1. 24–1 Reproduction With Cones and Flowers
Photo Credit: © Carl R. Sams II/Peter Arnold, Inc.
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2. 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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3. 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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4. Life Cycle of Gymnosperms
Pollen Cones and Seed Cones 
Pollen cones produce the male gametophytes, also called pollen grains.
One of the haploid nuclei in the pollen grain will divide later to produce two sperm nuclei.
Pollen cones
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5. 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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6. Life Cycle of Gymnosperms
Within the ovules, meiosis produces haploid cells that grow and divide to produce female gametophytes.
Each gametophyte may contain hundreds or thousands of cells.
When mature, each gametophyte contains a few large egg cells, ready for fertilization. egg cells.
Female gametophyte and egg cells
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7. 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.
There, some pollen grains are caught in a sticky secretion on one of the scales of the female seed cone.
This sticky material, known as a pollination drop, ensures that pollen grains stay on the female cone.
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8. Life Cycle of Gymnosperms
If pollen grains land on and enter an ovule, pollination occurs.
When the pollen grain lands near an ovule, the grain splits open and begins to grow a pollen tube, which contains two haploid sperm nuclei, and releases sperm near an egg.
Egg cells
Discharged sperm nucleus
Pollen tube
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9. Life Cycle of Gymnosperms
One sperm nuclei disintegrates when they reach the female gametophyte. The other fertilizes the egg.
If sperm from another pollen tube reaches the female gametophyte, more than one egg may be fertilized, but just one embryo develops.
Fertilization produces a diploid zygote which develops into a new sporophyte plant.
Zygote (2N)
(new sporophyte)
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10. Life Cycle of Gymnosperms
This zygote grows into an embryo and is encased within what will develop into a seed.
The seed consists of three generations of the life cycle: outer seed coat is part of the old sporophyte, haploid cells surrounding the embryo are female gametophyte, and embryo is new sporophyte.
Gametophyte tissue
Embryo (2N)
Seed coat
(old sporophyte)
Seed
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11. 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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12. 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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Structure of Flowers
Structure of Flowers
Flowers are reproductive organs that are composed of four kinds of specialized leaves:
Sepals
Petals
Stamens
Carpels
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Structure of Flowers
Sepals enclose the bud before it opens and protect the flower while it is developing.
In many plants, sepals are green and closely resemble ordinary leaves.
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 & other pollinators to the flower.
Because they do not produce reproductive cells, sepals and petals are sometimes called sterile leaves.
Flowers are reproductive organs that include sepals, petals, stamens, and carpels.
Petal
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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.
Some flowers have several carpels fused together to form a single compound carpel.
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.
Corn has separate male and female flowers on the same plant.
The tassel is a flower that produces male gametophytes, and the silk is the style of a flower that produces the female gametophyte.
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25. Life Cycle of Angiosperms
Reproduction in angiosperms takes place within the flower.
Following pollination and fertilization, the seeds develop inside protective structures.
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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26. Life Cycle of Angiosperms
Think of the beginning of the angiosperm life cycle as when the mature sporophyte produces flowers.
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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27. Life Cycle of Angiosperms
The nucleus of each pollen grain undergoes one mitotic division to produce two haploid nuclei.
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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28. 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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29. 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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30. 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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31. 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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Pollination
Pollination
Most gymnosperms and some angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals.
Botanists suggest that insect pollination is the factor largely responsible for the displacement of gymnosperms by angiosperms during the past million years.
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Pollination
Wind pollination
is less efficient than animal pollination
relies on weather and sheet numbers
Animal pollination
plants have bright colors and sweet nectar to attract animals
Animals have body shapes that enable them to reach nectar deep within certain flowers
benefits both the plants and the animals that pollinate them
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34. 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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35. Fertilization in Angiosperms
The generative nucleus within the pollen grain divides and forms two sperm nuclei.
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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36. 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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37. 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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38. Fertilization in Angiosperms
Because two fertilization events take place between the male and female gametophytes, this process is known as double fertilization.
This may be one of the reasons why the angiosperms have been so successful.
In gymnosperms, the food reserve built up in seeds is produced before fertilization takes place. If an ovule is not fertilized, those resources are wasted.
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