Plant Kingdom
Chapter 22
What Is A Plant?
• Plants are eukaryotic, multicellular organisms
that have chlorophyll a and chlorophyll b and
carry on photosynthesis.
• There cells have cellulose cell walls.
What Is A Plant?
• Plants are terrestrial organisms that can live in
just about any environment, including deserts,
arctic regions, swamps, shallow freshwater,
and shallow oceans.
• There are more than 250,000 species of
plants.
What Is A Plant?
• They range in size from the tiny floating
duckweed the size of a pencil eraser to
redwood trees over 100 meters tall.
• There are plants that lack chlorophyll and are
parasites, plants that digest animals, and
plants that have mutualistic relationships with
animals.
Plant Cell
Alternation Of Generations
• The plant life cycle consists of two
generations: the sporophyte generation and
the gametophyte generation.
• This is referred to as alternation of
generations.
Alternation Of Generations
• The sporophyte generation is diploid (2n).
There are plant parts in which meiosis
produces haploid (n) spores.
• In plants, the word spore refers to a haploid
cell produced by meiosis that germinates to
give rise to a multicellular haploid generation
(gametophyte generation).
Gametophyte Generation
• The gametophyte generation is haploid and
develops structures that produce gametes
(eggs and sperm).
• Mitosis is utilized to produce eggs and sperm
because the gametophyte is already haploid.
• When haploid gametes unite, a diploid zygote
is formed.
Sporophyte Generation
• The zygote is the first new cell in the
sporophyte generation.
• The zygote divides by mitosis, and a new
multicellular sporophyte generation results.
Evolution Of Plants
• At one point in time, all life was aquatic.
• Scientists believe that the ancestors of plants
were aquatic, photosynthetic algae.
• Green algae have the same kind of chlorphyll
(chlorophyll a and chlorophyll b) and the same
kinds of chloroplasts as plants.
• DNA comparison also supports this
evolutionary conclusion.
Trends In Plant Evolution
• 1. Plants have become more specialized to
live in a dry environment.
• 2. Plants have evolved toward a more
prominent role for the sporophyte generation.
Trends In Plant Evolution
• Most primitive plants lack vascular tissue and
are therefore limited to moist habitats.
• More advanced plants have vascular tissue to
transport water and materials throughout the
plant.
• Plants have also evolved seeds that can resist
drying.
Evolution Of Plants
• In more primitive plants, the gametophyte
generation is the dominant generation.
• In more advanced groups of plants, the
sporophyte generation is dominant.
Nonvascular Plants
• The nonvascular plants include mosses,
hornworts, and liverworts.
• They are commonly known as bryophytes.
• Characteristics of nonvascular plants:
– Lack vascular tissue.
– Do not have true roots or leaves.
– Gametophyte generation is most prominent.
– Sperm swim to the egg.
Nonvascular Plants
• They rely on diffusion and osmosis to move
dissolved materials through their bodies.
• Since the sperm swim to the egg, they must
have water to reproduce sexually.
• Most are small and live in moist
environments.
Moss Life Cycle
• The moss plant commonly recognized is the
gametophyte generation.
• The cells of the gametophyte have the haploid
number of chromosomes (same as gametes);
however, not all of them function as gametes.
Moss Life Cycle
• At the top of the moss gametophyte are two
kinds of structures that produce gametes:
– The antheridium is made up of a jacket of cells
surrounding the developing sperm.
– The archegonium is a flask shaped structure that
produces the egg.
• The archegonium usually only has one egg.
Moss Life Cycle
• When the sperm are mature, the outer jacket
of the antheridium splits open, releasing the
flagellated sperm.
• The sperm swims through a film of dew or
rainwater to the archegonium.
Moss Life Cycle
• When the sperm and egg fuse, a diploid
zygote is produced.
• The zygote is the first cell of the sporophyte
generation.
• The mature sporophyte grows out of the top
of the gametophyte.
Moss Life Cycle
Gametophyte Generation
Sporophyte Generation
Nonvascular Plants
• The mosses are the most common kind of
nonvascular plant.
• Each moss plant is composed of a central stalk
less than 5 centimeters tall.
• The gametophytes of liverworts and
hornworts are flat sheets on a few layers of
cells thick.
Nonvascular Plants
• Liverwort resembles the moist surface of a
liver.
• Hornworts have a long slender sporophyte
that protrudes from the gametophyte plant.
• Hornworts are unusual in that their cells
contain only one long chloroplast per cell,
whereas other plants have many per cell.
Moss
Liverwort
Hornwort
Significance Of Vascular Tissue
• Vascular tissue consists of tube-like cells that
allow plants to efficiently transport water and
nutrients about the plant.
• Vascular tissue is associated with the
development of roots, leaves, and stems.
Vascular Tissue In Plants
Significance Of Vascular Tissue
• Roots are underground structures that anchor
the plant and absorb water and minerals.
• Leaves are specialized structures for carrying
out the process of photosynthesis.
• Stems are structures that connect the roots
with the leaves and position the leaves so that
they receive sunlight.
Vascular Plant Parts
Two Kinds Of Vascular Tissue
• There are two kinds of vascular tissue: xylem
and phloem.
Vascular Tissue
Xylem
• Xylem consists of dead, hollow cells arranged
end to end to form a tube.
• The walls of these “cells” are strengthened
with extra deposits of cellulose and lignin.
• Xylem carries water and minerals up from the
roots through the stem to the leaves.
Xylem
• There are two kinds of xylem cells: vessel
elements and tracheids.
• Vessel elements are dead, hollow cells, up to
.7mm in diameter, with endwalls missing.
They forms long tubes.
Xylem
• Tracheids are smaller in diameter and consist
of cells with overlapping, tapered ends.
• Holes in the walls allow minerals and water to
move from one tracheid to the next.
Xylem
Phloem
• Phloem carries the organic molecules (sugars
and amino acids) produced in the leaves to
the other parts of the plant where growth and
storage takes place.
• There are two kinds of phloem cells: sieve
tube elements and companion cells.
Phloem
• Sieve tube elements lack a nucleus and most
organelles, but have cytoplasm.
• Sieve tube elements have holes in the
endwalls that allow the flow of water and
dissolved nutrients.
Phloem
• Companion cells have direct connections to
the sieve tube elements and assist in the
movement of sugars and amino acids by active
transport from cells in the leaves into the
sieve tube elements.
Phloem
Xylem & Phloem
Growth And Storage
• Growth takes place at the tips of roots and
stems and in the production of reproductive
structures (cones, flowers, fruits).
• The roots are typically the place where food is
stored, but some plants store food in their
stems.
Roots
• Roots are the underground parts of plants
that anchor the plant in the soil.
• Roots absorb water and nutrients, such as
nitrogen, phosphorus, potassium, and other
inorganic molecules from the soil.
Roots
• Vascular tissue distributes these substances to
other parts of the plant.
• Roots grow from their tips to search for new
water and nutrients.
• Most roots serve as a food storage place.
Roots
Root Types
Stems
• Stems have two main functions:
– They support the leaves.
– They transport raw materials from the roots to the
leaves and manufactured food from the leaves to
the roots.
Stems
• The nature of plant cell walls provides the
support in stems.
• Some plant cell walls thicken to provide
additional support.
• Woody plants have especially thick cell walls.
Stem
Leaves
• Leaves are the major sites of photosynthesis.
• Leaves have a large surface area to collect
light.
• Leaves are relatively thin to allow the
penetration of light to the maximum number
of cells.
• Leaves tend to be arranged so that they do
not shade one another.
Leaves
Herbaceous Plants
• Herbaceous plants have few cells with thick
cell walls.
• They are easily damaged.
• Mosses, grasses, and many garden plants are
herbaceous.
Herbaceous Plants
Woody Plants
• Woody plants have a great deal of tissue with
thick cell walls.
• There are ferns, gymnosperms, and
angiosperms that are woody.
Woody Plants
Annual Plants
• Annual plants live one year.
• They germinate from seeds, grow, produce
flowers and seeds, and die within 1 year.
• The seeds they produce germinate the
following year and the cycle continues.
Perennial Plants
• Perennial plants live many years.
• Most kinds of plants are perennials, including
mosses, ferns, horsetails, pines, and most
flowering plants.
Perennial Plants
• Most perennial plants are woody, such as
various kinds of trees.
• Some perennial plants produce above ground
parts that die back at the end of the growing
season. The plant grows the above ground
parts from the roots each year. Tulips,
daffodils, rhubarb, and ferns are examples.
Trees
• A tree is a large, woody plant that usually has
a single main stem with branches.
• There are tree ferns, most gymnosperms are
trees, and many flowering plants are trees.
Trees
Shrubs
• A shrub is a perennial woody plant that
generally has several main stems and is
relatively short.
Shrubs
Herbs
• Herbs are generally non-woody and small.
Herbs
Gymnosperms
• Several kinds of woody plants produce seeds
that are not enclosed.
• Their seeds are produced in woody structures
called cones.
• The seeds are said to be naked because they
are not enclosed.
• The cone-producing plants, such as conifers,
are called gymnosperms.
Gymnosperm
Cone
Angiosperms
• Angiosperms are plants that produce flowers
and have their seeds enclosed in a fruit.
• A fruit is a modification of the ovary wall into
a specialized structure that contains seeds.
Angiosperm
Angiosperm
Tropism
• Tropism is a growth or movement toward or
away from a stimulus.
• Phototropism - plants orient themselves
towards light.
• Thigmotropism – the ability of many vines to
wrap stringlike tendrils around sturdy objects.
Thigmotropism