Chapter 29: Plants
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Characteristics of Plants
Plants are multicellular, photosynthetic
organisms adapted to a land existence
with features such as a waxy cuticle.
Plants resemble algae in using
chlorophylls a and b and carotenoid
pigments.
But unlike algae, all plants protect the
developing embryo from drying out.
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The many divisions of plants can be
grouped into three main groups:
Nonvascular plants
Seedless vascular plants
Vascular plants with seeds
Plants are adapted to living on land
where light is more available and
carbon dioxide diffuses freely.
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Common plants today
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Life Cycle of Plants
Plants have a two-generation life cycle
called alternation of generations.
The sporophyte (2n) produces haploid
spores and the spores develop into a
gametophyte that produces the gametes.
When the sperm fertilizes the egg, the
zygote develops into a sporophyte.
Some plants have a dominant
gametophyte (haploid generation) and
others have a dominant sporophyte
(diploid generation).
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Nonvascular plant life cycle
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Seedless vascular plant life
cycle
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Seed plants are well adapted to
reproduction n land.
They produce heterospores: microspores
and megaspores.
A microspore develops into a pollen
grain.
The megaspore develops into an eggproducing gametophyte within an
ovule.
The ovule becomes a seed enclosing the
embryonic sporophyte.
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Seed plant life cycle
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Nonvascular Plants
Nonvascular plants include the
liverworts, hornworts, and the mosses.
Nonvascular plants lack vascular tissues
throughout their life cycle; they lack
true roots, stems, and leaves.
The gametophyte is the dominant
generation; the sporophyte is
dependent on the gametophyte.
Sperm require water to swim to the egg.
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Liverworts
The liverwort Marchantia has a
flattened, lobed body known as thallus.
Rhizoids (rootlike hairs) project from the
lower surface into the soil.
Marchantia reproduces asexually by
forming gemmae, groups of cells in
gemmae cups on the upper surface of
thallus.
In sexual reproduction, umbrella-like
gametophores produce gametes.
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Liverwort, Marchantia
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Mosses
In the moss life cycle, antheridia produce
swimming sperm that use external
water to reach the eggs in the
archegonia.
Following fertilization, the dependent
moss sporophyte consists of a foot,
stalk, and a capsule or sporangium
within which windblown spores are
produced by meiosis.
Each spore germinates to produce a
gametophyte.
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The gametophyte of mosses has two
stages.
First, there is the alga-like protonema, a
branching filament of cells.
Next, upright leafy shoots are seen at
intervals along the protonema.
Rhizoids anchor the shoots, which bear
the antheridia and archegonia.
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Moss life cycle
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Adaptations and Uses of
Nonvascular Plants
Mosses are usually found in moist
habitats because the sperm are
flagellated.
However, mosses can live in shady
cracks of hot, exposed rocks.
Sphagnum is bog or peat moss that is
used to hold water in garden soil.
Dried peat is sometimes used as fuel.
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Seedless Vascular Plants
Vascular plants have vascular tissue:
xylem (conducts water and minerals
from the soil) and phloem (transports
organic nutrients within the plant).
In the life cycle of vascular plants, the
sporophyte is dominant.
Vacular plants have true roots, leaves,
and stems.
Waxy cuticles prevent leaves from drying
out.
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Ferns and Their Allies
Whisk ferns, club mosses, horsetails,
and ferns are the seedless vascular
plants that were prominent in swamp
forests during the Carboniferous
period.
Their incomplete decomposition formed
much of the coal we burn today.
When the spores of these plants
germinate, the larger gametophyte is
independent of the sporophyte for
nutrition.
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The Carboniferous period
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Whisk Ferns
Whisk ferns (psilotophytes) are
represented by Psilotum in which an
erect stem that forks repeatedly is
attached to a rhizome.
There are no leaves and sporangia are
located at the ends of short branches
that photosynthesize.
It closely resembles a primitive vascular
plant (rhyniophyte) known only from the
fossil record.
The independent gametophyte produces
the gametes, and sperm are flagellated.
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Whisk fern, Psilotum
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Club Mosses
In club mosses, a branching rhizome
sends up aerial stems less than 30 cm
tall.
The sporangia are formed on terminal
clusters of leaves called stroboli that
are club-shaped.
These plants are common in moist
temperate woodlands, but the majority
live in the tropics where many of them
are epiphytes.
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Club moss, Lycopodium
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Horsetails
Rhizomes of horsetails produce aerial
stems about 1.3 meters tall.
Whorls of side branches give the
appearance of a green horse’s tail.
Some have stroboli on regular stems;
some have special stems for stroboli.
Silica in cell walls provide an abrasive
grit that made horsetails useful as an
abrasive cleanser.
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Horsetail, Equisetum
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Ferns
Ferns have very large fronds (leaves) that
grow from a rhizome; ferns have vascular
tissue and have true roots, stems and
leaves.
Sporangia are within sori on the underside
of the leaflets of a frond; meiosis occurs
within a sporangium, producing spores.
A windblown spore develops into a
separate gametophyte, a heart-shaped
prothallus, that bears both egg-producing
archegonia and sperm-producing
antheridia.
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When a flagellated sperm fertilizes an egg,
the zygote develops into a young
sporophyte.
Although ferns are likely to be found in
moist habitats due to flagellated sperm,
vegetative (asexual) reproduction is used
to disperse ferns in dry habitats.
Ferns are used to decorate bouquets and as
ornamental plants in homes and gardens.
Wood from tropical tree ferns is used as a
building material, and fiddleheads are
sometimes eaten as a delicacy.
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Fern diversity
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Fern life cycle
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Seed Plants
Both gymnosperms and angiosperms
disperse by seeds.
A seed has a seed coat and contains an
embryonic sporophyte and stored food
that supports growth when the seed
germinates.
Gymnosperms have exposed or “naked”
seeds.
In angiosperms (flowering plants), seeds
are enclosed by a fruit.
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Gymnosperms
This group includes cycads, the ginkgo,
and conifers.
Cycads are palm-like, tropical and
subtropical plants that flourished during
the era of dinosaurs.
The single species of ginkgo is planted in
parks because it does well in polluted
areas.
Conifers are the largest group of
gymnosperms and include cone-bearing
pine, spruce, fir, and redwood trees.
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Gymnosperm diversity
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Life Cycle of a Conifer
The gymnosperm microspore develops
into a pollen grain; this
microgametophyte develops in a pollen
cone.
The megagametophyte develops within
an ovule located on the scale of a seed
cone.
Following wind pollination and
fertilization that do not require external
water, the ovule becomes a winged
seed that is dispersed by wind.
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Pine life cycle
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Adaptation and Uses of Conifers
Conifers supply much of the wood used
for construction of buildings and
production of paper.
Many valuable chemicals are extracted
from resin, a substance that protects
conifers from fungi and insects.
The oldest trees in the world, at 4,500
years old, are bristlecone pines in
Nevada.
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Angiosperms
Angiosperms are flowering plants and
include tropical and subtropical
deciduous trees.
All hardwood trees are angiosperms.
Angiosperms are the source of clothing,
food, medicines, and many other
products used by humans.
Angiosperms are divided into monoots
(such as the grass family) and dicots
(such as the maple and rose families).
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Life Cycle of Angiosperms
Like conifers, angiosperms produce
heterospores, except angiosperms do
so within their flowers.
Microspores develop into pollen grains
within the pollen sacs of the anther.
The megaspore develops into an embryo
sac within an ovule.
Pollen is windblown or carried by bees
(or other animals) to the pistil.
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Double fertilization occurs where one
sperm joins with the egg to produce a
zygote, and a second sperm joins with
the polar nuclei to produce triploid (3n)
endosperm, which becomes stored
food.
The ovule develops into a seed
consisting of a seed coat, stored food,
and an embryo, but the ovary and
adjacent parts of the flower develop
into a fruit.
Fruits aid in seed dispersal.
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Flowering plant life cycle
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The Flower
The flower accounts for the success of
angiosperms.
The flower both attracts animals that aid
in pollination and produces seeds
enclosed by fruits that aid dispersal.
Sepals form a whorl around the colored
petals.
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The reproductive parts of a flower are the
pistil and the stamens.
A stamen consists of a filament and
anther with two pollen sacs.
The pistil consists of a stigma, style, and
ovary.
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Generalized flower
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Chapter Summary
Plants resemble algae in using
chlorophylls a and b and carotenoid
pigments, but unlike algae, plants
protect the embryo; this is an
adaptation that facilitates land
existence.
Presence of vascular tissues and
variation in reproductive strategies are
used to classify plants.
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Nonvascular plants are low-growing and
lack a means of water transport and
internal support, whereas vascular plants
have a system that transports water and
also provides internal support.
In nonseed plants, spores disperse the
species; in seed plants, seeds disperse
the species.
In seed plants, a germinating pollen grain
transports sperm to the egg.
Angiosperms and gymnosperms have
unique adaptations.
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