Plant Diversity

General Characteristics of Plants All plants are: Eukaryotic Autotrophic Multicellular Cell Walls with cellulose Chloroplasts w/ chlorophyll a, b, and carotenoids May have waxy cuticle to prevent water loss. Stomata allow gas exchange. Plants probably evolved from green algae (charophytes) Chloroplast similarity Biochemical similarities Cell Wall similarities

Charophytesv. Plants No alternation of generations No cuticle needed Jacketed gametes No protection of embryos Alternation of generations Cuticle (prevents water loss/dessication) Jacketed gametes (protects from dessication) Protected embryo (protects from dessication)

Alternation of Generations Sporophyte (2N) Meiosis Gametophyte (N) Zygote (2N) Spores (N) Gametes (egg & sperm fertilization Mitosis

Evolutionary Trend zygote SPOROPHYTE (2n) GAMETOPHYTE (n) GREEN ALGABRYOPHYTEFERNGYMNOSPERMANGIOSPERM Figure 23.2 Page 386

Classifying Plants Plants can be divided into 2 major categories based on their characteristics: Nonvascular Plants Do NOT have specialized tissues to transport water and nutrients Instead, these plants transport water from cell-to-cell by osmosis Vascular Plants Have specialized tissues to transport water and nutrients in plants Xylem – carries water upward from roots Phloem – carries nutrients and carbohydrates produced by photosynthesis

Nonvascular Plants (Bryophytes) Again, these plants do not have specialized tissues to transport water and nutrients and instead rely on osmosis Thus, these plants must be small Why? Major types of bryophytes (nonvascular plants): Mosses Liverworts Hornworts

Nonvascular Plants/ Bryophytes Mosses Have rhizoids that anchor them to the ground (instead of roots) Depend on water for fertilization The sperm must swim to the egg Therefore, nonvascular plants must live in MOIST environments Gametophyte is the dominant phase of the life cycle

Moss/ Bryophyte Life Cycle Zygote grows, develops into a sporophyte while still attached to gametophyte. Fertilization zygote sperm- producing structure egg- producing structure Diploid Stage Haploid Stage mature sporophyte Meiosis Spores germinate. male gametophyte female gametophyte Figure 23.5 Page 388

Vascular Plants/Tracheophytes Reminder: Vascular plants have specialized tissues to transport water and nutrients in plants Xylem & phloem Vascular plants (tracheophytes) can be divided into 2 categories: Seedless vascular plants Seed (vascular) plants

Seedless Vascular Plants Have true roots, leaves, and stems Consist of ferns, club mosses, and horsetails

Seedless Vascular Plants Ferns – A Close Up Diploid sporophyte is the dominant stage Have rhizomes, which are underground stems Fronds: large “leaves” where spores develop Develop spores in sporangia on underside of fronds Reproduce using spores A sorus (plural: sori) is a cluster of sporangia

Fern Life Cycle Spores are released Sporophyte still attached to gametophyte zygote fertilization Diploid Stage Haploid Stage egg sperm mature gametophyte Spores develop meiosis Spore germinates rhizome sorus Figure 23.9 Page 391

Seed (Vascular) Plants Have true roots, leaves, and stems Have the ability to form seeds, which are used for reproduction Seed plants are the most dominant group of photosynthetic organisms on land There are 2 types of seed (vascular) plants: 1. gymnosperms 2. angiosperms

Seed (Vascular) Plants Gymnosperms = “cone bearers” “naked seeds” – not enclosed in ovaries Bear seeds directly on the surfaces of cones Cones = sporophyte structures that produce gametophytes (seeds) Coniferous trees are the major example Pines, junipers, spruces, etc.

section through one ovule ovule surface view of one cone scale (houses two ovules) section through a pollen-producing sac surface view of one cone scale (houses a pollen-producing sac) meiosis fertilization seed coat embryo zygote mature sporophyte seeding pollen tube sperm- producing cell eggs female gametophyte pollination microspores form megaspores form seed Diploid Haploid Pine Life Cycle Figure Page 396

Seed (Vascular) Plants Angiosperms = flowering plants Seeds are enclosed by an ovary Flowers are reproductive organs Evolutionary advantage  attract pollinators Flowering plants contain ovaries Ovaries surround and protect seeds Ovary develops into a fruit after pollination & helps with seed dispersal when eaten Examples: Maple trees, tulips, grass

Flowering Plant Life Cycle Double fertilizationMeiosis microspores female gametophyte pollination mitosis without cytoplasmic division two sperm enter ovule Diploid Haploid Figure Page 399 sporophyte

Evolutionary Tree for Plants green algae zygophytes, related groups charophytes bryophytes lycophyteshorsetails cycadsconifers flowering plants seed plants euphyllophytes vascular plants embryophytes (land plants) (closely related groups) ferns ginkgos gnetophytes Nested monophyletic groups