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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

Bryophyte Structures Sporophyte Gametophyte

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

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

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

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

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

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

Fern Diversity

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

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

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. 21.12, p.340

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

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

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

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

Gymnosperms Conifer Cycad Ginkgo’s Gnetophyte

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

Life Cycle: Conifer

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. 21.15, p.343

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

Flowering Plant Structures

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

Evolution of Flowering Plants

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

Monocot Life Cycle: Lily

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. 21.19, p.346

Summary: Comparison of Major Plant Groups

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

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

Animation: Fern life cycle

Animation: Flower parts

Animation: Haploid to diploid dominance

Animation: Monocot life cycle

Animation: Moss life cycle

Animation: Pine life cycle

Animation: Pinus cones

Animation: Seedless vascular plants