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Chapter 21: Part 1
The Diversity of Plants
Adapted from
Lecture Outlines by Gregory Ahearn,
University of North Florida
Copyright © 2011 Pearson Education Inc.
How do plants affect the ecosystem?
 Photosynthesize
– Make sun’s energy available
to consumers
– Produce oxygen
 Plants build soil
– Dead plant material is
decomposed, making the soil
more fertile
– Roots hold the soil together
 Plants help keep
ecosystems moist
– Store water
– Preven runnoff and flooding
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
How do plants affect humans?
 Plants provide humans with
necessities and luxuries
– Plants provide shelter, fuel,
and medicine
– Plants provide pleasure
through flowers, gardens,
lawns, and parks and through
coffee, tea, and wine
Cocoa beans
Biology: Life on Earth, 9e
Sassafras
Quinine
Copyright © 2011 Pearson Education Inc.
21.3 What Is the Evolutionary Origin of Plants?
 Ancestors were photosynthetic protists (algae)
 Both:
– have similar DNA
– use the same type of chlorophyll
– store food as starch and have cell walls made of
cellulose
Biology: Life on Earth, 9e
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Green alga Chara, a Stonewort  plants’ closest living relatives
Fig. 21-3
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.3 What Is the Evolutionary Origin of Plants?
 The ancestors of plants were aquatic – this has
its advantages!
– Bathed in a nutrient-rich solution
– Supported by buoyancy
– Gametes and zygotes carried by water currents
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.4 How Have Plants Adapted to Life on Land?
 The invasion of the land brought many
advantages to plants
– Direct access to sunlight
– Access to nutrient-rich soil
 But… it also imposed some challenges
– No support from water
– Drying out an issue
– No wet medium to transport gametes
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.4 How Have Plants Adapted to Life on Land?
 Adaptations helped solve
these problems
– Roots
– Anchor the plant
– Absorb nutrients from the soil
– Waxy cuticle
– Limits the evaporation of
water
– Stomata
– Pores in the leaves and
stems that open and allow
gas exchange, but close
when water is scarce
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.4 How Have Plants Adapted to Life on Land?
 Adaptations helped solve these problems (cont.)
– Vascular tissues
–Conducting cells that transport materials
throughout plant
–Xylem – water and minerals
–Phloem – sugar and nutrients
– Lignin
–Rigid polymer in cell walls that supports the
plant body
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.4 How Have Plants Adapted to Life on Land?
 Some plants have additional
adaptations
– Seeds
– Protect embryo
– Provide food for embryo
– Pollen
– Contains male gamete
– Dispersed by wind and the
bodies of insects
– Flowers
– Attract pollinators
– Fruits
– Attract animal foragers
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Chapter 21: Part 2
The Diversity of Plants
Adapted from
Lecture Outlines by Gregory Ahearn,
University of North Florida
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Two major groups of land plants arose from ancient
green algal ancestors
– The nonvascular plants (called bryophytes) straddle the
boundary between aquatic and terrestrial life
– The vascular plants (called tracheophytes) have been
able to colonize dry habitats
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
The Evolutionary Tree of Some Major Plant
Groups
Nonvascular plants
Vascular plants
seed plants
Liverworts
Mosses
Ferns
Gymnosperms
Angiosperms
Flowers
and fruits
Seeds and pollen
True vascular tissue
and lignin
Ancestral green alga
Biology: Life on Earth, 9e
Fig. 21-4
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Nonvascular must live near water
–
–
–
–
They lack true roots, stems, or leaves
Cell walls aren’t as stuff – limits size
Flagellated sperm must swim to egg
Nonvascular plants include the
hornworts, liverworts, and mosses
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Vascular plants have conducting cells that also
provide support
– Have xylem and phloem
– Vascular tissues contain lignin in cell walls
– Vascular plants can be divided into two groups:
the seedless vascular plants and the seed plants
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 The seedless vascular
plants include the club
mosses, horsetails,
and ferns
– These plants have
swimming sperm and
require water for
reproduction
– They do not produce
seeds, but propagate
by spores
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 The seed plants are aided by two important
adaptations: pollen and seeds
– Pollen grains carry sperm-producing cells
–They are dispersed by wind or pollinators
–They eliminate the need for sperm to swim to
the egg
– Seeds have three components: an embryonic
plant, a food supply for the embryo, and a
protective outer coat
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Seeds
embryo
stored
food
seed
coat
Pine seed
(gymnosperm)
(a) Seeds
Biology: Life on Earth, 9e
Bean seed
(angiosperm)
Fig. 21-9
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Gymnosperms are
nonflowering seed plants
– Gymnosperms evolved
earlier than the flowering
plants
– They were the first fully
terrestrial plants to
evolve
– Today, four groups of
gymnosperms survive:
ginkgos, cycads,
gnetophytes, and
conifers
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Angiosperms are
flowering seed plants
– Angiosperms produce
flowers and fruits
– They are the most diverse
and widespread of all plants,
with more than 230,000
species
– They have a broad range in
size
– Duckweed (3 mm in
diameter)
– Eucalyptus tree (100
meters in height)
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
21.5 What Are the Major Groups of Plants?
 Angiosperms also have broad leaves
– Collect more sunlight for photosynthesis
– Some drop their leaves to conserve water
– BUT… tender leaves are more appealing to herbivores
than the tough, waxy needles of conifers
– We exploit some of these defenses
– Medicines (aspirin, codeine)
– Stimulants (nicotine, caffeine)
– Spicy flavors (mustard, peppermint)
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.
Author Animation: Adaptations in Plant Evolution
Nonvascular plants
Vascular plants
seed plants
Liverworts
Mosses
Ferns
Gymnosperms
Angiosperms
Flowers
and fruits
Seeds and pollen
True vascular tissue
and lignin
Ancestral green alga
Biology: Life on Earth, 9e
Fig. 21-4
Copyright © 2011 Pearson Education Inc.
Angiosperms can be divided into two groups
 Monocots
– Lilies, daffodils, tulips, palms, corn, grasses
– Seeds produce two cotyledons (part that
nourishes embryo)
 Dicots
– All “broad-leafed” plants – tomatoes, daisies,
cherry trees, maple trees
– Seeds produce only one cotyledon
 Some differences in root and stem structure
Biology: Life on Earth, 9e
Copyright © 2011 Pearson Education Inc.