1. Chapter 27 Plant Reproduction and Development (Sections 27.1 - 27.5)

2. 27.1 Plight of the Honeybee
Most food crops are flowering plants, which make pollen
The recent decline of honeybees used to pollinate crops is a huge threat to our agricultural economy
pollinator
An organism that moves pollen from one plant to another

3. Importance of Insect Pollinators
Many plant species will not develop fruits (or only develop inferior fruits) unless they receive pollen from other flowers
Figure 27.1 Importance of insect pollinators. Opposite, honeybees are efficient pollinators of a variety of flowers, including those of berry plants. Above, raspberry flowers can pollinate themselves, but the fruit that forms from a self-fertilized flower is of lower quality than that of a cross-pollinated flower. The two raspberries on the left formed from self-pollinated flowers. The one on the right formed from an insect-pollinated flower.

4. 27.2 Reproductive Structures of Flowering Plants
Petals and other parts of a typical flower are modified leaves that form in four spirals (whorls) at the end of a floral shoot
flower
Specialized reproductive shoot of an angiosperm sporophyte

5. Flower Formation
The outermost whorl develops into a ring of sepals (a calyx )
Petals form in the second whorl (the corolla)
A whorl of stamens (which produce male gametophytes) forms inside the ring of petals
The innermost whorl of modified leaves are folded and fused into carpels (which produce female gametophytes)

6. Key Terms
stamen
Reproductive structure that produces male gametophytes
In most plants it consists of a pollen-producing anther on the tip of a filament
carpel
Reproductive structure that produces female gametophytes
Sticky or hairlike stigma together with an ovary and a style

7. Carpels
Flowers may have one carpel, several carpels, or several groups of carpels that may be fused
A swollen region (the ovary) contains one or more ovules
A cell in the ovule undergoes meiosis and develops into the haploid female gametophyte

8. Key Terms
ovary
In flowering plants, the enlarged base of a carpel, inside which one or more ovules form and eggs are fertilized
ovule
In a seed-bearing plant, a structure in which a haploid, egg-producing female gametophyte forms
After fertilization, matures into a seed

9. Anatomy of a Typical Flower

10. Anatomy of a Typical Flower
stamen
carpel
filament
anther
stigma
style
ovary
Figure 27.2 Anatomy of a typical flower.
ovule (forms within ovary)
petal (all petals combined are the flower’s corolla)
sepal (all sepals combined are flower’s calyx)
receptacle
Fig. 27.2a.2, p. 430

11. Flower Structure
Flower structure varies among different plant species

12. carpel structure varies ovule position varies within ovaries
Flower Structure
carpel structure varies
Figure 27.2 Anatomy of a typical flower.
ovule position varies within ovaries
ovary position varies
B Flower structure varies among different plant species.
Fig. 27.2b, p. 430

13. Life Cycle of a Flowering Plant
The life cycle of flowering plants is dominated by a diploid, spore-producing sporophyte
Spores that form by meiosis inside flowers develop into haploid gametophytes, which produce gametes
At fertilization, a diploid zygote forms when male and female gametes meet inside an ovary

14. Life Cycle of a Flowering Plant

15. Life Cycle of a Flowering Plant
mature sporophyte (2n)
germination
zygote
in seed (2n)
meiosis in anther
meiosis in ovary
fertilization
microspores (n)
sperm (n)
Figure 27.3 Life cycle of a typical flowering plant.
male gametophyte
eggs (n)
megaspores (n)
female gametophyte
Fig. 27.3, p. 430

16. Life Cycle of a Flowering Plant
zygote
in seed (2n)
mature sporophyte (2n)
germination
megaspores (n)
microspores (n)
meiosis in anther
meiosis in ovary
female gametophyte
male gametophyte
eggs (n)
sperm (n)
fertilization
Figure 27.3 Life cycle of a typical flowering plant.
Stepped Art
Fig. 27.3, p. 430

17. Pollinators
Sexual reproduction in flowering plants involves transfer of pollen, typically from one plant to another
Animal pollinators pick up pollen and transfer it to the flower of a different plant
A flower’s shape, pattern, color, and fragrance are adaptations that attract specific animal pollinators

18. Coevolution ~90% of flowering plants have coevolved animal pollinators
An animal’s reward for a visit to a flower may be nectar, oils, nutritious pollen, or even sex
Butterflies, hummingbirds, and honeybees feed on nectar
Bats, moths, and flies are attracted to specific odors
Some flowers have specializations that prevent pollination by everything other than a specific pollinator species

19. Coevolution Zebra orchid mimics the scent of a female wasp
Female burnet moths ready to mate
Figure 27.4 Intimate connections between pollinator and flower. A A zebra orchid mimics the scent of a female wasp. Male wasps follow the scent to the flower, then try to copulate with and lift the dark red mass of tissue on the lip. The wasp’s movements trigger the lip to tilt upward, which brushes the wasp’s back against the flower’s stigma and pollen. B Female burnet moths perch on purple flowers—preferably those of field scabious— when they are ready to mate. The combination of colors and patterns attracts males.

20. Key Concepts Structure and Function of Flowers
Flowers are shoots that are specialized for reproduction
Modified leaves form their parts
Gamete-producing cells develop in their reproductive structures
Other parts such as petals are adapted to attract and reward pollinators

21. 27.3 A New Generation Begins
In flowering plants, fertilization has two outcomes:
It results in a diploid zygote, which becomes the mature sporophyte
It is the start of nutritive endosperm, which sustains rapid growth of the sporophyte seedling until true leaves form and photosynthesis begins

22. 10 Steps in the Flowering Plant Life Cycle
1. An ovule forms inside a flower’s ovary; one cell enlarges
2. Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell
3. In one megaspore, three rounds of mitosis with no cytoplasmic division result in a single cell with eight nuclei
4. Uneven cytoplasmic divisions result in a seven-celled embryo sac (female gametophyte) with eight haploid nuclei

23. 10 Steps in the Flowering Plant Life Cycle
5. Pollen sacs form in an anther
6. Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac
7. Mitosis and differentiation of a microspore produces a two-celled pollen grain, which enters dormancy, before being released from the anther

24. Key Terms megaspore Haploid spore that forms in ovule of seed plants
Gives rise to an egg-producing gametophyte
microspore
Walled haploid spore of seed plants
Gives rise to a sperm-producing gametophyte
dormancy
Period of temporarily suspended metabolism

25. 10 Steps in the Flowering Plant Life Cycle
8. Pollen grains are released from the anther; one lands on a stigma and germinates (pollination):
One cell in the pollen grain develops into a pollen tube
The other cell develops into two haploid sperm cells
9. The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it

26. 10 Steps in the Flowering Plant Life Cycle
10. The pollen tube reaches the ovule, penetrates it, and releases the two sperm nuclei (double fertilization)
One sperm fertilizes the egg and forms a diploid zygote
The other fuses with the endosperm mother cell, forming a triploid (3n) cell which gives rise to triploid endosperm

27. Key Terms pollination Arrival of pollen on a receptive stigma
double fertilization
Mode of fertilization in flowering plants in which one sperm cell fuses with the egg, and a second sperm cell fuses with the endosperm mother cell
endosperm
Nutritive tissue in the seeds of flowering plants

28. Life Cycle of a Eudicot

29. Life Cycle of a Eudicot
An ovule forms inside a flower’s ovary. A cell in the ovule enlarges. 1
an ovule
seedling
ovary wall
ovary
seed
Sporophyte (2n)
Meiosis in ovary
pollen tube
Four haploid (n) megaspores form by meiosis and cytoplasmic division of the enlarged cell. Three megaspores disintegrate. 2
megaspores (n)
endosperm mother cell (n + n)
In the remaining megaspore, three rounds of mitosis with no cytoplasmic division result in a single cell with eight nuclei. 3
egg (n)
Figure 27.5 Life cycle of cherry (Prunus), a eudicot.
sperm (n)
The pollen tube reaches the ovule, penetrates it, and releases the two sperm nuclei. One nucleus fertilizes the egg. The other fuses with the endosperm mother cell. 10
Double fertilization
Uneven cytoplasmic divisions result in a seven-celled embryo sac with eight haploid nuclei. This sac is the female gametophyte. 4
female gametophyte
Fig ,10, p. 433

30. mature male gametophyte
Life Cycle of a Eudicot
pollen sac
anther (cutaway view)
filament
Pollen sacs form in an anther. 5
a cell in the pollen sac
Meiosis in anther 6
Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac. 6
microspores (n)
In this plant, mitosis of a micro-spore followed by differentiation results in a two-celled pollen grain. 7 7
Figure 27.5 Life cycle of cherry (Prunus), a eudicot.
Pollen grains are released from the anther. One lands on a stigma and germinates. A cell in the grain develops into a pollen tube; the other, into two haploid sperm cells. 8 8
The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it. 9
pollen tube
stigma
style
sperm cells 9
mature male gametophyte
Fig , p. 432

31. mature male gametophyte
Life Cycle of a Eudicot
pollen sac
anther (cutaway view)
filament
a cell in the pollen sac
Pollen sacs form in an anther. 5
Meiosis in anther
Four haploid (n) microspores form by meiosis and cytoplasmic division of a cell in the pollen sac. 6
microspores (n)
In this plant, mitosis of a micro-spore followed by differentiation results in a two-celled pollen grain. 7
Figure 27.5 Life cycle of cherry (Prunus), a eudicot.
Pollen grains are released from the anther. One lands on a stigma and germinates. A cell in the grain develops into a pollen tube; the other, into two haploid sperm cells. 8
The pollen tube grows down through tissues of the carpel, carrying the two sperm nuclei with it. 9
pollen tube
stigma
style
sperm cells
mature male gametophyte
Stepped Art
Fig , p. 432

32. ANIMATION: Pollination32

33. ANIMATION: Plant Life cycle
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34. 27.4 From Zygotes to Seeds and Fruits
After fertilization, mitotic cell divisions transform a zygote into an embryo sporophyte encased in a seed
As embryos develop inside the ovules of flowering plants, tissues around them form fruits
Water, wind, and animals disperse seeds in fruits

35. The Embryo Sporophyte Forms
Double fertilization produces a zygote, which develops into an embryo sporophyte, and a triploid (3n) cell, which develops into nutrient-containing endosperm
When the embryo matures, layers of integuments separate from the ovary wall and become a protective seed coat
The embryo sporophyte, its reserves of food, and the seed coat become a mature ovule (seed)

36. A Seed
seed
Embryo sporophyte of a seed plant packaged with nutritive tissue inside a protective coat

37. A Seed root apical meristem seed coat embryo shoot tip cotyledons
Figure 27.6 Seed of shepherd’s purse (Capsella), a eudicot.
Fig. 27.6, p. 434

38. Fruits
Fruits include seed-containing “vegetables” such as beans, tomatoes, grains, and squash
Simple fruits(e.g. pea pod) form from a single ovary
Aggregate fruits (e.g. strawberry) form from separate ovaries of one flower
Multiple fruits (e.g. pineapple) form from fused ovaries of separate flowers
fruit
A seed-containing mature ovary of a flowering plant
Often with accessory tissues

39. Parts of a Fruit

40. Parts of a Fruit tissue derived from ovary wall carpel wall seed
Figure 27.7 Parts of a fruit that develop from parts of a flower. Left, the tissues of an orange (Citrus) develop from the ovary wall. Right, the flesh of an apple (Malus) is an enlarged receptacle.
enlarged receptacle
Fig. 27.7, p. 434

41. Aggregate Fruits

42. Aggregate Fruits
Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits.
Fig. 27.8a, p. 435

43. Aggregate Fruits
Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits.
Fig. 27.8b, p. 435

44. Aggregate Fruits
Figure 27.8 Aggregate fruits. A A strawberry (Fragaria) is not a berry. The flower’s carpels turn inside out as the fruits form. The red, juicy flesh is an expanded receptacle; the hard ‘seeds’ on the surface are individual dry fruits B. C Boysenberries and other Rubus species are not berries, either. Each is an aggregate of many fleshy, one-seeded fruits.
Fig. 27.8c, p. 435

45. Categories of Fruits Based on tissues:
True fruits develop from the ovary wall
Accessory fruits include the ovary and other parts developed from petals, sepals, stamens, or receptacles
Based on appearance:
Dry fruits (e.g. acorns, grains, strawberries)
Fleshy fruits (e.g. cherries, berries, apples)

46. Function of Fruits
The function of a fruit is to protect and disperse seeds
Specific dispersal vectors are reflected in a fruit’s form:
Water: Water-repellent outer layers
Wind: Lightweight with breeze-catching specializations
Animals: Hooks or spines that stick to feathers, feet, or fur
Animal feces: Colorful, fleshy, fragrant fruits

47. Key Concepts Plant Sexual Reproduction
In flowering plants, pollination is followed by double fertilization
After fertilization, ovules mature into seeds
As seeds develop, tissues of the ovary and other parts of the flower mature into fruits, which function to disperse seeds

48. ABC Video: Doomsday Vault Seed Collection

49. Animation: Double Fertilization

50. 27.5 Asexual Reproduction in Plants
Most flowering plants can reproduce by vegetative reproduction, a form of asexual reproduction that produces genetically identical offspring
Triploid species are sterile and can only reproduce asexually
vegetative reproduction
Growth of new roots and shoots from extensions or fragments of a parent plant

51. Tissue Culture Propagation
An entire plant may be cloned from a single cell with tissue culture propagation
This technique is used to improve food crops and to propagate rare ornamental plants such as orchids
tissue culture propagation
Laboratory method in which body cells are induced to divide and form an embryo

52. Key Concepts Asexual Reproduction of Plants
Many species of plants reproduce asexually by vegetative reproduction
Humans take advantage of this natural tendency by propagating plants asexually for agriculture and research