CHAPTER
14
Plants: Reproduction,
Growth, and Sustainability
Specific Expectations
In this chapter, you will learn how to . . .
• F1.2 evaluate, on the basis of research,
ways in which different societies or
cultures have used plants to sustain
human populations while supporting
environmental sustainability (14.3)
• F2.1 use appropriate terminology related
to plants (14.1, 14.2, 14.3)
• F2.2 design and conduct an inquiry to
determine the factors that affect plant
growth (14.2)
• F2.3 identify and draw biological
diagrams of the specialized plant tissues
in roots, stems, and leaves, using a
microscope and models (14.1)
• F2.4 investigate various techniques of
plant propagation (14.2)
• F3.2 compare and contrast monocot and
dicot plants in terms of their structures
and their evolutionary processes (14.1)
• F3.3 explain the reproductive
mechanisms of plants in natural
reproduction and artificial
propagation (14.1)
• F3.4 describe the various factors that
affect plant growth (14.2)
• F3.5 explain the process of ecological
succession, including the role of plants in
maintaining biodiversity and the survival
of organisms after a disturbance to an
ecosystem (14.3)
Farmers and gardeners in developed and developing countries
practise a tradition that dates back to the earliest days when humans
grew plants for food—they save and exchange their seeds. The seeds
of bean and pea plants, as well as those from tomato, cucumber,
and summer squash plants are commonly saved and planted the
following year. Growers save seeds from plants that have desirable
characteristics, such as those that remain disease-free, produce
flavourful fruit, or produce colourful flowers. This tradition helps
preserve the rich genetic legacy of the plants that have helped to
build our civilizations.
580 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Launch Activity
Germinate Some Seeds
Germination is the process by which a seed begins to sprout. How do seeds
change as they germinate?
Safety Precautions
• Wear latex (or vinyl) gloves when handling the seeds, since some seeds
are coated with a fungicide to preserve them.
Materials
• paper towels
• water
• spray bottle
• 2 petri dishes
• seeds (10 each of at least one monocot and one dicot)
Procedure
1. Use the spray bottle to moisten two pieces of paper towel so that they
are damp but not sopping.
2. Place each paper towel in a petri dish.
3. Place 10 monocot seeds in one petri dish and 10 dicot seeds in the
other. Make sure the seeds are spaced so they are separated as much
as possible from one another.
4. Place the petri dishes in a warm location. Observe the seeds each day
for up to one week. Moisten the seeds each day with the spray bottle.
5. Make notes and drawings to record your observations each day. You
could do this in the form of journal entries or an observation table.
Questions
1. How did the seeds change over the period during which you observed
them? Identify any differences between the monocots and dicots.
2. Seeds need water to germinate (begin to sprout), but water is not a
source of nutrition or energy for the seeds. What do you think is the
source of energy for the growth of the seeds?
3. What will happen to the germinated seeds if they are not placed or
planted in a location where they are exposed to sunlight? Explain why.
4. What factors affect the germination of seeds? Suggest a way to modify
this procedure to compare these factors. Include a hypothesis that
serves as the basis for your modified procedure.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 581
SECTION
14.1
Key Terms
pollination
sepal
petal
stamen
pistil
seed coat
germination
radicle
hypocotyl
artificial propagation
Plant Reproduction
In the plant kingdom, both sexual and asexual reproduction occur. Botanists (plant
scientists) define groups of plants by the way they carry out sexual reproduction.
(Asexual reproduction will be discussed later in this section.)
Recall from Chapter 3 that plants reproduce sexually by sporic reproduction,
which is also called alternation of generations. As shown in Figure 14.1, both a haploid
gametophyte and a diploid sporophyte are stages in the reproductive cycle of plants.
Haploid cells have one copy of each chromosome (1n), while diploid cells have two
copies of each chromosome (2n). The gametophyte (1n) produces gametes (1n), while
the sporophyte (2n) produces spores (1n). The male and female gametes unite to form
a sporophyte (1n + 1n = 2n). Through mitosis, the male and female spores grow into
male and female gametophytes. Sexual reproduction occurs when the male gamete
(a sperm cell) unites with the female gamete (an egg cell). This union of male and
female gametes is called fertilization.
Sporophyte
Cell divisions
occur
Diploid cells
(2n)
Fertilization forms
zygote (2n)
Male gamete
(sperm)
Cell divisions
occur
Reproductive
cells develop
Female gamete
(egg)
Meiosis forms
spores (n)
Haploid cells
(n)
Cell divisions
occur
Mature
gametophyte
Cell divisions
occur
Figure 14.1 All plants have a life cycle involving alternation of generations. The cycle varies
among species. The variation is mostly due to the type of structure that releases the spores.
Sexual Reproduction in Seedless Plants
Figure 14.2 Peat,
or sphagnum, moss
commonly grows in boggy
areas. Its antibacterial and
absorbent properties led
to its historic use, by some
Aboriginal peoples, as
dressing for wounds.
Seedless plants include the non-vascular mosses and the vascular ferns. In seedless
plants, fertilization requires the sperm to swim from the male gametophyte to the egg,
which is in the female gametophyte. Therefore, water must be present, and the sperm
must have a flagellum to enable it to move in the water.
In non-vascular plants, the gametophyte is the dominant generation, so the
gametophyte plant is larger and longer-lived. The smaller sporophyte depends on the
gametophyte for food and support. Figure 14.2 shows peat moss, which is a typical
non-vascular plant. The visible part of the plant is the gametophyte generation.
In vascular plants, the sporophyte is the dominant generation, and the gametophyte
is smaller and shorter-lived. In ferns, for example, the large, leafy part is the sporophyte,
while the gametophyte is a small, barely visible structure. In both groups of seedless
plants, however, the gametophyte is a free-living plant, independent of the sporophyte.
582 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Sexual Reproduction in Seed Plants
Seed plants include gymnosperms and angiosperms. In seed plants, the gametophytes
are not free-living plants. The male gametophytes, called microspores, are small
structures that develop into pollen grains that, in turn, produce sperm cells. The female
gametophytes, called macrospores, produce egg cells. In seed plants, the whole male
gametophyte—not just the sperm—travels to the female gametophyte. Pollination
occurs when the pollen (male gametophyte) lands on the female reproductive structure
of another plant of the same species. The pollen grain encases the cells that develop into
the sperm and protects them from drying out as they travel to the female gametophyte.
pollination the
transfer of the male
gametophyte (pollen
grain) to the female
reproductive structure
(pistil)
Sexual Reproduction in Gymnosperms
Pollination does not require water to transport sperm to a female gametophyte. As a
result, the sperm that develop from pollen grains do not have flagella. Instead, transfer
of sperm to the egg occurs by means of a pollen tube. This structure is an extension of a
pollen grain that grows toward the egg cell. Sperm develop in the pollen tube and move
toward the egg. Fertilization occurs when a sperm unites with an egg to form a zygote.
After fertilization, the zygote develops into an embryo. The embryo, together with
a small supply of stored food, is covered by a tough, waterproof coat to form a seed.
Seeds remain on the plant, within the female reproductive structure, until they are
mature. This can take from several months to three years. The seeds are then released
and carried away from the parent plant by the wind or by animals. At their new
locations, they may grow into new sporophyte plants when conditions are suitable.
The structure of pollen, the development of the pollen tube, and the structure of seeds
allow gymnosperms to reproduce in a dry environment. These same elements of the life
cycle are present in angiosperms, which are discussed next. The differences in sexual
reproduction between non-vascular plants, seedless vascular plants, gymnosperms, and
angiosperms are summarized in Figure 14.3.
Plant Reproduction
Asexual
Sexual
r sporic reproduction (alternation
of generations)
Seedless
Plants
Seed
Plants
Natural Vegetative
Propagation
r adapted for reproduction in
r adapted for reproduction in
wet environment
r swimming sperm
r independent gametophyte plant
r unprotected zygote, embryo,
and gametophyte
dry environment
r non-motile sperm
r dominant sporophyte generation
r dependent gametophyte generation
r protected zygote embryo
Non-vascular
r dominant
gametophyte
plant
Vascular
r dominant
sporophyte plant
Gymnosperms
r growth from roots, stems,
or leaves
Artificial
Propagation
r for example, dividing,
grafting, cuttings, layering,
tissue culturing)
Angiosperms
r Unprotected
r Protected seeds
seeds develop
on upper surface
of reproductive
structures
r Wind pollination
r Single
fertilization
develop within
ovary wall
r Wind, insect,
or animal
pollination
r Double
fertilization
Figure 14.3 This concept map compares
and summarizes modes of reproduction
in non-vascular and vascular plants.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 583
Sexual Reproduction in Angiosperms
sepal a non-fertile
part of the flower that
protects the flower bud
petal a non-fertile
part of the flower that
attracts pollinators
stamen the male
reproductive part of the
flower
pistil the female
reproductive part of the
flower
Angiosperms are the most diverse and widespread plants on Earth. The most
important factor in this success is the structure that contains their reproductive
organs—the flower.
In general flowers have four organs, as shown in Figure 14.4: sepals, petals, stamens,
and one or more pistils. Sepals protect the flower bud and can look like small leaves
or even resemble the flower’s petals. Petals are usually colourful structures that attract
pollinating insects and provide them with a platform on which to land.
Most flowers have several stamens, which are male reproductive organs. A stamen
is composed of a filament and the anther. The filament supports the anther, which
contains cells that undergo meiosis and mitotic cells divisions to form pollen grains.
Two sperm eventually form inside each pollen grain.
The female reproductive structure of a flower is the pistil. In the centre of a flower
is one or more pistils. A pistil usually has a stigma, a style, and an ovary. The stigma is
the tip of the pistil and is the place where pollination takes place. The style connects
the stigma to the ovary, which contains one or more ovules. A female gametophyte
develops in each ovule, and an egg forms inside each female gametophyte.
stamen
male reproductive organ
pistil
female reproductive organ
anther
where pollen is
produced and stored
stigma
sticky “lip” of the carpel that
captures pollen grains
pollen
cases that contain
male gametes
style
stalk that supports the stigma
ovary
swollen base of the carpel that
contains ovules
filament stalk
that supports the anther
ovules
sacs that contain female
gametes
petals
colourful structures
that attract pollinators
sepals
surround and
protect the flower bud
Figure 14.4 The reproductive structures in angiosperms are located in their flowers.
Compare and contrast the functions of the filament stalk and the style.
Learning Check
1. In gymnosperms, gametes that develop from pollen
grains do not have flagella. Why do the gametes not
require flagella?
2. What two characteristics of a seed give the plant
embryo the best possible chance of developing into
a seedling?
3. Identify the male and female reproductive organs of
flowers.
4. Describe two functions of flower petals.
584 MHR • Unit 5 Plants: Anatomy, Growth, and Function
5. A plant experiences a mutation that prevents the
sperm from being encased inside pollen grains
before they are released. Predict what will happen
to the frequency of pollination in this species, and
explain your prediction.
6. Angiosperms always produce two sperm cells in
each pollen grain. Refer to Figure 14.1 to identify
which process is responsible for the pairing of
sperm cells.
Variations among Flowers
Most flowers have all four of the organs described on the previous page. However,
many flowers have modifications to one or more organs. Botanists categorize flowers
using these modifications.
Structural Differences
Flowers with sepals, petals, stamens, and one or more pistils are called complete flowers.
Examples of complete flowers are roses, tulips, and lilacs. If a flower is missing one or
more of these organs, it is an incomplete flower. For example, flowers of wild ginger
(Asarum canadense) are incomplete, because they have no petals. The same is true of
most grasses.
Flowers that have both pistils and stamens are called perfect flowers. Flowers that
contain either pistils or stamens, but not both, are called imperfect flowers. In some
species, such as corn plants and oak trees, individual flowers are imperfect but the
plant bears both male and female flowers. These are called monoecious plants, because
all reproductive structures appear on one (mono-) plant. (The -ecious portion of the
word comes from the Greek word oikos, meaning house. This is the same Greek word
that gives us the word ecology.) Other plants carry either male or female flowers, but
not both. These are called dioecious plants, because the reproductive structures are
divided between two (di-) plants. For example, willow and ginkgo trees are dioecious.
The number of organs that each flower has varies from species to species. However,
the number of flower organs distinguishes monocots from dicots, as shown in
Figure 14.5. When the petal number for a flower is a multiple of four or five, the plant
is likely a dicot. The number of sepals, pistils, and stamens is often the same multiple
of four or five. For example, the meadow beauty (Rhexia virginica) is a common
Ontario flower that has four petals and eight stamens. A five-petalled example is
the sulfur cinquefoil (Potentilla recta). Monocots, on the other hand, have organs
in multiples of three. For example, Ontario’s provincial flower, the white trillium
(Trillium grandiflorum) has three sepals, three petals, and six stamens.
A
B
SuggestedInvestigation
Inquiry Investigation 14-A,
Comparing Flowers and
Their Structures
C
Figure 14.5 The meadow beauty (A) and sulfur cinquefoil (B) are dicots. The white trillium (C) is a monocot.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 585
Pollination Mechanisms
Recall that pollination is the transfer of pollen from the male anther to the female
stigma. Flowers show great variations in size, shape, colour, petal arrangement, and
scent. Many of these variations are pollination-related adaptations.
Self-pollination and Cross-pollination
Self-pollinating plants can pollinate themselves or another flower on the same plant,
but this can lead to inbreeding and loss of genetic variation. Most angiosperms are
cross-pollinating plants, meaning that they receive pollen from another plant, ensuring
genetic diversity. In dioecious trees, such as the holly (Ilex verticillata) shown in
Figure 14.6, the male and female plants must be close enough to each other for the
male to pollinate the female.
Figure 14.6 The crosspollinating Ilex verticillata is
a resident of swampy and
marshy areas of Ontario.
It displays plump berries
even in the midst of winter
leading to its common
name, winterberry.
Animal Pollination
Many animal-pollinated flowers are brightly coloured, have strong scents, or produce a
sweet liquid called nectar. When insects and other small animals move from flower to
flower searching for nectar, they can carry pollen from one flower to another, as shown
in Figure 14.7. Other insects collect pollen for food. The bright colours and sweet scents
of peonies, roses, and lilacs, for example, attract insects such as bees, butterflies, and
beetles. White or pale yellow flowers are more visible at dusk and at night, and attract
nocturnal animals, such as moths and bats. The fruity smell of some flowers attracts
fruit-eating bats that act as the flowers’ pollinators. Bird-pollinated flowers often give
off little or no aroma. (Birds generally have a poor sense of smell, so they tend to locate
flowers by sight.)
Wind Pollination
Figure 14.7 Pollen grains
stick to the body hair of a bee
as it collects pollen or nectar
from an apple blossom.
Plants that are pollinated by the wind usually lack colourful or fragrant flowers. They
do, however, produce great quantities of light pollen grains that can be carried by the
wind. The large volume of pollen increases the chances of some pollen landing on the
correct flower. Also, the stigma of the plant often extends beyond the petals, exposing it
to the wind directly.
Learning Check
7. Use a paragraph or a table to differentiate between
monoecious and dioecious plants.
8. Poison ivy has long been identified through the
rhyme, “Leaves of three, let it be.” Does this mean
that poison ivy is a monocot? Explain.
9. What is the benefit of cross-pollination over
self-pollination?
10. Which features of a wind-pollinated flower increase
the probability of cross-pollination?
586 MHR • Unit 5 Plants: Anatomy, Growth, and Function
11. A newly discovered flower has 9 petals and both
male and female structures. An aspiring botanist
proclaims that it is a “monoecious monocot!”
Do you agree with this description? Explain.
12. A genetic mutation is discovered that prevents the
flowers of a plant species from opening completely.
Over time this mutation is found in a large portion
of the population. What conclusion can be made
about this plant’s pollination mechanism?
The Life Cycle of Flowering Plants
The development of male and female gametophytes begins in an undeveloped flower.
Inside the flower’s ovary, an ovule containing the embryo sac begins to grow. Inside the
ovule, meiosis results in four haploid megaspores. Usually, three of the four megaspores
disintegrate, leaving one female gametophyte. Mitosis occurs in the remaining
megaspore three times, until the one megaspore contains eight haploid nuclei divided
into seven cells. One of the cells contains two nuclei, which are called polar nuclei.
In the anther, specialized cells undergo meiosis to produce microspores. Each
microspore undergoes mitosis to form a tube cell and a generative cell. A thick,
protective cell wall forms around a microspore. At this point, the microspore is an
immature male gametophyte, which is called a pollen grain.
When the pollen grain lands on a stigma of the correct species, the tube cell forms
a pollen tube. As the pollen tube grows, the generative cell undergoes mitosis, forming
two sperm cells. The pollen grain is now a mature male gametophyte. When the pollen
tube reaches the ovule, it releases the two sperm cells. One fuses with the egg, forming
the zygote—the new sporophyte. The other fuses with the polar nuclei, forming a
triploid (3n) cell that divides to form a nutrient-rich tissue called endosperm. The
endosperm nourishes the embryo as it grows.
The fertilization of an angiosperm egg is called double fertilization, because two
fertilizations occur. After fertilization, the ovule develops into the seed, and the ovary
develops into the fruit. Figure 14.8 summarizes the life cycle of a flowering plant.
Life Cycle of a Flowering Plant
Figure 14.8 The life cycle
of a flowering plant, such
as the peach shown here,
includes gametophyte and
sporophyte generations.
The male and female
gametophytes are
surrounded by sporophyte
tissue.
young
sporophyte
ovary develops into
fruit; ovule develops
into seed
Germination
sporophyte
seed coat
fruit
zygote
develops
into
embryo
embryo
Meiosis
ovule
microspores
3n endosperm
embryo
Fertilization
anther
Meiosis
pollen
grain
pollination
pollen tube
sperm
generative
nucleus
egg
tube
nucleus
mature male
gametophyte
tube nucleus
four
megaspores
female
gametophyte
three megaspores
degenerate
micropyle
three nuclear
divisions of the
remaining megaspore
nucleus take place
haploid (n)
diploid (2n)
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 587
Results of Reproduction
Fertilization is only the beginning of a long process that finally ends with the formation
of a seed. In angiosperms, a seed is part of a fruit that develops from the ovary, and
sometimes from other flower organs.
Seed and Fruit Development
The sporophyte begins as a zygote, or a 2n cell. Numerous cell divisions produce a
cluster of cells that eventually develops into an elongated embryo with one cotyledon
in monocots or two cotyledons in dicots. The 3n cell formed as a result of double
fertilization develops into the endosperm. In some monocots, such as coconuts, the
endosperm is the major component of the seed and makes up most of its mass. In dicots,
the cotyledons absorb most of the endosperm tissue as the seed matures, and they provide
much of the nourishment for the embryo. Figure 14.9 compares monocot and dicot seeds.
Figure 14.9 Seeds
of monocots differ in
structure and function
from those of dicots.
Monocot
seed coat
Dicot
endosperm
seed coat
cotyledon
Identify the embryo’s
food source in each seed.
embryo
embryo
cotyledon
seed coat the hard
outer layers of the ovule
that form a protective
coat around the seed
Activity
14.1
As the endosperm matures, the outside layers of the ovule harden and form a
protective tissue called the seed coat. You might notice the seed coats of beans or peas
when you eat them. The seed coat is the thin, outer covering that often comes off or
loosens as seeds are cooked. Depending on the plant, the ovary can contain one ovule
or hundreds. As the ovule develops into a seed, changes occur in the ovary that lead to
the formation of a fruit.
A fruit forms mainly from the ovary wall. In some cases, the fruit consists of the
ovary wall and other flower organs. For example, the seeds of the apple are in the core,
which develops from the ovary. The juicy tissue that we eat develops from other flower
parts. Other fleshy fruits include peaches and oranges. In contrast, some fruits are dry
and hard, such as walnuts and grains.
Comparing Seeds
In this activity, you will examine the structures of monocot
and dicot seeds.
Safety Precautions
Procedure
1. Obtain a pre-soaked and split bean seed and corn seed
from your teacher.
2. Observe each seed with the hand lens, and gently use
the forceps to examine the structures you see.
• Wear latex (or vinyl) gloves when handling the seeds, since
some seeds are coated with a fungicide to preserve them.
Materials
• bean seed and corn seed that have been soaking in water
and cut lengthwise
• hand lens
• forceps
588 MHR • Unit 5 Plants: Anatomy, Growth, and Function
3. Draw and label the structures you see, including the seed
coat, endosperm, cotyledon, and embryo. If necessary,
use Figure 14.9 to help you.
Question
Use a graphic organizer to compare and contrast the
structures of the corn seed with the bean seed.
Seed Dispersal
As well as protecting seeds, fruits help disperse them. Dispersal of seeds away
from the parent plant increases the survival rate of offspring. This is important
when many plants compete for resources such as light, water, and soil nutrients.
Fruits that are attractive to animals can be transported great distances
away from the parent plant. Animals that gather and bury or otherwise
store fruits usually do not recover all of them, so the seeds might sprout.
Some animals, such as deer, bears, and birds, consume fruits. The seeds
pass through their digestive tracts undamaged and are deposited on
the ground along with the animals’ wastes. Some seeds have structural
modifications that enable them to be transported by water, animals, or
wind, as shown in Figure 14.10.
A water dispersal
B animal dispersal
Figure 14.10 Seeds of
different species are
adapted to be dispersed
in different ways.
Infer the characteristics
of each seed shown here
that suits it for its method
of dispersal.
i d dispersal
C wind
Seed Germination
Once the seeds have been dispersed and land in an area that provides sufficient water,
warmth, and oxygen, they may begin to grow into seedlings or may remain dormant.
As a seed matures, it loses water and enters dormancy, a state in which its metabolic
processes slow down dramatically. Some seeds can remain dormant for hundreds
or thousands of years. The process of resuming growth after being dormant is called
germination. It begins when a seed absorbs water, which causes it to swell and breaks
open the seed coat. The stored food in the endospore or cotyledons begins to break down,
and nutrients are made available to the embryo. The food and the presence of oxygen
allow cellular respiration to occur, which provides energy to the embryo for growth.
The first part of the embryo to appear outside the seed is a structure called the
radicle, which starts absorbing water and nutrients from its environment. The radicle
develops into the plant’s roots, as shown in Figure 14.11. The hypocotyl is the region of
the stem nearest the seed. In many plants, it is the first part of the seedling to appear
above the soil. In some dicots, as the hypocotyl grows it pulls the cotyledons and the
embryonic leaves out of the soil. Photosynthesis begins as soon as the seedling’s cells
that contain chloroplasts are above the ground and exposed to light. In monocots, the
cotyledon usually stays in the ground when the stem emerges from the soil.
germination the
process by which
growth resumes in a
seed after a period of
being dormant
radicle a structure
created by the division
and lengthening of
embryonic root cells
inside a germinating
seed; it develops into the
primary root of the plant
hypocotyl a hookshaped structure in
dicots that eventually
emerges above the
ground as the primary
root grows down into
the soil
first leaves
seed coat
radicle
monocot
cotyledons
first leaf
seed coat
cotyledons
radicle
dicot
monocot
dicot
monocot
dicot
Figure 14.11 As shown here, seed germination differs in monocots and dicots.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 589
Asexual Reproduction in Flowering Plants
SuggestedInvestigation
Inquiry Investigation 14-B,
Techniques of Artificial
Propagation
In asexual reproduction, a parent plant produces offspring that are genetically identical
to it and to each other. Thus, they are clones. Asexual reproduction can be an advantage
when environmental conditions are stable and an organism is well-adapted to its
environment. The genetically identical offspring will also be adapted to that environment.
Table 14.1 Common Techniques of Artificial Propagation
Type of
Vegetative Propagation
What It Looks Like
Purpose or Advantage
Plants Propagated
Using This Method
Division (Splitting)
A plant is split into two or more
pieces, each containing intact
shoots and roots. Daughter
plants are repotted or planted in
a new location, where they grow
independent of the parent.
• simplest, fastest, and most
inexpensive method of
vegetative propagation
• often used to thin out
plants that have spread
over a large area
• bulbs such as tulips and
daffodils
• plants that have more than
one stem, such as peonies,
hostas, geraniums, phlox,
irises, chrysanthemums,
and day lilies
Grafting
A bud, portion of the stem, or
section of the root is cut from
one plant and joined to another
by placing the vascular cambium
tissue of the two pieces in contact
with each other. In cleft grafting
the roots of one plant, called the
rootstock, are split and the stem
section of another plant, the scion,
is inserted into it. The graft is
covered to prevent water loss
from the cut tissue.
• can be used to produce
a plant or tree with
characteristics from two or
more individuals
• can be used to repair
damaged trees
• can significantly shorten
the amount of time needed
before a tree will bear fruit,
since the tree does not have
to grow from a seedling
• fruit trees such as apple
and pear
• nut trees such as walnut
and almond
• grapevines
• ornamental shrubs
• cacti
Leaf Cutting
A leaf, or part of a leaf, is cut from
a plant and placed in a growth
medium, such as potting soil or
vermiculite. Cells near the cut
surface form undifferentiated
meristematic tissue, which
develops into roots or shoots. Shoot
buds grow from the base of the leaf
cutting. The newly developed roots
supply water and nutrients to the
developing shoots, and each shoot
bud forms an independent plant.
• provides genetically
identical copies of a parent
plant
• a simple and inexpensive
method to produce a new
plant faster than it can be
grown from seed
• can be used to “rescue”
leaves that have broken off
a parent plant
• can be taken in any season
• African violets
• begonias
• geraniums
• snake plants (Sansevieria
species)
• succulents such as jade and
aloe vera
Stem Cutting
A shoot tip or part of a stem is cut
from a parent plant and placed in a
growth medium, where it develops
roots. The stem cutting forms an
independent plant.
• provides genetically
identical copies of a parent
plant
• produces a new plant faster
than it can be grown from
seed
• is simple and inexpensive
• depending on the plant,
stem cuttings can be taken
at different times of year
and at various stages of
development, from new
growth in spring to mature
stems at the end of the
growing season
• herbs such as basil, oregano,
rosemary, sage, thyme
• many gymnosperm trees
such as gingko, pine, and
spruce
• many angiosperm trees such
as poplar, willow, and elm
• grapevines
• flowering bushes such as
rose, lilac, rhododendron,
and jasmine
• chrysanthemums
• carnations
• spider plants
590 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Artificial Propagation
In asexual reproduction in plants, also called vegetative propagation, new individuals
are grown from a portion of the roots, stems, or leaves of the existing plant. Artificial
propagation involves using plants’ natural ability to reproduce vegetatively. This
process enables farmers and gardeners to select the parent plants for specific traits.
Table 14.1 shows some common artificial propagation techniques.
Type of
Vegetative Propagation
What It Looks Like
Purpose or Advantage
artificial propagation
the cloning of a plant
from a portion of its
roots, stems, or leaves
Plants Propagated
Using This Method
Root Cutting
A small section of a root is cut
from a parent plant and placed in
a growth medium. Root cuttings
are placed vertically in the growth
medium, with the bottom end—
the end of the cutting that was
closest to the root tip—pointing
downward. Root cuttings
from smaller plants are placed
horizontally on a bed of soil and
covered by a thin layer of compost.
The bottom end of the cutting
develops into a new root system,
while the top end develops into
the shoot system. The root cutting
forms an independent plant.
• provides genetically
identical copies of a parent
plant
• produces a new plant faster
than it can be grown from
seed, or from leaf or stem
cuttings
• simple and inexpensive
• provides a way to propagate
plant material when it is in
its dormant stage, in late
autumn or early spring
• provides an alternative
form of vegetative
propagation for plants that
do not easily form roots
from stem or leaf cuttings
• cattails
• irises
• goldenrods
• trilliums
• hostas
• periwinkle
• mint
• rhubarb
• ginger
• fennel
• oregano
• thyme
• sage
Simple Layering
In plants with long vine-type stems
or low-hanging branches, a
section of stem is bent to touch the
ground. Then it is cut to promote
the growth of roots. The wounded
part of the stem, still attached to
the parent plant, is then buried
in the ground. Once a new root
system has developed, the stem is
cut away from the parent plant and
can grow independently.
• produces a plant that is
genetically identical to the
parent
• a large, mature daughter
plant can be produced
faster than it can be grown
from seed
• water and nutrients from
the parent plant support
root growth, which speeds
up the rooting process
• climbing roses
• grapevines
• rhododendrons
• honeysuckle
• junipers
• willows
• rosemary
• hibiscus
• hydrangeas
Air Layering
A strip of outer bark is removed
from a woody stem. Moist
sphagnum moss is packed around
the wounded part of the stem.
Plastic is wrapped around the
moss and secured tightly to the
stem to prevent water loss. Once
a new root system has developed,
the stem is cut away from the
parent plant and planted in soil,
forming an independent plant.
• produces a plant that is
genetically identical to the
parent
• a large, mature daughter
plant can be produced
faster than it can be grown
from seed
• can be performed on
woody plants or small trees
that cannot be propagated
using simple layering or
cuttings
• tropical plants such
as rubber trees (Ficus
species) and dumb canes
(Dieffenbachia species)
• magnolias
• rhododendrons
• azaleas
• holly
• lilacs
• fruit trees such as apple,
pear, and orange
• nut trees such as pecan
Cell Culturing (Tissue Culturing)
An individual cell or a small piece
of plant tissue is placed in or on
a sterile nutrient medium that
contains chemicals that promote
shoot and root growth. Tiny
plantlets develop from the parent
plant tissue, and these are planted
in soil or another solid growth
medium to mature.
• used to produce large
• a huge variety of
numbers of genetically
bryophytes, ferns,
identical plants; a small
gymnosperms, and
piece of parent tissue can
angiosperms
yield a million plantlets in
• some species cannot be
a year
propagated using this
• can be used to generate
method due to lack of
plants from genetically
knowledge about the
modified plant cells
nutrient medium that will
• used to establish collections
support the tissue culture
of endangered plants
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR
591
Section 14.1
RE V IE W
Section Summary
• Flowers are the reproductive structures of plants, and
they include four main organs: sepals, petals, stamens,
and pistils.
• Plant seeds disperse away from their parent plant
through the action of wind or animals such as insects
and mammals.
• There are three key stages in the haploid part of the plant
life cycle: development of pollen cells, development of
eggs, and fertilization.
• Plants can propagate sexually through seeds or asexually
by vegetative propagation. In vegetative propagation, also
called artificial propagation, new individual plants are
grown from a portion of the roots, stems, or leaves of an
existing plant.
• Fertilization ends when a seed is formed. Seeds are
usually contained in a mature ovary called a fruit and
surrounded by a protective seed coat.
Review Questions
1.
K/U Why is water required for seedless plant
fertilization?
2.
T/I A species of flower is genetically engineered to
grow without sepals. Make a prediction about the
ability of this new plant to reproduce.
3.
10.
11.
Make a sketch of the germinating seed shown
below and label the radicle and hypocotyl. Name the
structure, which is hidden from view in this photo, that
will play a crucial role in the plant’s early life.
C
4.
K/U Make a labelled sketch to show the process of
double fertilization in angiosperms.
5.
In monocots the endosperm is a large portion
of the seed, while in dicots this structure is virtually
absent. Explain the absence of the endosperm in
dicots.
6.
C
Construct a table that lists animals associated
with pollination and the plant features that assist in the
attraction.
7.
K/U An organism that has both male and female
reproductive organs is called a hermaphrodite. In
humans and many other animal species, this is quite
rare, but in the plant kingdom the opposite is true.
What structures are associated with these
hermaphroditic plants, and what general term is used
for these plants?
8.
9.
K/U
K/U Describe the role of meiosis in the reproduction
of angiosperms.
592 MHR • Unit 5 Plants: Anatomy, Growth, and Function
A
Various flavours of honey are specific to certain
geographic regions around the world. Suggest one
reason why honey is not consistent in taste.
K/U
Describe three methods of fruit seed dispersal.
C
Copy the Venn diagram below into your
notebook to compare and contrast germination in
monocots and dicots.
Monocot
Both
Dicot
12.
K/U In monocots and dicots germination occurs in
the absence of light. For the first few days the seed
relies on its own energy stores. In which structures of
the plants are these energy stores found?
13.
T/I When plant cuttings are taken the sample is
placed in a growth medium. In addition to water, what
substances might this medium contain?
14.
Study the diagram below.
a. Identify the vegetative propagation technique
shown.
b. What feature will make the resulting plant unique?
15.
A
K/U
Table 14.1 summarizes vegetative propagation
techniques. What advantages do these techniques offer
over traditional farming?
SECTION
Plant Growth and Development
14.2
When a seed germinates, the further development of the plant depends on the activities
of the meristematic tissues, which interact with the environment. The shoot and root
apical meristems differentiate into all the other cells of the adult plant. But what makes
one cell of a plant embryo develop to become a conducting cell and another develop
to become an epidermal cell? It depends on which genes are turned on or off in the
embryo cell. Plant hormones play a role in determining cellular differentiation and,
therefore, in which genes are expressed in any given cell.
Key Terms
hormone
apical dominance
nastic response
tropism
phototropism
gravitropism
thigmotropism
Plant Hormones
Plants produce chemical compounds, called hormones, that act as chemical signals
between cells and tissues in different parts of the plant. Some hormones stimulate
growth activity in the plant, while others inhibit growth activity. Because they regulate
growth, plant hormones are often called plant growth regulators.
The five main plant hormones are auxins, cytokinins, gibberellins, ethylene,
and abscisic acid. Table 14.2 outlines their main functions. Additional information
about each of these hormones is provided on the next pages. Keep in mind that plant
hormones rarely act independently of one another. In fact, they usually interact in
various complex ways to regulate the differentiation of plant cells and the responses of
plants to a given stimulus, such as light level, gravity, and touch.
hormone a chemical
compound produced
in one part of the plant
that controls growth
activity in another part
of that plant
Table 14.2 Some Key Functions of Major Plant Hormones
Hormone
Selected Key Functions
Where Produced or Found in Plant
Stimulatory Hormones
Auxins
• stimulate cell division and
elongation in stems and roots
• regulate cell expansion in plant
responses to light and gravity
• developing leaves and seeds
• shoot tips
Cytokinins
• stimulate cell division
• prevent ageing of leaves
• root tips
Gibberellins
• stimulate cell elongation
• stimulate seed germination
• young shoots
• developing seeds
Inhibitory Hormones
Ethylene
• promotes ripening of fruit
• all parts, especially when under
stress, ageing, or ripening, as
shown below in Figure 14.12
Abscisic acid
• induces and maintains seed
dormancy
• inhibits shoot growth
• closes stomata
• mature leaves
• plants under stress
Figure 14.12 Bananas
and other fruits ripen due
to ethylene.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 593
apical dominance a
condition of a plant
stem in which growth
is mainly upward, with
little growth laterally
from side branches
Auxins
The term auxins (from a Greek word that means “to increase”) refers to a group of
compounds that stimulate the elongation of plant cells. One of the most commonly
occurring auxins is indoleacetic acid (IAA), which is produced in apical meristems,
buds, young leaves, and other tissues that grow rapidly. Many popular weed killers
contain a synthetic auxin that is very similar to IAA, called 2,4-D. The synthetic
compound works by accelerating growth so much that a plant quickly uses up its food
reserves and effectively starves to death.
Auxins produced by the apical meristem create an effect called apical dominance,
in which plant growth is mostly upward with few or no side branches. Removing the
apical meristem decreases the amount of auxin present, which promotes the growth of
side branches, as shown in Figure 14.13.
The effect of auxins in a plant varies depending on its concentration and location.
In some plants the concentration of auxin that promotes stem growth can inhibit root
growth. Low concentrations of auxin usually stimulate cell elongation, but at higher
concentrations, auxin can have the reverse effect.
A Apical meristem intact
B Apical meristem removed
Figure 14.13 (A) Auxin
stimulates apical meristem
growth and inhibits the
growth of side branches.
(B) Removing the apical
meristem decreases the
amount of auxin. As a result,
side branches grow.
side branch
Cytokinins
Cytokinins promote cell division and differentiation. Cytokinins promote cell division
by stimulating the production of the proteins needed for mitosis and cytokinesis.
Cytokinins also delay the ageing of leaves and fruit. The presence of other hormones,
especially auxins, influences the effects of cytokinins. For example, IAA alone stimulates
cell elongation. When IAA is combined with a cytokinin, it promotes rapid cell division
and, thus, rapid growth.
Gibberellins
Like auxins, gibberellins are produced in the apical meristem, and there are many
different kinds. Gibberellins are transported in the vascular tissue. They stimulate plant
growth by changing the plant’s cell walls, stop dormancy in seeds, and can reverse
genetic dwarfism in plants.
Gibberellins promote the growth of taller, stronger plants and plants that flower
early. They are used in commercial crops all over the world to increase fruit size and
to increase cluster size in grapes. Finding ways to increase fruit yield means that more
food can be produced with a similar amount of effort. However, increasing yield can
also create problems. Grapes, for example, require extra care because the vines do not
naturally support such heavy fruit.
594 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Ethylene
Ethylene, which is the only known gaseous hormone, is in the tissues of ripening fruits,
dying leaves, and flowers. Since ethylene is a gas, it can diffuse through the spaces
between cells. It is also transported within the phloem. Although ethylene can affect other
parts of plants, it mainly affects the ripening of fruits. Ethylene weakens the cell walls of
unripe fruit and breaks down complex carbohydrates (such as starches) into simple sugars
(such as sucrose and fructose). Because ripe fruits and vegetables are bruised easily during
shipping, growers often pick and ship unripe fruits and vegetables. Once they reach their
destinations, a treatment with ethylene is used to speed up the ripening process.
Abscisic Acid
Synthesized in mature green leaves, fruits, and root caps, abscisic acid (ABA) is a plant
hormone that generally inhibits growth. ABA inhibits the growth of buds in plant
stems and blocks the intake of carbon dioxide by controlling the opening and closing of
leaf stomata. Abscisic acid also blocks the action of growth-promoting hormones.
Learning Check
13. What is the main function of plant hormones?
14. What are two functions of abscisic acid?
15. What role do hormones have in early plant
development?
16. Identify two hormones farmers rely on to improve
crop yield and quicken the ripening process.
18. A group of students plants bean seeds. One plant
grows rapidly, and within three weeks it is twice the
height of all the others. The students conclude that
this plant has a genetic variation causing excessive
auxin production. List five questions you would
ask about the scientific validity of these results and
conclusion.
17. Explain why cutting or trimming a plant often
causes it to become bushier.
Plants Responses to Environmental Stimuli
The leaves of house plants grow toward light-bringing windows, vines climb trellises,
and roots grow downward and around obstructions. These are examples of how plants
respond to stimuli in their environment. A stimulus can cause a plant to grow toward
it or away from it. This kind of plant growth is called a tropism or a tropic response.
Tropisms are discussed on the next page.
Alternatively, a plant’s response to a stimulus may be independent of the direction
of the stimulus. Such a response, called a nastic response, is not a growth response, is
reversible, and can be repeated. An example is the opening of flower petals during the day
and the closing of petals at night to conserve heat. Figure 14.14 (B) shows another example.
Before
nastic response a
plant’s movement in
response to a stimulus
that is not associated
with the direction of the
stimulus
After
Figure 14.14 Nastic movements in the leaves of this sensitive plant (Mimosa pudica) are caused
by changes in water pressure in the leaf cells. When the stimulus ends, the leaves return to their
original orientation.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 595
tropism a plant’s
growth response to
external stimulation
coming from one
direction in the
environment
phototropism a plant’s
growth response to light
gravitropism a plant’s
growth response to
gravity
thigmotropism a
plant’s growth response
to touch or contact
Tropic Responses
A tropism is the growth response of a plant to an external stimulus. If the resulting
plant growth is toward the stimulus, it is called a positive tropism. If the resulting plant
growth is away from the stimulus, it is called a negative tropism. Three main types of
tropism are phototropism, gravitropism, and thigmotropism.
Phototropism, shown in Figure 14.15, is a growth response to light caused by an
unequal distribution of auxin. There is less auxin on the side of the plant toward the
light source than there is on the side away from the light source. Because auxin can
cause cell elongation, the cells on the side away from the light elongate, making that
side of the stem longer. As a result, the stem curves in the direction of the light.
Gravitropism is a growth response to gravity. Roots generally show a positive
gravitropism. The downward growth of roots into soil helps to anchor the plant and
brings roots in contact with water and minerals. However, a stem exhibits a negative
gravitropism when it grows upward, pushing against gravity. This growth positions
leaves for maximum exposure to light.
Thigmotropism is a growth response to mechanical stimuli, such as contact
with an object, another organism, or even wind. Thigmotropism is evident in vines
that twist around a nearby structure, such as a fence or tree.
Figure 14.15 This plant
is growing toward the
light coming in through
the window.
Activity
14.2
Exploring Gravitropism
Safety Precautions
2. Place five seeds on top of the paper towels. Apply a small
drop of glue to the top of each seed. Press the bag flat to
affix the seeds to the plastic. Allow glue to dry for several
minutes.
• Handle glue carefully to avoid skin contact.
3. Use strong tape to fix the plastic bag to a wall. Leave the
bag unsealed so the seeds are exposed to air.
Examine what happens to the growing tissue of sprouted
seedlings if their orientation to the ground changes.
Materials
•
•
•
•
•
•
paper towels
5 seeds (such as peas, radish, navy bean)
resealable plastic bag
glue
tap water
strong tape (or thumbtacks)
Procedure
1. Fold several layers of paper towels so they will fit inside
a plastic bag. Wet them with water so they are moist but
not dripping wet. Place the folded towels inside the bag.
596 MHR • Unit 5 Plants: Anatomy, Growth, and Function
4. Observe the growth of the seeds over a few days. When
the roots have grown to at least 2 or 3 cm, gently turn
the bag and reattach it to the wall at a different angle.
5. Predict how the roots and stems will respond to the
change in orientation. After a few days, record your
observations.
Questions
1. Explain how turning the bag affected the direction of
root and stem growth.
2. Were your predictions accurate? Explain why or why not.
Other Factors That Affect Plant Growth
You have learned that internal regulators (hormones) affect plant growth, as do stimuli
from the external environment (tropisms). Light energy from the Sun, along with
carbon (from carbon dioxide in the air around the plant) and water are also essential
requirements for plants to produce their own food through photosynthesis. A plant
gets most of the water it needs from the soil in which it grows. Soil water is also a
source of dissolved nutrients, which plants need to carry out growth, reproduction,
and other cellular processes that sustain their lives.
SuggestedInvestigation
Plan Your Own Investigation
14-C, Factors That Affect
Plant Growth
Nutrients
Most plant nutrients are available in the form of dissolved chemical compounds and
ions. Nutrients needed in amounts greater than 1 percent of a plant’s dry weight are
called macronutrients, and they include nitrogen, potassium, calcium, magnesium,
phosphorus, and sulfur. Micronutrients, which are needed in much smaller amounts,
are chlorine, iron, boron, manganese, zinc, copper, and molybdenum. Some key
functions of these nutrients are listed in Table 14.3.
Table 14.3 Important Plant Macronutrients and Micronutrients and Their Functions
Plant Nutrient
Percent of Plant’s Dry Weight
Selected Functions
nitrogen (N)
1.5
Part of chlorophyll, proteins, nucleic acids
potassium (K)
1.0
Controls opening and closing of stomata
calcium (Ca)
0.5
Component of cell walls and membranes
magnesium (Mg)
0.2
Part of chlorophyll; needed to make proteins
phosphorus (P)
0.2
Part of proteins, nucleic acids, and cell
membrane
sulfur (S)
0.1
Part of many proteins
chlorine (Cl)
0.01
Water balance (osmosis)
iron (Fe)
0.01
Part of chlorophyll and some proteins
boron (B)
0.002
Growth of pollen tubes and sugar transport
zinc (Zn)
0.002
Part of many proteins and hormones
manganese (Mn)
0.005
Photosynthesis
copper (Cu)
0.000 6
Part of proteins; helps in formation of
lignin and xylem
molybdenum (Mo)
0.000 01
Helps plant use nitrogen and produce
abscisic acid
Soil pH
Soils typically range from being slightly or somewhat acidic to slightly basic (or
alkaline). Recall that the pH scale is used to identify substances as acidic, basic, or
neutral. The scale ranges from 0 to 14, with the mid-point of the scale, 7, being neutral.
Substances with pH values less than 7 are acidic, with the strength increasing as the
values decrease. Substances with pH values greater than 7 are basic (alkaline), with
strength increasing as the values increase.
Most plants grow well within only a very narrow range of pH values. For example,
most plants thrive in slightly acidic soils ranging from pH 6 to 7. Common examples
include pine, spruce, dogwood, blueberry, hydrangea, magnolia, holly, potatoes,
peanuts, and cranberries. Fewer plant species tolerate basic soils of pH 7 to 8. Examples
include geraniums, petunias, lawn grass, beans, beets, lettuce, pears, and plums.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 597
STSE
BIOLOGY Connections
Plants and Their Defences
When you think of a food chain, you might picture a predator
stalking and capturing prey. However, plants are sessile—they
cannot move away from herbivores. How do plants defend
themselves against their predators? Understanding plant
chemical defences helps humans devise strategies to protect
crops and other vegetation.
DEFEND OR DIE Some plants have evolved adaptations, such
as hairs, spines, prickles, or thorns on the surface of leaves or
stems, to repel predators. Others, such as horsetail, have silica
inside their leaves, which makes them tough to eat and wears
down the predator’s teeth.
Many plants produce secondary chemical compounds
not needed for plant metabolism. These substances might
taste bitter or be toxic to the predator. Some interfere with
the predator’s digestion, growth, or reproduction. In 2005,
researchers discovered that the roots of a type of cabbage
produce substances that protect the plant by killing a wide
variety of bacteria in the soil.
Plants can distinguish between an insect
attack and other types of damage, such as pruning. Scientists
have learned that some plants respond to certain chemicals in
insect saliva. For example, a team of biochemists determined
that when an insect nibbles on a plant’s leaves, a chemical
signal spreads throughout the plant. This signal stimulates
increased toxin production by all the leaves—not just the
attacked leaves.
INSECT OR NOT
CALLING FOR HELP When some plants are damaged by
herbivores, the plant releases chemical signals that attract
natural enemies of the herbivores. For example, the cabbage
plant in the photograph guides a parasitic wasp (Cotesia
glomerata) to the caterpillar (Pieris brassicae) eating the
cabbage leaves.
Chemical labelling studies confirmed that the signalling
chemicals are not stored in the undamaged plant. Plants
develop and release the signals soon after damage begins,
and release them most strongly during the time when the
natural enemies are most active. Also, different herbivores
elicit different signals from a plant. Although advances in
chemical technology and biotechnology are speeding the
discovery of natural plant signals that might help protect
crops, there is evidence that these signals might also help
herbivores locate food.
Connect to the Environment
Suppose that you have developed a pesticide based on natural
plant defences. Write a magazine advertisement for your
product. Describe how it works and why it is environmentally
friendly. A partner will then write an email to the magazine’s
editor in response to your advertisement, pointing out
potential environmental drawbacks to the product. In a group,
discuss and evaluate the two points of view.
When caterpillars feed on cabbage leaves, the
plant releases chemical compounds into the air
that attract a parasitic wasp. The wasp paralyzes
the caterpillar and then lays eggs on its body.
After the eggs hatch, the wasp
larvae consume the caterpillar.
598 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Section 14.2
RE V IE W
Section Summary
• Plant growth after fertilization begins with the process of
germination.
• Plants manufacture many hormones or growth
regulators, including auxins and gibberellins. Each
serves a specific purpose, usually related to growth or
the inhibition of growth.
• Plant tropisms are growth responses to environmental
stimuli that include light (phototropism), gravity
(gravitropism), and touch or contact (thigmotropism).
• In addition to hormones, light, and water, other factors
that affect plant growth include availability of soil
minerals (nutrients) and soil acidity (pH).
• Plants respond to their environment with nastic
responses, which are reversible, and with tropic
responses, which are irreversible.
Review Questions
A
Topiary is the art of moulding shrubs into
specific shapes through cutting, trimming, and
pruning. An example is shown below. When a final
shape is complete, two hormones can be administered
to the plant to preserve its shape. Which hormones
are best suited for this task? Explain your answer.
2.
A
How has knowledge of plant hormones
contributed to the invention of herbicides?
3.
T/I Suppose that you are doing an investigation
with plants that are unable to produce auxins. You
place the plants on a bright windowsill in a dark room.
Predict what you will see when you make observations
after five days. Explain your reasoning.
4.
5.
6.
The Niagara region of Ontario is famous for its
grapes. If grape vines were treated with gibberellins, list
two accommodations that would have to be made to
ensure the effects of the treatment were maximized.
7.
K/U Distinguish between micronutrients and
macronutrients.
8.
C
Draw a spider map illustrating plant hormones
and their functions. Make connections associating each
hormone with its respective function(s). For hormones
with an inhibitory effect, use an arrow with an “X” over
it. Use Table 14.2 as your primary data source.
9.
A
A Niagara grape grower tries to maximize profit.
The grower plants a new species of grape that has been
engineered without thigmotropism. This ensures that
all available energy goes into grape production. Is this
a good investment? Explain fully.
10.
T/I What is the long-term outcome of a plant that
demonstrates only negative gravitropism?
11.
T/I A researcher has been studying the effects of
gibberellins placed on the roots of bean plants. The
graph below shows the results of placing different
concentrations of gibberelin on the roots. Write a
suitable inference based on the data in the graph.
Increase in height after
10 days (mm)
1.
K/U
A student works at a greenhouse that only has
windows facing south. The placement of the plants must
be rotated each day. Explain why this is an essential part
of the student’s job, and describe the hormone response
in the plants that makes this task necessary.
K/U
K/U Describe two situations in which a plant needs
to produce abscisic acid.
60
50
40
30
20
10
0
0
200
400
600
800
Concentration of gibberellin (ppm)
12.
13.
K/U
How does acid rain affect a pine forest?
A
A student is conducting an experiment comparing
soil pH and plant growth. To ensure scientific validity,
the student makes a list outlining the independent
variable, three possible dependent variables, and three
factors that must remain constant between trials. What
would you expect to see in the list?
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 599
SECTION
14.3
Key Terms
ecological succession
primary succession
pioneer species
climax community
secondary succession
Figure 14.16 (A) Herbivores,
such as this deer, depend
on plants directly for food.
(B) Other organisms, such
as raccoons, use plants as
a home. (C) Wetlands are
excellent water filters.
Succession and Sustainability
As you learned in Chapter 13, plants provide many important ecosystem services,
including providing humans with sources of fibre, fuel, pharmaceuticals, and beauty.
As primary producers, plants provide food for many organisms either directly or
indirectly, as shown in Figure 14.16. From the canopy created by tall trees in a forest
to small pools of water that collect in leaves of plants, plants provide habitat for many
organisms. Through photosynthesis, plants release oxygen into the atmosphere and
take up carbon dioxide, serving as a sink for CO2. Plants are also involved in the
cycling of nutrients, such as nitrogen and phosphorus, through global systems. Plants
detoxify and decompose waste materials, generate and revitalize soil, and purify the
air. The presence of plant roots helps reduce soil erosion. Plants, such as those in the
wetlands shown in Figure 14.16, are natural water filters, removing chemicals and
other pollutants from water. Plants also play a role in establishing and developing
communities, a process known as ecological succession.
A
B
C
Plants as Ecosystem Pioneers
ecological succession
the change in an
ecosystem that happens
when one community
replaces another; it
results from changes in
abiotic and biotic factors
An event that changes the structure of a biological community—sometimes destroying
all actively growing organisms—is called an ecological disturbance. Examples of
ecological disturbances include forest fires, floods, volcanic eruptions, and retreating
glaciers. Following an ecological disturbance, an area may appear barren. Within
months, however, new vegetation may sprout, and then animals may repopulate
the area. Years later, the same area will likely be thick with life. This process, called
ecological succession, is the sequence of invasion and replacement of species in an
ecosystem over time. Succession is driven by abiotic factors, such as climate, and biotic
factors, such as competition for changing available resources.
600 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Primary Succession
Primary succession is the establishment of a community in an area after an ecological
disturbance has left exposed rock that does not have any topsoil. For example, bare rocks
left behind by a retreating glacier and the hardened bed of lava from a volcanic eruption
have no topsoil. Plant species play an important role in primary succession. In some
cases, plants, such as liverworts, are one of the first species to colonize a barren area. The
first organisms that appear in primary succession are called pioneer species. Pioneer
species, which can include bacteria, algae, lichens, and plants, form a pioneer community.
The first species in a pioneer community are usually small, opportunistic organisms
that can grow in harsh conditions. Soil starts to form as some of these organisms die.
As the soil builds up, its nutrient content, moisture content, and pH change, as shown
in Figure 14.17 (A). This allows larger species, such as mosses, to grow in the area.
Grasses, annual herbs, shrubs, and trees follow, thus expanding the diversity of species,
as shown in Figure 14.17 (B).
Changes in Soil Nitrogen
during Primary Succession
B
Number of Plant Species
Nitrogen Concentration
(g/m2 of surface)
A
300
250
200
150
100
50
0
Time
Changes in Number of Plant
Species during Primary Succession
50
40
30
primary succession the
establishment of a
community in an area of
exposed rock that does
not have any topsoil
pioneer species the
first organisms to appear
in primary succession
Figure 14.17 Scientists
measured changes in the
nitrogen content and the
number of plant species
during primary succession
in Glacier Bay, Alaska.
Describe how the nitrogen
concentration in soil
changed over time.
20
10
0
50
100
150
Years
(A) When primary succession begins, there is
no soil and very few nutrients available to the
organisms. As the organisms die and soil builds
up, so do soil nutrients, including nitrogen.
Organisms from different species can then
use the nutrients from the soil. They may also
change the composition of the soil.
(B) By studying different sites from which a
glacier had retreated, ecologists found that
plant diversity increased in the first 200 years
of primary succession, and then levelled off.
As the plants grow, they compete for light and living space. Some populations are
better able to survive the competition and the changing habitat. These populations
replace those that are not able to survive. Animals may join the community and, as the
species of plants change, so do the species of animals. The latecomers in the process of
succession form a climax community. This community may remain relatively stable
if there are no major environmental changes. Figure 14.18 shows the changes in plant
composition as a community undergoes primary succession.
climax community the
final stage of ecological
succession
Figure 14.18 Succession
is a gradual change in
community structure,
beginning with a pioneer
community and leading
toward a climax community.
grass
low shrub
pioneer community
high shrub
shrub-tree
low tree
high tree
climax community
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 601
Secondary Succession
secondary succession
the changes that take
place in an ecosystem
that has been damaged,
or in communities that
have been destroyed
but the soil has
remained intact
0
Secondary succession is the recolonization of an area after an ecological disturbance in
which soil has remained intact. For example, soil, which contains nutrients and organic
matter, usually survives disturbances such as forest fires, floods, and agricultural activity.
Often, the seeds and roots of vascular plants remain buried in the soil, as do the spores of
ferns and mosses. In fact, some plant species produce seeds that will germinate only after
they are exposed to the extreme heat of a forest fire. The jack pine (Pinus banksiana) and
the lodgepole pine (Pinus contorta) are two examples of this. This adaptation ensures
that there will be plenty of light and nutrients available for new seedlings.
Like primary succession, secondary succession, shown in Figure 14.19, includes
changes in the composition and number of species over time. The stages of succession
may occur over weeks in an area recovering from a flood. In other areas, such as a
new forest, succession may continue for 150 years. According to the classical model
of succession, once the climax community has developed, it will remain stable unless
there is a major ecological disturbance.
Annual
plants
Shrubs
Grasses/
herbs
Pines
Young oak/
hickory
Pines die,
oak/hickory
mature
1–2 years
3–4 years
4–15 years
5–15 years
10–30 years
50–75 years
Mature
oak/hickory
forest
Figure 14.19 Secondary succession is a series of changes that leads to a mature community.
Frequency of Ecological Disturbances
SuggestedInvestigation
Plan Your Own Investigation
14-D, Succession of
Microbial Organisms
In the past, scientists believed that ecological disturbances did not occur very often.
However, ecologists now think that ecological disturbances are the norm rather
than the exception in many communities. Even a tree falling in a rainforest creates a
small ecological disturbance. This kind of event, and larger disturbances such as the
clearcutting of a forest, open a space in the canopy, allowing light to hit the ground
and secondary succession to occur. Thus, ecological disturbances are important for
many plants. Research shows that the magnitude of a disturbance affects the types of
organisms that will later inhabit an area. Spruce (Picea), a shade-tolerant plant, does
well following a small ecological disturbance in a forest. A large disturbance in a forest
provides plenty of light and allows shade-intolerant plants, such as the lodgepole pine,
to flourish. Ecological disturbances are also important for animals. The berry bushes
that grow up a few years after a forest fire are an important food for grizzly bears as
they gain body mass in preparation for hibernation.
Ecologists must consider how ecological disturbances affect different species when
trying to establish—or preserve—healthy natural communities. Understanding the role
of ecological disturbances in structuring communities is currently an important area of
investigation in ecology.
602 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Learning Check
19. Make a spider map to organize the ecosystem
services of plants.
20. What is ecological succession?
21. What is the difference between primary succession
and secondary succession?
22. Explain the role of ecological disturbances in the
structure of a community.
23. If you were volunteering to help revitalize a forest
after it had been destroyed by a mudslide, why
would it be important to understand what the
pioneer species for the region are?
24. Name at least two places where you could observe
succession occurring in an urban area.
Plant Biodiversity and Ecosystem Resilience
Recall from Chapter 1 that ecosystems with greater species diversity have better
resilience—the capacity to survive changing conditions. This is particularly true
when it comes to plant diversity. A long-term study completed by researchers at the
University of Minnesota showed that as the number of plants species increased in an
ecosystem, the stability of the ecosystem also increased. Ecosystems with high diversity
are better able to withstand disruption, such as disease, competition from invasive
species, and extreme weather events such as a drought. When there is a high diversity
of plants in an ecosystem, it is more likely that at least some plants will survive a
disruption to the ecosystem.
Plants, Sustainability, and the Biosphere
You have read about the ecosystem services of plants and of the ecosystems they
inhabit. All of the ecosystem services of plants benefit the biosphere, which includes all
organisms living on Earth. Maintaining sustainable natural ecosystems, such as forests,
wetlands, and coral reefs, and human-made ecosystems, such as agricultural systems, is
critical to the health of the biosphere. Plants play an important role in ecosystems and
in the biosphere as a whole.
As shown in Figure 14.20, when viewing Earth from space,
the green leaves of plants are the most prominent evidence of
the biosphere. When plants are removed from ecosystems, their
importance as the anchor for an ecosystem becomes evident. For
example, when large areas of rainforest are cleared, the conditions
of that area change drastically. Soil erosion increases, water cycling
changes, and the habitats and food sources for many animals are
destroyed. The University of Minnesota researchers found that
diverse grasslands, the ecosystem in which they collected data, were
240 percent more productive than grasslands with only one plant
species. Plants are of critical importance in issues ranging from food
security and sustainable agriculture to biofuels and global climate
change. In addition to providing food, fuel, and materials for shelter,
plants are sources of medicine and sinks for carbon dioxide. Plants
also serve vital roles in conserving the biodiversity of Earth and
ensuring the sustainability of the biosphere.
Figure 14.20 “Looking outward to the blackness of space, sprinkled with
the glory of a universe of lights, I saw majesty—but no welcome. Below
was a welcoming planet. There, contained in the thin, moving, incredibly
fragile shell of the biosphere is everything that is dear to you, all the human
drama and comedy. That’s where life is; that’s where all the good stuff is.”
—Astronaut Loren Acton
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 603
Section 14.3
RE V IE W
Section Summary
• Plants provide ecosystem services such as adding
nutrients to soil, draining and filtering water, and
providing food and oxygen for other organisms.
• Ecological succession is the changes that occur in
ecosystems as one community replaces another after
a disturbance.
• Primary succession occurs when there is no soil for plants
to grow in.
• Secondary succession occurs when the ecosystem has
been damaged but there is still soil.
• The greater the plant diversity in an ecosystem, the more
resilient the ecosystem is to disturbances.
Review Questions
1.
K/U What is the role of the pioneer species in
primary succession?
2.
K/U Is the climax community that results from
secondary succession likely to be the same as the
climax community before secondary succession was
forced to take place? Explain your answer.
10.
T/I Describe an example of an ecological
disturbance that could benefit wildlife.
11.
What processes and events contribute to
succession?
T/I You come across an abandoned mining town
where the processing of the mine has polluted the
surrounding area so much that the plants and animals
have all died or left the area. Assume that the polluted
area will grow back. What would you expect to see
growing in the area in about five years? Explain why.
12.
T/I How does plant diversity enhance the survival
rates of wildlife?
13.
A
Clearcutting, shown below, involves the cutting
and removal of all trees in a given area of forest.
3.
4.
C
Create a flowchart or other concept organizer to
show the process of succession at the base of a volcano,
beginning after an eruption. Assume that it takes
100 years for a climax community to form and that
the volcano erupts every 100 years.
5.
T/I How could you test the hypothesis that mosses
and lichens play a role in secondary succession?
6.
How is plant diversity linked to ecosystem
resilience?
7.
A
Some people have suggested that the value of
the ecosystem services provided by plants should be
translated into a dollar amount. How do you think this
would affect society’s opinions on the importance of
maintaining sustainable ecosystems?
8.
Copy the table below into your notebook. Fill
in the blanks to compare primary and secondary
succession. Give the table a title.
9.
K/U
14.
T/I Explain why succession in the desert does not
result in a rainforest climax community.
15.
C
After fire destroyed much of the plant life in a
park, wildlife officials suggested that people could help
the park recover by planting their own plants and trees
and feeding wildlife such as rabbits and deer. Write a
supported opinion piece with your views of the
advantages and disadvantages of humans intervening
in the natural processes of recovery in an ecosystem.
16.
List five contributions that living trees make to
a community.
Secondary
Succession
Where?
When?
Sequence of
events?
How fast?
Leads to?
604 MHR • Unit 5 Plants: Anatomy, Growth, and Function
K/U
a. What changes to ecosystems do you think occur
when clearcutting is done?
b. What type of succession occurs after an area has
been clearcut?
c. What types of plants would grow in the area after
clearcutting has occurred?
C
Primary
Succession
K/U Define ecological disturbance and provide three
examples.
A
Inquiry
INVESTIGATION
14-A
Skill Check
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Safety Precautions
Comparing Flowers and Their Structures
In this investigation, you will examine the different structures of flowers.
Pre-Lab Questions
1. How can you identify a monocot or dicot from its flowers?
2. What are the organs found in flowers?
3. What is the difference between a perfect and an imperfect flower?
• Always wash hands before and
after handling plant materials.
• Use extreme care when handling
the scalpel.
Materials
• whole flowers (various species)
Question
How do the structures of flowers vary?
Procedure
1. Obtain flowers of several different species from your teacher.
• forceps
2. Identify the organs of each flower, making note of the similarities and
differences. Record the number of petals, sepals, stamens, and/or pistils
for each flower.
• scalpel
3. Carefully remove some petals and sepals and observe the pistil.
• magnifier or dissecting microscope
4. Draw a diagram of at least one of your flowers. Label all of the structures.
5. Select a flower with a large pistil. Use a scalpel to carefully make a vertical
incision through the pistil and ovary. Draw and label a diagram of the inside
of the pistil.
Analyze and Interpret
1. Compare and contrast the structures of the flowers you observed.
2. Although sepals and petals do not have a reproductive function, they are
important to the success of reproduction. Explain why.
3. a. What feature of the stigma makes it suited for capturing pollen grains?
b. What feature of a pollen grain makes it suited for being brushed off
onto animals?
Conclude and Communicate
4. Without referring to your notes or this textbook, sketch a flower and label
as many reproductive organs and structures as you can. Include their
functions.
Go to Biological Drawing in Appendix A
for help with making your diagrams.
Extend Further
5. INQUIRY Spring winds blow millions of pollen grains through the air at
once. Based on your observations, how do you think seed-bearing plants
prevent their egg from being fertilized by sperm from a different species?
Write a hypothesis for an investigation to test your ideas.
6. RESEARCH Unlike humans, pollinating birds and insects can see ultraviolet
light. Research to find out how different flowers look to the eyes of these
pollinators.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 605
Inquiry
INVESTIGATION
14-B
Skill Check
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Safety Precautions
Techniques of Artificial Propagation
In this investigation, you will test and compare three methods of plant
propagation.
Pre-Lab Questions
1. What are some advantages of artificial propagation?
2. Identify at least three different methods for propagating plants artificially.
• Wash hands well before and
after handling plants and plants
chemicals, especially hormone
products.
Materials
• various house plants, such as
philodendron, spider plant,
African violet
• sharp scissors
• beakers, or large test tubes in a rack
• masking tape
• marker
• water
• soil
• plastic bags
3. What safety precautions will you take when working with plants and plant
chemicals?
Question
How can you compare plant propagation methods?
Procedure
1. Using sharp, clean scissors, take three cuttings from each plant. Clean the
scissors and dry them well before taking each cutting.
2. Place one cutting from each plant in a test tube of water. Label each test
tube as appropriate to track the species of each cutting. Add water to the
test tubes as needed throughout the investigation to keep water levels up.
3. Place one cutting from each plant directly into moist soil. Cover the pot
and cutting with a plastic bag, pierce the bag with a couple of small holes,
and secure with an elastic band. Label each pot as appropriate to track the
species of each cutting.
• elastic bands
4. For the third cuttings, apply a root hormone to the cut edge, and place in
moist soil as in step 3. (The hormone will help the cutting develop new
roots quickly.)
• root hormone product
5. Put all cuttings in a well-lit area and observe over several days.
• pots
Analyze and Interpret
1. Which cuttings showed the best results? Suggest a reason why.
2. Which growing medium gave the best results? Suggest a reason why.
Conclude and Communicate
3. Which species that you tested seemed best suited to artificial propagation?
Explain why you think this is the case.
Extend Further
4. INQUIRY Design an investigation to find out how light conditions (for
example, bright light versus partial light) affect growth of artificially
propagated plants.
5. RESEARCH Which professions do you think need knowledge and skills
related to plant propagation? What kinds of courses would people interested
in these professions need to take? Which educational institutions provide
such courses?
606 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Plan Your Own
INVESTIGATION
14-C
Skill Check
✓
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Factors That Affect Plant Growth
In this investigation, you will design and test a procedure to investigate how
a factor that you select affects the growth of plants.
Safety Precautions
Question
What factors affect plant growth?
• Always wash hands before and
after handling plants and soil.
Hypothesis
Form a hypothesis based on the factor you have chosen to investigate.
• Be extremely careful when
handling chemical products such
as fertilizers.
Plan and Conduct
1. Decide which condition you are going to vary in your experiment. Prepare
a list of possible ways to test your hypothesis.
Suggested Materials
• bean or radish seeds (or other
quick-growing seeds)
2. Decide on one approach for your investigation that can be done in the
classroom. Your design should test one variable at a time. Plan to collect
quantitative data.
• labels
3. Write a full procedure for your investigation. Include all safety precautions
as well as a list of all the materials and equipment you will need. You may
find the following questions helpful in developing your plan and procedure.
• What will be your independent variable, dependent variable(s), and
controlled variable(s)?
• How will you apply the different treatments to the plants in the
appropriate labelled pots?
• How will you determine whether your variable has had an effect on
plant growth?
• How will you record the data and information you collect?
• potting soil
• water
• small pots or planting trays
• equipment and materials
appropriate to the factor being
tested (e.g., soil testing kit, vinegar,
lime, litmus paper, fertilizer)
4. Obtain your teacher’s approval before conducting your investigation.
Analyze and Interpret
1. How did the variable affect the growth of your plant?
2. Compare your results with those of classmates who investigated the same
variable. In what ways are the results similar and different?
Conclude and Communicate
3. Did your results support your hypothesis? Explain why or why not.
4. Identify and explain at least two changes you would make to improve the
design of your investigation.
Go to Scientific Inquiry in Appendix A for
help with designing your experiment.
Extend Further
5. INQUIRY Predict how the variable you investigated would affect a plant of
a different species. Design an investigation to test your prediction.
6. RESEARCH What differences might you observe in the plant variable you
investigated if you conducted your experiment in a different climatic region
of Canada?
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 607
Plan Your Own
INVESTIGATION
14-D
Skill Check
✓
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Suggested Materials
• pond water (supplied by your
teacher)
• wood shavings or dried grass
Succession of Microbial Organisms
Recall from Chapter 2 that many microscopic organisms, such as Paramecium,
Euglena, and diatoms, are found in aquatic ecosystems, including ponds.
The oxygen-poor mud at the bottom of the pond likely contains methaneproducing bacteria or sulfate-reducing bacteria. What happens to populations
of these micro-organisms when they are contained in a micro-environment?
Pre-Lab Questions
1. Which type of micro-organisms do you expect to find in the pond water?
• pH paper
2. What are the independent and dependent variables in your investigation?
• paper towels
3. What safety precautions should you take due to the gases produced in the
micro-environments?
• 2 glass jars with lids
• refrigerator
Safety Precautions
• long plastic pipettes
• microscope slides
• microscope
• cover slips
• To avoid creating completely anaerobic conditions in the jars and to prevent
gases from building up in the jars, leave the lids on the jars loose.
• Do not leave the micro-environments near open flames. Gases produced in
the micro-environments may ignite.
• Be careful not to smell the micro-environments solution directly. Breathing in
hydrogen sulfide gas is dangerous.
• Wash your hands after working with the micro-environments.
Go to Scientific Inquiry in Appendix A for
help with designing your experiment.
Questions
How can you demonstrate microbial succession over time? What factors
influence succession in a micro-environment?
608 MHR • Unit 5 Plants: Anatomy, Growth and Function
Plan and Conduct
1. Use the library or Internet resources to refresh your
memory about the role of micro-organisms in the
carbon cycle.
2. Using the list of suggested materials as a starting
point, decide with your group which environmental
factor your group will manipulate. For example, will
you examine the effect of temperature on succession
in the micro-environments? Will you examine the
effect of frequent aeration on succession in the
micro-environments?
3. Decide exactly how you will set up each
micro-environment, and how and when you will
observe them. How will you detect changes in the
microbial community? How will you detect population
growth in a specific population?
4. Write a step-by-step procedure for your experiment.
Be sure to include safety precautions.
5. Once your group has agreed on the procedure, have
your teacher approve it.
6. Set up your micro-environments, and make and record
your initial observations.
7. Make and record periodic observations throughout the
duration of the experiment.
Conclude and Communicate
3. Describe how the microbial communities in each
micro-environment changed over the course of the
experiment. Which micro-organisms were most
abundant at the beginning, middle, and end of the
experiment? Which micro-organisms were least
abundant at these three times?
4. How did the environmental factor that you tested
affect the growth of particular populations in the
micro-environments?
Extend Further
5. INQUIRY Estimate the total number of organisms
in your microsystem. Your answer should include a
complete explanation of all your calculations and list
the assumptions you made.
6. RESEARCH Your experiment focussed on a small-scale
ecosystem and succession. Scientists have conducted
similar research on a larger scale using hundreds
of organisms and humans to simulate ideal living
conditions. Prepare a summary of Biosphere 2,
the boldest attempt thus far. Refer to Appendix A,
Developing Research Skills, for Internet research
guidelines and note-taking suggestions.
8. Follow your teacher’s instructions on how to clean up
when your investigation is complete.
Analyze and Interpret
1. Which environmental factor did you test?
2. How were you able to identify changes in the
microbial community over time?
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 609
Chapter 14
Section 14.1
SUMMARY
Plant Reproduction
Plants reproduce sexually by producing seeds and
asexually by vegetative propagation.
KEY TERMS
artificial propagation
germination
hypocotyl
petal
pistil
pollination
radicle
seed coat
sepal
stamen
KEY CONCEPTS
• Flowers are the reproductive structures of plants, and
they include four main organs: sepals, petals, stamens,
and pistils.
Section 14.2
• Fertilization ends when a seed is formed. Seeds are usually
contained in a mature ovary called a fruit and surrounded
by a protective seed coat.
• Plant seeds disperse away from their parent plant through
the action of wind or animals such as insects and mammals.
• Plants can propagate sexually through seeds or asexually
by vegetative propagation. In vegetative propagation,
also called artificial propagation, new individual plants are
grown from a portion of the roots, stems, or leaves of an
existing plant.
Plant Growth and Development
Plant growth is influenced by hormones and conditions
in the environment.
KEY TERMS
apical dominance
gravitropism
hormones
nastic response
phototropism
thigmotropism
tropism
KEY CONCEPTS
• Plant growth after fertilization begins with the process
of germination.
Section 14.3
• There are three key stages in the haploid part of the plant
life cycle: development of pollen cells, development of
eggs, and fertilization.
• Plants manufacture many hormones or growth regulators,
including auxins and gibberellins. Each serves a specific
purpose, usually related to growth or the inhibition of
growth.
• Plants respond to their environment with nastic responses,
which are reversible, and with tropic responses, which are
irreversible.
• Plant tropisms are growth responses to environmental
stimuli that include light (phototropism), gravity
(gravitropism), and touch or contact (thigmotropism).
• In addition to hormones, light, and water, other factors
that affect plant growth include availability of soil minerals
(nutrients) and soil acidity (pH).
Succession and Sustainability
Plants play an important role in succession and in the
sustainability of ecosystems.
KEY TERMS
climax community
ecological succession
pioneer species
primary succession
secondary succession
KEY CONCEPTS
• Plants provide ecosystem services such as adding nutrients
to soil, draining and filtering water, and providing food and
oxygen for other organisms.
610 MHR • Unit 5 Plants: Anatomy, Growth, and Function
• Ecological succession is the changes that occur in
ecosystems as one community replaces another after a
disturbance.
• Primary succession occurs when there is no soil for plants
to grow in.
• Secondary succession occurs when the ecosystem has
been damaged but there is still soil.
• The greater the plant diversity in an ecosystem, the more
resilient the ecosystem is to disturbance.
Chapter 14
REVIEW
Knowledge and Understanding
Select the letter of the best answer below.
1. From which structure did the structure labelled A in
the diagram below develop?
6. Cytokinins are found in this part of the plant.
a. root tip
d. leaf
b. root system
e. shoot tips
c. stem
7. What is the significance of the human-made auxin
2,4-D?
a. It causes decreased plant growth.
b. It works as a seed germinator.
c. It reduces yield in crops.
d. It promotes seed maturation.
e. It acts as a weed killer.
8. A vine naturally grows in and around a wire fence.
This is an example of which type of tropism?
d. thigmotropism
a. phototropism
b. ecotropism
e. negative tropism
c. gravitropism
A
a.
b.
c.
d.
e.
hypocotyl
radicle
auxin
cotyledon
monocot
Answer the questions below.
9. When does the dormant period of a seed end?
2. Which artificial propagation technique allows one
plant to have two branches from different species?
a. division
b. grafting
c. leaf cutting
d. stem cutting
e. air layering
3. Which is true regarding artificial propagation?
a. It limits genetic variation.
b. It results in slower growth.
c. It increases germination wait-time.
d. It increases diversity when used in farming.
e. It is common, and occurs often in nature.
10. Which plant growth hormone is gaseous?
What is its function?
11. What happened to promote the growth of
the side branches on the plant shown below?
12. Use a flowchart to outline the key steps in
primary succession.
4. Which could describe a dicot plant?
a. has a flower with four petals
b. has a flower with five petals
c. has a flower with six petals
d. a and b
e. b and c
13. Why would plants on the International Space Station,
in orbit around Earth, have difficulty germinating?
5. Which of these options best describes the function of
pioneer species during primary succession?
a. produce oxygen
b. provide lodging for carnivores
c. break down nutrients
d. die and decompose to become soil
e. remove toxins for future animal habitation
14. Examine the illustration that was used in question 11
above. Suppose that you wanted to encourage a plant to
grow vertically with minimal growth of side branches.
What would you do, and why?
15. Identify the following flower structures as male,
female, or other, and state their functions in each case.
a. style
e. stigma
b. stamen
f. anther
c. petal
g. sepal
d. pistil
h. filament
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 611
Chapter 14
REVIEW
16. Make a sketch to summarize the sexual reproduction
of plants by sporic reproduction. (Hint: What is
another name for sporic reproduction?)
27. Compare and contrast complete and incomplete
flowers. Use a graphic organizer such as a Venn
diagram to organize your answer.
Thinking and Investigation
28. Define a tropism in plants. Draw an example of a
positive tropism and of a negative tropism.
17. Is the flower of an angiosperm a tissue, an organ, or a
system? Give evidence to justify your answer.
18. To test the effects of pH, a student decides to
administer five unique solutions to five unique plants.
From least to greatest pH, the student uses solutions of
cola, vinegar, water, milk, and diluted bleach. Give the
student two suggestions to improve the validity of the
results that will be obtained. Explain your reasoning in
each case.
19. Although simple layering is a method of artificial
propagation, describe a situation in which this could
naturally occur.
20. “Pollination by animals is more efficient than
pollination by wind.”
a. Do you agree or disagree with this statement?
b. Provide examples to support your opinion.
21. Describe an investigation to test the effect of light on
growth in one plant.
a. What would be your control situation?
b. What variables would you use?
c. Write a hypothesis for your investigation.
d. Describe data that you would expect to collect if
your data supported your hypothesis.
e. Describe data that you would expect to collect if
your data did not support your hypothesis.
29. Fruit trees in orchards often have scars on their trunks.
While you are picking apples, you overhear a person
commenting that it was lucky the trees were able to
heal after having their stems broken by last year’s
ice storm. Is that the most likely explanation for the
scarring on trees in an orchard?
30. It is Plant Appreciation Day in your community. Write
a short public service announcement, about 180 words,
letting people know the significance of plants to the
community.
31. A chef writes an article for a food magazine in which
fruits and vegetables are distinguished on the basis of
how they are prepared, how they are eaten, and their
sweetness. Write a letter to the magazine explaining,
respectfully, how the scientific use of the term fruit
differs from the chef ’s use.
32. Construct a diagram showing positive phototropism
in a small plant. Shade regions of the plant darker
where higher auxin levels are found.
33. Study the diagram below.
22. Artificial propagation techniques can result in many
identical plants, or they can be used to encourage
variation. Describe two examples of when each would
be desirable.
23. A plant is developed with negative phototropism. What
prediction can you make about auxin levels and the
plant’s chances of survival?
24. Suggest reasons why seeds found in an ancient
Egyptian tomb may prove useful to scientists today.
Communication
25. Use a graphic organizer such as a Venn diagram to
compare the internal structures of a monocot seed with
those of a dicot seed.
26. Create an illustration that shows the stages of
development of a monocot seed from germination to
mature plant.
612 MHR • Unit 5 Plants: Anatomy, Growth, and Function
a. Identify the type of artificial propagation shown.
b. Write a caption that explains more about this
technique.
34. Summarize your learning in this chapter using
a graphic organizer. To help you, the Chapter 14
Summary lists the Key Terms and Key Concepts. Refer
to Using Graphic Organizers in Appendix A to help
you decide which graphic organizer to use.
Application
40.
35. You buy some raspberries that are wrapped in plastic.
When you go to eat them the next day, they have
spoiled. Your friends comment that they never buy
fresh raspberries because they always go bad before
they get a chance to eat them. What could you say in
response?
36. Infer why monofloral honey is more expensive than
standard honey. Hint: To answer this question, first
determine what monofloral means. If necessary, refer to
Appendix B, Greek and Latin Prefixes, for help.
37. Study the photo below, which shows a plant growing
around a pole.
Plant variety is critical to the survival and
sustainability of ecosystems. Describe at
least three examples from your studies of plants, and
other units that you have studied this year, that support
this statement.
41. Animals and plants require many of the same
nutrients.
a. Research the nutrients that animals require.
b. List seven nutrients and their functions that the
two kingdoms have in common.
42. The diagram below shows the treatment of four
seedlings for an investigation. In 1, the leaves were
cut from the top of the seedling. In 2, a foil cap was
placed over the top of the seedling. In 3, a foil tube
was wrapped around the base of each seedling. In 4,
the seedling received no treatment. The four seedlings
were covered with a three-sided box that exposed
the seedlings to plentiful sunlight from one side only
and prevented light from entering at the top or other
three sides.
a. Predict what you will observe about each of the
seedlings when you remove the box in two days.
b. Write a hypothesis that could have been used by the
students who designed this investigation.
foil cap
a. Identify the type of tropic response the plant is
displaying.
b. Explain how you could investigate the role of pea
plant cells in the plant’s response to touch.
38. You have been hired to teach a Grade 6 class at a local
school about secondary succession. Design the lesson
that you would use to help the students understand
this concept in the world around them. Your lesson
should include the following:
• an imaginary field trip involving the class and its
teacher
• a script you would use during the field trip to point
out specific aspects of secondary succession
39.
Plants have specialized structures with
distinct functions that enable them to
respond and adapt to their environment. Demonstrate
the validity of this statement by describing at least
two examples associated with plant reproduction.
foil tube
1
2
3
4
43. Table 14.1 summarizes the advantages of vegetative
propagation. What are at least three disadvantages of
vegetative propagation?
44. Explain why commercial nurseries routinely pump
carbon dioxide into their greenhouses.
45. A vegetable storage container is designed to allow air
circulation around vegetables. The advertisement for
the container states that this reduces the amount of
ethylene surrounding the vegetables, which keeps them
fresh longer. Is this fact or fiction? Explain.
Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 613
Chapter 14
SELF-ASSESSMENT
Select the letter of the best answer below.
1.
2.
3.
4.
5.
K/U Which is true of the sperm cells in seedless
vascular plants?
a. They use cilia for movement.
b. Their movement resembles that of an amoeba.
c. They use a flagellum for movement.
d. They do not require water for movement.
e. All of the above are true.
K/U How does a plant benefit from inhibition of
its growth caused by abscisic acid?
a. energy is stored
b. fruit matures
c. root system develops
d. stomata remain open to ensure energy is made
e. Both a and c are true.
6.
K/U Which combination of variables does seed
germination require?
a. water and oxygen
b. water, oxygen, and suitable temperatures
c. water and suitable temperatures
d. a tropical climate and water
e. a nearby angiosperm species and oxygen
K/U Which of the following can inhibit apical
dominance?
a. injecting the plant with auxin
b. cutting the leaves
c. removing the top of the plant
d. adding micronutrients to the plant’s diet
e. increasing the soil pH
7.
Which of the following includes a pioneer
species?
a. deer, goats, trees
b. lichens, deer, ticks
c. ants, bushes, birds
d. cats, catnip, dogs
e. shrubs, wildflowers, bees
a.
b.
c.
d.
e.
K/U
K/U Touching the leaves of Mimosa pudica plant
shown below has caused them to fold up quickly.
After a short time, the leaves begin to unfold.
What kind of response is this?
a. phototropism
b. nastic movement
c. thigmotropism
d. gravitropism
e. negative movement
614 MHR • Unit 5 Plants: Anatomy, Growth, and Function
Which pair of terms means the same thing?
asexual propagation; artificial propagation
sexual propagation; artificial propagation
asexual propagation; artificial selection
asexual reproduction; artificial production
asexual propagation; artificial prorogation
K/U
K/U Which of the following terms could describe
a monocot flower?
a. 4 sepals, 4 petals
b. 5 sepals, 10 petals
c. 12 sepals, 12 petals
d. 4 sepals, 8 petals
e. All of the above are correct.
9. K/U Which of the following statements about
cross-pollination is correct?
a. It leads to genetic diversity.
b. Most plants also pollinate themselves.
c. It may occur between plants and fungi.
d. It occurs only in monoecious plants.
e. All of the above are correct.
10. K/U Which of the following do monocot and dicot
plants have in common?
a. number of leaves at germination
b. radicle becoming the root structure
c. cotyledons are visible after sprouting
d. a fibrous root system
e. the exterior endosperm
8.
Use sentences and diagrams as appropriate to answer the
questions below.
11.
K/U Use perfect or imperfect, and complete or
incomplete, to describe the flower in the diagram
below. Explain how you made your choices.
12.
Explain the role that animals play in pollination,
and give three examples.
13.
What adaptations are seen in plants that rely on
the wind for pollination?
14.
Explain the concept of double fertilization in
angiosperms.
15.
At some time in human history, people
discovered the type of artificial propagation that is now
called simple layering. Write a story in one or two
paragraphs that describes how this discovery might
have been made.
16.
K/U
17.
T/I Potassium is a plant nutrient that helps in the
opening and closing of stomata. Predict how a
deficiency of potassium would affect a plant’s growth.
Refer to specific plant processes in your answer.
18.
A
How could the retreat of a glacier help scientists
to understand succession?
19.
A
Ecological disturbances can dramatically change
the course of an ecosystem. Classify the following
disturbances in order of increasing severity: oil spill,
forest fire, clearcutting. Justify your answer.
20.
A
List five ways in which plants are important in
a. your daily life
b. the daily life of a bird
c. the whole planet
21.
C
Construct a graph that demonstrates the
relationship between an ecosystem’s resilience and its
diversity. When making your graph, consider the
independent (x-axis) and dependent (y-axis) variables.
22.
T/I Describe an imaginary plant that has flowers
adapted for pollination that involves water.
T/I
C
C
K/U
23.
A
Study the diagram below.
Study the plant in the photo below.
a. Which method of artificial propagation is shown?
b. Provide two reasons why you would recommend
this method to someone wanting to grow an
orchard in a short period of time.
a. What type of tropism is the plant displaying?
b. Identify and describe two other types of tropisms.
24.
Cherry trees must be grown in pairs. Explain
why, and then describe a way to get around this
situation.
25.
C
Construct a dichotomous key to determine
whether a plant is monoecious or diecious, and
whether the flowers are perfect or imperfect.
12
13
A
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Chapter 14 Plants: Reproduction, Growth, and Sustainability • MHR 615