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Chapter Presentation
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Visual Concepts
Standardized Test Prep
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Chapter 26
Plant Growth and Development
Table of Contents
Section 1 How Plants Grow and Develop
Section 2 Regulating Growth and Development
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Chapter 26
Section 1 How Plants Grow and
Develop
Objectives
• Compare seed germination in beans and corn.
• Contrast annuals, biennials, and perennials.
• Explain how primary and secondary growth are
produced.
• Describe several traits of bread wheat.
• Contrast development in plants and animals.
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Chapter 26
Section 1 How Plants Grow and
Develop
Seeds Sprout
• A seed contains a plant embryo that is in a state of
suspended animation.
• A seed cannot sprout until water and oxygen
penetrate the seed coat.
• If enough water and oxygen are available after the
seed coat breaks, the young plant, or seedling,
begins to grow.
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Chapter 26
Section 1 How Plants Grow and
Develop
Seeds Sprout, continued
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.
• After the shoot of a seedling emerges, its roots and
shoots continue to grow throughout its life.
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Chapter 26
Section 1 How Plants Grow and
Develop
Seed Germination
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Chapter 26
Section 1 How Plants Grow and
Develop
Germination of a Monocot
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Chapter 26
Section 1 How Plants Grow and
Develop
Germination of a Dicot
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Chapter 26
Section 1 How Plants Grow and
Develop
Seeds Sprout, continued
Plant Life Spans
• A perennial is a plant that lives for several years.
Most perennials reproduce many times during
their life span.
• 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.
• A biennial is a flowering plant that takes two
growing seasons to complete its life cycle.
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Chapter 26
Section 1 How Plants Grow and
Develop
Meristems
• Plants grow by producing new cells in regions of
active cell division called meristems.
• Growth that increases the length or height of a plant
is called primary growth.
• Growth that increases the width of stems and roots is
called secondary growth.
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Chapter 26
Section 1 How Plants Grow and
Develop
Meristem
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Chapter 26
Section 1 How Plants Grow and
Develop
Meristems, continued
Primary Growth
• Apical meristems, which are located at the tips of
stems and roots, produce primary growth through cell
division.
• 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.
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Chapter 26
Section 1 How Plants Grow and
Develop
Apical Meristems
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Chapter 26
Section 1 How Plants Grow and
Develop
Primary Growth in Plants
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Chapter 26
Section 1 How Plants Grow and
Develop
Meristems, continued
Secondary Growth
• 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, lies within
the bark and produces cork cells.
• The other meristem, called the vascular cambium,
lies just under the bark and produces vascular
tissues.
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Chapter 26
Section 1 How Plants Grow and
Develop
Meristems, continued
Secondary Growth
• A woody stem develops in three steps:
Step 1 A young woody stem has a ring of vascular bundles
between the cortex and the pith.
Step 2 A vascular cambium forms between the xylem and
phloem in each vascular bundle. Cork cambium forms under the
epidermis.
Step 3 In a mature stem, the vascular cambium adds new layers
of secondary xylem and phloem each year. The layers are
called annual rings.
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Chapter 26
Section 1 How Plants Grow and
Develop
Development of a Woody Stem
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Chapter 26
Section 1 How Plants Grow and
Develop
Secondary Growth in Plants
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Chapter 26
Section 1 How Plants Grow and
Develop
Bread Wheat
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Chapter 26
Section 1 How Plants Grow and
Develop
Bread Wheat (cont.)
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Chapter 26
Section 1 How Plants Grow and
Develop
Plant Development
• Plants 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. 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.
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Chapter 26
Section 2 Regulating Growth and
Development
Objectives
• Identify the major nutrients plants need to grow.
• Describe how plant hormones control plant growth.
• Relate environmental factors to plant growth.
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Chapter 26
Section 2 Regulating Growth and
Development
Nutrients
• Plants need only two raw materials—carbon dioxide
and water—to make all the carbohydrates in their
tissues.
• Like animals, plants also need oxygen for cellular
respiration.
• Plants also require small amounts of at least 14
mineral nutrients, which are elements absorbed
mainly as inorganic ions.
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Chapter 26
Section 2 Regulating Growth and
Development
Major Mineral Nutrients Required by Plants
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Chapter 26
Section 2 Regulating Growth and
Development
Mineral Nutrients and Plants
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Chapter 26
Section 2 Regulating Growth and
Development
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.
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Chapter 26
Section 2 Regulating Growth and
Development
Hormonal Control of Growth, continued
• The steps in Went’s experiment are:
Step 1 Went removed the tip of an oat shoot and placed the tip
on an agar block.
Step 2 Went then transferred the agar block to the cut end of a
shoot, which caused the shoot to grow.
Step 3 Went placed a block with auxin on one side of a shoot,
and the shoot grew in the opposite direction.
Step 4 As a control, Went placed an agar block without auxin on
the cut end of other shoots. These shoots did not grow.
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Chapter 26
Section 2 Regulating Growth and
Development
The Steps in Went’s Experiment
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Chapter 26
Section 2 Regulating Growth and
Development
Hormonal Control of Growth, continued
Auxin
• Auxin is one of many plant hormones. 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 to elongate as they
grow. Auxin accumulates on the dark side of a stem.
• Auxin also inhibits the growth of the buds along a
stem. This inhibition is called apical dominance.
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Chapter 26
Section 2 Regulating Growth and
Development
Auxins
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Chapter 26
Section 2 Regulating Growth and
Development
Apical Dominance
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Chapter 26
Section 2 Regulating Growth and
Development
Hormonal Control of Growth, continued
Hormones in Agriculture
• 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.
• Gibberellins are produced in developing shoots and seeds. They
stimulate stem elongation, fruit development, and seed
germination.
• Cytokinins, which are produced in root tips, stimulate cell
division and slow the aging of some plant organs.
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Chapter 26
Section 2 Regulating Growth and
Development
Types of Plant Hormones
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Chapter 26
Section 2 Regulating Growth and
Development
Ethylene
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Chapter 26
Section 2 Regulating Growth and
Development
Cytokinins
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Chapter 26
Section 2 Regulating Growth and
Development
Environmental Influences on Growth
Tropisms
• A tropism is a response in which a plant grows
either toward or away from a stimulus.
• 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.
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Chapter 26
Section 2 Regulating Growth and
Development
Tropism
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Chapter 26
Section 2 Regulating Growth and
Development
Gravitropism
in Plants
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Chapter 26
Section 2 Regulating Growth and
Development
Environmental Influences on Growth,
continued
Photoperiodism
• The response of a plant to the length of days and
nights is called photoperiodism.
• A plant that responds when days become shorter
than a certain number of hours is said to be a
short-day plant.
• A plant that responds when days become longer
than a certain number of hours is called a long-day
plant.
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Chapter 26
Section 2 Regulating Growth and
Development
Flowering and
Photoperiodism
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Chapter 26
Section 2 Regulating Growth and
Development
Photoperiodism
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Chapter 26
Section 2 Regulating Growth and
Development
Environmental Influences on Growth,
continued
Responses to Temperature
• Temperature affects growth and development in
many plants.
• 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.
• Dormancy is the condition in which a plant or a seed
remains inactive, even when conditions are suitable
for growth.
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Chapter 26
Section 2 Regulating Growth and
Development
Dormancy
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Chapter 26
Standardized Test Prep
Multiple Choice
The diagram below summarizes an experiment
investigating the hormonal control of growth in an oat
shoot. Use the diagram to answer questions 1–3.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
1. What happened in step 2?
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.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
1. What happened in step 2?
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.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
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.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
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.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
3. What would likely happen if an agar block without
auxin were placed on the cut end of an oat shoot?
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.
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Chapter 26
Standardized Test Prep
Multiple Choice, continued
3. What would likely happen if an agar block without
auxin were placed on the cut end of an oat shoot?
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.
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