chapter 3 plants
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Chapter 3: Plants
Summary
Why are plants important?Evolution4 major groupsLife cycle – generalKey lineages
Why are Plants Important?
3 categories: Ecosystem services Fuels and fibers Other
Evolution
It started with green algae, confined to a watery environment, ~ 570 mya.
Land plants 1st appeared about 450 mya, preceding land animals.
Evolution
Invasion of land presented some of the same problems for plants as it did for animals:
4 Major Groups
Based on similar characteristics and order of evolution. Non-vascular land plants, mosses, liverworts and
hornworts Vascular plants
Seedless vascular plants, club mosses, ferns and horsetails
Gymnosperms have “naked” seeds that protect embryo, conifers, cycads and ginkgos.
Angiosperms have enclosed seeds (fruits) and flowers.
Life Cycle
Alternates between sporophyte (2n) and gametophyte (n) generations.
In early land plants the gametophyte stage predominates, later the sporophyte stage dominates.
Nonvascular Plants (Bryophytes)
Characteristics Gametophytes are photosynthetic, sporophytes are
attached to gametophytes and depend on them for nutrition.
Require water to reproduce Most are small and live in moist, temperate
environments.
Non Vascular Plants
Phylum Hepaticophyta – liverworts
Nonvascular plants
Phylum Anthocerophyta – hornworts Gas Exchange:
Stomata (the rest of the plant kingdom has stomata).
Tiny “broom handles” extending from rhizoids (above ground anchors to substrate).
Phaeocerus leavis
Nonvascular Plants
Phylum Bryophyta – mosses *source of peat Rhizoid = anchor,
supports “leaves” which are 1 cell thick.
Vascular Plants
Major developments Vascular tissues to…
Vessels – vascular tissue modified to provide structure in later species.
2 groups: seedless and seed bearing
Seedless Vascular plants
Characteristics Primitive vascular tissue. Roots *Still dependent on water for transport of sperm to
egg.
Seedless Vascular Plants
Phylum Lycophyta – club mosses Extinct varieties were
tree-like but surviving species are small.
Major source of coal.
Seedless Vascular Plants
Phylum Psilotophyta Whisk ferns: no leaves or
roots, grow on rhizoids or they are epiphytes.
Horsetails: photosynthetic stems, leaves are less prominent than stems in some varieties. Grow well in wet, boggy areas.
Seedless Vascular Plants
Phylum Pteridophyta - ferns Most abundant, closest
relative to seed plants.
Fern sporangia
Seed-bearing Vascular Plants Ch 28
Characteristics Sporophyte stage dominates. Major development is the seed that protects embryo
and allows for a dormant period. 2 types of gametophytes or structures:
Male (pollen-sperm) and Female (ovary – eggs)
Seed-bearing Vascular Plants
2 groups Gymnosperms – “naked” seeds. Ovules (eggs) are
partially exposed on scales; sperm are motile or nonmotile.
Angiosperms – “vessel” seeds (fruit). Ovules are totally enclosed, sperm are motile.
Seed-bearing Vascular Plants
Gymnosperms – 4 phyla Gnetophyta –
Cycadophyta (cycads) –
Ginkgophyta –
Cycad Ginkgo
Seed-bearing Vascular Plants
Gymnosperms – 4 phyla cont’d Coniferophyta (conifers) – largest group; pines, firs,
cedars, yews, cypresses, etc. Produce male and female cones. Pollen grains and ovules develop at the base of scales.
Pollen grains float into female cones and stick on ovules. Female cones take 1-2 seasons to mature and release
their seeds.
Seed-bearing Vascular Plants
Anthophyta (Angiosperms) – Characteristics Flowers and fruits Dominate the plant world
Seed-bearing Vascular Plants
Anthophyta – 6 clades. Basal angiosperms: Amborella, water lilies, star
anise. Core angiosperms:
Magnoliids – magnolias, laurels, etc. Monocots – derived from Magnoliids, 1 cotyledon (seed
leaf), no woody tissue, leaf veins parallel, flower parts are multiples of 3. Lilies, grasses, yucca, irises
Eudicots (true dicots) – 2 cotyledons, leaf veins are web-like, woody tissue, flower parts are multiples of 4-5. Trees, shrubs, annuals.
Angiosperms – what is the purpose of flowers?
Figure 30-23Figure 30-23aFigure 30-23a
“Corpse” flowers smell like rotting flesh and attract carrion flies.