Introduction to Plants PPT

By: Elaine Wang and Ananya Murali

Chapter 23: Plants

Introduction: Pioneers In a New World

• Transition from water -> land began in the precambrian period with cyanobacteria (green algae)

• Developed into world’s 1st plants• Adaptations necessary for

survival on land- Obtaining and preserving

water- Reproduction

23.1: Trends In Plant Evolution• Vascular plants: most diverse plants w/ internal tissue systems that conduct water

and solutes through roots, stems and leaves • Seedless vascular plants: whisk ferns, lycophytes, horsetails, ferns• Gymnosperms: seed-bearing vascular plants

– Cycads, ginkgos, gnetophytes, conifers• Angiosperms: vascular plants w/ flowers and seeds

– Magnoliids, eudicots, monocots• Bryophytes: nonvascular plants

– Liverworts, hornworts, mosses• Root systems: underground absorptive structures of a cumulatively large surface

area – Rapidly take up soil water and mineral ions– Anchor for plants

• Shoot systems: stems and leaves absorb energy from sun, CO2 from the air – Developed taller/branched stems after developing the capacity to

synthesize/deposit lignin in cell walls• Xylem: vascular tissue that distributes water and dissolved ions in plants• Phloem: vascular tissue that distributes dissolved sugars and other photosynthetic

products

• Cuticle: protective waxy coat that helps conserve water on hot, dry days• Stomata (stoma): tiny openings across surfaces of leaves and some stems to

control CO2 absorption and restrict evaporative water loss• Gametophytes: gamete-producing bodies that dominate the haploid phase of algal

life cycles – mostly aquatic plants

• Sporophyte: multicelled diploid plant body • After a diploid zygote undergoes mitosis->Forms spores: haploid resting cells

– fertilization could be timed with suitable environmental conditions– Diploid dominance is an adaptation to land

• Heterospory: plants that produce 2 types of spores (both seedless an seed-bearing)

• Homospory: plants that produce one type of spore• Pollen grains: cellular structures that become mature, sperm-bearing male

gametophytes– Microspores that reach eggs via air currents, insects, and birds– Contributed to radiation of seed-bearing plants to high/dry habitats

• Seed: an embryo sporophyte, nutritious tissues, and outer coat; Developed from female gametophytes

23.1: Trends In Plant Evolution

• Species of mosses, liverworts, hornworts – Adapted to moist habitats– Mosses, however, can be found in deserts as well

• Sensitive to air pollution• Most common

• Nonvascular: leaf/stem/root parts lack a xylem or phloem– Instead, have rhizoids: elongated cells/threadlike absorptive structures that attach the gametophytes

to the soil, and absorb water and minerals• Show three features that were adaptive during the transition to land

– 1. Cuticle: stomata to prevent water loss– 2. Cellular jacket around parts that produce sperm/eggs: holds in moisture– 3. Embryo sporophyte: sporophytes that begin life inside a female gametophyte

• Sporophytes remain attached to the gamete-producing body for nutrition (do not disperse)• Mosses (most common)

– Gametophytes grow in clusters to form cushiony mounds, or grow in branched patterns on tree trunks (humid conditions)

– Eggs and sperm develop in gametangia at shoot tips of familiar moss plants– After fertilization, the zygote develops into a mature sporophyte

• Develop a sporangium: stalk and jacketed structure where spores develop• o Examples

• Peat mosses: used to soak up water (5x more than cotton), used as antiseptic, and also burned for electricity

• peat bogs: moist mats of the remains of peat mosses

23.2: The Bryophytes

• Whisk ferns, lycophytes, horsetails, and ferns• Different from bryophytes b/c sporophytes that develop independently of gametophytes

– sporophytes that have well-developed vascular tissues– larger, longer-lived sporophyte phase of its life cycle

• Sporophytes can live on land, while gametophytes cannot• Lycophytes: small club mosses on the forest floor

– “ground pines” – sporophytes with true roots, stems, small leaves with vascular tissue– strobili (strobilius) bear spores that germinate, forming small, free-living gametophytes

• heterosporous• Whisk ferns: not true ferns; resemble whisk brooms

– have rhizomes: short, branched, mainly horizontal absorptive stems that grow underground– no leaves, made of scale-like branches– popular ornamental plants common to tropical/subtropical areas

• Horsetails– sporophytes have rhizosomes– scalelike leaves whorl around a hollow, photosynthetic stem– spores produced inside cone-shaped clusters of leaves at shoot tip– found in streambank muds and other disrupted habitats

• Ferns– have rhizosomes and fronds: aerial leaves that coil into what resembles a fiddlehead– sporangia: clusters of spores on the lower surface of the fronds

23.3: Existing Seedless Vascular Plants

• Lycophyte trees: giant club mosses that developed during the Carboniferous era– strobili that produced 8 billion microspores or hundreds of

megaspores– 40m tall

• 20m tall horsetails• Many swamp forests had sediments that compressed undecayed remains

of plants into peat mosses– Pressure transformed the peat into coal: a renewable fossil fuel

23.4: Ancient Carbon Treasures

• Most successful vascular plants because independent of water for fertilization– Seed ferns, gymnosperms, angiosperms

• Different than seedless vascular plants because:– Microspores: develop into pollen grains to carry sperm

to female structures (pollination)– Megaspores: develop within ovules: female

reproductive structures that, when mature, produce seed

• § female gametophyte, nutrient rich tissue, jacket of cell layers (to develop a seed coat)– Traits to conserve water: Thicker cuticles, stomata

underneath leaves• Pre-Carboniferous: dominated by seed ferns (simlar

to progymnosperms): earliest seed-producing plants

23.5: The Rise Of Seed-Bearing Plants

• Gymnosperm sporophyte stages are conspicuous trees and shrubs; the seeds are rather unprotected ("naked seeds") perched at the surface of reproductive parts.

• Conifers (Coniferophyta) – The conifers (cone-bearers) are woody trees with needlelike or scalelike

leaves. – Most are evergreens, some are deciduous. – Produce true cones: repro. structures in clusters of papery/wood-like

scales that bear exposed to ovules on upper surface• Lesser Known Gymnosperms

– Cycads (Cycadophyta) • These palmlike trees flourished during the Mesozoic era, but only about 100 species

still exist--confined to the tropics and subtropics. • They bear massive cone-shaped strobili that produce either pollen (transferred by

air currents or insects) or ovules. – Ginkgos (Ginkgophyta)

• From the diversity of this group during the Mesozoic, only one species has survived. • They are remarkably hardy, showing resistance to insects, disease, and air

pollutants. – Gnetophytes (Gnetophyta) are the most unusual gymnosperms; they live in tropical and

desert areas.

23.6: Gymnosperms-Plants With “Naked” Seeds

• Pine Life Cycle – The pine tree produces two kinds of cones:

• Male cones produce sporangia which yield microspores that develop into pollen grains (male gametophyte).

• Female cones produce ovules that yield megaspores (female gametophyte).

– Pollination is the arrival of a pollen grain on the female reproductive parts, after which a pollen tube grows toward the egg.

– Fertilization, which is delayed for up to a year, results in a zygote that develops into an embryo within the conifer seed.

• Deforestation and the Conifers – Although conifers still dominate in certain climates, their

slow reproductive pace puts them at a disadvantage compared to angiosperms.

– However, deforestation by clear-cutting for their commercial value has put them at even greater risk.

23.7: A Closer Look At The Conifers

• Characteristics of Flowering Plants – Only angiosperms produce specialized reproductive structures called flowers.

• Of all the divisions of plants, angiosperms ("vessel seed") are the most successful and most diverse.

• Most flowering plants coevolved with pollinators--insects, bats, birds, etc. – There are three major groups of flowering plants:

• Magnoliids include magnolias, avocados, nutmeg, and black pepper plants.

• Eudicots include familiar shrubs, trees (except conifers), and herbaceous plants.

• Monocots include grasses, lilies, and the major food-crop grains. • Representative Life Cycle--A Monocot

– The diploid sporophyte has extensive root and shoot systems; it also retains and nourishes the gametophyte.

– Embryos are nourished by the endosperm within the seeds, which are packaged inside fruits.

23.8: Angiosperms - Flowering, Seed-Bearing Plants

• Artificial selection of plants led to the development of domesticated grains including wheat and barley (11,000 yrs ago)

• Different trees have been used for their wood pliability (paper, furniture, rope)

23.9: Seed Plants And People

Works Cited

Starr, Cecie and Ralph Taggart. Biology: The Unity and Diversity of Life. 10th Ed. Belmont: Brooks/Cole, 2004. Print.