Download Kingdom Plantae - Toronto District Christian High School

S E C T I O N
13.2
Kingdom Plantae
E X P E C TAT I O N S
Describe anatomical and
physiological characteristics
of plants.
Learn the life cycle of select
plants.
Classify representative plants.
Demonstrate an understanding
of the diversity of living
organisms.
Figure 13.6 Members of the
plant kingdom are able to thrive
in unexpected locations, such
as this epiphyte, which lives on
the surface of another plant.
Imagine you are walking beside a stream in a
forest. Beds of soft green moss cover rocks beside
the water and clumps of ferns spring from the
decaying trunk of a fallen tree. Seeing a patch of
sunlight ahead, you leave the shade of the tall
pines and enter a clearing filled with the pinkishpurple spikes of fireweed. This short journey has
taken you past examples of all four major groups
within the plant kingdom. In fact, a short walk
through most places on Earth will take you past
members of the same four groups: mosses and their
relatives, ferns and their relatives, cone-bearing
plants, and flowering plants.
Classification of Plants
There is a huge variety of plants in the world, but
they can all be arranged into a few major groups on
the basis of several fundamental characteristics,
such as the presence or absence of vascular tissue
and seeds. Figure 13.7 shows members of these
four groups. Each large group contains several
Divisions, which are each roughly equivalent to
a Phylum.
Figure 13.7 The Kingdom Plantae is divided into four major groups. Plants range
in size from tiny mosses to giant pine trees.
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469
Non-vascular Plants
(Mosses and Their Relatives)
Instead, they have small root-like structures called
rhizoids, which develop from their lower surfaces.
Non-vascular plants are the only groups of
plants in which the life cycle is dominated by the
gametophyte phase. The identifiable green plants
that are common in moist shady areas are
gametophytes. Male gametophytes produce sperm,
and female gametophytes produce eggs. For
fertilization to occur, there must be enough moisture
on the plant surface for the sperm to swim to an
egg. After fertilization, the zygote remains on the
female plant and develops into a sporophyte.
There are three divisions of non-vascular plants:
mosses (Bryophytes), hornworts (Anthocerophytes),
and liverworts (Hepatophytes). These plants do not
have vascular tissue, and they are dependent on
the processes of diffusion and osmosis to transport
nutrients. They usually grow in mats of low,
tangled vegetation that can hold water like a
sponge, allowing them to survive periods of cold
and dry. Non-vascular plants have no roots.
A The gametophyte
generation produces
sporophytes that
grow up on tall
stalks above the
gametophyte.
meiosis
spores
sporophyte (2n)
B Within the end capsule of the
sporophyte, spores are produced
through the process of meiosis.
Spores are released when the capsule
bursts and they disperse with the
wind. The spore germinates on the
ground and develops into a male or
female gametophyte.
gametophyte (n)
spore
Sporophyte
generation
Gametophyte
generation
zygote (2n)
F A zygote is
produced, which
undergoes mitosis
and forms a new
sporophyte.
male gametophyte
(n)
female gametophyte
(n)
fe
rti
liz
at
io
n
antheridium
sperm
archegonium
(n)
Egg
(n)
E The antheridium releases
sperm, which swim to the
archegonium and
fertilization takes place.
sperm
archegonium
Figure 13.8 The life cycle of a moss
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MHR • Diversity of Living Things
egg
D The male gametophyte
develops an antheridium,
which is the structure that
produces sperm.
C The female gametophyte
develops an archegonium,
which is the structure that
produces eggs.
Mosses (Bryophytes)
Bryophytes, commonly known as mosses, lack
vascular tissue and do not have well-developed
roots, so they absorb most of their water directly
through their surface. When the air is dry, mosses
become dry; when wet conditions return, mosses
quickly absorb water. Although they seem to have
disadvantages compared with other plants, mosses
are very successful and widespread. They thrive in
such diverse habitats as bogs, tundra, on bare
exposed rocks, and in deep shade where other
plants may be unable to grow. In fact, mosses are
the most diverse group of plants after flowering
plants, and there are twice as many species of
mosses as of mammals.
A typical moss sporophyte consists of a sporebearing capsule growing on the end of a stalk
called the seta. Sporophytes do not contain
chlorophyll and receive all their nourishment from
the gametophyte. Spores are produced by meiosis
in the capsule of the sporophyte as shown in
Figure 13.8 on the previous page. As the
sporophyte dries out, the capsule releases spores. If
these spores germinate once they land on the
ground, they will become either a male
gametophyte, called an antheridium (plural
antheridia) or a female gametophyte, called an
archegonium (plural archegonia). Sperm are
released from the antheridium and swim to the
archegonium, where they fertilize the egg. A zygote
develops, and grows to become a new sporophyte.
You can often see a scattering of sporophytes
standing up above a bed of green moss
gametophytes as shown in Figure 13.9.
BIO
FACT
Scientists are still discovering how some mosses withstand
extreme drying. The cells of Tortula ruralis appear similar to
those in the leaves of vascular plants. When this moss is
dried out, it folds up tightly and its cells lose much of their
cytoplasm. Their mitochondria and chloroplasts shrink and
the cells lose their stored starch. Photosynthesis ceases and
respiration slows or stops. Despite such apparently serious
damage to their cellular structure, the plants unfold and
return to their normal hydrated state within two minutes
after water is added. Photosynthesis resumes about
24 h later. Much of the cell repair appears to be controlled
by one or more genes. If scientists can locate and copy
these genes, they may be able to add them to crop plants to
increase their drought tolerance.
Liverworts (Hepatophytes)
Hepatophytes, known commonly as liverworts,
grow flat and close to the ground and are rarely
more than 30 cells thick. There are two types of
liverworts, with different appearances shown in
Figure 13.10. About 80% of species have “leafy”
gametophytes that resemble mosses. Leafy
liverworts are most abundant in tropical forests
and in humid climates. In appearance, their
gametophyte generation resembles mosses. The
remaining species are thallose liverworts, called
this because the gametophytes are made up of
flattened, lobed bodies called thalli (singular
thallus). The common name, liverwort, comes
from the appearance of these gametophytes, which
resemble the lobes of animals’ livers.
A
Figure 13.9 The spore-bearing capsules of a moss stand
B
up on brown stalks above the leafy gametophyte.
Figure 13.10 Liverworts may be (A) thallose or (B) leafy.
The leafy liverwort resembles moss.
Plants and Animals • MHR
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BIO
FACT
Using DNA analysis, scientists have uncovered evidence that
liverworts are more closely related to the first land plants
than any other plants living today. Researchers searched the
DNA from 352 species of plants for three pieces of genetic
material called introns. Nearly all of the mosses, hornworts,
ferns, conifers, and flowering plants the scientists examined
had at least two of the three introns. Only liverworts, like
aquatic green algae, lacked all three. This suggests that
liverworts are the closest relatives of algae on land. As land
plants evolved and diversified, they acquired the introns
missing in liverworts and green algae.
Investigation
Liverworts produce sporophytes that grow on
the body of the gametophyte. Spores are formed
inside an egg-shaped capsule held at the top of a
translucent or white stalk. When it matures, the
capsule splits open into four equal quarters,
releasing the spores into the air. Liverwort
sporophytes are not often seen because they shrivel
up and disappear shortly after releasing their
spores. Liverworts can also reproduce asexually by
means of tiny pieces of tissue that become
detached from the thallus.
Hornworts (Anthocerophytes)
Anthocerophytes are commonly known as
hornworts. Their gametophytes are broad, flat,
usually less than 2 cm in diameter, and have a
blue-green colour. Figure 13.11 shows the mature
SKILL FOCUS
1 3 • B
Performing and recording
Alternation of Generations in Mosses
In mosses, both the spore-bearing sporophyte and the gamete-bearing
gametophyte are visible to the naked eye. In this investigation, you
will study the structure of both generations.
Analyzing and interpreting
Communicating results
Conducting research
Pre-lab Questions
Is the gametophyte haploid or diploid?
In which generation does meiosis occur?
Problem
What are the characteristics of the alternating
generations in mosses?
Prediction
Predict the importance of identifying the
reproductive structures of both generations
of mosses.
CAUTION: The scalpel blade is sharp.
Always cut away from your body.
Materials
microscope
microscope slides
single-edged razor
forceps
blade or scalpel
dropper
water
moss plants with male and female
gametophytes and sporophytes
paper towels
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MHR • Diversity of Living Things
Procedure
1. Obtain moss gametophytes with both
male and female reproductive structures.
You may use Figure 13.8 on page 470
for reference.
2. Using forceps, remove all leaves from the
upper part of one stem, being careful not to
damage the reproductive structure at the tip
of the stem. Repeat with a stem of the
opposite sex.
sporophyte, which look like miniature green cattle
horns thus giving the group its common name. The
sporophyte continues to grow throughout its life.
As in other bryophytes, it remains attached to its
parent. Eventually the sporophyte splits into two
halves lengthwise, releasing the maturing spores.
Although hornworts and liverworts are similar
in appearance, they can be distinguished from each
other. The best way to differentiate them is to look
at their cells under a low-power microscope.
Hornworts usually have one large chloroplast per
cell, while liverworts typically have many small
chloroplasts per cell.
sporophyte with
sporangium (2n)
gametophyte (n)
Figure 13.11 Hornwort sporophytes and gametophytes.
3. With a sharp blade, cut off the top 1 cm of
each stem you have prepared.
4. Place each stem tip at opposite ends of a
clean slide. Add several drops of water, and
place a second glass slide over the first.
5. Gently press down with the eraser end of a
pencil to slightly squash the reproductive
structures.
6. Place the sandwiched slides on a
microscope stage, using the stage clips to
keep them from slipping apart. Observe the
reproductive structures under low-power
magnification only.
7. Draw both types of reproductive structures.
Using Figure 13.8 as a guide, label the male
and female gametophytes, antheridium, and
archegonium.
8. Obtain a sample of moss with sporophytes.
9. Using forceps, carefully remove a small
capsule from the tip of a stalk, and mount it
in several drops of water on a microscope
slide.
10. Add a second slide on top of the first and
carefully squash the capsule as in the
procedure above.
11. Observe the squashed capsule under lowpower magnification only. Draw and label
the sporophyte, capsule, and spores.
Wash your hands thoroughly at the end of
this procedure.
Post-lab Questions
1. Which structure is responsible for a) sexual
reproduction? b) asexual reproduction?
2. What type of reproductive cell is formed by
the a) archegonium? b) antheridium?
c) sporophyte?
3. Which cells are a) haploid? b) diploid?
Conclude and Apply
4. Diagram the life cycle of a moss, using your
own observations. Use different colours to
indicate the haploid and diploid stages.
Mark where fertilization and meiosis occur.
5. Are eggs or sperm cells produced in greater
numbers? Suggest an explanation for your
answer.
Exploring Further
6. The most important bryophytes to humans
are probably peat mosses. Prepare a brief
report describing these plants and some of
the ways in which they are useful to people.
Plants and Animals • MHR
473
Seedless Vascular Plants
(Ferns and Their Relatives)
Non-vascular plants represent the pioneers of plant
life on land, but about 300 million years ago they
were literally overshadowed by the first vascular
plants. If you could travel back to this time in
Earth’s history, you would find vast swampy forests.
You would notice insects and some amphibians,
but no birds, mammals, or even dinosaurs. The
plants you would see growing in forests around
you would contain vascular tissues, roots, stems,
and leaves. These first forests are the source of
some of our non-renewable fossil fuels.
Whisk Ferns (Psilotophytes)
Looking like small green whisk brooms,
psilotophytes or whisk ferns are among the
simplest of living vascular plants (Figure 13.13).
They do not have leaves or roots, but grow to about
30 cm in height from short rhizomes, which are
horizontal underground stems. Photosynthesis
takes place in the outer cells of the branching stems.
PLAY
To view videos on the alternation of generations and on
fern development, turn to your Electronic Learning Partner.
These early seedless vascular plants were
different from the non-vascular plants in several
ways. Not only had they developed the vascular
tissue that allowed them to grow tall, but they had
the sporophyte generation as the dominant stage in
their life cycle. Their gametophytes were reduced
to tiny, short-lived structures that still depended on
moisture to carry out sexual reproduction. Nearly
all the trees that covered the land in that era are
now extinct. There are a few remaining groups of
those early vascular plants that live on today,
however. They include the whisk ferns, club
mosses, horsetails, and ferns like the one shown
in Figure 13.12.
Figure 13.13 The small yellowish clusters on this whisk fern
are sporophytes.
The tips of the stems of a whisk fern produce
yellow sporangia. After the spores are released,
they disperse and germinate into tiny, colourless
gametophytes beneath the soil surface. Only a few
millimetres long, the subterranean gametophytes
obtain their nutrition by absorbing dissolved
substances from the surrounding soil. At sexual
maturity, they develop both egg and sperm cells.
Fertilization produces the next generation of
sporophytes, which begin to grow on their parent
gametophyte. Eventually, the sporophyte grows
into a mature whisk fern.
BIO
Figure 13.12 Giant relatives of ferns like these helped form
Earth’s forests millions of years before dinosaurs evolved.
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MHR • Diversity of Living Things
FACT
Young fern sporophytes first appear as tightly coiled
fiddleheads that later unroll to form a mature frond. Today,
fiddleheads are eaten as a seasonal delicacy. At one time,
the fine silky hairs that cover the fiddleheads of some larger
tropical tree ferns were stripped off and used to stuff
pillows and mattresses. During the late 1800s, over
1900 metric tons of this fern hair were shipped from
Hawaii to North America.
Club Mosses (Lycopodophytes)
The lycopodophytes, or club mosses, that we see
today are mostly small evergreen plants that grow in
dense mats on moist temperate and tropical forest
floors. Extinct club mosses, however, were prominent
members of Earth’s forests for 40 million years. They
formed trees more than 35 m tall and up to 2 m in
diameter. Despite their name and appearance, club
mosses are not related to true mosses.
The sporophytes of all club mosses have true
stems and roots. Tiny leaves grow from their stems
in spirals, whorls, or pairs. Each narrow leaf has a
single, unbranched vein of vascular tissue along its
centre, whereas most plant leaves have multiple,
branching veins. At the end of a stem, specialized
spore-bearing leaves form compact clusters called
strobili (singular strobilus), which protect the
reproductive cells. Strobili resemble pine cones,
and because of this club mosses are sometimes
called ground pines (Figure 13.14).
A lycopodophyte spore germinates to form a
tiny, independent gametophyte called a prothallus.
Some species of lycopodophytes produce two
different types of spores: large megaspores and
small microspores. The megaspore germinates to
form a female prothallus and the microspore
produces a male prothallus. The prothallus lives on
the soil and produces either sperm or eggs. In wet
conditions, sperm swim to an egg and fertilize it.
The resulting zygote grows into the larger,
dominant sporophyte.
We b
LINK
The vast swampy forests found on early Earth about
300 million years ago are the source of most of our nonrenewable fossil fuels. Find out more about the extinct species
of vascular plants that made up these forests. To conduct your
research, go to Science Resources, then go to BIOLOGY 11
and follow the links to find out where to go next. What was the
geographical distribution of these forests? Did the species of
plant vary from place to place? Think about where fossil fuel
reserves are located in Canada. Is this correlated to these forests?
www.school.mcgrawhill.ca/resources/
Figure 13.14 This club moss, Lycopodium, is sometimes
called a ground pine because it is evergreen and looks
similar to a tiny pine tree.
Horsetails (Sphenophytes)
Sphenophytes, or horsetails, are another group of
seedless vascular plant that once included treesized members but now contain plants that only
grow to about a metre in height. These plants are
often found in damp areas or along roadsides.
Their hollow stems have a ribbed appearance, with
whorls of tiny, scale-like leaves growing from each
joint or node along the stem (Figure 13.15 on the
next page). These plants are also known as
scouring rushes, because they have a rough texture
that can be used for scrubbing pots or polishing
wood. The roughness is due to granules of silica
stored within the plant cells.
The life cycle of horsetails is similar to that of
club mosses. In spring, the tips of the stems
produce spore-bearing strobili. The spores
germinate to form male and female gametophytes.
Each female gametophyte has several eggs and may
develop more than one sporophyte after fertilization.
Plants and Animals • MHR
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divided into small leaflets called pinnae. The
conspicuous fern plant is the sporophyte, and you
can often see small spore-producing structures
called sori (singular sorus) clustered on the
underside of the pinnae (Figure 13.16).
FAST FORWARD
Turn to Chapter 14, Section 14.3 to learn more about
the processes and structures involved in gas exchange
in plants.
Figure 13.15 Horsetails have small leaves, and their
photosynthesis occurs mainly in the stems.
A
Horsetails have traditionally been used by North
American Aboriginal people and Asians for various
medicinal purposes. Some Aboriginal groups
burned the stems and used the ashes to treat burns
or sore mouths; some ate the strobili to cure
diarrhea; and others boiled horsetail stems in water
to make a shampoo for controlling head lice.
Ferns (Pteridophytes)
Pteridophytes, commonly known as ferns,
dominated the forests during the Carboniferous
Period (315 million to 280 million years ago).
Although their numbers have declined since their
peak, pteridophytes remain the most familiar and
successful of seedless vascular plants. Ferns
evolved several adaptations to life on land that are
also found in seed-bearing plants. In addition to
roots and vascular tissue, ferns have a waxy,
thickened outer epidermis that reduces water loss
by evaporation. Small openings in the epidermis,
called stomata, allow gases to enter and leave for
the processes of photosynthesis and cellular
respiration.
Ferns have an enormous range of form and
structure, with the greatest diversity being found in
the tropics. It is possible to find tiny ferns less than
1 cm in diameter as well as giant tree ferns up to
25 m tall. The fronds, or fern leaves, grow up from
a thick, underground rhizome and are commonly
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MHR • Diversity of Living Things
B
Figure 13.16 The small round structures often seen on the
underside of a fern frond (A) are called sori. They consist of
clusters of sporangia (B).
Ferns produce millions or even billions of spores
during their lifetime, but very few ever land in a
spot suitable for growth. A germinating spore does
not produce a new fern plant with fronds; rather, it
grows into a small, heart-shaped prothallus. The
gametophyte generation is unnoticed by most
people, because the prothallus is usually just over
1 cm across and lies flat on the ground. It is an
independent structure with its own rhizoid system
to provide it with nutrients and water. The
prothallus contains female organs, called
archegonia, and male organs called antheridia. You
can observe the structure of a fern prothallus for
yourself in the next mini lab.
Gymnosperms
(Conifers and Their Relatives)
There are two groups of plants that disperse by
means of a seed, gymnosperms and angiosperms.
Seeds allow plants to reproduce sexually without
needing water, and also provide protection against
harsh environmental conditions. As seeds, plants
can survive without water for many years. They
can be carried by different means to disperse across
continents and begin growing in new areas. The
first small seed-bearing plants appeared about
280 million years ago, among forests of ferns, club
mosses, and horsetails. At that time, the global
climate had begun to grow cooler and drier. Most
of the large spore-producing plants could not
survive long periods of drought and freezing, and
they became extinct. Gymnosperms have seeds that
are exposed on the surface of cone scales. The
word gymnosperm actually means “naked seed.”
This group includes the cone-bearing trees
(conifers) such as pines, firs, yew, spruce, cedars,
redwood, and many other large trees (Figure 13.17).
As well as the conifers, gymnosperms include three
other small groups: cycadophytes, gnetophytes, and
ginkgophytes shown in Figure 13.19 on page 479.
Reproduction in Gymnosperms
Recall that club mosses and horsetails bear spores
in strobili — structures made of compact clusters of
specialized leaves. Cones are simply large, woody
strobili. Female cones develop ovules in archegonia
that grow on the upper surface of each cone scale.
Male cones produce microspores that develop into
pollen grains. Each pollen grain is a four-celled
male gametophyte enclosed in a hard, water-
MINI
resistant coat. Many hundreds of thousands of
dust-like pollen grains are produced in each male
cone and dispersed to female cones by wind. When
a pollen grain lands next to an archegonium, it
produces a pollen tube, which grows into the tissue
of the female gametophyte. Sperm pass along this
tube to the egg. After fertilization, the zygote
develops into an embryo in the female cone. The
embryo, together with a small supply of stored
food, is covered by a tough, waterproof coat to form
a seed. Female cones remain on the tree until the
seeds have matured, which may take from several
months to two years. The evolution of pollen,
pollen tubes, and seeds allowed plants to reproduce
sexually without the need of moisture. This ability
helped them survive cold, dry conditions.
Figure 13.17 This conifer is one example of a gymnosperm.
LAB
Investigating the Fern Prothallus
Most people have seen fern plants, but few have observed
the gametophyte generation, which produces the gametes.
In this lab, you will study the structure of a fern prothallus.
Obtain a mature fern prothallus from your teacher and
prepare a wet mount. Observe all standard safety
procedures, especially when using electricity and glass.
Examine the prothallus under the low power of a
microscope. Make a labelled sketch indicating its general
shape and features. Use Figure 13.18 on the next page as
a reference if you need to. Identify the female organs,
located near the notch of the heart-shaped plant, and the
male organs, located near the pointed end of the prothallus.
Using the eraser end of a pencil, press gently on the cover
slip over the area bearing the male organs. Study your
specimen under medium power to see if any sperm were
released. If so, observe their structure and behaviour.
Analyze
1. What is the name of the structure that produces eggs?
that produces sperm?
2. Is the prothallus haploid or diploid?
3. What type of cell division produces the gametes?
4. Sketch and label a diagram showing the stages in the
fern life cycle between the gametophyte generation and
the sporophyte generation.
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A A sporangium produces haploid
spores that germinate to form a
gametophyte called a prothallus.
gametophyte
spore
rhizoids
B The prothallus
produces antheridia
(male organs) and
archegonia (female
organs).
prothallus
meiosis
egg
sperm
sporangium
F Sori develop on the
pinnae. Spores are
formed in the sori
by meiosis.
antheridium
archegonium
egg
sori
fertilization
C Sperm from the
antheridia swim via
a droplet of water to
an egg produced by
the archegonium.
sperm
zygote
mitosis
pinna
fronds
new sporophyte
gametophyte
sporophytes
rhizome
roots
E The sporophyte matures,
and roots and fronds develop
out of the growing rhizome.
Figure 13.18 The life cycle of a fern.
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MHR • Diversity of Living Things
D The fertilized egg begins
to grow into a sporophyte.
Conifers
Conifers are the largest group of gymnosperms, and
they form vast forests in cold regions of the world.
As well as being able to reproduce without water,
they have other adaptations to cold, dry habitats.
Their protective covering of bark helps protect the
stem and reduce water loss.
The pyramidal shape of many conifers, such as
the one shown previously in Figure 13.17, together
with their flexible branches, helps snow and ice
slide off the tree. This reduces the risk of a heavy
buildup of snow that could break branches.
The needle-like leaves of conifers have a thick,
waxy cuticle and sunken stomata, which reduce
the rate of evaporation (Figure 13.20 on the next
page). Pine needles are usually semicircular or
round in cross section, resembling a cylindrical
leaf. The shape reduces surface area, which in
turn reduces water loss by evaporation. Most
conifers are evergreen, so they continually lose
and replace their needle-like leaves all year long
rather than losing all of their leaves at once like a
deciduous tree.
A Conifers bear seeds in cones like the ones on this
Eastern Hemlock.
B Welwitschia (Gnetophyta) is an odd-looking plant
found only in deserts in southern Africa, where the
average rainfall is less than 2.5 cm per year. Its short
stem produces two broad leaves that continue
growing throughout the life of the plant. Welwitschia
may live 100 years, and the older ends of its leaves
become tattered and weathered.
C Cycads (Cycadophyta) were common trees during
the Mesozoic era when dinosaurs shared the forests
with the first birds and mammals. About 100 species
exist today, mainly in the tropics. They are short,
palmlike trees with scaly trunks, but they are not
closely related to palms. Male and female cones
grow on separate trees. The cones of some cycads
may grow to a metre in length.
D Ginkgo biloba (Ginkgophyta) is the only living species
of a group of plants common during the Jurassic
period 200 million years ago. It has distinctive lobed
leaves. Ginkgos were cultivated in Asian temple
gardens for thousands of years, which may have
helped protect them from extinction.
Figure 13.19 Gymnosperms bear their seeds in cones. This group includes
conifers, gnetophytes, cycads, and ginkgos.
Plants and Animals • MHR
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By keeping leaves through winter, they are able
to start photosynthesis early in the spring, as soon
as the weather grows warmer. This is a great
advantage at high latitudes where the growing
season is short. Conifers are also better able to grow
in nutrient-poor soils, because they do not need to
grow a complete new set of leaves all at once.
stomata
Angiosperms (Flowering Plants)
Each spring, brightly coloured packages of plant
seeds, like those shown in Figure 13.21, are
displayed in gardening stores. On the outsides of
the packages are pictures of flowers or vegetables.
Inside each package is a number of small, dry, hard
seeds. These tiny waterproof capsules contain plant
embryos, ready to grow as soon as you add water.
vascular tissues
Figure 13.20 A cross section of a pine needle
Figure 13.21 The dry hard seeds of angiosperms are often
sold in packages in order to be planted in a garden.
DESIGN YOUR OWN
Investigation
SKILL FOCUS
1 3 • C
Initiating and planning
Identifying Conifers
Performing and recording
How can you tell one coniferous tree from another? In this
investigation, you will study the characteristics of several different
species of coniferous plants and develop a key to identify them.
Analyzing and interpreting
Communicating results
Problem
Identify different species of conifers found in
your area.
Hypothesis
Make a hypothesis about what specific
characteristics will best distinguish among
several coniferous species.
Materials
twigs, needles, and cones collected from several
different conifers in your area
a field guide to trees
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Experimental Plan
1. Make a list of characteristics in which
species of conifers might differ in order to
test your hypothesis. From the
characteristics in your list, decide which
ones would be most useful in a key.
These plants grow and develop seeds that are
enclosed within a fruit. Plants that protect their
seeds within the body of a fruit are called
angiosperms or flowering plants.
The first flowering plants appeared on Earth
about 150 million years ago. More than three
quarters of all species of living plants are seedbearing, flowering plants. Angiosperms include
trees, shrubs, herbs, grasses, vines, and water
plants, which may have inconspicous flowers,
and they grow almost everywhere on land from
the tropics to the tundra.
Angiosperms are divided into two large classes,
based on the number of seed leaves, or cotyledons,
on the embryo within the seed. Angiosperms with
one seed leaf are called monocots, and those with
two seed leaves are dicots. Figure 13.22 on the
next page shows examples of these different
flowering plants.
PLAY
To see a video of different types of seed dispersal, use your
Electronic Learning Partner.
2. Decide in which order the characteristics
should appear in the key.
3. Collect samples of different local conifers.
Checking the Plan
1. Traits are described in a key as sets of two
alternative choices. For example, if you
decide that the arrangement of needles is a
useful characteristic for identification, one
choice in your key might be:
needles grouped in bundles, or
needles growing singly
2. When writing your key, remember that it
must be clear enough to be used by any
person not familiar with conifer
identification.
Data and Observations
Create your key. Examine your conifer samples
and list the characteristics you observe. Identify
the samples of conifers that you have brought
into class using your key.
FAST FORWARD
Turn to Chapter 14, Section 14.1, for more information on
monocots and dicots.
Reproduction in Angiosperms
What are flowers, and what advantages do they
provide to plants? One clue is that colourful and
scented flowers are not only attractive to people
but also to some other animals. The flower contains
the structures used for sexual reproduction in the
plant, and when animals visit flowers to get pollen
or nectar, they help flowering plants carry out the
process of reproduction.
Recall that the pollen grains of gymnosperms are
dispersed in vast numbers by wind. This method of
transport is quite imprecise, and most pollen grains
do not land on an appropriate female cone. Some
angiosperms also scatter their pollen on the wind,
but the majority of flowering plants have more
specific methods of transferring pollen from the
male to the female of the same species. This is
known as pollination, and flowers play an active
role in this process.
Analyze
1. Was your hypothesis supported? Explain
your answer.
2. Exchange your key with students from a
different group. Using the new key, identify
your conifer specimens. Does the key work?
Are you able to correctly identify your
specimens?
Conclude and Apply
3. Is there only one correct way to design a key
to identify conifers? Explain your answer.
Exploring Further
4. Mount and label your specimens. Display
them in your classroom along with other
students’ specimens. Try to provide
examples of all the conifers in your area.
Be sure to highlight the identifiable
characteristics of each sample.
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A
B
C
D
Figure 13.22 Monocots include (A) lilies and (B) grasses while dicots include
(C) daisies and (D) deciduous trees.
Many different organisms depend on flowers for
food, because most flowers produce nectar — a
concentrated liquid mixture of proteins and sugars.
When an insect, a bird, or even a bat lands on a
flower to collect nectar, it becomes brushed with
pollen from the anthers (Figure 13.23). Then, as the
organism flies on to the next flower, the pollen
grains are brushed onto the stigma, where they can
fertilize the ovum.
BIO
FACT
Civilization as we know it would not have been possible
without members of the grass family. Nine species in this
family, including wheat, barley, rice, oats, and corn, provide
over 75% of the food eaten by people worldwide today. The
development of agriculture and the cultivation of cereal
crops thousands of years ago allowed people to produce
surplus food, settle in large populations, and create cities
for the first time.
PAUSE
RECORD
You have learned about the different ways that plants
reproduce. What are the similarities in how all plants
reproduce? What are the main differences among the four
groups of plants? Create a short checklist or diagram to
organize these similarities and differences.
Figure 13.23 As a bee lands on the lower petal of this
flower, the anther deposits pollen on the bee’s back.
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MHR • Diversity of Living Things
Adaptations for Pollination
Most methods of pollination in flowering plants
involve close relationships between flowers and
certain species of insects, birds, and bats.
Flowering plants and the animals that pollinate
them evolved together. For example, flowers
pollinated by bats are open at night (Figure 13.24).
Flowers pollinated by butterflies usually store their
nectar at the base of a long corolla, where it can
only be reached by moths or butterflies with their
longer specialized mouth parts.
Specialization is an advantage to both the plant
and the pollinator. The distinct colour, shape, and
scent of a flower helps the pollinator easily
recognize it as a reliable source of food
(Figure 13.25). Differences between the flowers of
different species increase the chance that a
pollinator will search for nectar from only one
species at a time. Transporting rose pollen to a
daisy, or vice versa, would not help either plant
become pollinated and complete its life cycle
(which is shown in Figure 13.27 on the next page).
After a pollinator deposits pollen on a stigma,
each pollen grain grows a pollen tube to reach the
ovule. Only the first tube to reach the ovule will
penetrate and fertilize it. This process leads to
pollen-tube competition. The fastest growing
pollen tube usually carries the best genes and
results in more vigorous offspring.
Because a single plant often produces many
flowers, there is a risk that the plant may selfpollinate (that is, that pollen may be transferred
from one flower to another flower on the same
plant). Although self-pollination results in the
development of seeds, it does not involve the
exchange and recombination of genetic material
that helps create diversity within a population.
Self-pollination produces offspring with the same
genome as the parent.
Flowering plants have evolved several strategies
to favour cross-pollination over self-pollination.
Some plants have separate male and female flowers
that mature at different times. This ensures that
male flowers have already dispersed their pollen
before female flowers on the same plant are ready
to be fertilized. Other species have chemical
barriers that prevent fertilization by pollen from
the same plant. In flowers with both male and
female parts, the stigma usually extends much
farther than the anthers, keeping the two parts well
separated so they do not self-pollinate accidentally.
Figure 13.25 The markings on this flower are only visible to
the human eye when illuminated with ultraviolet light. These
same markings are easily seen by pollinating insects.
REWIND
Turn to Chapter 4, Section 4.2, to review cross- and
self-fertilization.
Seed Development and Dispersal
Flowering plants are diploid sporophytes. Unlike
the earlier plant groups you have studied, however,
angiosperms do not produce spores. The pollen
grains and ovum cells are all that remain of the
gametophyte generation in flowering plants.
Fertilization produces a diploid sporophyte embryo,
which is enclosed in a hard case to form a seed.
Angiosperm seeds are further protected by the
fleshy walls of the ovary. As the ovary matures, it
swells to form a fruit or seed pod like the one
shown in Figure 13.26. Fruits also help in seed
dispersal. When the fruit is eaten by an animal,
seeds are carried away from the parent plant in the
animal’s digestive tract. The seeds resist digestion
and pass out with the animal’s feces to germinate
in a new spot.
Angiosperm
fruit
seeds
sepals
Figure 13.26 A fruit such as an apple consists of the fleshy
Figure 13.24 Flowers pollinated by bats must be large
enough to support the weight of the bat.
walls of the ovary enclosing the seeds. You can see the
remains of the flower sepals at the bottom of the apple,
opposite the stalk that attaches the fruit to a stem.
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anther
pollen grain
haploid
microspores
in fours
ovary
male
gametophyte
sperm
ovule
haploid
megaspores
female
gametophyte
meiosis
Gametophyte
generation
n
egg
pollen
tube
fertilization
flowers
pollen tube
young
seedling
Sporophyte
generation
2n
zygote
germinating
seed
adult
sporophyte
plant
seed
fruit (containing seed)
Figure 13.27 The life cycle of a flowering plant
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Biology Magazine
TECHNOLOGY • SOCIETY • ENVIRONMENT
Adjusting the Balance
Animal and plant species change over time, sometimes
evolving into different forms and sometimes going extinct.
As the human population grows, it disturbs more and
more land mass, driving many plants and animals into
extinction. For example, the vast forests in the
Mediterranean region disappeared by Roman times.
Some scientists believe humans may have caused the
extinction of large mammals like the North American
mammut (a kind of mastodon) more than 10 000 years
ago. The list of species that have been negatively
affected by humans keeps growing.
The loss of plant and animal species affects all other
animal and plant species with which the lost species
interact. It is only recently that biologists have begun to
study such interactions and to understand the farreaching impact of mismanaging our ecosystems. As our
understanding of the importance of interactions grows,
so does the need to protect the plant and animal species
threatened by human expansion.
forests. However, logging continued in and around the
sanctuaries, and more and more of the monarchs’ winter
home was converted into oat and corn crops. To make
matters worse, as the trees were cut, the remaining trees
became subject to strong winds, drying the normally
moist habitat and making the standing trees more prone
to disease. Some conservationists rallied to the cause of
the monarch butterflies, calling for stronger policing of the
Oyamel sanctuaries. However, they ignored the economic
needs of the farmers. The competing needs of the
butterflies and the people created a dilemma — how to
find a solution that would take into account the needs of
both the monarchs and the people who live in the area.
Forests for People and Forests for Monarchs
Maintaining a keystone species in a community — a plant
or animal that is crucial to the overall health of the
ecosystem — may have a direct economic benefit for
humans. But conservation efforts sometimes have
indirect economic benefits that seem surprising. The
work being done by conservationists to protect monarch
butterflies and the forests they live in is an excellent
example of this.
Robert L. Small of Oakland, California and Jose Luis
Alvarez of El Rosario, Mexico started a project in 1997
that may satisfy the needs of both the monarchs and the
farmers. With the help of donations from conservationists
in the United States, Small has been able to send fir
seedlings to Alvarez, who distributes them to willing
farmers. The goal is to use the donated trees to create a
new forest that can be planted, harvested, and replanted
by the farmers, while at the same time allowing the
monarchs their current habitat. Five farmers planted 7000
donated trees in 1997, 20 farmers planted 40 000 trees
in 1998, and the project continues to grow. The
reforestation project promises so much success that the
Mexican government is considering similar projects of
its own.
The Monarchs and the Oyamel Forests
Follow-up
The Oyamel fir forests in
central Mexico are the winter
home of monarch butterflies,
whose yearly migration from
Canada and the eastern
United States has captured
the imaginations of people
worldwide. Unfortunately,
the indigenous farmers
(ejidatarios) who live in the
area depend on logging
these forests for their
livelihood. For the past
20 years, the Oyamel
forests have been slowly
Monarch butterflies migrate
shrinking, thus threatening
the monarchs’ winter habitat. by the thousands to these
forests in Mexico.
In 1986, the Mexican government created monarch
sanctuaries by banning logging in parts of the Oyamel
1. The Oyamel reforestation project shows how even
the conservation of species that do not affect the
human economy can have a positive impact on
whole communities, including human populations.
Briefly write down your thoughts on conservation that
is not driven directly by economic need.
2. A new potential threat to monarch butterflies has
surfaced. Genetically modified corn crops, whose
pollen kills certain corn pests, may be affecting the
monarch caterpillars in the United States. Studies of
the corn/butterfly connection have brought attention
to the controversy surrounding genetically modified
plants (and animals) and how they affect whole
communities. Write a paragraph outlining possible
steps that could be taken to avoid further damage to
the monarch butterfly populations. Which do you
think is more important: developing a better food
source for hungry people, or conserving the monarch
butterfly? Explain your answer.
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Asexual Reproduction and
Multiple Chromosomes
Nearly half (47%) of all angiosperms are polyploid
— that is, they have more than two (2n) sets of
chromosomes. They may have 3n, 4n, or more.
This situation is caused by irregularities during
meiosis. It results in sterile offspring that can still
reproduce asexually, and has been an important
mechanism in the evolution of plants. For example,
polyploidy can produce larger cells, thicker and
fleshier leaves, and larger flowers and fruits. The
original South American ancestor of the potato is
tetraploid (4n), and many common food plants
such as strawberries and apples are polyploid. A
species of wheat commonly grown for bread
(T. aestivum) is hexaploid (6n = 42 chromosomes).
SECTION
K/U Which three characteristics do plants share with
green algae?
2.
K/U Name two characteristics that adapt plants to
life on land.
3.
K/U Name the four broad groups into which the
plant kingdom is divided.
4.
K/U What are the products of meiosis in the four
different groups of plants?
5.
K/U What are bryophytes? How do they differ from
the other groups of plants?
7.
8.
K/U
C Sketch the life cycle of a fern, clearly showing the
sporophyte and gametophyte generations. Indicate
which is haploid and which diploid.
To most people, it is fairly clear that carrots are a type of
vegetable, and apples are a type of fruit. Some people argue
that tomatoes can be classified as either a fruit or a vegetable.
What are the differences? To botanists, a fruit is a mature plant
ovary that contains seeds. Thus, tomatoes, string beans,
cucumbers, and squashes are all fruits. Make up your own
definition of a vegetable. Do all vegetables fit your definition?
9.
I Suppose you find yourself in a wilderness area in
a part of the world you have never been before. How
might a knowledge of plant classification help you
determine the typical climate of the area? Describe
the steps you would take to do this.
10.
I Copy and complete the following table about the
growth patterns of certain conifers. Use the graph
shown on the left below for your information. Give
your table a title.
Maximum
height
Age at maximum
height
Height at
45 years
How does the graph below show that these
conifers grow according to their own growth pattern?
spruce
larch
pine
I
fir
spruce
33
Height (m)
LINK
fir
Which two plant groups produce seeds?
39
larch
pine
27
21
9
3
0 10
11.
MC Why do some angiosperms have showy flowers
while others have inconspicuous flowers? What does
flower type indicate about the plant? If you wanted to
farm a plant with showy flowers, name one challenge
you would face and explain how you would deal
with it.
UNIT ISSUE PREP
15
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Wo rd
REVIEW
1.
6.
Odd-number polyploids are sterile because they
cannot segregate chromosomes evenly into gametes
during meiosis (odd numbers are not divisible by
two). Sterility caused by triploidy produces such
results as seedless bananas and less bitter
cucumbers.
20
30
40
50 60 70
Age in years
MHR • Diversity of Living Things
80
90 100
If you have decided to investigate the status of a plant
species in your Unit 4 Issue Analysis, make sure you have
noted the characteristics of the phylum to which your
species belongs. These characteristics may have an
impact on how your species can be protected.