Essentials of Biology
Sylvia S. Mader
Chapter 18
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
18.1 Onto Land
• Plants are a diverse group of eukaryotic
organisms.
• Plants are classified into four groups.
– Mosses, hornworts, and liverworts
– Ferns and the fern allies
– Gymnosperms (conifers)
– Angiosperms (flowering plants)
18.1 Onto Land (cont.)
• These plant groups can be associated with four
evolutionary events that helped adapt plants to
existence on land.
• The first is the nourishment of the multicellular
embryo within the body of the female plant.
• The second event was the evolution of vascular
tissue to distribute water, nutrients, and
carbohydrates through the plant.
18.1 Onto Land (cont.)
• The third event was the evolution of
seeds.
• The fourth event was the evolution of the
flower.
18.1 Onto Land (cont.)
Alternation of Generation
• The plant life cycle differs from the life
cycle of animals.
• Plants undergo alternation of generation,
meaning that there are two forms of a
plant.
– The spore-bearing sporophyte is diploid.
– The gamete-producing gametophyte is
haploid.
Alternation of Generation (cont.)
• The production of haploid spores by plants
occurs as a result of meiosis.
• Spores undergo mitosis to produce the
plant gametophyte.
• The zygote formed by fertilization also
undergoes mitosis to form the sporophyte.
Alternation of Generation (cont.)
The Dominant Generation
• The dominant generation of a plant is the form
that we recognize as the plant.
– For non-vascular plants, the gametophyte is the
dominant generation.
– For vascular plants, the sporophyte is the dominant
generation.
• During the evolution of land plants, the
sporophyte developed vascular tissue and
became the larger, dominant generation of
plants.
The Dominant Generation (cont.)
18.2 Diversity of Plants
• Non-vascular plants (those lacking
vascular tissue) were the first land plants
to evolve.
• Vascular plants evolved from non-vascular
plants.
Nonvascular Plants
• The nonvascular plants include the
bryophytes (liverworts and true mosses).
• Bryophytes lack true roots, stems, leaves,
and have a dominant gametophyte.
• Bryophytes are found in every
environment.
Nonvascular Plants (cont.)
Vascular Plants
• Vascular plants generally have true roots,
stems, leaves.
• Vascular plants have vascular tissue
consisting of the xylem and phloem.
• The xylem can be reinforced with lignin.
Vascular Plants (cont.)
Seedless Vascular Plants
• Seedless vascular plants include the club
mosses, horsetails, and ferns.
– Club mosses are found in temperate forests.
– Horsetails are taller stems with whorls of slender
green branches.
• During the Carboniferous period, these plants
were as tall as trees.
• These compressed remains of these plants are
what formed coal.
Ferns
• Ferns are a widespread group of plants with
large leaves called fronds.
• The fern gametophyte is dependent upon water
to achieve fertilization, so ferns are found in
moist environments.
• Some ferns produce rhizomes which allow them
to scavenge water and survive in drier areas.
Ferns (cont.)
General Biology of Bacteria
• There are several commercial uses for
ferns and fern tissues.
– Ferns are ornamental plants.
– The wood of tropical ferns can be used as a
building material because it resists decay and
insect damage.
– Some ferns can be used as food.
– Some ferns have medicinal value.
Seed Plants
• Seed plants are the most common plants.
• Recall that seeds have three major parts.
– The embryo
– The stored food supply
– The seed coat
• Seed plants have two types of spores and two
types of gametophytes.
– Male
– Female
Seed Plants (cont.)
Seed Plants (cont.)
• In seed plants the gametophytes are
microscopic in size.
• The desiccation-tolerant pollen grains are
the male, sperm-producing gametophyte.
• Pollination occurs when the pollen grain
fertilizes the female gametophyte.
Seed Plants (cont.)
• The female gametophyte develops within
an ovule, which develops into the seed.
• In gymnosperms, the ovule is not
completely enclosed by sporophyte tissue
at pollination.
• In angiosperms, the ovule is completely
enclosed by sporophyte tissue (the ovary)
at pollination.
Seed Plants (cont.)
Gymnosperms
• The ovules and seeds
of gymnosperms are
exposed on a
modified leaf called
the scale.
• “Gymnosperm”
means “naked seed”.
• Cycads and conifers
are gymnosperms.
Conifers
• Conifers are plants that produce cones.
• The needles of conifers have adaptations
that resist water loss, allowing these plants
to grow in frozen soils where water may be
limiting.
• Conifers also produce resins to protect the
tree from insect or fungal attack.
Angiosperms
• The angiosperms (“covered seeds”) are
the flowering plants.
• Angiosperms are also found in nearly all
climates and can vary greatly in size from
species to species.
The Flower
• Flowers have several common structures.
• The sepals, which form the calyx, protect the
flower bud before it opens.
• The petals, which form the corolla, help to attract
pollinators.
• The stamen (male reproductive structure)
consists of the filament and a pollen-producing
anther.
The Flower (cont.)
• The carpels have three major regions.
– The ovary (female reproductive structure)
contains the ovules.
– The style elevates the stigma.
– The stigma collects pollen.
• The ovary also produces nectar in some
flowers to attract pollinators.
The Flower (cont.)
Flowering Plant Life Cycle
• The flower anther produces male
microspores, which divide mitotically to
form pollen.
• The pollen is released from the anther.
• Within the ovule, female megaspores
undergo mitosis to produce the egg.
Flowering Plant Life Cycle
(cont.)
• During pollination, a pollen grain is
transported to the stigma.
• The pollen tube germinates and extends a
pollen tube to the ovule.
• The pollen tube delivers two sperm to the
egg to carry out double fertilization.
Flowering Plant Life Cycle
(cont.)
• The sperm are involved in two fusion
events.
– One sperm fuses with an egg to form a diploid
zygote.
– One sperm fuses with two other ovule cells to
form the triploid endosperm.
• The ovule develops into the seed, bearing
the embryo and the stored nutrients.
Flowering Plant Life Cycle
(cont.)
• In some angiosperms, the embryo uses
the seed endosperm as nourishment
during germination.
• In other angiosperms, the endosperm is
absorbed into the cotyledon (seed leaves).
• A fruit is derived from an ovary and in
some species parts of the flower.
Flowering Plant Life Cycle
(cont.)
Adaptations and Uses of
Angiosperms
• Angiosperms have a variety of mechanisms that
facilitate the distribution of pollen and seeds.
• Pollination can be accomplished by wind, water,
insects, or animals.
• The structure of the flower is specific to the
mode of pollination.
• The fruit serves two primary purposes.
– The fruit protects the seeds.
– The fruit aids in the dispersal of the seeds.
18.3 The Fungi
• Like plants and animals, fungi are
generally multicellular eukaryotes.
• However fungi have several unique
characteristics that differentiate them from
these two types of organisms.
• DNA sequence data has indicated that
fungi are more closely related to animals.
18.3 The Fungi (cont.)
General Biology of a Fungus
• Fungi are composed of thin filaments of cells
called hyphae.
• The hyphae are typically organized into a mass
called a mycelium.
• The mycelium penetrates soil, wood, or other
media to acquire nutrients.
• Most fungi are saprotrophic, degrading the
remains of other organisms in the soil.
General Biology of a Fungus
(cont.)
Black Bread Mold
• The hyphae of some fungi, like black
bread mold, grow horizontally and
vertically to anchor the fungi and acquire
nutrients.
• The mycelia are also involved in fungal
reproduction.
Black Bread Mold (cont.)
• The hyphae can also develop stalks
bearing sporangia for spore production.
• During asexual reproduction, the fungal
spores are distributed and divide
mitotically to produce new hyphae.
• The sexual reproduction of fungi involves
the conjugation of mycelia between fungi.
Black Bread Mold (cont.)
• The mycelia of sexually-reproducing fungi must
be of different mating types.
– One is the positive (+) mycelium.
– One is the negative (-) mycelium.
• The hyphal tips of these fungi fuse to form a
zygospore.
• The zygospore germinates to form
sporangiophores.
Black Bread Mold (cont.)
• Meiosis occurs in the sporangiophores to
produce spores of each mating type.
• The spores are distributed and divide
mitotically to produce new hyphae.
• Except for the zygospore, all stages of the
fungal life cycle are haploid.
Black Bread Mold (cont.)
Mushroom
• A mushroom is the fruiting body of a fungi.
• The fruiting body is also spore producing.
• The mushroom forms when a positive and
negative hyphae fuse but the nuclei do not fuse.
• This dikaryotic nuclei forms the stalk and cap of
the mushroom.
Mushroom (cont.)
• Club-like, spore-producing structures
develop within the gills of the cap.
• The spores are distributed by the wind.
• In some instances, the fungal mycelium
forms a ring as it explores the soil.
Mushroom (cont.)
Mutualistic Relationships
• In a mutualistic relationship, two different
species contribute positively to each other’s
growth.
• Lichens are a mutualistic relationship between a
fungi and a cyanobacteria or algae.
• Lichens are important because they are
colonizers of disturbed soils.
Mutualistic Relationships (cont.)
Mutualistic Relationships (cont.)
• There are three varieties of lichens.
– Compact crustose, seen on rocks and bark
– Fruticose, which are shrublike
– Foliose, which are leaflike.
• Lichens have three cell layers.
– An upper and lower fungal cell layer
– A middle algal or cyanobacteria layer
• Lichens generally reproduce asexually.
Mutualistic Relationships (cont.)
• Mycorrhizal fungi form mutualistic
relationships with plant roots.
• Mycorrhizal fungi live within plant roots are
growing on the surface of roots.
• These fungi help roots obtain water and
nutrients by increasing the absorptive
surface area.
Mutualistic Relationships (cont.)
Fungi as Disease-Causing
Organisms
• Certain fungi can cause disease in plants
and animals, acting as pathogens.
Fungi and Plant Diseases
• Fungal pathogens of plants usually enter
through wounds or the stomata.
• Some fungal diseases impact agricultural
production.
– Rice blast disease
– Corn smut
– Rusts
– Leaf curl
Fungi and Plant Diseases (cont.)
Fungi and Human Diseases
• Mycoses are diseases caused by fungi.
• Mycoses have three levels of infection.
– Cutaneous mycoses only affect the epidermal
layers.
– Subcutaneous mycoses affect deeper skin
layers.
– Systemic mycoses spread throughout the
body.
Fungi and Human Diseases
(cont.)
• The widest array of
fungal diseases are
caused by Candida
albicans.
– Yeast infections
– Oral thrush
Fungi and Human Diseases
(cont.)
• Fungi from the genus
Tinea contribute to
the ringworm and
athlete’s foot.
• Histoplasma
capsulatum is a soil
fungi that causes
“fungal flu”.
Fungi and Human Diseases
(cont.)