1. Biology: Life on Earth Lecture for Chapter 21 The Diversity of Plants
Teresa Audesirk • Gerald Audesirk • Bruce E. Byers
Biology: Life on Earth
Eighth Edition
Lecture for Chapter 21
The Diversity of Plants
Copyright © 2008 Pearson Prentice Hall, Inc.

2. Chapter 21 Outline 21.1 What Are the Key Features of Plants? p. 404
21.2 What Is the Evolutionary Origin of Plants? p. 405
21.3 How Have Plants Adapted to Life on Land? p. 406
21.4 What Are the Major Groups of Plants? p. 407

3. Section 21.1 Outline 21.1 What Are the Key Features of Plants?
Plants Have Alternating Multicellular Haploid and Diploid Generations
Plants Have Multicellular, Dependent Embryos
Plants Play a Crucial Ecological Role
Plants Provide Humans with Necessities and Luxuries
Plants Are Adapted to Life on Land

4. Key Features of Plants Multicellularity
Ability to photosynthesize (most)
Exhibit alternation of generations (a multicellular diploid generation alternates with a multicellular haploid generation)

5. Alternation of Generations
Diploid sporophyte plant produces haploid spores through meiosis
Spores divide by mitosis and develop into haploid gametophyte plants
Haploid gametophyte plant produces haploid gametes through mitosis
Gametes fuse to form diploid zygotes, which divide by mitosis and develop into diploid sporophytes

6. FIGURE 21-1 Alternation of generations in plants
As shown in this generalized depiction of a plant life cycle, a diploid sporophyte generation produces haploid spores through meiosis.
FIGURE 21-1 Alternation of generations in plants
As shown in this generalized depiction of a plant life cycle, a diploid sporophyte generation produces haploid spores through meiosis. The spores develop into a haploid gametophyte generation that produces haploid gametes by mitosis. The fusion of these gametes results in a diploid zygote that develops into the sporophyte plant.
The spores develop into a haploid gametophyte generation that produces haploid gametes by mitosis. The fusion of these gametes results in a diploid zygote that develops into the sporophyte plant.

7. Multi-cellular Dependent Embryos
Have multi-cellular, dependent embryos
Zygotes develop into multi-cellular embryos
Embryos are retained within, and receive nutrients from the gametophyte parent

8. Crucial Ecological Role
Through photosynthesis, plants provide food, directly or indirectly, for ALL of the animals, fungi, and non-photosynthetic microbes on land
Plants produce oxygen gas as a byproduct of photosynthesis, continually replenishing oxygen in the atmosphere

9. Crucial Ecological Role
Plants help create and maintain soil
Dead plant material is decomposed by fungi, prokaryotes, and other decomposers
Decomposed plant tissue becomes part of the soil, making it more fertile
Roots of living plants help hold soil together, preventing erosion by wind and water

10. Human Necessities and Luxuries
Plants provide shelter
Wood is used to construct housing
Plants provide fuel
Wood: important fuel for warming and cooking in many parts of the world
Coal: derived from the remains of ancient plants that have been transformed by geological processes

11. Human Necessities and Luxuries
Plants provide medicine
Many medicines and drugs were originally found in and extracted from plants, e.g. aspirin, Taxol, morphine
Plants provide pleasure
Flowers, gardens, and lawns
Coffee, tea, and wine

12. Section 21.2 Outline 21.2 What Is the Evolutionary Origin of Plants?
Green Algae Gave Rise to Plants
The Ancestors of Plants Lived in Fresh Water

13. The Plant Evolutionary Tree
Certain anatomical features represent milestones in the evolution of plants
Appearance of vascular tissue and lignin
Appearance of pollen and seeds
Appearance of flowers and fruits

14. FIGURE 21-2 Evolutionary tree of some major plant groups

15. Green Algae
Several lines of evidence support the hypothesis that green algae gave rise to plants:
DNA comparisons show that green algae are plants’ closest living relatives
Both use the same type of chlorophyll and accessory pigments in photosynthesis
Both store food as starch
Both have cell walls made of cellulose

16. Section 21.3 Outline 21.3 How Have Plants Adapted to Life on Land?
Plant Bodies Resist Gravity and Drying
Plant Embryos Are Protected and Plant Sex Cells May Disperse Without Water

17. Terrestrial Adaptations
Roots or root-like structures
Anchor plant
Absorb water and nutrients from soil
Waxy cuticle covers leaves and stems
Reduces evaporative water loss

18. Terrestrial Adaptations
Stomata (singular, stoma)
Allow gas exchange when open
Reduce evaporative water loss when closed
Conducting vessels
Transport water and nutrients throughout plant
Lignin
Stiffening agent found in cell walls; supports plant body

19. Reproduction Without Water
Pollen
A reduced male gametophyte that allows wind (instead of water) to carry sperm to eggs
Seeds
Nourish, protect, and help disperse developing embryos
Flowers
Attract pollinators
Fruits
Attract animals to disperse seeds

20. Section 21.4 Outline 21.4 What Are the Major Groups of Plants?
Bryophytes Lack Conducting Structures
Vascular Plants Have Conducting Vessels That Also Provide Support
The Seedless Vascular Plants Include the Club Mosses, Horsetails, and Ferns
The Seed Plants Dominate the Land, Aided by Two Important Adaptations: Pollen and Seeds

21. Section 21.4 Outline
21.4 What Are the Major Groups of Plants? (continued)
Gymnosperms Are Nonflowering Seed Plants
Angiosperms Are Flowering Seed Plants
More Recently Evolved Plants Have Smaller Gametophytes

22. Major Groups of Plants Bryophytes (non-vascular plants)
Lack well-developed structures for conducting water and nutrients
Vascular plants (tracheophytes)
Have a complex vascular system

23. Table 21-1 Features of the Major Plant Groups

24. The Bryophytes Lack true roots, stems, or leaves
Have rhizoids, root-like anchoring structures
Limited body size (most less than 2.5 cm tall)
Non-vascular
Cell walls lack a stiffening agent
Most are restricted to moist habitats
Motile sperm must swim to egg

25. The Bryophytes Gametophyte generation is dominant
Sporophyte remains attached to and is nutritionally dependent on parental gametophyte
Include liverworts, hornworts, and mosses

26. (b) Liverworts grow in moist, shaded areas
(b) Liverworts grow in moist, shaded areas. This female plant bears umbrella-like archegonia, which hold the eggs. Sperm must swim up the stalks through a film of water to fertilize the eggs.
FIGURE 21-3a Bryophytes
The plants shown here are less than inch (about 1 centimeter) in height. (a) The horn-like sporophytes of hornworts grow upward from archegonia that are embedded in the gametophyte body.

27. FIGURE 21-3c Bryophytes
(c) Moss plants, showing the stalks that carry spore-bearing capsules.
FIGURE 21-3d Bryophytes
(d) Mats of Sphagnum moss cover moist bogs in northern regions.

28. The Bryophytes: Reproduction
Gametes develop within protected structures on gametophyte
Archegonia (singular, archegonium) produce eggs
Antheridia (singular, antheridium) produce sperm
Archegonia and antheridia may be located on the same plant or on different plants

29. FIGURE 21-4 Moss life cycle
The leafy green gametophyte (lower right) is the haploid generation that produces sperm and eggs. The sperm must swim through a film of water to the egg. The zygote develops into a stalked, diploid sporophyte that emerges from the gametophyte plant. The sporophyte is topped by a brown capsule in which haploid spores are produced by meiosis. These are dispersed and germinate, producing another green gametophyte generation. (Inset) Moss plants. The short, leafy green plants are haploid gametophytes; the reddish brown stalks are diploid sporophyte

30. The Bryophytes: Reproduction
Sperm swim to egg
Fertilization occurs and diploid sporophyte develops within archegonium of gametophyte
Sporophyte produces encapsulated spores via meiosis
Haploid spores disperse and germinate into new gametophytes

31. The Vascular Plants Have roots, stems, and leaves
Have vessels impregnated with the stiffening agent lignin
Sporophyte generation is dominant
Include the seedless vascular plants and the seed plants

32. The Seedless Vascular Plants
Gametes develop within archegonia and antheridia
Motile sperm swim to egg
Formed the first forests
Gave rise to present-day coal deposits
Include club mosses, horsetails, and ferns

33. Club Mosses Present-day club mosses are only a few inches tall
Leaves are small and scalelike
Lycopodium (ground pine) grows on temperate forest floors

34. FIGURE 21-5a Some seedless vascular plants
Seedless vascular plants are found in moist woodland habitats. (a) The club mosses (sometimes called ground pines) grow in temperate forests. This specimen is releasing spores.

35. Horsetails
Present-day horsetails (Equisetum) rarely exceed a meter in height
Leaves reduced to scales on branches
Outer layer of cells contain silica (glass)
Abrasive texture led early European settlers to call them “scouring rushes”

36. FIGURE 21-5c Some seedless vascular plants
Seedless vascular plants are found in moist woodland habitats. (b) The giant horsetail extends long, narrow branches in a series of rosettes. Its leaves are insignificant scales. At right is a cone-shaped spore-forming structure. .

37. Ferns Largest and most diverse group of seedless vascular plants
Have well-developed, broad leaves
Leaves emerge from coiled fiddleheads
Reach significant heights in tropics

38. (d) Although most fern species are small, some, such as this tree fern, retain the large size that was common among ferns of the Carboniferous period.
FIGURE 21-5b Some seedless vascular plants
Seedless vascular plants are found in moist woodland habitats. (c) The leaves of this deer fern are emerging from coiled fiddleheads.

39. Ferns: Reproduction
Sporophyte produces haploid spores within sporangia (singular, sporangium)
Spores disperse and germinate into tiny, independent gametophytes
Archegonium produces egg
Antheridium produces sperm
Sperm swim to egg
Fertilization occurs and zygote develops into a diploid sporophyte

40. FIGURE 21-6 Fern life cycle
The dominant plant body (upper left) is the diploid sporophyte. Haploid spores, formed in sporangia located on the underside of certain leaves, are dispersed by the wind to germinate on the moist forest floor into inconspicuous haploid gametophyte plants. On the lower surface of these small, sheet-like gametophytes, male antheridia and female archegonia produce sperm and eggs. The sperm must swim to the egg, which remains in the archegonium. The zygote develops into the large sporophyte plant. (Inset) Underside of a fern leaf, showing clusters of sporangia.

41. The Seed Plants Produce pollen and seeds
Pollen grains contain sperm-producing cells
Dispersed by wind or pollinators
Eliminate need for sperm to swim to egg
Seeds consist of:
Embryonic plant
Seed coat (protects embryo)
Food supply (nourishes emerging plant)

42. FIGURE 21-7a,b Seeds
Seeds from (a) a gymnosperm and (b) an angiosperm. Both consist of an embryonic plant and stored food confined within a seed coat.
Seeds exhibit diverse adaptations for dispersal, including (c) the dandelionﾍs tiny, tufted seeds that float in the air and (d) the massive, armored seeds (protected inside the fruit) of the coconut palm, which can survive prolonged immersion in seawater as they traverse ocean

43. Seeds May remain dormant for days, months, or years
May possess adaptations for dispersal by wind, water, and animals

44. FIGURE 21-7d Seeds
Seeds exhibit diverse adaptations for dispersal, including (c) the dandelion’s tiny, tufted seeds that float in the air and (d) the massive, armored seeds (protected inside the fruit) of the coconut palm, which can survive prolonged immersion in seawater as they traverse ocean.

45. The Seed Plants
Gametophytes greatly reduced in size and dependent on sporophyte for nutrition
Female gametophyte is a small group of haploid cells
Male gametophyte is pollen grain
Include gymnosperms and angiosperms

46. Gymnosperms Non-flowering seed plants
First fully terrestrial plants to evolve
Includes ginkgos, cycads, gnetophytes, and conifers

47. Gymnosperms: Ginkgos
Present-day ginkgos represented by a single species, Ginkgo biloba (maidenhair tree)
Trees are either male or female
Female trees bear foul-smelling, fleshy seeds
Male trees extensively planted in U.S. cities (resistant to pollution)
Ginkgo extract purportedly improves memory

48. FIGURE 21-8a Gymnosperms
(a) This ginkgo, or maidenhair tree, is female and bears fleshy seeds the size of large cherries.

49. Gymnosperms: Cycads Probably evolved from ferns
Most abundant in tropical or subtropical climates
Are either male or female
Grow slowly and live for a long time
One Australian specimen estimated to be 5000 years old

50. FIGURE 21-8b Gymnosperms
(b) A cycad. Common in the age of dinosaurs, these are now limited to about 160 species. Like ginkgos, cycads have separate sexes.

51. Gymnosperms: Gnetophytes
70 species of shrubs, vines, small trees
Leaves of Ephedra species contain compounds used as stimulants and appetite suppressants
The leaves of gnetophyte Welwitschia mirabilis may be hundreds of years old…

52. FIGURE 21-8c Gymnosperms
(c) The leaves of the gnetophyte Welwitschia may be hundreds of years old.

53. Gymnosperms: Conifers
Include pines, firs, spruce, hemlocks, and cypresses
Most abundant in cold latitudes and at high elevations
Adapted to dry, cold conditions:
Retain green leaves throughout the year (evergreen)
Thin, needle-like leaves covered with waterproofing material to reduce evaporation
Produce an “antifreeze” in sap

54. FIGURE 21-8d Gymnosperms
(d) The needle-shaped leaves of conifers are protected by a waxy surface layer.

55. Conifer Seeds Develop in Cones
Male cones are relatively small
Produce pollen (male gametophytes) by meiosis
Pollen dispersed by wind
Pollen grain germinates and forms a pollen tube if it lands near female gametophyte
Pollen tube slowly burrows into female gametophyte (may take 14 months)

56. Conifer Seeds Develop in Cones
Female cones consist of numerous woody scales arranged spirally around a central axis
Two ovules (immature seeds) located at base of each scale
Cells within each ovule undergo meiosis to produce haploid female gametophytes
Female gametophytes produce egg cells

57. Conifer Seeds Develop in Cones
Pollen tube releases sperm when it comes into contact with egg
Fertilization occurs and seed develops
Seeds released when cone is mature
Seeds dispersed by wind
Seeds germinate to form sporophyte trees

58. FIG 21-9 Pine life cycle
The pine tree is the sporophyte generation (upper left) and bears both male and female cones. Haploid female gametophytes develop within the scales of female cones and produce egg cells. Male cones produce pollen, the male gametophytes. A pollen grain, dispersed by the wind, may land on the scale of a female cone. It then grows a pollen tube that penetrates the female gametophyte and conducts sperm to the egg. The fertilized egg develops into an embryonic plant enclosed in a seed. The seed is eventually released from the cone, germinates, and grows into a sporophyte tree.

59. Seed Plants: Angiosperms
Seed plants that produce flowers and fruits
Most diverse and widespread of all plants
Have broad range in size
Smallest is duckweed (3 mm in diameter)
Largest is eucalyptus tree (100 meters in height)

60. FIGURE 21-10a Angiosperms
(a) The smallest angiosperm is the duckweed, found floating on ponds. These specimens are about 1/8 inch (3 millimeters) in diameter. (b) The largest angiosperms are eucalyptus trees, which can reach 325 feet (100 meters) in height. Conspicuous flowers, such as those on a eucalyptus tree (b, inset), entice insects and other animals that carry pollen between individual plant

61. Seed Plants: Angiosperms
Three major adaptations have contributed to dominance of angiosperms
Flowers
Fruits
Broad leaves

62. Flowers
Flowers are reproductive structures in which both male and female gametophytes are formed
Believed to have evolved when gymnosperm ancestors formed an association with animals
Animals benefited by eating some of the protein-rich pollen
Plants benefited by using animals as pollinators

63. Flowers
Most flowers are showy and attract animal pollinators (e.g. insects)

64. Flowers
Some flowers are inconspicuous and rely on wind for pollination
FIGURE 21-10b Angiosperms
Both (c) grasses and many trees, such as (d) this birch, in which flowers are shown as buds (green) and blossoms (brown), have inconspicuous flowers and rely on wind for pollination.

65. Life Cycle of an Angiosperm
Flowers develop on dominant sporophyte plant
Male gametophytes (pollen) develop inside anthers
Female gametophyte develops from an ovule inside the ovary
Egg develops within female gametophyte

66. Life Cycle of an Angiosperm
Pollination occurs when pollen grain lands on the stigma of a flower
Fertilization occurs when growing pollen tube releases sperm into the ovule
Fertilized ovule develops into a seed
Seed is dispersed and germinates to form a sporophyte plant

67. FIGURE 21-11 Life cycle of a flowering plant
The dominant plant body (upper right) is the diploid sporophyte, whose flowers normally produce both male and female gametophytes. Male gametophytes (pollen grains) are produced within anthers. The female gametophyte develops from a spore within the ovule, and contains one egg cell. A pollen grain that lands on a stigma grows a pollen tube that burrows down to the ovule and into the female gametophyte. There it releases its sperm, one of which fuses with the egg to form a zygote. The ovule gives rise to the seed, which contains the developing embryo and its food source. The seed is dispersed, germinates, and develops into a mature sporophyte.

68. Fruits Encourage Seed Dispersal
Fruits are mature ovaries that contain developing seeds
Various fruit adaptations help disperse seeds
Edible fruits entice animals to eat them (seeds pass through digestive tract unharmed)
Burrs cling to animal fur
Winged fruits are carried through the air

69. Broad Leaves
Broad leaves of angiosperms collect more sunlight for photosynthesis than narrow leaves of gymnosperms
Temperate angiosperms drop leaves to conserve water when it is in short supply (fall, winter)
Tropical and subtropical angiosperms are evergreen
May shed leaves during dry season

70. Broad Leaves
Photosynthetic advantage is offset by fact that broad, tender leaves are more appealing to herbivores than tough, waxy needles of conifers
Angiosperm defenses include
Physical defenses (thorns, spines, resins)
Chemical defenses (make plant tissue poisonous or distasteful)

71. Chemical Defenses
Many defensive compounds have been exploited by humans for medicinal and culinary uses
Medicines (aspirin, codeine)
Stimulants (nicotine, caffeine)
Spicy flavors (mustard, peppermint)

72. Smaller Gametophytes ‘Evolve’
Earliest plants (nonvascular plants)
Gametophyte dominates
Small, dependent sporophyte attached to larger gametophyte
Later plants (seedless vascular plants)
Sporophyte dominates
Small gametophyte is independent of sporophyte
Recently evolved plants (seed plants)
Microscopic, dependent gametophyte attached to larger sporophyte