Chapter 24- Seeds & Flowers

1. 24–1 Reproduction With Cones and Flowers
Freedom from water

2. 2

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 join to form a zygote
that begins the next sporophyte generation.
In mosses & ferns, the two stages of
the life cycle are distinct, independent
plants.

4. 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.
Alternation of Generations

5. 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.
Life Cycle of Gymnosperms

6. Pollen Cones and Seed Cones
Pollen cones produce the male
gametophytes, also called pollen
grains.
Pollen grain (N)
(male gametophytes)
Life Cycle of Gymnosperms

7. 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.
Life Cycle of Gymnosperms

8. Within the ovules, meiosis produces haploid
cells that grow and divide to produce female
gametophytes.
Each gametophyte contains egg cells.
Life Cycle of Gymnosperms

9. 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.
Life Cycle of Gymnosperms

10. Meiosis
Fertilization
Life Cycle of Gymnosperms

11. Male Cones
Mature sporophyte
Pollen
cone
Pollen grain (N)
(male gametophytes)
Life Cycle of Gymnosperms

12. Female Cones
Mature sporophyte
Seed
cone
Cone scale
Ovules
Diploid cell (2N)
Ovule
Four haploid
cells (N)
Female
gametophyte
(N)
Life Cycle of Gymnosperms

13. 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
Life Cycle of Gymnosperms

14. Fertilization produces a diploid zygote which
develops into a new sporophyte plant.
Zygote (2N)
(new sporophyte)
Life Cycle of Gymnosperms

15. The resulting embryo is encased
within a seed coat that protects the
seed from drying out.
Gametophyte tissue
Embryo (2N)
Seed coat
(old sporophyte)
Seed
Life Cycle of Gymnosperms

16. The seed is then dispersed by wind.
When conditions are favorable, the
seed germinates and its embryo
grows into a seedling.
Life Cycle of Gymnosperms

17. Structure of Flowers
Flowers are
reproductive organs
that have four kinds of
specialized leaves:
sepals, petals, stamens, and
carpels.

18. Sepals enclose the bud before it
opens and protect the flower
while it is developing.
Sepal
Structure of Flowers

19. Petals are often brightly colored and are
found just inside the sepals.
Petals attract insects and other
pollinators to the flower.
Petal
Structure of Flowers

20. The male parts of a flower
consist of an anther and a
filament, which together make up
the stamen.
Filament
Anther
Stamen
Structure of Flowers

21. An anther is an oval sac where meiosis takes
place, producing pollen grains.
Anther
Structure of Flowers

22. The filament is a long, thin stalk that supports an
anther.
Filament
Structure of Flowers

23. The innermost female parts are
carpels(pistils).
CarpelStyle
Stigma
Ovary
Structure of Flowers

24. Each carpel has a broad base forming an ovary
where female gametophytes are produced.
Ovary
Ovule
Structure of Flowers

25. The narrow stalk of the carpel is the style.
Style
Structure of Flowers

26. At the top of the style is the stigma—a sticky
portion where pollen grains frequently land.
Stigma
Structure of Flowers

27. Ovary
Ovule
CarpelStyle
Stigma
Ovary
Filament
Anther
Stamen
Parts of a Typical Flower
Sepal
Petal
Structure of Flowers

28. 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.
Structure of Flowers

29. Life Cycle of Angiosperms
Reproduction in angiosperms takes
place within the flower. Following
pollination and fertilization, the
seeds develop inside protective
structures.

30. Life Cycle of Angiosperms

31. Each flower contains anthers and an ovary.
In anthers, cells undergo meiosis
to make a haploid spore cell.
Spore nuclei undergo mitosis to
make two haploid pollen grains.
Life Cycle of Angiosperms

32. The pollen grain
usually stops
growing until it is
released from the
anther and
deposited on a
stigma.
Pollen grains (N)
(male gametophyte)
Stigma
Life Cycle of Angiosperms

33. In the ovule, a single diploid cell
undergoes meiosis to produce four
haploid cells that become the
female gametophyte.
Haploid cell
(N)
Ovule
Ovary (2N)
Life Cycle of Angiosperms

34. Only one of the four
cells undergoes mitosis
to produce eight nuclei,
called the embryo sac.
Pollen tubeEgg cell
Sperm
Polar nuclei
Embryo sac (N)
(female gametophyte)
Life Cycle of Angiosperms

35. The embryo sac is the
female gametophyte.
One of the eight nuclei
is the egg nucleus—the
female gamete.
Pollen tube
Embryo sac (N)
(female gametophyte)
Egg cell
Sperm
Polar nuclei
Life Cycle of Angiosperms

36. When fertilization takes place, this cell becomes
the zygote that grows into a new sporophyte
plant.
Endosperm
(3N)
Zygote (2N)
Life Cycle of Angiosperms

37. Fertilization in Angiosperms
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

38. The pollen
tube grows
into the style,
reaches the
ovary, and
enters the
ovule.
Pollen grains (N)
(male gametophyte)
Pollen tubes
Ovule
Fertilization in Angiosperms

39. 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)

40. The other sperm
nucleus fuses with
two polar nuclei in the
embryo sac to form a
triploid (3N) cell =
endosperm.
This cell will grow into a food-
rich tissue known as
endosperm, which nourishes
the seedling as it grows.
Endosperm
(3N)
Zygote (2N)
Fertilization in Angiosperms

41. Because two fertilization events take place
between the male and female gametophytes, this
process is known as double fertilization.
1 makes zygote
1 makes endosperm
Fertilization in Angiosperms

42. Pollination
Most gymnosperms and
some angiosperms are wind
pollinated, whereas most
angiosperms are pollinated
by animals.

43. 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

44. 24-2 Seed Development and Germination

45. As angiosperm seeds mature, the ovary
walls thicken to form a fruit that encloses
the developing seeds.
Seed and Fruit Development

46. A fruit is a ripened ovary that
contains angiosperm seeds.
As seeds mature, the ovary walls thicken to
form a fruit that encloses the developing
seeds.
Seed and Fruit Development

47. Seed Dispersal
Seeds are dispersed by
•Animals- typically in fleshy,
nutritious fruits.
•Wind- flying seeds
•Water- floating seeds
WIDE DISPERSAL MEANS
LESS COMPETITION.

48. Seeds of many plants are eaten by animals.
These seeds are covered with tough
coatings that protect them from digestive
chemicals, allowing them to pass through
an animal’s digestive system unharmed.
The seeds then sprout in the feces
eliminated from the animal.
Seed Dispersal

49. Seeds dispersed by
wind or water are
typically lightweight,
allowing them to be
carried in the air or to
float on the surface of
the water.
Seed Dispersal

50. Seed Dispersal
Some seeds are encased in winglike
structures that spin and twirl, helping them
glide from their parent plants.

51. Seed Dispersal
A coconut is buoyant enough to float in
seawater within its protective coating for
many weeks.

52. Seed Dispersal
Tumbleweed plants break off at their roots
and scatter their seeds as they are blown by
the wind.

53. Seed Dormancy
•Many seeds will not grow when they first
mature.
•Many seeds enter a period of
dormancy, during which the
embryo is alive but not growing.
•The length of dormancy varies in
different plant species.

54. Seed Dormancy
Environmental factors such as
temperature and moisture can
cause a seed to end dormancy
and germinate.
Seed dormancy can be adaptive in several
ways:
•allows for long-distance dispersal
•allows seeds to germinate under ideal
growth conditions

55. Seed Germination
•Seed germination is the early
growth stage of the plant embryo.
•Seeds absorb water which causes
food-storing tissues to swell and
crack open the seed coat.
•The young root grows through the
cracked seed coat.

56. Seed Germination
In most monocots, the single cotyledon
remains underground.
The growing shoot emerges while protected
by a sheath.

57. Seed Germination
Corn (monocot)
Young
shoot
Germinating
seed
Primary
root
Foliage
leaves

58. Seed Germination
In dicots, germination takes place in one of
two ways.
•In some species, the cotyledons emerge
above ground, protecting the stem and
first foliage leaves.
•In other species, the cotyledons stay
underground and provide a food source
for the growing seedling.

59. Seed Germination
Cotyledons
Bean (dicot)
Germinating
seed
Primary
root
Young
shoot Cotyledons
Seed coat
Foliage
leaves

60. 24-3 Plant Propagation and Agriculture

61. Vegetative Reproduction
Vegetative reproduction is a
method of asexual reproduction
used by flowering plants that
enables a single
plant to produce
many offspring
genetically
identical to itself.

62. Vegetative
reproduction
includes the
production of new
plants from
horizontal stems,
from plantlets, and
from underground
roots.
Vegetative Reproduction

63. Some angiosperms produce tiny plants, or
plantlets, at the tips of elongated stems.
Vegetative Reproduction

64. Some plants grow horizontal
stems, called stolons, that produce
roots when they touch the ground.
Vegetative Reproduction

65. Once the roots are well established, each
stolon may be broken, forming a new
independent plant.
Vegetative Reproduction

66. Plant Propagation
In plant propagation,
horticulturists make many
identical copies of a plant or
produce offspring from
seedless plants.

67. Plant Propagation
Cuttings
•One of the simplest ways to reproduce
plants vegetatively is by cuttings.
•A grower “cuts” a plant stem that includes
buds containing meristematic tissue.
•That stem is then partially buried in soil or
in a special rooting mixture.
•Some plants are treated with rooting
powders to help them grow.

68. Plant Propagation
Grafting and Budding
•Grafting and budding are used to
reproduce seedless plants and
varieties of woody plants that do
not produce strong root systems.
•A piece of stem or a lateral bud is cut
from the parent plant and attached to
another plant.

69. Plant Propagation
The cut piece is called the scion, and the
plant to which it is attached is called the
stock.
When stems are used as scions, the
process is called grafting.
When buds are used as scions, the process
is called budding.

70. Agriculture
Agriculture is the systematic cultivation
of plants.

71. Agriculture
Worldwide Patterns of Agriculture
•Most of the people of the world depend
on a few crop plants, such as wheat,
rice, and corn, for the bulk of their food
supply.
•Roughly 80 percent of all U.S. cropland
is used to grow wheat, corn, soybeans,
and hay.

72. Agriculture
Changes in Agriculture
•The efficiency of agriculture has been
improved through:
improvements in farming techniques
the selective breeding of crop plants
•Selective breeding allows only
organisms with certain traits to produce
the next generation.

73. Agriculture
Improvements in farming techniques have
contributed to dramatic improvements in
crop yields.
Some of the most important techniques
have been the use of pesticides and
fertilizers.