1. Plant Evolution

2. The Plant Kingdom Nearly all are multicelled
Vast majority are photoautotrophs
Energy from sun
Carbon dioxide from air
Minerals dissolved in water

3. Setting the Stage for Plants
Earth’s atmosphere was originally oxygen free
Ultraviolet radiation bombarded the surface
Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer

4. Invading the Land
Cyanobacteria were probably the first to spread into and up freshwater streams
Later, green algae and fungi made the journey together
Every plant is descended from species of green algae

5. Adaptations to Land Root systems Shoot systems Vascular tissues
Waxy cuticle for water conservation

6. Evolutionary Trend in Plant Life Cycles
Algae and bryophytes put most energy into making gametophytes
Land plants put energy into structures that produce spores and retain, nourish, and protect gametes

7. Evolutionary Trend

8. Milestones in Plant Evolution
charophytes
bryophytes
lycophytes
horsetails ferns
cycads
ginkgos
conifers
gnetophytes
flowering plants
seed plants
plants with true leaves
vascular plants
land plants
(closely related groups)

9. Pollen
Pollen grains are sperm-bearing male gametophytes that develop from microspores
Allows transfer of sperm to egg without water
Can drift on air currents, or be carried by pollinators

10. Seeds Ovules are female reproductive structures that become seeds
Consist of:
Female gametophyte with egg cell
Nutrient-rich tissue
Jacket of cell layers that will form seed coat

11. Nonvascular Plants Bryophytes Include 24,000 species of: Liverworts
Hornworts
Mosses

12. Bryophytes Small, nonvascular, nonwooody
Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts
Usually live in wet habitats
Flagellated sperm require water to reach eggs

13. Moss Life Cycle
Development of mature sporophyte (still attached to gametophyte)
Zygote
Diploid Stage
Fertilization
Meiosis
Haploid Stage
Spores released
male
gametophyte
tip
Sperm
Male gametophyte
female
gametophyte
tip
Female gametophyte
Egg

14. Marchantia: A Liverwort
Reproduces asexually by way of gemmae cups
Sexual reproduction
Gametophytes are male or female
Gametes are produced on elevated structures

15. Vascular Plants Majority of plants
Have internal tissues that carry water and solutes
Two groups
Seedless vascular plants
Seed-bearing vascular plants

16. Seedless Vascular Plants
Produce spores but no seeds
Main groups:
Lycophytes
Horsetails
Ferns

17. Seedless Vascular Plants
Like bryophytes:
Live in wet, humid places
Require water for fertilization
Unlike bryophytes:
Sporophyte is free-living and has vascular tissues

18. Ferns 12,000 species, mostly tropical Most common sporophyte structure
Perennial underground stem (rhizome)
Roots and fronds arise from rhizome
Young fronds are coiled “fiddleheads”
Spores form on lower surface of some fronds

19. Fern Life Cycle zygote Diploid Stage Haploid Stage
The sporophyte (still attached to the gametophyte) grows, develops
Sori
zygote
rhizome
Diploid Stage
fertilization
meiosis
Haploid Stage
Spores are released
Spores develop
egg-producing structure
egg
mature gametophyte (underside)
sperm-producing structure
sperm
Spore germinates
gametophyte

20. Seed-Bearing Vascular Plants
Gymnosperms arose first
Cycads
Ginkgos
Conifers
Angiosperms arose later
Monocots
Dicots

21. Seed-Bearing Plants Microspores that give rise to pollen grains
Megaspores inside ovules
More water-conserving than seedless vascular plants

22. Special Traits of Seed-Bearing Plants
Pollen grains
Arise from megaspores
Develop into male gametophytes
Can be transported without water
Seeds
Embryo sporophyte inside nutritive tissues and a protective coat
Can withstand hostile conditions

23. Gymnosperms Plants with “naked seeds” Seeds don’t form inside an ovary
Conifers Ginkgos
Cycads

24. Conifer Characteristics
Woody trees or shrubs
Most are evergreen
Bear seeds on exposed cone scales
Most produce woody cones

25. Cycads Only 130 living species Two species of Zamia are native to U.S.
Palmlike appearance
Pollen-bearing and seed-bearing cones on different plants

26. Ginkgos Only surviving species, Ginkgo biloba, is native to China
Deciduous tree with fan-shaped leaves
Trees are male or female
Female trees produce seeds covered with a fleshy, foul-smelling coat

27. Pine Cones
Woody scales of a “pine cone” are the parts of where megaspores formed and developed into female gametophytes
Male cones, where microspores and pollen are produced, are not woody

28. Pine Life Cycle Female cone Sporophyte Ovule Male cone Pollen sac Seed
Fertilization
Meiosis
Egg
View inside
ovule
Microspores
Megaspores
Pollen tube

29. Angiosperms Flowering plants Dominant land plants (260,000 species)
Defining feature: Ovules and (after fertilization) seeds are enclosed in an ovary
Two classes: Monocots and dicots

30. Plants and Pollinators
Pollen:
Sperm packed inside a nutritious package
Transferred first by wind currents
Later transferred by insects
Plants that attracted insect pollinators with flowers had a reproductive advantage

31. Pollen Formation Each anther has four pollen sacs
Inside the pollen sacs, cells undergo meiosis and cytoplasmic division to form microspores
Microspores undergo mitosis to form pollen grains

32. Double Fertilization A pollen tube grows down through the ovary tissue
It carries two sperm nuclei
When pollen tube reaches an ovule, it penetrates embryo sac and deposits two sperm
One fertilizes the egg, other fuses with both nuclei of endosperm mother cell

33. Endosperm Formation Occurs only in angiosperms
Fusion of a sperm nucleus with the two nuclei of the endosperm mother cell produces a triploid (3n) cell
This cell will give rise to the endosperm, the nutritive tissue of the seed

34. Seeds and Fruits The seed is the mature ovule
wall of ovary
The seed is the mature ovule
The fruit is the mature ovary

35. Structure of a Seed
Protective seed coat is derived from integuments that enclosed the ovule
Nutritious endosperm is food reserve
Embryo has one or two cotyledons
Monocot has one
Eudicot has two

36. Seed Formation
Fertilization of the egg produces a diploid sporophyte zygote
The zygote undergoes mitotic divisions to become an embryo sporophyte
Seed: A mature ovule, which encases an embryo sporophyte and food reserves inside a protective coat

37. Seed Dispersal Fruit structure is adapted to mode of dispersal
Some modes of seed dispersal:
Wind currents
Water currents
Animals

38. Double Fertilization Distinctive feature of angiosperms
Male gametocyte delivers two sperm to an ovule
One fertilizes egg; other fertilizes a cell that gives rise to endosperm that supports embryo

39. Flower Structure

40. Flowering Plant Life Cycle
Diploid
Double fertilization
Meiosis
Meiosis
Haploid
Mitosis without cytoplasmic division
Microspores
Pollination
Two sperm enter ovule
Female gametophyte

41. Deforestation
Result of demand for wood as fuel and lumber; cultivation of land for agriculture
Greatest occurrence in Brazil, Indonesia, Columbia, and Mexico