Download How Plants Grow and Develop

Section 1
How Plants Grow
and Develop
Section 1
Focus
Overview
Before beginning this section
review with your students the
objectives listed in the Student
Edition. This section begins by
describing seed germination. Then,
after defining perennials, annuals,
and biennials in the context of plant
life spans, the section explains
meristems and their role in primary
and secondary plant growth.
Bellringer
Ask students to draw the structure
of a seed. (The drawings should show
an embryo, a stored food supply, and
a protective outer covering.) Ask
students to share their drawings so
that you can determine their prior
knowledge before beginning this
section. Allow ELL students to
label their drawings in their native
language and English. LS Visual
Motivate
Activity
Provide students with bean seeds
and corn seeds that you have germinated. (Place the seeds between
sheets of wet paper towels, and put
the wet towels with seeds in a
closed black garbage bag. Place the
bag in a warm spot for 3–4 days.
Check seeds at days 2 and 3.) Have
students slice the germinating seeds
longitudinally, or provide pre-cut
germinating seeds. Ask students to
view the seeds under stereomicroscopes, and identify the structures
shown in Figure 1. Bio 10C, 13B
Seeds Sprout
Objectives
A seed contains a plant embryo that is in a state of suspended animation. Some embryos can remain in suspended animation inside a
13B TAKS 3 seed for thousands of years. Seeds sprout with a burst of growth in
Contrast annuals, biennials,
10C 13A 13B response to certain changes in the environment. These changes,
and perennials.
TAKS 3
such as rising temperature and increasing soil moisture, usually sigExplain how primary and
nal the start of favorable growing conditions.
secondary growth are
Many seeds must be exposed to cold or to light before they can
produced.
10C 13A 13B TAKS 3
sprout. The seed coats of other seeds must be damaged before they
Describe several traits of
can sprout. Exposure to fire, passing through the digestive system of
bread wheat.
10C 13A 13B
an animal, and falling on rocks are several natural ways that seed
TAKS 3
Contrast development in
coats are damaged. A seed cannot sprout until water and oxygen
5A
plants and animals.
penetrate the seed coat. When water enters a seed, the tissues in the
seed swell, and the seed coat breaks. If enough water and oxygen are
Key Terms
available after the seed coat breaks, the young plant, or seedling,
begins to grow.
germination
● Compare seed germination
10C 13A
in beans and corn.
●
●
●
●
perennial
annual
biennial
primary growth
secondary growth
apical meristem
cork cambium
vascular cambium
annual ring
Germination
A plant embryo resumes its growth in a process called germination.
The first sign of germination is the emergence of the embryo’s root.
What happens next varies somewhat from one type of plant to
another, as you can see in Figure 1. The young shoots of some plants,
such as beans, form a hook. The hook protects the tip of the shoot
from injury as it grows through the soil.
Figure 1 Seed germination
Beans and corn show two characteristic patterns of seed germination.
1. The hooked shoot of a germinating bean seed straightens
after the cotyledons emerge
from the soil.
Bean (dicot)
Leaves
572
Corn (monocot)
First leaf
Embryonic shoot
Hook
Young shoot
Cotyledons
Embryonic
root
Seed coat
Cotyledon
Embryonic
root
Young
shoot
572
Chapter Resource File
pp. 572–573
Student Edition
TAKS Obj 3 Bio 7B
TAKS Obj 3 Bio 13A
TEKS Bio 5A, 7B, 10C, 13A, 13B
Teacher Edition
TAKS Obj 1 Bio/IPC 2A, 2C
TAKS Obj 3 Bio 13A
TEKS Bio 10C, 13A, 13B
2. The shoot of a germinating corn
seed is covered by a sheath. The
shoot grows straight up, but the
cotyledon stays underground.
• Lesson Plan GENERAL
• Directed Reading
• Active Reading GENERAL
• Data Sheet for Skills
Practice Lab GENERAL
Transparencies
TT Seed Germination
TT Bellringer
Chapter 26 • Plant Growth and Development
Planner CD-ROM
• Reading Organizers
• Reading Strategies
• Portfolio Project Plant Focus
Worksheet GENERAL
Sheath
The young shoots of other plants, such as corn, have a protective
sheath around their shoots. In some plants, such as beans and
marigolds, the cotyledons emerge from the soil and unfold aboveground. In other plants, such as corn and peas, the cotyledons
remain underground. After the shoot of a seedling emerges, its roots
and shoots continue to grow throughout its life.
www.scilinks.org
Topic: Texas Perennials
Keyword: HXX4020
READING
SKILL
BUILDER
Plant Life Spans
Interactive Reading Assign
Chapter 26 of the Holt Biology
Guided Audio CD Program to
help students achieve greater
success in reading the chapter.
As you have read in a previous chapter, bristlecone pines are the oldest known trees. They are estimated to be about 5,000 years old. In
contrast, some plants live for only a few weeks. Depending on how
long it lives, a plant can be classified as one of three basic types:
perennial, annual, or biennial.
Perennials Many herbaceous plants and all woody plants are
perennials. A perennial is a plant that lives for several years. Most
perennials reproduce many times during their life span. Others, like
the herbaceous perennial shown in Figure 2, reproduce only once
before they die. Chrysanthemums, daffodils, and irises are familiar
herbaceous perennials. These plants store nutrients for the next season’s growth in fleshy roots or underground stems. The aboveground
shoots of herbaceous perennials often die after each season of
growth. Trees, shrubs, and many vines are woody perennials. Some
woody perennials drop their leaves each year. Plants that drop all of
their leaves each year, such as elms, maples, and grapevines, are
known as deciduous (dee SIHJ oo uhs) plants.
Those that drop a few leaves at a time throughout the year, such as firs, pines, and junipers,
are called evergreens.
SKILL
Figure 2 A herbaceous
perennial. Century plants live
for many years but reproduce
only once. Like the dried-up
plant on the left, this flowering
century plant will die when its
seeds are mature.
Annuals Sunflowers, beans, corn, and many
weeds are annuals. An annual is a plant that
completes its life cycle (grows, flowers, and
produces fruits and seeds) and then dies within
one growing season. Virtually all annuals are
herbaceous plants. Most annuals grow rapidly
when conditions are favorable. Individual
plants can become quite large if they get
enough water and nutrients.
two growing seasons to complete its life cycle.
During the first growing season, biennials produce roots and shoots. The shoots consist of a
short stem and a rosette (circular cluster) of
leaves. The roots store nutrients. In the second
growing season, a biennial plant uses the stored
nutrients to produce a flowering stalk. The
plant dies after flowering and producing fruits
and seeds.
573
CONNECTION
Take students on a walk around the school
grounds or a park, and have them keep a log of
the plants they see, using general terms such as
flower, tree, grass, or shrub. Have students
write a paragraph that answers the following
questions based on what they observe. What
types of plants did you see? Did you see more
of one type of plant than another? If so, what
might account for the difference? (More annuals
tend to be present in spring and summer; only
woody perennials may be present in winter.)
BUILDER
did you know?
Plant Collections The Royal Botanic Gardens,
Kew, located about 10 km southwest of London,
England, is recognized as a global center of
excellence in the study of plant diversity. The
world’s largest documented living and preserved
plant collections are located there.
GENERAL
Interpreting Visuals Bring students’ attention to Figure 1. Have
students compare the structures of
the germinating corn seed and bean
seed. Ask students how monocot
and dicot seedlings differ in the way
they emerge from the soil. (Dicot
seedlings have a stem that hooks as it
emerges to protect the delicate tip,
whereas monocots grow straight out
of the soil. Monocot seedlings have a
protective sheath that guards the tip.)
Ask students what other differences
they notice. (The cotyledon and seed
coat of the corn seed remain underground, while the cotyledons of the
bean emerge from
English Language
Learners
the soil.) Bio 13B
Group Activity
Biennials Carrots, parsley, and onions are biennials. A biennial is a flowering plant that takes
REAL WORLD
Teach
GENERAL
Design a Flower Bed Have students work in groups of four to
design a flower garden that will
provide color in every season (or in
three seasons, if you live in an area
with a harsh winter climate). Let
students use nursery catalogs to
find examples of annuals, biennials,
and perennials, as well as to determine where each plant will grow
and when it will bloom. Assign
each group a set of conditions under
which its garden must grow (e.g.,
size, distribution of sun and shade,
soil type). Finally, tell them to consider aesthetic factors (e.g., color
combinations, taller plants in back,
shorter plants in front). Have each
student design a graphic that shows
the group’s garden from the top
during one of the seasons and
identifies their plants. LS Visual
TAKS 1 Bio/IPC 2A
TAKS 3 Bio 13A; Bio 13B
LS Interpersonal TAKS 1 Bio/IPC 2C, Bio 13B
Chapter 26 • Plant Growth and Development
573
Meristems
Teach, continued
continued
Activity
GENERAL
Apical Meristems Let students
observe prepared slides of the
apical meristems of the shoots and
roots of several plants. Have them
draw what they see and label the
parts identified in Figure 3. Have
students write a brief paragraph
describing how the cells in the
apical meristems differ from those
in the surrounding tissues. (The
cells of the apical meristems are small
and unspecialized. The surrounding
cells tend to be larger and longer
and have thicker walls, and some
have specialized structures such as
chloroplasts or root hairs.) LS Visual
Compare and Contrast
To compare and contrast
primary growth and secondary growth, make a
two-column list. In one
column write the ways in
which the two are alike.
In the other column,
write the ways in which
they are different.
www.scilinks.org
Topic: Primary Growth
in Plants
Keyword: HX4148
Bio 5A
Teaching Tip
GENERAL
Removal of the Apical Meristem
Ask students what they think would
happen if the apical meristem of
a stem or root were removed.
(Removing or damaging the apical
meristems of a plant would stop or
limit the vertical growth of the stem
or root.) This frequently occurs in
nature, as tips of stems are broken
off by wind or animals, killed by
disease, or eaten by insects or other
animals. Lateral buds often begin
to grow after the apical meristem is
removed. If the plant is a tree, one
of these lateral buds will take over
as the main trunk, and the tree will
take on its normal form again in a
few years. If the plant is a shrub or
an herbaceous plant, the growth of
many lateral buds will make the
plant bushier, and it will not grow
as tall. TAKS 3 Bio 13A; Bio 5A
Transparencies
TT Apical Meristems
Primary Growth
Apical (AP ih kuhl) meristems, which are located at the tips of stems
and roots, produce primary growth through cell division. As shown
in Figure 3, apical meristems are regions of small, undifferentiated
cells. To better understand how primary growth occurs in most
plants, imagine a stack of dishes. As you add more dishes to the top,
the stack grows taller but not wider. Similarly, the cells in the apical
meristems of most plants add more cells to the tips of a plant’s body.
New cells are added through cell division. The cells then lengthen.
Thus, primary growth makes a plant’s stems and roots get longer
without becoming wider. To learn about primary growth in a
monocot, look at Up Close: Bread Wheat later in this section.
The tissues that result from primary growth are called primary
tissues. The new cells produced by apical meristems differentiate
into the primary dermal, ground, and vascular tissues of roots,
stems, and leaves. Some of the cells produced by the root apical
meristem also become part of the root cap. These cells replace cells
that are worn away as the root pushes through the soil.
Figure 3 Apical meristems
Both shoot tips and root tips contain apical meristems, where cell division occurs.
Root tip of a
radish plant
Shoot tip of a
coleus plant
Apical meristems
574
MEDICINE
CONNECTION
Flowering plants and ferns are the original
sources of approximately 25% of all drugs
prescribed each year in North America. In
fact, botany was considered a branch of
medicine until the early to mid 1800s.
pp. 574–575
Student Edition
TAKS Obj 3 Bio 7B
TEKS Bio 7B
Teacher Edition
TAKS Obj 3 Bio 13A
TEKS Bio 5A, 5B, 5C, 13A
574
Plants grow by producing new cells in regions of active cell division
called meristems. Almost all plants grow in length by adding new
cells at the tips of their stems and roots. Growth that increases the
length or height of a plant is called primary growth. Many plants
also become wider as they grow taller. Growth that increases the
width of stems and roots is called secondary growth. After new cells
are formed by cell division, they grow and undergo differentiation.
Recall from your reading that differentiation is the process by which
cells become specialized in form and function.
Chapter 26 • Plant Growth and Development
Cultural
Awareness
The Asian Art of Bonsai Bonsai is the cultivation of miniature specimens of plants that
would normally be much larger. The effect is
obtained by frequent, selective pruning of both
the shoot and the roots. Bonsai plants are
typically grown in small containers. The word
bonsai comes from the Japanese characters
bon, meaning “tray,” and sai, meaning
“plant.” The Chinese practiced bonsai in
approximately the third century B.C., but
it was the Japanese Buddhist monks who
perfected the art.
Secondary Growth
Secondary growth occurs in parts of many herbaceous plants, such
as in carrot roots. However, it is most dramatic in woody plants.
Secondary growth is produced by cell division in two meristems,
which form thin cylinders near the outside of woody stems and
roots. One meristem, called the cork cambium (KAM bee uhm), lies
within the bark and produces cork cells. The other meristem, called
the vascular cambium, lies just under the bark and produces vascular tissues. The tissues that result from secondary growth are called
secondary tissues. Figure 4 shows how woody stems develop.
Step
Demonstration
A young woody stem has a ring of vascular bundles between
the cortex and the pith. Each vascular bundle contains primary xylem and primary phloem.
Vascular cambium develops between the primary xylem
and the primary phloem in each vascular bundle.
Secondary phloem is produced toward the outside of the
stem. Secondary xylem is produced toward the inside of the
stem. The cork cambium forms when the epidermis is
stretched and broken as the stem grows in diameter.
Step
Step
Eventually, the vascular bundles merge into solid cylinders.
No cortex or primary phloem remains. The cork, cork
cambium, and secondary phloem make up the bark. The
vascular cambium and secondary xylem lie inside the bark.
Thick layers of secondary xylem, or wood, often form rings.
Since one new ring is usually formed each year, the rings
are called annual rings.
www.scilinks.org
Topic: Secondary Growth
in Plants
Keyword: HX4160
Figure 4
IO
B
graphic
1
Development of a Woody Stem
Bio 5A, 5B, 5C
The wood in a woody stem results from secondary growth.
Initially, the stem is covered
by epidermis and contains
cortex, pith, and a ring of
vascular bundles with
primary xylem and phloem.
2
A vascular cambium forms
between the xylem and
phloem in each vascular
bundle. Cork cambium
forms under the epidermis.
3
Teaching Tip
In a mature stem, the vascular cambium
adds new layers of secondary xylem
and phloem each year.
Bark
Primary phloem
Primary xylem
Epidermis
Pith
Cork
cambium
Cork
Secondary
phloem
Cork
cambium
Primary phloem
Vascular
cambium
GENERAL
Provide students with prepared
slides of a cross section of a woody
stem. Have them examine the slides
under a compound microscope.
Point out that vascular cambium is
only one layer of cells. It is found
just under the bark of a woody
stem and can be located in microscope slides of woody stem cross
sections by finding the phloem cells
and the large, thickened xylem
cells. Also point out that both
xylem and phloem develop from
the vascular cambium cells, so they
develop in rows on either side of
this “meristematic” tissue. Have
students locate the layer between
the two types of cells in a woody
stem cross section. This is the row
of vascular cambium cells. Have
students describe how xylem and
phloem originate from vascular
cambium. (Xylem and phloem
originate through cell division and
cell differentiation.) LS Visual
Secondary
phloem
Cork
GENERAL
Summarizing Plant Growth
Have students prepare a sequential
diagram that summarizes how
herbaceous plants grow by primary
growth and how woody plants
grow by both primary and secondary growth. An example of a
completed diagram appears in the
Graphic Organizer on this page.
LS Visual Bio 5A, 5B
Pith
Primary
xylem
Cortex
Vascular
bundle
Secondary
Vascular
xylem
cambium
Transparencies
575
TT Development of a Wood Stem
Graphic Organizer
Use this graphic organizer with
Teaching Tip on this page.
Apical
meristem
Primary
tissues
Cell division and
differentiation
Herbaceous
plant
Differentiation
Cork and vascular
cambia
Secondary
tissues
Woody
plant
Chapter 26 • Plant Growth and Development
575
Up Close
Up Close
Bread Wheat
Bread Wheat TAKS 3 Bio 13A; Bio 5A,
Scientific name: Triticum aestivum
5B, 5C, 10C, 13B
Size: 0.3 to 0.8 m (1 to 2.5 ft) tall
Range: Agricultural regions worldwide
Habitat: Cultivated fields in temperate and subtropical
grasslands
Importance: Wheat is the principal staple food in temperate
regions of the world. The grains of Triticum aestivum are usually
ground into flour that is used to make bread.
External Structures
▼
Leaves Wheat, a member of the grass family,
is a monocot. Its leaves are long but only
about 2 cm (0.8 in.) wide, with parallel
Leaf
veins. The leaves are attached
blade
to the stem by a sheath,
which wraps around
Leaf
sheath
the stem.
▼
Teaching Strategies
• Show students specimens of
living or preserved wheat
plants.
• Let students dissect grains, or
kernels, of wheat and locate
the endosperm, bran, and
germ of the kernels. Explain
that the endosperm serves as
a food supply for the embryo
when it begins to grow.
White wheat flour contains
only endosperm and whole
wheat flour contains both
endosperm and bran.
• For interest, have students
make bread so that they
notice the elasticity of the
dough, which is caused
by gluten.
pp. 576–577
Student Edition
TAKS Obj 3 Bio 13A
TEKS Bio 5A, 5B, 5C, 13A
Teacher Edition
TAKS Obj 3 Bio 13A
TEKS Bio 5A, 5B, 5C, 10C, 13A, 13B
TEKS Bio/IPC 3C
576
Floret
Palea
Anther
Stigma
Lemma
▼ Flower spike
jointed stems called culms. Given
plenty of space, mature plants
may develop as many as 100
culms. Each culm in a plant may
have from three to six leaves.
▼
Bio/IPC 3C
Awn
Stems Wheat plants have hollow,
Activity
The Debate about Food
Irradiation Food irradiation is
the process of exposing food to
radiation—the energy emitted by
the unstable nuclei of certain atoms
in the form of waves or rays. As it
travels through the food, radiation
kills organisms such as bacteria and
insects. Have students research the
history of and the current debate
over food irradiation in preparation for a class debate. (Pro: Food
irradiation makes the food supply
safer, provides a better quality of food,
and extends the shelf life of food.
Con: irradiation induces chemical
changes in food, which may affect the
color, odor, and texture of food and
lower the nutritional value of food.)
TAKS 3
Flowers The flowers, which
occur in dense clusters called
spikes, develop at the top of
each culm. Spikes range from
5 to 13 cm (2 to 5 in.) in length.
Like all grass flowers, wheat
flowers lack petals and sepals.
Instead, two modified leaves
called the palea and the lemma
enclose the stamens and pistil
of each tiny flower, or floret. The
lemmas of some bread-wheat
varieties have a long bristle
called an awn.
Culms
Adventitious
roots
▼
Roots Wheat plants have a fibrous root
system composed of adventitious roots, as
do most grasses. The extensive root system
may be more than 2.2 m (7 ft) deep.
Fruit A kernel, or grain, of wheat
is a one-seeded fruit with a crease
on one side and a brush of tiny
hairs at one end. The grains
are high in gluten, a sticky
mixture of proteins that
make dough elastic.
576
Wheat Varieties Students may be surprised
to learn that more than 200 varieties of wheat
are grown in the United States. Hard red
wheats, the varieties grown for making bread
flour, belong to the species Triticum aestivum.
Durum wheats, or macaroni wheats, which
are grown for making pasta because they contain less gluten, belong to the species Triticum
Chapter 26 • Plant Growth and Development
dicoccum. Wheat may be planted in either the
fall or the spring. The term winter wheat
refers to a crop that is planted in the fall,
overwinters as seedlings, and is harvested in
late spring or summer. The term spring wheat
refers to a crop that is planted in the spring
for harvest in the fall.
Internal Structures
Nucleus
Fruit structure A wheat kernel
is about 85 percent starchy endosperm. The kernel’s outer layers,
called the bran, make up about
12 percent of the kernel. The bran
consists of the ovary wall, seed
coat, and aleurone layer, which
contains protein and oils. The
embryo, or wheat
germ, makes up
less than 3 percent
of the kernel.
Bread Wheat
Bread-wheat
karyotype
Bread-wheat
cell
Bran
Chromosomes Bread-wheat cells
Endosperm
Embryo
(wheat germ)
Kernel
(longitudinal section)
▼ Apical meristem
have 42 chromosomes. A karyotype reveals
that a bread-wheat cell has three sets of 14
chromosomes (7 pairs), shown here in different
colors. Thus, bread wheat is not diploid (2n).
Instead, it is hexaploid (6n)—a polyploid with
six of each kind of chromosome. Polyploidy,
having many sets of chromosomes, is
common among cultivated plants. Among
plants, polyploidy enables hybrids to result
from crosses among different species. Such is
the case with bread wheat, which is a natural
hybrid of three closely related species
of wheat.
Apical meristems The apical
meristems are located within the
culms at a point that is usually at
or just beneath the surface of the
soil. Thus, the apical meristems
are protected from being eaten by
grazing animals. Each new leaf
grows up within a hollow culm
and emerges from the
sheath of the culm’s
uppermost leaf.
Up Close
Leaf sheath
(oldest leaf)
Leaf sheath
(younger leaf)
New leaf
Discussion
• The chemical 2, 4-D is used to
kill dicots. Will it kill wheat
plants? Why or why not? (No,
wheat is a monocot as it has the
typical characteristics of monocots such as parallel leaf veins,
fibrous roots, and seeds with a
single cotyledon.)
• How did our ancestors help
produce the bread wheat varieties that exist today? (From
wild hybrids, they selected
plants with desirable characteristics such as higher yields,
larger seeds, and more gluten.)
• How would a human karyotype differ from the wheat
karyotype? (A human karyotype normally has 23 pairs of
chromosomes, while a wheat
karyotype has seven sets of six
similar chromosomes, in which
there are three homologous
pairs.)
• Is polyploidy beneficial to all
living organisms? Why or
why not? (No, polyploidy
may be beneficial in plants
because it causes plants
to be larger, have showier
flowers, and be more vigorous.
In most animals, including
humans, polyploidy is usually
detrimental.) LS Interpersonal
READING
577
Trends in Agriculture
Municipal Sewage In recent years, a great
deal of research has been conducted to investigate the use of municipal sewage as a fertilizer.
Such wastes must receive treatments that
remove or kill organisms that might pose a
health hazard to humans. One serious concern
about these materials is the tendency they
have to contain excesses of heavy metals such
as lead and cadmium, especially if certain types
of industries contribute to the waste. These
metals can be harmful to humans even at low
levels. Municipal wastes are not recommended
for use in the fertilization of food crops for
this reason. LS Intrapersonal
SKILL
BUILDER
Paired Summarizing Pair students.
Have one student read silently about
the external structures of bread
wheat and the other about the
internal structures. Then have one
student summarize his or her section
aloud without referring to the text.
The partner should listen without
interrupting and be prepared to
point out any inaccuracies or omissions in the summary. At this point
students can refer to the text. Have
students switch roles. Co-op Learning
Bio 5A, 5B, 5C
Chapter 26 • Plant Growth and Development
577
Plant Development
Plant Tissue Culture
Genes guide the development of both plants and animals, but their
patterns of development are very different. As an animal develops,
sets of genes that control development are inactivated and may not
be used again. Most animals stop developing when they become
adults. Plants, in contrast, continuously make new cells in meristems. These cells differentiate and replace or add to existing tissues.
Thus, a plant continues to develop throughout its life.
Many cells in a mature plant can activate all of their genes. Such
cells can divide and form masses of undifferentiated cells. In a
sense, they can reverse their development. These cells can undergo
differentiation and develop into a mature plant. A technique called
tissue culture is used to grow new plants from tissue that can reverse
its development. A tissue culture is prepared by placing tissue on a
sterile nutrient medium. Masses of undifferentiated cells that form
grow into plants that are genetically identical to the parent plant.
www.scilinks.org
Topic: Plant Life Spans
Keyword: HX4141
TAKS 2 Bio 4B
Teaching Strategies
Point out that tissue culture
requires sterile conditions
and new plants are grown in
controlled environmental
conditions.
Discussion
What enables cells from part of
a plant to grow into a whole
plant? (Undifferentiated plant
cells can differentiate into several
different types of cells.)
Plant Tissue Culture TAKS 2
Magnification: 810⫻
T
Close
Reteaching
Have students work in cooperative
groups to summarize the growth of
a plant, from a seed to a mature
adult. Co-op Learning
Quiz
GENERAL
1. When you buy seeds in a packet,
why have they not germinated?
(Water and oxygen must penetrate
the seed coat for the seed to sprout.)
2. When you plant perennials, what
would you expect to happen
after one season of growth?
(The plant would live for more
than two years.)
Alternative
Assessment
Protoplast Fusion
Protoplast fusion has been used
to produce hybrid petunias, potatoes, and carrots. A protoplast is
a plant cell that has had its cell
walls removed by enzymes. Certain chemicals or an electrical
shock can cause two protoplasts
to fuse, as the photo at right
shows. If the protoplasts came
from genetically different plants, a
hybrid cell results. The hybrid is
then placed in a tissue culture
and grown into an adult plant.
Genetic Engineering
Tissue culture is also an essential
part of producing genetically
engineered plants. First, foreign
genes are inserted into a plant’s
cells. The genetically altered cells
are then grown into adult plants
in tissue culture.
GENERAL
pp. 578–579
Student Edition
TAKS Obj 2 Bio 4B
TEKS Bio 4B, 5A, 10C, 11A, 11B,
13A, 13B
Teacher Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 13A
TAKS Obj 4 IPC 7D, 7E
TEKS Bio 4B, 5A, 13A, 13B
TEKS IPC 7D, 7E
www.scilinks.org
Topic: Genetic Engineering
Keyword: HX4092
Section 1 Review
Compare and contrast the germination of bean
seeds and corn seeds.
10C 13A 13B
Summarize the basic differences between
10C 13B
annuals, biennials, and perennials.
Provide students with prepared
microscope slides of plant tissues,
and ask them to identify meristematic and vascular tissues by drawing
what they see. LS Visual Bio 5A
578
issue culture is used to propagate orchids, houseplants,
and fruit plants. Thousands of
cultures can be made from a single
plant. Tissue culture can also be
used to produce plants with new
characteristics.
Explain how primary growth and then secondary
13A 13B
growth produce a woody stem.
Critical Thinking Analyzing Methods In
what ways does plant development differ from
5A
animal development?
TAKS Test Prep Growth that increases the
width of a plant’s stems and roots is called
13B
A germination.
C primary growth.
B differentiation.
D secondary growth.
578
Answers to Section Review
1. Corn seedlings grow straight up, and the cotyledon stays in the soil. Bean seedlings form a hook
as they grow, and the two cotyledons emerge.
TAKS 3 Bio 13A; Bio 10C, 13B
2. Annuals live for one growing season, reproduce
once, and then die. Biennials live for two growing seasons, reproduce once during the second
season, and then die. Perennials live for more
than two years and may reproduce many times.
Bio 10C; Bio 13B
3. Primary growth lengthens the stem and forms
new primary dermal, ground, and vascular
tissues. Secondary growth increases the stem’s
Chapter 26 • Plant Growth and Development
diameter by producing layers of cork and
secondary xylem and phloem.
TAKS 3 Bio 13A; Bio 13B
4. Plant development is continuous and
“reversible,” while animal development is not.
Bio 5A
5. A. Incorrect. Germination is the growth of a
plant embryo. B. Incorrect. Differentiation is
the process by which cells become specialized
in form and function. C. Incorrect. Primary
growth increases the length or height of a
plant. D. Correct. Secondary growth increases
the width of stems and roots. Bio 13B
Regulating Growth
and Development
Section 2
Section 2
Focus
Overview
Nutrients
Objectives
Like all multicellular organisms, plants grow by adding new cells
through cell division. Plants must have a steady supply of the raw
materials they use to build new cells in order to grow. Plants need only
two raw materials—carbon dioxide and water—to make all the carbohydrates in their tissues. As you learned earlier in this book, carbon
dioxide and water are needed for photosynthesis.
Like animals, plants also need oxygen for cellular respiration.
Although the green parts of a plant produce oxygen during photosynthesis, most of the oxygen used by leaves and stems comes from
the air. Roots, which usually do not carry out photosynthesis, get
oxygen from the air spaces between soil particles. If the soil around
a plant’s roots becomes compacted or saturated with water, it may
not provide enough oxygen for the roots, and the plant could die.
However, carbon dioxide, water, and oxygen do not satisfy all of a
plant’s needs for raw materials. Plants also require small amounts of
at least 14 mineral nutrients, which are elements absorbed mainly
as inorganic ions. Table 1 lists the six mineral nutrients needed in
the greatest amounts for healthy plant growth and describes the
importance of each nutrient. Commercial fertilizers may contain
most of these mineral nutrients.
● Identify the major
nutrients plants need to
grow.
10C 13B
● Describe how plant
hormones control plant
growth.
10C 11B 13B
● Relate environmental
factors to plant
growth.
11A 11B
Bellringer
Key Terms
Ask students to identify the substances plants need for survival.
After taking attendance, write their
responses on the board. (Initially,
they will probably identify light,
water, and carbon dioxide.) Prompt
them to identify other needs by
asking why people fertilize their
yards. Ask students how they think
plants might regulate their growth
and development without having
a nervous system as animals do.
(They produce hormones.)
mineral nutrient
auxin
hormone
apical dominance
tropism
photoperiodism
dormancy
Table 1 Major Mineral Nutrients Required by Plants
Nutrient
Importance
LS Interpersonal TAKS 2 Bio 4B
Nitrogen
Part of proteins, nucleic acids, chlorophylls, ATP,
and coenzymes; promotes growth of green parts
Phosphorus
Part of ATP, ADP, nucleic acids, phospholipids
of cell membranes, and some coenzymes
Potassium
Needed for active transport, enzyme activation,
osmotic balance, and stomatal opening
Calcium
Part of cell walls; needed for enzyme activity and
membrane function
Magnesium
Part of chlorophyll; needed for photosynthesis
and activation of enzymes
Sulfur
Part of some proteins and coenzyme A; needed for
cellular respiration
Motivate
Discussion/
Question
579
IPC Benchmark Fact
Have students find the six mineral nutrients listed in
Table 1 on the periodic table. Ask them to compare
and contrast the properties of these elements based
on their location in the periodic table. Which elements
are most alike and most different? Identify whether
each mineral nutrient naturally occurs as an element,
compound, or both. TAKS 4 IPC 7D (grade 11 only),
7E (grade 10 only)
Before beginning this section
review with your students the
objectives listed in the Student
Edition. This section focuses on factors that influence plant growth and
development, including nutrients,
hormones, and environmental influences such as sunlight, temperature,
and the seasons.
Chapter Resource File
• Chapter Resource File
• Lesson Plan GENERAL
• Directed Reading
• Active Reading GENERAL
• Data Sheet for Quick Lab GENERAL
• Data Sheet for Data Lab GENERAL
• Data Sheet for Math Lab GENERAL
Ask students what growth factors
soil provides plants, and whether
plants can grow without soil.
(Usually, soil provides minerals that
plants need for growth. Using a practice known as hydroponics, plants
are grown with their roots immersed
in water through which oxygen is
bubbled and to which the minerals
needed for plant growth are added.)
Consider the possibility of developing a small hydroponic garden in the
classroom. LS Verbal TAKS 2 Bio 4B
Planner CD-ROM
• Reading Organizers
• Reading Strategies
• Supplemental Reading Guide
A Feeling for the Organism
The Life and Work of
Barbara McClintock
Chapter 26 • Plant Growth and Development
579
Hormonal Control of Growth
For centuries, people have known that plants bend strongly toward a
light source as their shoots elongate. In the 1920s, the Dutch biologist
Frits Went showed that a chemical produced in the shoot tip causes
this bending response. Went named the growth-promoting chemical
that causes stems to bend auxin (AWK sin). The steps in Went’s
experiment are summarized in Figure 5.
Real Life
Teach
Real Life
Answer Bio 11C
The chemicals found in
Agent Orange are 2,4-D
(2,4-dichlorophenoxyacetic acid),
2,4,5-T (2,4,5-trichlorophenoxyacetic acid), and trace
amounts of dioxin. Exposure to
Agent Orange has been blamed
for miscarriages, skin diseases,
cancers, and birth defects.
The herbicide Agent
Orange contains two
synthetic auxins.
This herbicide was used
to defoliate plants in the
jungles of Vietnam during
the Vietnam War. One
ingredient of Agent Orange
is still commonly used as
a herbicide.
Finding Information
Find out the names of
the chemicals in Agent
Orange, and identify the
health problems to which
11C
it has been linked.
Step
Went removed the tip of an oat shoot and placed the tip on
an agar block. Auxin diffused from the tip into the block.
Step
Went then transferred the agar block to the cut end of a
shoot, which caused the shoot to grow.
Step
When Went placed an agar block with auxin on either side
of cut shoots, the shoots grew in the opposite direction.
Step
As a control, Went placed an agar block without auxin on
the cut end of other shoots. These shoots did not grow.
Auxin
Auxin is one of many plant hormones. The word hormone comes
from the Greek word horman, meaning “to set in motion.” A
hormone is a chemical that is produced in one part of an organism
and transported to another part, where it causes a response. Auxin
causes plant cell walls to become more flexible, which allows the cells
READING
SKILL
BUILDER
Reading Hint Tell students that
this textbook uses typographic
aids, such as boldfaced words and
in-text pronunciation guides, to
help them learn new terms. Tell
students that before they read a
section of the book, to find the
boldfaced terms and determine
their meanings by reading the sentence in which each term appears.
Figure 5
IO
B
graphic
1
Using the Figure
The Steps in Went’s Experiment
Auxin causes oat seedlings to elongate and bend toward light.
Auxin diffused
from the cut tip of
an oat shoot into
an agar block.
2
Application of the
agar block with the
auxin to a second
shoot resulted in
growth.
3
Cut shoots grew
away from contact
with agar with
auxin.
4
Agar without auxin
did not cause a cut
oat shoot to grow.
Shoot
tip
Walk students through Figure 5,
which summarizes the steps of Fritz
Went’s classic experiment on the
effects of auxin. Help students to
understand that when the agar is
purple, it contains auxin. Ask students to state the significance of
step 4. (It is a control designed to
show that agar is not the cause of
the effect.) Bio 3F
Agar
block
Agar
block
with
auxin
Auxin
580
did you know?
pp. 580–581
Student Edition
TAKS Obj 1 Bio/IPC 2B, 2C
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 13A
TEKS Bio 4B, 10C, 11C, 13A, 13B
TEKS Bio/IPC 2B, 2C
Teacher Edition
TAKS Obj 1 1 Bio/IPC 2B, 2C
TAKS Obj 1 IPC 3A, 3B
TAKS Obj 4 IPC 8A
TEKS Bio 3F, 11B, 11C, 13B
TEKS Bio/IPC 2B, 2C
TEKS IPC 3A, 3B, 8A
580
Darwin’s Plant Research Charles Darwin
did many experiments with plants. In the
mid-1800s, Darwin and his son Francis did the
earliest experiments on phototropism. They
discovered that a grass seedling responds to
light coming from one direction with growth
on the opposite (shaded) side, resulting in the
seedling bending toward the light source.
Bio 3F, 11B
Chapter 26 • Plant Growth and Development
IPC Benchmark Fact
Have students review Went’s experiment on the hormone auxin. Ask them to determine if his experimental
results demonstrate a physical or chemical change in
the plant. Have them defend their answers. In addition, instruct students to analyze and critique Went’s
experiment as to its strengths and weaknesses using
the information provided. TAKS 1 IPC 3A
TAKS 4 IPC 8A
to elongate as they grow. Auxin accumulates on the dark side of a
stem. As a result, the cells on the dark side of a stem elongate more
than the cells on the light side. The difference in elongation causes the
stem to grow toward the light. Auxin also inhibits the growth of the
buds along a stem. This inhibition is called apical dominance.
Cutting off the tip of a stem removes the source of auxin and enables
the other buds to grow. That is why pruning the stems of a plant
makes the plant become bushier.
Investigating the
Effects of Ethylene
on a Plant
TAKS 1 Bio 2B, 2C; Bio 13B
Skills Acquired
Observing, making
comparisons, drawing
conclusions
Hormones in Agriculture
More than a century ago, citrus farmers discovered that they could
cause citrus fruits to ripen by storing them in a room heated by a
kerosene stove. The ripening was caused by ethylene, which is a
gaseous organic compound produced when kerosene is incompletely burned. Most plant tissues produce ethylene. Today, ethylene
is used to promote the ripening of tomatoes, bananas, and other
fruits that are harvested before they ripen. Ethylene also loosens the
fruit of cherries, blackberries, and blueberries, making it easier to
harvest these crops mechanically.
Gibberellins (jihb uhr EHL ihnz) are produced in developing
shoots and seeds. They stimulate stem elongation, fruit development,
and seed germination. Gibberellins are used to enlarge Thompson
seedless grapes. Other seedless fruits treated with gibberellins
include apples, cucumbers, mandarin oranges, and peaches.
Cytokinins (sie toh KIE nihnz), which are produced in root tips,
stimulate cell division and slow the aging of some plant organs.
Cytokinins are sprayed on cut flowers to keep them fresh and on
fruits and vegetables to extend their shelf life. Cytokinins are
added to tissue-culture media to cause undifferentiated cells to
form shoots.
Investigating the Effects
of Ethylene on a Plant
Teacher’s Notes
Tell students that ethylene
affects plants in many ways.
For example, when some plants
are exposed to ethylene gas,
they do not elongate normally.
Ethylene also promotes the production of male flowers in plants
such as squash and cucumbers.
Ethylene is used by citrus-fruit
growers to ripen fruits that are
picked while they are still green.
www.scilinks.org
Topic: Plant Hormones
Keyword: HX4140
Answers to Analysis
1. Answers will vary. Plants in
jars containing an apple should
begin to lose their leaves after
a few days.
2. Answers will vary. From the
results of this experiment,
students should conclude that
ethylene promotes plant aging
and leaf drop.
2B 2C 13B
TAKS 1
You can use a ripe apple to see one of the
effects of ethylene on plants.
Materials
4 L glass jars with lids (2), 2 plants in 5 cm pots,
small ripe apple
IPC Benchmark
Mini-Lesson
Procedure
1. Place a plant inside one of
the jars. Tightly secure the lid.
3. Observe both jars for several
days. Record what you see.
2. Place the other plant and
the apple inside the other jar.
Tightly secure the lid.
Analysis
1. Describe any changes in
the plant in each jar.
2. Critical Thinking
Drawing Conclusions
A ripe apple gives off ethylene
gas. Based on your observations, how does ethylene
affect a plant?
581
MISCONCEPTION
ALERT
Anthropomorphizing Plants It is common
for students to attribute human characteristics to nonhuman organisms, such as plants
and animals. Thus, students might think that
a plant’s response to light, for example, is
somehow conscious, or that plants bend
toward the light because they see it.
Emphasize that a plant’s response to light,
gravity, or other environmental stimuli is
simply a hormonal stimulus-response. Plants
do not perceive environmental stimuli in the
same way that humans and animals do. Bio 11B
Rotten Apples The expression “One rotten
apple spoils the whole barrel” is commonly
used to refer to people whose unacceptable
behavior may influence others to behave unacceptably. This expression comes from the
observation by food growers and handlers that
a rotten apple in a barrel of apples results in all
the apples rotting. The explanation is that rotting fruit give off ethylene, which promotes the
ripening of other nearby fruits. The rotting
fruit is infected with a fungus, which easily
infects other fruit after they ripen. Bio 11B
IPC Skills TAKS 1 IPC 3B
Draw inferences based on data related
to promotional materials for products
and services.
Activity Bring in advertisements, packages or containers for products that
claim they can cause muscle growth
and increased strength. Have the students research the substances in the
products to determine if the products
are truly effective.
Transparencies
TT Major Mineral Nutrients Required
by Plants
TT Bread Wheat
TT Went’s Experiment
Chapter 26 • Plant Growth and Development
581
Environmental Influences
on Growth
Teach, continued
continued
READING
SKILL
BUILDER
Reading Organizer Before students
finish reading this section, have them
make a list of the following terms:
auxin, tropism, phototropism,
gravitropism, and thigmotropism.
As they learn about the terms, have
them write a brief definition of
each term. Have them save their
list of terms and definitions for use
later in the Reteaching exercise at
the end of this section. LS Verbal
Teaching Tip
The word thigmotropism
comes from the Greek
words thigma, meaning
“touch,” and tropos,
meaning “turn.”
Tropisms
A tropism (TROH piz uhm) is a response in which a plant grows
either toward or away from a stimulus. Auxin is responsible for producing tropisms. Figure 6 shows examples of three common types of
tropisms. Phototropisms are responses to light. Responses to gravity
are called gravitropisms. A thigmotropism is a response to touch. If
a plant grows toward a stimulus, the response is called a positive
tropism. If a plant grows away from the direction of the stimulus,
the response is called a negative tropism. Thus, a shoot that grows
up out of the ground shows both positive phototropism (growing
toward the light) and negative gravitropism (growing away from the
pull of gravity).
GENERAL
Tissue Culture Tell students that
the growth of whole plants from
pieces of plants in tissue culture
requires the addition of plant
hormones in order for them to
differentiate properly. The relative
amounts of the hormones affect the
process of differentiation. Typically,
auxins and cytokinins are first
added to the culture medium to
promote the formation of a mass of
undifferentiated cells. Next a high
level of auxins and a low level of
cytokinins are added to the culture
medium. This promotes root formation. Then a low level of auxins
and a high level of cytokinins are
added to the culture medium. This
promotes shoot formation.
Because most plants are anchored in one spot, they cannot move
from an unfavorable environment to a more favorable one as
animals do. Instead, plants respond to their environment by
adjusting the rate and pattern of their growth. For example, a plant
that receives plenty of water and mineral nutrients may grow
much faster and larger than it would if it received very little water
and mineral nutrients. Also, a plant grown in full sun may grow
much faster and larger than it would if it were grown in the shade
or indoors. So the availability of light and nutrients affect the rate
of plant growth. Many of a plant’s responses to environmental
stimuli, however, are triggered by the hormones that regulate
plant growth.
Figure 6 Tropisms
Tropisms are growth responses that occur either toward or away from a stimulus.
TAKS 2 Bio 4B; Bio 5B, 5C
The bending of an amaryllis toward
the light is a positive phototropism.
The upward growth of shoots is a negative gravitropism; the downward growth
of roots is a positive gravitropism.
The coiling of grapevine tendrils
around a wire is a thigmotropism.
582
Career
pp. 582–583
Student Edition
TAKS Obj 3 Bio 13A
TEKS Bio 13A, 13B
Teacher Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 7B, 13A
TEKS Bio 3D, 4B, 5B, 5C, 7B, 11B,
13A, 13B
582
Horticulturist Horticulturists study fruits,
vegetables, and ornamental plants. These plant
scientists are interested in producing better
fruit, vegetable, and ornamental crops with less
pesticides, fertilizers, and water. Have students
work in teams to use library references or
on-line databases to find information about
the role of horticulturists in food production.
Have students investigate current research
projects in horticulture, and have them report
their findings to their classmates. Bio 3D
Chapter 26 • Plant Growth and Development
Trends in Plant Genetics
Genetic Diversity The National Plant
Germplasm System (NPGS) is a cooperative
effort to preserve the genetic diversity of
plants. When plants lose their genetic diversity,
which happens when only a few varieties of a
species are cultivated, these species can be
wiped out easily by a single disease or environmental condition to which they are sensitive.
However, when many varieties of a species are
cultivated, some varieties will have genes that
confer resistance to various pests and diseases,
or allow the plant to survive certain adverse
conditions. TAKS 3 Bio 7B, 13A
0100010110
011101010
0010010001001
1100100100010
0000101001001
1101010100100
0101010010010
Interpreting Annual Rings
13A 13B
Background
TAKS 3
The annual rings of a woody stem provide important
clues to annual variations in the rainfall an area receives
over time. Thick rings form in years with heavy rainfall.
Relatively thin rings form in dry years. Use the photo at
right to answer the following questions.
TAKS 3 Bio 13A; 13B
0100010110
011101010
0010010001001
1100100100010
0000101001001
1101010100100
0101010010010
A
B
Analysis
1. Critical Thinking
Interpreting Data What do
the annual rings indicate
about the climate where this
plant grew?
Interpreting
Annual Rings
2. Critical Thinking
Drawing Conclusions
Which ring, A or B, indicates a
year when this plant received
more rainfall?
3. Critical Thinking
Making Predictions How
will the annual rings of a
nearby tree of the same age
and species compare with
those of this tree?
Photoperiodism
Certain plants bloom in the spring and others bloom in the summer
or fall. Some plants bloom as soon as they reach a mature size. In
many plants, seasonal patterns of flowering and other aspects of
growth and development are caused by changes in the length of
Figure 7 Flowering and
days and nights. The response of a plant to the length of days and
photoperiodism. Long-day
plants flower when nights are
nights is called photoperiodism.
short. Short-day plants flower
Most plants can be categorized as one of three types in reference
when nights are long. If a flash
to photoperiodism. A plant that responds when days become shorter
of light interrupts a long night,
than a certain number of hours is said to be a short-day plant. A
long-day plants flower and
plant that responds when days become longer than a certain numshort-day plants do not.
ber of hours is called a long-day
Early summer
Late fall
Night interrupted
plant. Plants whose growth and
Midnight
Midnight
Midnight
development are not affected by day
6 A.M.
6 A.M.
6 A.M.
6 P.M.
6 P.M.
6 P.M.
length are known as day-neutral
plants. It is really the length of the
Noon
Noon
Noon
nights, however, rather than the
length of the days that controls
photoperiodism, as Figure 7 shows.
Long-day plant: Bearded iris
Knowledge of photoperiodism is
very important to the nursery and
floral industries. The length of days
and nights is controlled artificially in
greenhouses where plants such as
poinsettias and chrysanthemums are
grown. Thus, commercial growers
Short-day plant: Poinsettia
force the plants to produce flowers
at times of the year when they ordinarily would not. This makes it
possible for poinsettias to be available
for Christmas and chrysanthemums
to be available year round.
583
MISCONCEPTION
ALERT
GENERAL
Plant ”Food“ Fertilizers are often referred
to as plant “food.” However, the term food
is usually reserved for organic substances
that provide a source of energy and organic
molecules for living things when they are
broken down. Because minerals do not contain usable energy and are not broken down
in plants, they should not be referred to as
food. Plants do not eat food; rather, they
produce their own organic molecules during
photosynthesis.
Skills Acquired
Making observations,
analyzing data, making
conclusions
Teacher’s Notes
Point out to students that it is
the number of rings in a tree
trunk that indicates its age,
not the diameter of the trunk.
A number of environmental
factors can influence the width
of an annual ring.
Answers to Analysis
1. Answers will vary. The rings
indicate that the tree grew in a
temperate climate and that the
amount of rainfall varied from
year to year.
2. A
3. They should be very similar.
Using the Figure
GENERAL
Walk students through Figure 7
by first following what happens to
long-day (short-night) and shortday (long-night) plants when the
days are long and the nights are
short. Then follow what happens
to long-day (short-night) and shortday (long-night) plants when the
days are short and the nights are
long. Finally, follow what happens
to long-day (short-night) and shortday (long-night) plants when they
are grown under long nights that
are interrupted by a flash of light
in the middle of the night. Tell students that poinsettias are short-day
(long-night) plants that are desirable ornamentals for the Christmas
holidays. Ask students if these plants
would normally produce flowers in
late December. (yes) Ask students
what would happen if lights were
turned on during the night in a
greenhouse where poinsettias are
grown? (The plants would not bloom.)
Bio 11B
Transparencies
TT Flowering and Photoperiodism
Chapter 26 • Plant Growth and Development
583
6C
Responses to Temperature
Temperature affects growth and development in many plants. For
example, most tomato plants will not produce fruit if the nighttime
temperatures are too high. Many plants that flower in early spring
will not produce flowers until they have been exposed to cold temperatures for a certain number of hours. Most deciduous woody
plants drop their leaves in the fall in response to shorter periods of
daylight. Thick, protective scales develop around their buds, as
Figure 8 shows. After a period of low temperatures, the buds begin
growing into new leaves or sections of woody stem.
Dormancy is the condition in which a plant or a seed remains
inactive, even when conditions are suitable for growth. Many plants
and seeds remain dormant until they have been exposed to low temperatures for several weeks. Dormancy helps plants to survive by
keeping buds from growing and seeds from germinating during
warm spells before winter has ended.
Teach, continued
continued
76
0
2
x 2+ 6x
5
-7-0
<
493
Analyzing the
Effect of Cold on
Seed Germination
Bio 10C, 11B, 13B
Figure 8 Bud dormancy.
Thick scales cover the
dormant buds on this twig
from an apple tree.
Skills Acquired
Interpreting graphs,
analyzing data
8
493
x 2+ 6x
0
2
5
-7-0
<
Teacher’s Notes
Seeds with true dormancy cannot germinate until the plant
hormone abscisic acid is either
washed away or broken down.
Answers to Analysis
1. Cold temperatures promote
the germination of apple seeds.
2. 45 days ⫼ 7 days/week ⫽
6.43 weeks
3. 30 percent
4. 100 percent
TAKS 9 TAKS 10
Background
In some plants, a period of low temperatures is needed
to break seed dormancy. The graph at right shows how
being stored at a low temperature (4ºC) affected the
ability of apple seeds to germinate. Use the graph to
answer the following questions.
Reteaching
Have students list the boldfaced
terms in this section with their
definitions. Have them create a
crossword puzzle using the definitions as clues and the terms as
words in the puzzle. LS Logical
GENERAL
True or False:
1. Minerals and water satisfy all of a
plant’s raw materials needs. (false)
2. Auxin is a type of plant
hormone. (true)
Effect of Cold Storage
100
80
60
40
20
0 10 20 30 40 50 60 70
Number of days at 4ºC
Analysis
1. Summarize the overall effect
of cold temperatures on the
germination of apple seeds.
Close
Quiz
Analyzing the Effect of Cold
on Seed Germination 10C 11B 13B
Percent germination
18
2. Calculate the number of
weeks that apple seeds must
be stored at 4ºC for at least
80 percent of the seeds to
germinate.
3. Critical Thinking
Interpreting Graphs What
percentage of apple seeds
germinate after storage at 4ºC
for 20 days?
4. Critical Thinking
Predicting Patterns What
percentage of apple seeds will
germinate after being stored at
4ºC for 80 days?
Math TAKS Obj. 10, 8.14C; Obj 9, 8.3B
Section 2 Review
List the six mineral nutrients that plants require
Critical Thinking Predicting Outcomes Why
in the greatest amounts.
is it an advantage for plant growth and development to be regulated by environmental stimuli?
Explain how auxin causes a stem to grow
toward a light source.
11B
Describe an example of a negative
gravitropism.
11B
11A
TAKS Test Prep When a vine responds to the
touch of a fence wire by growing a tendril around
11B
the wire, the vine is exhibiting
A gravitropism.
C phototropism.
B thigmotropism.
D photoperiodism.
584
Alternative
Assessment
GENERAL
Ask students to summarize the roles
of the plant hormones discussed in
this section.
pp. 584–585
Student Edition
TAKS Obj 3 Bio 13A
Math TAKS Obj 9 Math 8.3B
Math TAKS Obj 10 Math 8.14C
TEKS Bio 10C, 11B, 13A, 13B
Teacher Edition
TEKS Bio 10C, 11A, 11B, 13B
584
Answers to Section Review
1. nitrogen, phosphorus, potassium, calcium,
magnesium, sulfur
2. Auxin diffuses to the side of a stem away from
a light source. There, it stimulates cells to grow
longer than they do on the side of the stem
facing the light source. This results in the stem
bending toward the light source. Bio 11B
3. An example of a negative gravitropism is a
shoot growing upward from the soil after a
seed germinates. Bio 11B
Chapter 26 • Plant Growth and Development
4. It is an advantage for plant growth to be regulated by environmental stimuli because plants
are unable to move to a new environment
when conditions become unfavorable. Bio 11A
5. A. Incorrect. Gravitropism is the response of
a plant to gravity. B. Correct. Thigmotropism is
the response of a plant to touch. C. Incorrect.
Phototropism is the response of a plant to light.
D. Incorrect. Photoperiodism is the response of
a plant to the length of days and nights. Bio 11B
Study
CHAPTER HIGHLIGHTS
ZONE
Alternative Assessment
Key Concepts
Key Terms
Organize students into groups. Have
each group use the information in
Chapter 26 to prepare a multimedia
presentation on plant growth and
development that they could give
to a middle-school science class or
to the general public.
Section 1
1 How Plants Grow and Develop
●
Germination is the resumption of growth by the embryo in a
seed. Water and oxygen must penetrate the seed coat before
germination can occur.
●
Annuals complete their life cycle in one growing season.
Biennials complete their life cycle in two growing seasons.
Perennials live several years and may reproduce many times.
●
Apical meristems located at the tips of shoots and roots
produce primary growth. The tissues that result from
primary growth are known as primary tissues.
●
Secondary growth increases a plant’s stem and root width.
In woody stems, secondary growth is produced by the cork
cambium and vascular cambium, two meristems near the
outside of the stem.
●
Bread wheat is a cereal grass with long leaves, hollow
stems, and clusters of tiny flowers. The fruits, or grains,
are usually ground into flour that is used to make bread.
●
Plants develop throughout their lives. Plant development
is reversible. Many mature plant cells can divide to form
masses of undifferentiated cells, which can develop into
a new plant.
germination (572)
perennial (573)
annual (573)
biennial (573)
primary growth (574)
secondary growth (574)
apical meristem (574)
cork cambium (575)
vascular cambium (575)
annual ring (575)
Chapter Resource File
• Science Skills Worksheet
• Critical Thinking
Worksheet
• Test Prep Pretest GENERAL
• Chapter Test GENERAL
GENERAL
Section 2
2 Regulating Plant Growth and Development
●
Plants need at least 14 mineral nutrients for growth. They
also need carbon dioxide and water for photosynthesis and
oxygen for cellular respiration.
●
Hormones regulate plant growth and development. Auxin
is a hormone that causes shoots to elongate and inhibits the
growth of lateral buds.
●
Plants modify their growth in response to the direction
of light, gravity, and touch. Such growth responses are
called tropisms.
●
Seeds and many mature plants survive periods of unfavorable
environmental conditions by becoming dormant.
●
In many plants, seasonal patterns of flowering and other
aspects of growth and development are caused by changes in
the length of days and nights.
mineral nutrient (579)
auxin (580)
hormone (580)
apical dominance (581)
tropism (582)
photoperiodism (583)
dormancy (584)
585
Answer to Concept Map
The following is one of several possible answers
to Performance Zone item 15.
apical meristem
which produces
primary tissues
Meristems
include
vascular cambium
cork cambium
which produces
which produces
secondary xylem
secondary phloem
by
by
in
bark
primary growth
secondary growth
which increases the
which increases the
length
width
of
of
stems
cork
roots
stems
roots
Chapter 26 • Plant Growth and Development
585
Performance
CHAPTER REVIEW
ZONE
CHAPTER 26
ANSWERS
Using Key Terms
Using Key Terms
1. The first sign of germination of a bean seed
1. a Bio 13B
2. c Bio 13B
3. c Bio 13B
4. d Bio 5A TAKS 3 Bio 13A
5. a. Germination is the term for
the resumption of growth by
the embryo in a seed.
b. A perennial is a plant that lives
for more than two years and
may reproduce many times.
c. Apical dominance is the inhibition of the growth of side
buds that is caused by auxin
produced in the tip of a shoot.
d. Dormancy is the condition in
which seeds or buds do not
grow even when environmental
conditions are favorable for
growth to occur. Bio 11B
6. a Bio 5B, 10C
7. d
8. b
9. b Bio 10C, 11B
10. d Bio 11B, 13B
11. b TAKS 3, Bio 11A, 11B, 13A, 13B
12. Cytokinins stimulate cell division
and slow aging. They are used in
agriculture to prolong freshness of
cut flowers, fruits, and vegetables
and to stimulate shoot growth
in tissue cultures. Gibberellins
stimulate stem elongation, fruit
development, and seed germination. They are used in agriculture
to induce fruit formation without
seeds and to enlarge seedless fruits.
Bio 11B
is the emergence of the embryo’s
13B
a. root.
c. sheathed shoot.
b. hooked shoot.
d. cotyledons.
2. Plants that live several years or more are
known as
13B
a. annuals.
b. biennials.
10. Which of the following caused the growth
patterns of the mums shown below?
a. apical meristem
b. auxin
c. apical dominance
d. all of the above
c. perennials.
d. terminals.
3. Providing cells for growth at the tips of a
plant is the main function of the
a. cork cambium.
b. root cap.
c. apical meristems.
d. lateral meristems.
4. Cell division that increases the diameter of
a woody stem occurs in the
a. pith.
b. primary tissues.
c. apical meristems.
d. vascular cambium.
5A
5. Write a sentence that shows your under-
11. The response of a plant to the length of
standing of each of the following terms.
a. germination
b. perennial
c. apical dominance
d. dormancy
11B
6. Plant and animal development differ in
that plant development
5B
a. is continuous and reversible.
b. stops after a plant reaches maturity.
c. is not affected by environment.
d. is controlled by genes that cannot be
reactivated.
7. Which of the following is not a raw
material needed for plant growth?
a. carbon dioxide
b. water
c. oxygen
d. vitamins
8. Major mineral nutrients required by plants
include all of the following except
a. nitrogen.
c. phosphorus.
b. lead.
d. potassium.
days and nights is
a. gravitropism.
b. photoperiodism.
c. phototropism.
d. thigmotropism.
11A 11B
12. How do cytokinins and gibberellins affect
plant growth, and how are these hormones
11B
used in agriculture?
13. Up Close How does the chromosome
number of bread wheat differ from that of
6A 6D
diploid organisms?
14.
How is tissue culture used to
produce hybrid varieties of plants?
6D
15.
Concept Mapping Construct a
concept map that describes growth in
vascular plants. Try to include the following terms in your map: meristems, apical
meristem, primary growth, primary tissues,
cork cambium, secondary growth, cork,
secondary phloem, secondary xylem, and
vascular cambium.
2C
586
10 only)
14. Hybrid cells, made from the fusion of two cells
from two different types of plants, are grown
into new, hybrid plants in tissue culture.
TAKS 2 Bio 6D (grade 10 only)
pp. 586–587
Review and Assess
TAKS Obj 1 Bio/IPC 2B, 2C, 2D
TAKS Obj 2 Bio 6A, 6D
TAKS Obj 3 Bio 13A
TEKS Bio 3D, 5A, 5B, 6A, 6B, 10C,
11A, 11B, 13A, 13B
11B
13B
13. Wheat cells have six of each kind of chromosome rather than two of each kind as in
diploid organisms. TAKS 2 Bio 6A, 6D (grade
586
9. Auxin causes cells to
11B
a. have less flexible cell walls.
b. elongate more as they grow.
c. bend toward light.
d. develop lateral buds.
15. One possible answer to the concept map is
found at the bottom of the Study Zone page.
TAKS 1 Bio/IPC 2C
Chapter 26 • Plant Growth and Development
Assignment Guide
Section
1
2
Questions
1–5b, 13–16, 18, 19, 21
5c–d, 6–12, 17, 20
Critical Thinking
Alternative Assessment
Critical Thinking
16. Analyzing Methods Some seeds are soaked
20. Finding and Communicating Information
16. Answers will vary. Students should
realize that acid would probably
damage the seed coat. Water can
then penetrate the seed, and the
seed will sprout. Seeds treated
with acid germinate more quickly
and more uniformly than do
untreated seeds.
17. The energy for a carrot plant’s
second year of growth comes
from compounds that are stored
in the root. Bio 13B
18. The cells in these plant parts are
able to reverse their development.
These cells can produce cells that
are undifferentiated, which can
then undergo differentiation to
form all of the tissues necessary
to grow an entire new plant.
in acid before they are packaged and sold
to farmers and home gardeners. What is
the purpose of this treatment?
17. Applying Information Carrots are biennials.
What role does the root of a carrot plant play
in the plant’s second year of growth?
13B
18. Forming Reasoned Opinions Why is it
possible for people to grow new plants
from pieces of leaf, stem, or root tissue in
which the cells have already undergone
differentiation?
5A
19. Evaluating Results A student placed a
green banana in each of 10 plastic bags.
The student also placed a ripe pear in five
of the bags and then sealed all of the bags.
The bananas in the bags without pears took
longer to ripen than the bananas in the
bags with pears. Evaluate these
experimental results.
2C
Use the media center or Internet resources
to learn how commercial growers produce
plants such as poinsettias and chrysanthemums that flower at times when they
would not flower in nature. Summarize
your findings in a written report.
2B 2D
21. Organizing Information Research bonsai—
the Asian art of growing miniature plants.
Relate your findings in a report that explains
plant growth and development in bonsai.
22. Career Connection Agronomist Agrono-
mists study soil management and crop
production. Write a report that includes
a job description, training required, kinds
of employers, growth prospects, and
starting salary.
3D
Bio 5A
TAKS Test Prep
The diagram below summarizes an experiment
investigating the hormonal control of growth in
an oat shoot. Use the diagram and your knowledge of science to answer questions 1–3.
Shoot
tip
1
Agar
block
Agar block
with auxin
2
3
Auxin
Oat shoot
13B
2. What happened in step 3?
F The weight of the agar block caused the
shoot to bend.
G Exposing one side of the shoot to auxin
caused the shoot to grow in the opposite
direction.
H The agar block shielded one side of the
shoot from light, causing the shoot to
grow in the opposite direction.
J Auxin from the agar block caused the
shoot to exhibit positive gravitropism.
3. What would likely happen if an agar block
1. What happened in step 2?
13B
A Auxin from the agar block stimulated the
shoot to grow.
B The shoot produced auxin in response to
the agar block.
C The agar block stopped further growth of
the shoot.
D The shoot grew straight up in response to
an agar block.
1. A. Correct. Auxin is a growth-promoting
chemical. It diffused from the agar block into
the shoot, causing it to grow. B. Incorrect. Agar
does not stimulate plants to produce auxin.
C. Incorrect. Agar does not stop the growth.
D. Incorrect. Agar does not stimulate shoots.
Bio 13B
2. F. Incorrect. If the weight of the agar block
were to cause the shoot to bend, it would bend
in the direction of the block, where the weight
is applied. G. Correct. The auxin diffused from
the agar block into the side of the shoot.
Growth on this side of the shoot resulted in
without auxin were placed on the cut end of
an oat shoot?
13B
A The shoot would grow straight up.
B The shoot would grow straight down.
C The shoot would bend and grow around
the agar block.
D The shoot would not grow.
Test
Carefully study all of the details of a diagram before
answering the question or questions that refer to it.
587
bending in the opposite direction. H. Incorrect.
Light is not the direct cause of plant growth.
J. Incorrect. Gravitropism is a response to
gravity, not to auxin. Bio 13B
3. A. Incorrect. An agar block without auxin
would not stimulate the shoot to grow.
B. Incorrect. The shoot cannot grow straight
down. C. Incorrect. An agar block without
auxin would not stimulate the shoot to grow.
D. Correct. An agar block without auxin
would not stimulate the shoot to grow.
Bio 13B
19. Ripe pears give off ethylene, which
promoted ripening in the bananas.
TAKS 1 Bio/IPC 2C
Alternative Assessment
20. Answers will vary.
TAKS 1 Bio/IPC 2B, 2D
21. In the practice of bonsai, plants
are shaped by selective pruning
and training and are kept small
by pruning their roots and shoots,
potting them in small containers,
and watering and fertilizing them
sparingly.
22. Agronomists are plant scientists
who traditionally study crops and
soils. Many agronomists work in
the field, in government and at
universities. Others work for private industry or state agricultural
extension services. Positions are
available for individuals with
bachelor’s degrees, master’s
degrees, and PhD’s in agronomy
or soil science. Starting salary will
vary by region. Bio 3D
TAKS Test Prep
• The Science TAKS Prep Appendix
in this book provides integrated
biology and IPC TAKS practice.
• The Holt Science TAKS Practice
Workbook provides a review of
biology, chemistry, and physics
concepts tested on the grades 10
and 11 science TAKS.
Chapter 26 • Plant Growth and Development
587