1. How Did Plants Adapt to Dry Land?
Chapter 22
How Did Plants Adapt to Dry Land?
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Key Questions
How did plants adapt to life on land?
How do bryophytes survive on land without vascular tissues?
What are the advantages of a vascular system?
How are seeds an adaptation to a dry, terrestrial environment?
What roles do flowers and fruits play in angiosperm reproduction?
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What Is a Plant?
Multicellular organism that performs photosynthesis and develops from an embryo
Almost all live on land
Descendants of protists
Land invasion depended on evolution of different structures
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Land Adaptations
Waxy cuticle — reduces water loss
Ability to absorb water from a variety of sources
Enclosed reproductive organs, called gametangia, in which gametes form
Enclosed sporangia in which spores form
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5. Identify Different Plant Types
Identify as many different plants as you can. How are they different from one another?
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6. Vascular vs. Nonvascular
Vascular or tracheophytes
Have pipelike tissues that conduct water
Grow large
Examples: fir trees, ferns
Nonvascular or bryophytes
Lack a vascular system
Much smaller
Less diverse
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7. The Divisions of Plants
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Evolution of Plants
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Plant Evolution
Evidence comes from fossils and comparisons with living species
First plants evolved from a common ancestor that resembled a green alga
Vascular plants predate nonvascular plants
First seedless plants — Carboniferous Period
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Kingdom Plantae
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Angiosperm Evolution
Angiosperms — flowering plants
First fossils — about 125 million years ago
Evolved from gymnosperms — plants that have no fruits or flowers
Many adaptations
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12. Mosses, Liverworts and Hornworts
Nonvascular Plants or bryophytes
Depend on free standing water for photosynthesis and fertilization
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13. Bryophyte Characteristics
All parts of their bodies are adapted to absorb water
This gives them a spongy feel
Exhibit alternation of generations — a sexual life cycle in which haploid and diploid phases are both multicellular
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Life Cycle of a Moss
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Vascular Plants
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Vascular Plants
Called tracheophytes
Have division of labor with separate transport systems for water (xylem) and sugars (phloem)
Diploid Phase dominates the life of the plant
Seeds are protected by coat, and food is stored inside for germination
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17. Seed-Lacking Tracheophytes
4 divisions that lack seeds:
Pterophytes (ferns)
Psilotophytes
Lycophytes
Equisetophytes
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Life Cycle of a Fern
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Life Cycle of a Fern
A fern releases haploid spores
Spores mature into haploid gametophytes
Gametophytes make sperm and egg
Fusion of sperm and egg
Zygotes grow right out of the gametophyte for a new fern
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Lycophytes
Have true roots, stems and simple leaves
Also called lycopods
Example: club mosses
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Equisetophytes
Referred to as horsetails
Have true roots, stems and complex leaves
Stems are jointed
Outer cell walls are reinforced with silica
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22. Reproduction in Seed Plants
Manage fertilization without water
Use a form of internal fertilization
Sperm and ovum fused, and develop within the female gametophyte
Seeds consist of a diploid zygote and a source of food encased in a seed coat
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Gymnosperms
Seed plants without flowers
Evergreen
Conifers produce male and female gametophytes in cone-shaped strobili (the cones)
Male and female cones on same tree
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Life Cycle of a Pine
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Cycads
Large-leafed plants that look like palms
No flowers or fruits
Bear naked seeds
Produce male and female strobili
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Ginkgos
Either male or female
Resemble cycads in their life cycle
Resemble conifers in their growth patterns
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27. Uses of Flowers and Fruits
Flowers ensure distribution of pollen through a variety of methods
Fruits are mature ovaries that enclose and protect seeds
Fruits usually enhance dispersal of seeds
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28. Life Cycle of a Flowering Plant
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29. Angiosperm Reproduction
Flowers reproduce by means of double fertilization
2 sperm nuclei from the pollen grain fertilize 2 ova from the ovary
A diploid zygote is formed and a triploid cell forms the endosperm
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Flower Parts
Stamen — anther and filament (male)
Carpel — style and ovary (female)
A corolla or petals and a calyx of sepals surround stamens and carpels
Not all flowers have all parts
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Key Concepts
A plant is a multicellular organism that photosynthesizes and develops an embryo
Nonvascular plants lack vascular tissues
The vascular system enables plants to transport water and nutrients, to grow large, and to diversify
Seeds allow plant to withstand dry environments
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