Plant Diversity

What Is A Plant? Multicellular eukaryotes Cell walls with cellulose Photosynthesis using green pigments chlorophyll a and b Autotrophs Some are parasites or saprobes

What Plants Need To Survive Sunlight Water and minerals Gas exchange Movement of water and nutrients

Early Plants For most of Earth’s history plants did not exist Origins in the water Green algae: the first plants evolved from an organism much like the multicellular green algae living today Depended on water to complete their life cycles

The First Plants Life on land favored the evolution of plants: More resistant to the drying rays of the sun More capable at conserving water More capable of reproducing on dry land

The First Plants Like today’s mosses Gave rise to the plants of today! Non-vascular Plants Seedless Vascular Plants Gymnosperms Angiosperms Four groups based on: Water-conducting tissues Seeds Flowers Today scientists can classify plants more precisely by comparing DNA sequences of various species

The Plant Life Cycle: Alternation of Generations Haploid gametophyte (N): gamete-producing phase of an organism Diploid sporophyte (2N): spore-producing phase of an organism

SEEDLESS PLANTS

Green Algae First plants Mostly aquatic Fresh and salt water, some moist areas on land Absorb water and nutrients from surroundings Life Cycle: switch between haploid and diploid No specialized cells

Bryophytes Mosses, liverworts, hornworts Depend on water Sperm swim through water to reach eggs of other plants No vascular tissue Can draw up water by osmosis only a few cm above the ground

Mosses The most common bryophytes Well adapted to wet habitats and nutrient-poor soils Gametophyte dominant Reproduce  produce thin stalks with sporophyte Rhizoids: long, thin cells that anchor them in the ground and absorb water and minerals from the surrounding soil No true roots

Life Cycle of A Moss Archegonia: produces eggs Antheridia: produces sperm Sperm of the bryophyte must swim to an egg for fertilization to occur A diploid zygote results from fertilization Sporophyte: the zygote Grows out of the gametophyte and depends on it for water and nutrients When ready, haploid spores are released to start the cycle again

VASCULAR PLANTS

Vascular Plants: Tracheophytes Vascular tissue: a type of tissue that is specialized to conduct water and nutrients through the body of the plant Tracheid: hollow plant cell in xylem tissue with thick cell walls that resist pressure One of the great evolutionary innovations of the plant kingdom!

Vascular Plants Xylem and Phloem: Allow vascular plants to: move fluids throughout the plant body even against the force of gravity Allow vascular plants to: grow upright reach great heights

Structure of Vascular Tissue Xylem: vascular tissue that carries water upward from the roots to every part of the plant Phloem: vascular tissue responsible for the transport of nutrients & carbohydrates produced by photosynthesis

Vascular Plants Roots: absorb water and minerals Leaves: photosynthetic organisms that contain one or more bundles of vascular tissue Stems: supporting structures that connect roots and leaves, carrying water and nutrients between them

SEEDLESS VASCULAR PLANTS

Seedless Vascular Plants Club mosses, horsetails, and ferns Ferns have survived Earth’s long history in numbers greater than any other group of spore-bearing vascular plants More than 11,000 species live today Strong roots Rhizomes: creeping or underground stems Fronds: large leaves Can thrive in areas with little light Most abundant in wet or seasonably wet habitats

Life Cycle of Ferns Sporophyte = Dominant Produce haploid spores on the underside of their fronds in sporangia Spores are released Spores germinate into haploid gametophytes Diploid zygote is produced from fertilization Sporophyte grows and the gametophyte withers away

SEED PLANTS

Seed Plants Seeds include: Seed plants are divided into two groups: Acorns, pine nuts, dandelion seeds, kernels of corn, etc. Seed plants are divided into two groups: Gymnosperms Angiosperms

Seed Plants Reproduction free from water Can live just about anywhere Adaptations to reproduce without water: Flowers or cones Transfer of sperm by pollination Protection of embryos in seeds

Cones and Flowers Gametophyte of seed plants grow and mature within sporophyte structures called cones (gymnosperms) and flowers (angiosperms)

Pollen Pollen Grain: male gametophyte is contained in a tiny structure The wind, insects, birds and small mammals may carries pollen grains Pollination: the transfer of the pollen grain to the female gametophyte

Evolution of Seed Plants The seed was very important evolutionarily Seed: embryo of a plant encased in a protective covering and surrounded by a food supply Mosses and ferns underwent major adaptive radiation 300-400 mya Land environments were much wetter than they are today As the land became drier, it became harder for seedless plants to survive Fossils of seed-bearing plants exist from almost 360 mya The original seed plants resembled ferns

GYMNOSPERMS

Gymnosperms…Cone Bearers The most ancient surviving seed plants Include cycads, ginkgoes, and conifers “Naked Seed”: these plants all reproduce with seeds that are exposed

Conifers The most common gymnosperms with more than 500 known species Pines, spruces, firs, cedars, sequoias, redwoods, yews Some, like the bristlecone pine tree, can live for more than 4000 years Others, such as the giant redwood, can grow to more than 100 meters in height

Ecology of Conifers Thrive in a wide variety of habitats: on mountains, in sandy soil, and in cool, moist areas Leaves have adaptations to dry conditions The leaves are long and thin, like pine needles This shape reduces the surface area from which water can be lost Waxy layer also prevents water loss Most are evergreens: they retain their leaves through the year

Cones Pollen Cones (male cones): produce pollen Seed Cones (female cones): produce female gametophytes in two ovules The complete life cycle takes 2 years to complete The direct transfer of pollen to the female cone allows fertilization to take place without the need for gametes to swim through standing water

ANGIOSPERMS

Angiosperms…Flowering Plants Flowering plants first arrived about 135 mya Originated on land and became the dominant plant life on Earth The majority of living plant species reproduce with flowers

Flowers: An Evolutionary Advantage Attract animals which transport pollen from flower to flower More efficient than wind pollination of most gymnosperms Flowers contain ovaries, which surround and protect the seeds

Angiosperms…”Enclosed Seeds” After pollination, the ovary develops into a fruit, which protects the seed and aids in its dispersal Fruit: thick wall of tissue surrounding the seed Adds to the success of angiosperms

Monocots and Dicots Monocots Dicots Angiosperm whose seeds have one cotyledon Parallel veins Floral parts often in multiples of 3 Stem vascular bundles are scattered Fibrous root Angiosperm whose seeds have two cotyledons Branched veins Floral parts often in multiples of 4-5 Stem vascular bundles are arranged in a ring Taproot

Comparing Monocots and Dicots

Woody Plants Woody plants are made primarily of cells with thick cell walls that support the plant body Trees All types! Shrubs Blueberries, rhododendrons, roses Vines Grapes and ivy

Herbaceous Plants Smooth and non-woody plants that do not produce wood as they grow Dandelions, zinnias, petunias, sunflowers

Growing Season Annuals: Flowering plants that complete a life cycle within one growing season Garden plants, marigolds, petunias, pansies, zinnias, wheat and cucumbers too! Biennials: Flowering plants that complete a life cycle in two years Primrose, parsley, celery, foxglove Perennials: Flowering plants that live for more than two years Peonies, asparagus, grasses: herbaceous perennials Palm trees, sagebrush, maple trees, honeysuckle: woody perennials