1. Plant Evolution Chapter 21
Biology Concepts and Applications, Eight Edition, by Starr, Evers, Starr. Brooks/Cole, Cengage Learning 2011.

2. 21.1 Speaking for the Trees Forests
Release oxygen
Absorb water, and slowly release it
Hold soil in place
prevent erosion, flooding, and sedimentation
Fuel and lumber
Tropical Forests – Biological treasure
Hold 50% o fall land-dwelling species for 10,000 years

3. Speaking for the Trees Deforestation Tree –planting campaign 1977
Affect evaporation rates, runoff, and regional patterns of rainfall
Annual rainfall declines  decrease fertility and moisture content of the soil
Tree –planting campaign 1977
Green Belt Movements, Kenya

4. 21.2 Adaptive Trends Among Plants
Plants evolved about 475 million years ago from charophytes (a group of green algae)
Most modern plants are photoautotrophs on land
Defining trait of land plants  multicelled embryo
Clade of land plants are called embryophytes

5. Plant Adaptations to Land
Most groups are adapted to dry and often cold habitats through structural modifications
Stomata across epidermal surfaces
Stoma  opening in plant’s cuticle and epidermis
opened for gas exchange
OR closed to prevent water loss
Waterproof cuticle  secreted covering
Lignin-reinforced tissues
Stiffens cell walls of vascular plants
Xylem (water and dissolved ions) and phloem (sugars)  vascular tissues
Vascular plant  plant with a xylem and phloem

6. The Plant Life Cycle
Land plants alternate between gametophyte (haploid) and sporophyte (diploid) generations

7. multicelled sporophyte (2n) mitosis zygote (2n) DIPLOID fertilization
meiosis
HAPLOID
gametes
(n)
spores
(n)
multicelled
gametophyte
(n)
mitosis
mitosis
Fig. 21.2, p.334

8. sporophyte’s importance
zygote is only
diploid phase
sporophyte’s importance
gametophyte’s importance
green algae
bryophytes
ferns
gymnosperms
angiosperms
Fig. 21.2, p.334

9. From Haploid to Diploid Dominance
Dominant stages
Haploid body (algae and nonvascular plants)
Diploid body (most modern plants)
Complex sporophytes retain, nourish, and protect new generations through seasons
Production of two spore types allows evolution of pollen grains and seeds in two lineages

10. flowering plants gnetophytes ginkgos conifers cycads seed plants
with
complex
leaves
ferns
whisk ferns
horsetails
vascular
plants
lycophytes
hornworts
liverworts
mosses
land
plants
charophytes
plants and
close relatives
Fig. 21.3, p.335

12. Pollen and Seeds Seed plants  vascular plants Do not release spores
Instead spores give rise to gametophytes inside structures on the sporophyte body
Pollen grain  Immature male gametophyte
Released and transported by wind or animals
Can allow for fertilization in the driest conditions
Fertilization
Seed  embryo sporophyte and nutritive tissue inside a waterproof coat ( a mature ovule)

13. Key Concepts: MILESTONES IN PLANT EVOLUTION
Earliest known plants date from 475 million years ago
Since then, environmental changes have triggered divergences, adaptive radiations, and extinctions
Structural and functional adaptations of lineages are responses to some of the changes

14. 21.3 Bryophytes Haploid Gametophyte-dominant life cycle
Mosses, liverworts, and hornworts
Nonvascular (no xylem or phloem)
Rhizoids store moisture, anchor gametophyte

15. Life Cycle: Bryophytes
Sperm swim through water droplets or film of water to eggs
Gametes form in a chamber (a gametangioum) that develops in or on the gametophyte’s surface
Diploid sporophyte remains attached to the gametophyte and makes spores by meiosis
Wind disperses the spores
Some are drought tolerant – become dormant in drought and resume growth during rain
Most reproduce asexually  Fragmentation

16. Life Cycle: Bryophytes - Moss
nonvascular plant with a leafy green gametophyte and an attached, dependent sporophyte consisting of a capsule on a stalk
Rhizoid: threadlike structure that anchors the bryophyte

17. fertilization meiosis mature sporophyte (spore-producing
structure and stalk), still dependent
on gametophyte
Zygote grows,
develops into a
sporophyte while still attached to
gametophyte.
zygote
Diploid Stage
fertilization
meiosis
Haploid Stage
Spores form by
way of meiosis
and are released.
Sperm reach eggs
by moving through
raindrops or film of
water on the plant
surface.
Spores germinate.
Some grow and
develop into male
gametophytes.
rhizoids
sperm-producing
structure at shoot
tip of male
gametophyte
egg-producing
structure at shoot
tip of female
gametophyte
Other germinating spores
grow and develop into
female gametophytes.
Fig. 21.5, p.336

18. Bryophyte Structures
Sporophyte
Gametophyte

19. Peat Bogs: Sphagnum Peat  carbon rich plant remains
can be dried for fuel

20. Key Concepts: NONVASCULAR PLANTS
Bryophytes are nonvascular, with no internal pipelines to conduct water and solutes through the plant body
A gamete-producing stage dominates their life cycle, and sperm reach the eggs by swimming through droplets or films of water

21. 21.4 Seedless Vascular Plants
Lycophytes, horsetails, whisk ferns, true ferns

22. Life Cycle: Seedless Vascular Plants
Vascular tissue that produces spores
Dominated by the sporophyte
Spore-bearing structures
Strobili of horsetails
Sori of ferns
Sorus  cluster of spore-producing capsules on a fern leaf
Sperm swim through water to reach eggs

23. Life Cycle: Fern
Ferns
Tropical ferns are epiphytes, plants that attach to and grow on a trunk or branch of another plant but do not withdraw any nutrients

24. The sporophyte
(still attached to
the gametophyte)
grows, develops.
zygote
rhizome
sorus
Diploid Stage
fertilization
meiosis
Haploid Stage
Spores are
released.
Spores develop.
egg-producing
structure
egg
mature
gametophyte
(underside)
sperm-producing
structure
A spore
germinates,
grows into a
gametophyte.
sperm
Fig. 21.9, p.339

25. Fern Diversity

26. Key Concepts: SEEDLESS VASCULAR PLANTS
Lycophytes, whisk ferns, horsetails, and ferns have vascular tissues but do not produce seeds
A large spore-producing body that has internal vascular tissues dominates the life cycle
As with bryophytes, sperm swim through water to reach eggs

27. 21.5 History of the Vascular Plants
Coal
One the our premier fossil fuels
Fossil fuel was formed over millions of years by compaction and heating of plant remains
Took millions of years of
Photosynthesis
Burial by layers of sediment which protected them from decomposers
Compaction to form coal
Nonrenewable source of energy

28. stem of a giant lycophyte ( Lepidodendron),
which could grow 40 meters (131 feet) tall
stem of a giant horsetail ( Calamites),
which was almost 20 meters (66 feet) tall
seed fern ( Medullosa); its seeds
were about the size of walnuts
Fig , p.340

29. Rise of the Seed Plants – Gymnosperms and Angiosperms
Gametophytes of a seed plants form inside reproductive parts on a sporophyte body
In contrast to gametophytes of seedless vascular plants which develop from spores that were released into the environment

30. Rise of the Seed Plants Microspores Megaspores
Haploid spore formed in pollen sacs of seed plants
Pollen sac  reproductive structure develops sperm-bearing gametophytes (pollen grains)
Develop into sperm-producing male gametophytes
Megaspores
Haploid spore formed in ovule of seed plants
Ovule  reproductive structure develops egg-bearing gametophytes
After fertilization gametophyte matures  seed
Develop into egg producing female gametophytes

31. Rise of the Seed Plants Seed: A mature ovule
Part of ovule forms nutritive tissue and seed coat (protects embryo sporophyte)

32. 21.6 Gymnosperms: Naked Seeds
Conifers, cycads, ginkgos, and gnetophytes
Many are well adapted to dry climates
Conifers  nonmotile sperm and woody cones
Ex. Pine
Cycads  tropical or subtropical gymnosperm with flagellated sperm, palm like leaves, and fleshy seeds
Ginkgos  flagellated sperm, fan shaped leaves, and fleshy seeds
Gnetophytes  vineline with nonmotile sperm

33. Gymnosperms
Conifer
Cycad
Ginkgo’s
Gnetophyte

34. Gymnosperms: Naked Seeds
Seed plants that does not make flowers or fruits
Life cycle: No ovaries
Ovules form on exposed surfaces of strobili or (in conifers) female cones
“Naked” seed because unlike angiosperms they are not inside a fruit

35. Life Cycle: Conifer

36. Fig. 21.15, p.343 section through one ovule (the red “cut”
in the diagram
to the left)
surface view of a
female cone scale
(houses two ovules)
ovule
section through
a pollen sac
(red cut)
surface view of a
scale of a male
strobilus (houses
two pollen sacs)
mature
sporophyte
seed
coat
embryo
nutritive
tissue
zygote
seedling
seed formation
Diploid Stage
fertilization
meiosis
meiosis
pollen tube
Haploid Stage
sperm-producing cell
(view inside
an ovule)
pollination
(wind deposits
pollen grain
near ovule)
Microspores
form, develop
into pollen
grains.
Megaspores
form; one
develops into
the female
gametophyte.
Germinating pollen grain (the
male gametophyte). Sperm
nuclei form as the pollen tube
grows toward the egg.
eggs
female gametophyte
Fig , p.343

37. 21.7 Angiosperms: Flowering Plants
Only angiosperms can make flowers and fruit
Many coevolved with birds, bees, bats, and other animal pollinators
Flower  selective advantage
Reproductive shoot of a flowering plant
Fruit  mature flowering plant ovary
After fertilization, an ovule matures into a seed and the ovary around it becomes the fruit

38. Flowering Plant Structures

39. 21.7 Angiosperms: Flowering Plants
Most widely distributed and diverse plant group
Two largest classes: Eudicots and monocots
Monocots 
includes grasses, orchids and palms
Eudicots 
includes herbaceous plants, woody trees, and cacti

40. Evolution of Flowering Plants

41. Life Cycle: Flowering Plants
Monocot life cycle: An example of sexual reproduction in flowering plants
Formation of pollen and eggs
Double fertilization produces an embryo sporophyte and nutritive tissue (endosperm) that supports it
Protective seeds form in ovaries
Outer ovary tissues later develop into fruits

42. Monocot Life Cycle: Lily

43. Fig. 21.19, p.346 a flowering stem of the mature sporophyte (2n)
ovules
inside
ovary
pollen sac,
where each
one of many
cells will
give rise to
microspores
cell in ovule
that will give
rise to a
megaspore
seed coat
embryo (2n)
endosperm (nutritive tissue)
seed
Diploid Stage
Haploid Stage
double fertilization
meiosis
meiosis
Pollination and pollen
tube formation:
Microspores
form, then
develop into
pollen grains.
Megaspore gives
rise to haploid cells
in ovule. In one of
the cells, mitosis
without cytoplasmic
division gives it two
nuclei; it will give
rise to endosperm.
male
gametophyte
pollen tube
sperm (n)
Pollen is
released.
cell from which
endosperm
will form
The pollen tube enters an ovule.
egg
(line of cut
of diagram
at left)
female gametophyte
ovary
Fig , p.346

44. Summary: Comparison of Major Plant Groups

45. Key Concepts: SEED-BEARING VASCULAR PLANTS
Gymnosperms and, later, angiosperms radiated into higher and drier environments
The packaging of male gametes in pollen grains and embryo sporophytes in seeds contributed to the expansion of these groups into new habitats

46. Key Concepts: SEED-BEARING VASCULAR PLANTS (cont.)
Angiosperms alone make flowers, which wind, water, and animals help pollinate
In distribution and diversity, angiosperms are the most successful group of plants
Nearly all plant species that we rely upon for food are angiosperms

47. Animation: Fern life cycle

48. Animation: Flower parts

49. Animation: Haploid to diploid dominance

50. Animation: Monocot life cycle

51. Animation: Moss life cycle

52. Animation: Pine life cycle

53. Animation: Pinus cones

54. Animation: Seedless vascular plants