules located on cone scales.
Mature sporophyte
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13. Life Cycle of Gymnosperms
Cone scale
Diploid cell (2N)
Female Cones
Ovule
Seed cone
Ovules
Four haploid cells (N)
Female gametophyte (N)
A pine tree—the mature sporophyte—produces male and female cones. Male cones produce pollen, and female cones produce ovules located on cone scales. If an egg is fertilized by the sperm, it becomes a zygote that is nourished by the female cone.
Mature sporophyte
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14. Life Cycle of Gymnosperms
If pollen grains land on and enter an ovule, pollination occurs.
A pollen tube grows out of each pollen grain and releases sperm near an egg.
Egg cells
Discharged sperm nucleus
Pollen tube
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15. Life Cycle of Gymnosperms
Fertilization produces a diploid zygote which develops into a new sporophyte plant.
Zygote (2N)
(new sporophyte)
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16. Life Cycle of Gymnosperms
This zygote grows into an embryo and is encased within what will develop into a seed.
Gametophyte tissue
Embryo (2N)
Seed coat
(old sporophyte)
Seed
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17. Life Cycle of Gymnosperms
The seed is then dispersed by wind.
When conditions are favorable, the seed germinates and its embryo grows into a seedling.
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Structure of Flowers
What are the reproductive structures of angiosperms?
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Structure of Flowers
Structure of Flowers
Flowers are reproductive organs that are composed of four kinds of specialized leaves: sepals, petals, stamens, and carpels.
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Structure of Flowers
Sepals enclose the bud before it opens and protect the flower while it is developing.
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
Sepal
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Structure of Flowers
Petals are often brightly colored and are found just inside the sepals.
Petals attract insects and other pollinators to the flower.
Petal
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
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Structure of Flowers
The male parts of a flower consist of an anther and a filament, which together make up the stamen.
Anther
Stamen
Filament
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
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Structure of Flowers
An anther is an oval sac where meiosis takes place, producing pollen grains.
Anther
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Structure of Flowers
The filament is a long, thin stalk that supports an anther.
Filament
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Structure of Flowers
The innermost floral parts are carpels, also called pistils, which produce the female gametophytes.
Stigma
Carpel
Style
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
Ovary
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Structure of Flowers
Each carpel has a broad base forming an ovary.
The ovary contains one or more ovules where female gametophytes are produced.
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
Ovary
Ovule
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Structure of Flowers
The narrow stalk of the carpel is the style.
Style
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Structure of Flowers
At the top of the style is the stigma—a sticky portion where pollen grains frequently land.
Stigma
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Structure of Flowers
Parts of a Typical Flower
Stigma
Anther
Stamen
Filament
Carpel
Style
Ovary
Ovary
Petal
Sepal
Ovule
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Structure of Flowers
A typical flower produces both male and female gametophytes.
In some plants, male and female gametophytes are produced in separate flowers on the same individual.
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31. Life Cycle of Angiosperms
Reproduction in angiosperms takes place within the flower. Following pollination and fertilization, the seeds develop inside protective structures.
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32. Life Cycle of Angiosperms
This illustration shows the life cycle of an iris. The developing seeds of a flowering plant are protected and nourished inside the ovary, which is located at the base of the flower. Reproduction in angiosperms takes place within the flower. After pollination, the seeds of angiosperms develop inside protective structures.
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33. Life Cycle of Angiosperms
Each flower contains anthers and an ovary.
Inside the anthers, each cell undergoes meiosis and produces haploid spore cells.
Each spore cell becomes a single pollen grain.
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34. Life Cycle of Angiosperms
The pollen grain usually stops growing until it is released from the anther and deposited on a stigma.
Pollen grains (N)
(male gametophyte)
Stigma
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35. Life Cycle of Angiosperms
In the ovule, a single diploid cell undergoes meiosis to produce four haploid cells.
Haploid cell
(N)
Ovule
Ovary (2N)
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36. Life Cycle of Angiosperms
Only one of the four cells undergoes mitosis to produce eight nuclei.
The eight nuclei and the surrounding membrane are called the embryo sac.
Embryo sac (N)
(female gametophyte)
Sperm
Pollen tube
Egg cell
Polar nuclei
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37. Life Cycle of Angiosperms
The embryo sac is the female gametophyte.
One of the eight nuclei is the egg nucleus—the female gamete.
Embryo sac (N)
(female gametophyte)
Sperm
Pollen tube
Egg cell
Polar nuclei
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38. Life Cycle of Angiosperms
When fertilization takes place, this cell becomes the zygote that grows into a new sporophyte plant.
Endosperm
(3N)
Zygote (2N)
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39. Fertilization in Angiosperms
If a pollen grain lands on the stigma of a flower of the same species, it grows a pollen tube.
Pollen grains (N)
(male gametophyte)
Pollen tubes
Ovule
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40. Fertilization in Angiosperms
The pollen tube grows into the style, reaches the ovary, and enters the ovule.
Pollen grains (N)
(male gametophyte)
Pollen tubes
Ovule
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41. Life Cycle of Angiosperms
One of the sperm nuclei fuses with the egg nucleus to produce a diploid zygote.
The zygote will grow into the new plant embryo.
Zygote (2N)
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42. Fertilization in Angiosperms
The other sperm nucleus fuses with two polar nuclei in the embryo sac to form a triploid (3N) cell.
This cell will grow into a food-rich tissue known as endosperm, which nourishes the seedling as it grows.
Endosperm
(3N)
Zygote (2N)
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43. Fertilization in Angiosperms
Because two fertilization events take place between the male and female gametophytes, this process is known as double fertilization.
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Pollination
How does pollination differ between angiosperms and gymnosperms?
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Pollination
Pollination
Most gymnosperms and some angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals.
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46. Copyright Pearson Prentice Hall
Pollination
Wind pollination
is less efficient than animal pollination
relies on weather
Animal pollination
plants have bright colors and sweet nectar to attract animals
benefits both the plants and the animals that pollinate them
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24–1
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48. Copyright Pearson Prentice Hall
24–1
In a gymnosperm, fertilization occurs inside the
ovule.
pollen tube.
seed cone.
pollen cone.
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49. Copyright Pearson Prentice Hall
24–1
The pollen-producing structure of angiosperms is the
stigma.
carpel.
anther.
sepal.
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50. Copyright Pearson Prentice Hall
24–1
In an angiosperm, a structure that results from fertilization is the
female gametophyte.
pollen grain.
zygote.
ovary.
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51. Copyright Pearson Prentice Hall
24–1
Which term applies to the chromosome number of a seed plant embryo?
haploid
diploid
triploid
polyploid
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24–1
Pollination in most gymnosperms and some angiosperms is carried out by
water transport.
insects.
wind.
birds and bats.
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53. END OF SECTION