Plant Diversity I: How Plants Colonized Land Chapter 29 Notes Plant Diversity I: How Plants Colonized Land

Background More than 280,000 species of plants inhabit the Earth today Although some are aquatic, most are terrestrial: deserts, grasslands, forests Land plants evolved from certain green algae called charophyceans

Four main groups of land plants: 1. Bryophytes 2. Pteridophytes 3. Gymnosperms 4. Angiosperms

4 Main Groups of Land Plants Bryophytes: mosses; distinguished from algae by advances that allow for life on land Pteridophytes: ferns; contain vascular tissue (transport water and food); “seedless plants” Gymnosperms: conifers; “naked seed” (seeds are not enclosed in a special chamber) Seed: consists of a plant embryo packaged with food and a protective coat Angiosperms: flowering plants; “container seed”; most modern-day plants

Evolution of Plants Flow Chart algal ancestors  bryophytes  vascular plants  the origin of seeds  the evolution of flowers

Things to Remember Charophyceans are the green algae most closely related to land plants Plasma membranes contain rosette cellulose-synthesizing complexes - synthesize the cellulose of cell walls Same enzymes in peroxisomes that help minimize the loss of product due to photorespiration

Concept 29.1

Things to Remember Several terrestrial adaptations distinguish land plants from charophycean algae - growth in length is from apical meristems - multicellular, dependent embryos - alternation of generations: gametophyte and sporophyte

Apical Meristem

Gametophyte v. Sporophyte The multicellular haploid form in organisms undergoing alternation of generations that mitotically produces haploid gametes that unite & grow into the sporophyte generation Sporophyte The multicellular diploid form in organisms undergoing alternation of generations that results from a union of gametes & that meiotically produces haploid spores that grow into the gametophyte generation.

Gametophyte & Sporophyte

Alternation of Generations Gametophyte & Sporophyte generations are the two multicellular body forms that alternate the life cycle of land plants. Cells of the gametophyte are haploid and produce gametes. Fusion of eggs and sperm during fertilization results in diploid zygotes.

Alternation of Generations cont. Mitotic division of the zygote results in the multicellular , diploid sporophyte. Meiosis in a mature sporophyte will result in haploid reproductive cells called spores. A spore is a reproductive cell that can develop into a new organism without fusing with another cell. Mitotic division will then produce new multicellular gametophytes.

Plant Adaptations as a result of being terrestial There are other adaptations that are common in many land plants 1. Adaptations for water conservation: - formation of a cuticle - stomata contain guard cells

Plant Adaptations 2. Adaptations for water transport: Except for bryophytes, land plants have true roots, stems, and leaves with vascular tissue - xylem: carry water and minerals up from root - phloem: distribute sugars and amino acids throughout the plant

Xylem & Phloem

Plant Adaptations…. 3. Adaptations to shallow water preadapted plants for living on land - natural selection would favor those that could withstand occasional drying

Plant History Land plants evolved from charophycean algae over 500 mya - chloroplasts: chlorophyll b and beta-carotene - homologous cell walls - peroxisomes

Plant History Alteration of generations in plants may have adapted by delayed meiosis Charophycean zygote undergoes meiosis to produce haploid spores Plant zygote undergoes mitosis to produce a multicellular sporophyte to produce haploid spores by meiosis

Four different groups of Land Plants NON-VASCULAR PLANTS Bryophytes VASCULAR PLANTS Seedless Pteridophytes Seeds Gymnosperms Angiosperms

Bryophytes Bryophytes are represented by 3 phyla: 1. Hepatophyta (liverwarts) 2. Anthocerophyta (hornworts) 3. Bryophyta (mosses)

Bryophyte pictures…

The gametophyte is the dominant generation in the life cycle of bryophytes - sporophytes are typically smaller and present only part of the time - up to 50 million spores can be generated in one spore capsule

Bryophyte cycle

Mosses are able to exist in very harsh climates - able to loose most of their body water without dying, then rehydrate later Bryophytes were the only plants on Earth for 100 million years

Vascular Plants Modern vascular plants include ferns (pteridophytes), gymnosperms, and flowering plants (angiosperms) Differ from bryophytes - contain phloem and xylem - dominant sporophyte generation

Seedless v Seed Plants 2 phyla of seedless vascular plants: phylum Lycophyta and phylum Pterophyta (ferns) Pteridophytes (seedless vascular plants) provide clues to the evolution of roots and leaves

Pteridophytes Most pteridophytes have true roots with lignified vascular tissue Lycophytes have small leaves with only a single unbranched vein; known as microphylls - modern leaves are known as megaphylls

Sporophytes A sporophyte-dominant life cycle evolved in seedless vascular plants Homosporous plants: produce one type of spore Heterosporus plants: produce megaspores (female) and microspores (male)

Chapter 30 Plant Diversity II: Seed Plants Introduces the Seed Plants Seed plants are vascular plants that produce seeds Sporophyte is the dominant generation Becomes diploid and can carry recessive alleles from one generation to the next

All seed plants are heterosporous Megasporangia – produce megaspores that will produce female (egg-containing) gametophytes Microsporangia – produce microspores that will produce male (sperm-containing) gametophytes

Layers of sporophyte tissue called integuments cover the megasporangium The developing embryo is encased in a protective seed coat and supplied with its own source of food (endosperm or cotyledons)

Diagram of a Gymnosperm Seed

Seeds allow the embryo to be moved away from the parent by wind, water, and animals Seed plants are not tied to water for fertilization; pollen grains do not need to be transported by liquid

Gymnosperms Gymnosperms lack enclosed chambers in which seeds develop; instead, seeds develop on the surfaces of specialized leaves called sporophylls. About 900 species of gymnosperms are divided into 4 phyla: 1. Ginkgo 2. Cycads 3. Gnetophytes 4. Conifers

Ginkgophyta Phylum Ginkgophyta: - Ginkgo biloba is the only extant species - used in herbal medicine - produce pollen and seeds on separate trees (dioecious: “two houses”)

Gingko Images

Cycadophyta Phylum Cycadophyta: - about 100 cycad species - palm-like appearance (but not a palm) - seeds are often passed by beetles and bees

Gnetophyta Phylum Gnetophyta: - consists of three genera that are very different in appearance - Ephedra grows in U.S. deserts - Welwitschia grow in Africa

Coniferophyta Phylum Coniferophyta: - conifer = “cone bearer” - called evergreens because they retain their needle-shaped leaves - male and female gametophytes appear on the same tree (monoecious: “one house”) conifers are among the oldest and largest organisms on Earth we get much of our lumber and paper pulp from conifers

Concept 30.2

Anthophyta Phylum Anthophyta: - all angiosperms are placed in one phylum Two classes: monocots and dicots Monocots Parallel Leaf Veins Complex arrangement of Vascular Bundles Fibrous Root System Flower Parts in multiples of 3 Dicots Netlike Leaf Veins Vascular Bundles arranged in a ring Taproot usually present Flower Parts in multiples of 4 or 5

Anothophyta cont. - all are heterosporous - gametophyte is greatly reduced reproductive parts of the flower male parts: stamen contains the anther and filament female parts: carpel contains the stigma, style, and ovary

Anthophyta - after fertilization, the ovule develops into a seed; the endosperm is retained in the cotyledon - as the seed develops, the ovary begins to mature around the seed to form fruit

Concept 30.3