Download Plant Responses to Stimuli

S E C T I O N
15.1
Plant Responses to Stimuli
E X P E C TAT I O N S
Describe the effects of growth
regulators.
Design and carry out
experiments to study factors
that affect the growth of
plants.
Describe the structure and
function of a vascular plant.
Describe some of the
industrial processes that
use plants.
Figure 15.1 Some plants can
propogate, or grow new
individuals, from a leaf.
Plants as living organisms have the ability to:
use energy to obtain materials from the external
environment, and
use energy to rearrange those materials into new
plant substances.
With very few exceptions, plants acquire all the
matter and energy they need:
without changing location (as must most animals,
protists, and bacteria),
without preying on other living organisms
(as animals do), and
without relying on matter assembled by other
organisms (as fungi do).
Some plants, such as the Bryophyllum shown in
Figure 15.1 can grow new individuals from a leaf.
Some trees, such as sumac and poplar, grow new
individuals, called suckers, from the roots. Spider
plants and strawberries grow stems from which
new individuals can become established at some
distance from the original plant. This is shown in
Figure 15.2. Many grasses grow from nodes in their
roots. A field that has been ploughed or overgrazed
will be covered by a new blanket of grasses that
grew from the roots of the old plants.
Wo rd
LINK
The term “plant” comes from the Latin word planta which
means sprout, slip, or cutting. Today we apply the term “plant”
to entire organisms, not just slips or cuttings.
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MHR • Plants: Anatomy, Growth, and Functions
Figure 15.2 Plants such as this spider plant are able to
grow new individuals from stems from the plant.
Herbivorous animals eat and gain nutrients from
plants. Most plants however, obtain their nutrients
from the air and the soil. Some plant species
however, are able to “prey”, or eat and gain
nutrients from animals. Figure 15.3 on the next
page shows the pitcher plant (the provincial flower
A pitcher plant
B Venus’s-flytrap — open
C Venus’s-flytrap — closed
Figure 15.3 Plants such as the pitcher plant and the Venus’s-flytrap are
consumers. They are not able to meet their nutritional requirements from
the air and the soil.
of Newfoundland and Labrador) and the Venus’sflytrap, both of which are consumers. They trap
and digest insects in order to obtain nutrients that
are not available in the nutrient-poor soil they grow
in. These plants are also producers because they
photosynthesize, as well.
repeatedly, they begin to differ in shape, in the
relative proportions of their various organelles, and
in the functions they can perform. These changes
result in the cells becoming specialized for
particular functions, such as photosynthesis,
storage, and support.
Development in the Meristem
What gives plants their amazing ability to grow
throughout their lives? Although mitosis and
cell division occurs throughout a plant as it
grows, eventually new growth is restricted to
small regions of unspecialized tissue
collectively called the meristems shown in
Figure 15.4. Growth in meristem tissue results
from the accumulation of rapidly dividing
cells. When a cell in the meristem divides, one
of the two resulting cells remains in the
meristem. The other cell becomes part of the
plant body. Initially, all meristem cells are
identical in structure, and they have no
specialized function. As they divide
terminal meristem
shoot apical meristem
lateral meristems
root apical
meristems
Figure 15.4 At first, the small, actively dividing cells of
meristem tissue are identical. With repeated division, they
“differentiate.” That is, they become specialized for different
plant functions.
Using Plants • MHR
555
Types of Meristem Tissue
annual
growth rings
vascular
cambium
Figure 15.5 The meristem in a tree stem is located in the
vascular cambium.
DESIGN YOUR OWN
Investigation
There are two main types of meristem tissue. The
first type is called apical meristem tissue. It is
located in the root and shoot tips of plants.
Division of apical meristem cells results in growth
of roots, leaves, and flowers. In the root, the apical
meristem is protected by a root cap. In the stem it
is protected within a terminal bud. In colder
climates, the terminal buds stop growing in the
winter and resume growing in the spring. These
buds are protected by bud scales, which fall off
when growth begins in the spring.
Lateral meristem results in the growth of tissue
beneath the bark of tree stems, as shown in Figure
15.5. The division of cells in the lateral meristems
results in the thickening of cylinders of tissue.
Most woody plants have two kinds of lateral
meristems: a vascular cambium and a cork cambium.
SKILL FOCUS
1 5 • A
Hypothesizing
Factors Affecting Plant Growth
Identifying variables
There are many different factors that will determine how well a plant
will grow. What external factors affect plant growth? The list includes:
the amount of light; the type of soil; the amount of water; the amount
of minerals and other nutrients; and temperature. Which of these
factors can be explored in an experimental setting? In this
investigation, you will design an experiment to identify and
investigate one external factor affecting plant growth.
Problem
What is the effect of an external factor on the
growth of plants?
Make a hypothesis about the effect of an
external factor (of your choice) on plant growth.
CAUTION: Wash your hands thoroughly after
working with soil.
potting soil (or other
factors that you will be
types of potting material)
testing such as different
fertilizers, water, or salt
1. Decide which condition you are going to
vary in your experiment. Prepare a list of
possible ways you might test your
hypothesis.
2. Decide on one approach for your experiment
that could be conducted in the classroom.
3. Your design should test one variable at a
time. Plan to collect quantitative data.
Materials
556
Analyzing and interpreting
Experimental Plan
Hypothesis
bean seeds (or other
easy to grow seeds)
labels
Performing and recording
plant pots or planting trays
water
ruler
MHR • Plants: Anatomy, Growth, and Functions
4. Outline a procedure for your experiment
listing each step.
The lateral meristem, called the vascular cambium
produces xylem and phloem cells in the stems and
roots. The other lateral meristem, called the cork
cambium, produces a tough covering for the
surface of stems and roots. The outer bark of a tree
is produced by the cork cambium.
Meristem tissue enables plants to grow from
cuttings. Growing plants from cuttings is the basis
of plant cloning. Cloning technology, especially
relevant to agriculture, is the process of growing
genetically identical copies of an organism from a
single cell or part of an organism. For some
species, growing plants from cuttings can be much
faster than growing them from seed.
REWIND
Turn to Chapter 6, Section 6.2, to review cloning techniques
and the results of cloning experiments.
5. Show an outline of your plan to your
teacher. Get your teacher’s approval before
continuing.
Checking the Plan
PAUSE
RECORD
Make a chart with two columns headed “now” and “later.”
In the “now” column, record a definition of plant as you
understand the term today, using your knowledge from
Chapters 13 and 14. Your personal definition will grow and
develop as you progress through this chapter. Use the
“later” column to record your new understandings. On a
separate page, write your ideas of why plants are important
to Earth, the weather, animals, and other plants.
Internal Regulation of Plant
Growth and Development
Plants can grow to their maximum height when
environmental conditions are optimal. Optimal
conditions include adequate moisture, warmth,
light, and nutrients. Fertilizers promote plant
growth and development by providing additional
nutrition. Pesticides and fungicides promote plant
2. Suggest reasons why your plant may not
have grown as well in the other conditions.
3. Do your results support your hypothesis?
Give reasons for your answer.
1. What will be your independent variable?
What will be your dependent variable(s)?
What will be your control variable(s)?
4. If the results were different than what you
expected, what might be the reasons for
these results?
2. What will your experimental steps be? How
would you apply the different treatments to
the plants in the appropriate labelled pots?
5. Determine which treatment was the most
beneficial and which treatments were the
least beneficial. Look at other factors that
may have affected your experiment. Were
there any that you did not control?
3. What will you measure or count? How will
you determine if your variable has had an
effect on plant growth?
4. Design a table to record your data.
Data and Observations
Conduct your experiment and make your
measurements. Enter the data into your table.
Make a graph of your results. CAUTION: Make
sure you are wearing all the appropriate safety
equipment while you perform your experiment.
Analyze
1. At what level of the variable you were
testing did your plant grow best?
Conclude and Apply
6. Based on your results, what
recommendations would you make to
farmers growing crops of your plant?
Exploring Further
7. What would happen if you varied two of the
treatments at one time? Would you be able
to tell which treatment affected the plants?
8. How do scientists determine what factors
affect plant growth under field conditions
when there are many variables (or
treatments) that are affecting growth?
Using Plants • MHR
557
growth by controlling numbers of insects and fungi
that feed on plants. However, plant growth and
development are also controlled by the plant’s own
hormones.
From your previous studies, you learned that a
hormone is a chemical compound manufactured by
specialized tissue in one body part of an organism
but that governs or regulates the activity of another
body part or parts. Even though a hormone may
circulate throughout an organism, it will act only
on specific “target” tissues or organs.
Investigation
Hormonal Control of Plant Growth
In the early 1800s, experiments undertaken by
Charles Darwin and his son Francis described the
effects of a mysterious “influence” that affected the
growth of grass seedlings. The seedlings normally
grew toward a light source, however this behaviour
was not seen if the tips of the grass seedlings were
covered with an opaque capsule that did not let
light through. The remainder of the plant, where
the growth actually occurs, was still exposed to
light. If the tip of the seedling were covered with a
gelatin capsule, which allowed light to pass
through, then the seedling would grow towards the
light as expected. For many years, researchers
SKILL FOCUS
1 5 • B
Predicting
How Gibberellic Acid Affects Plant
Growth and Development
Performing and recording
Many garden centres stock chemicals that promote growth. Brand
names differ, but the labels reveal that many contain the same main
ingredient: gibberellic acid. What does this compound do for plants?
Conducting research
Pre-lab Questions
Procedure
What are the classes of plant hormone growth
promoters?
What are the effects of these different classes
of hormones?
Problem
How does gibberellic acid affect the growth of
bean plants?
Prediction
Predict what will happen to the rate of growth
as plants absorb gibberellic acid.
CAUTION: Wash your hands thoroughly after
handling seeds, seedlings, soil, or gibberellic acid.
Materials
recycled 6-compartment
planting tray
labels and marking pens
soil or potting mixture
water
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Analyzing and interpreting
pre-soaked bean seeds,
6 per group
ruler
gibberellic acid
graph paper
MHR • Plants: Anatomy, Growth, and Functions
1. Label the tray with your group’s name. Fill
each compartment with soil or potting
mixture.
2. Plant one pre-soaked bean seed in each
compartment. Place the tray in a brightly lit
location that is warm enough for plant
growth but not too hot.
3. Every day, add enough water to keep the
potting mixture moist, using equal amounts
of water in each compartment.
4. When most seedlings are over 10 cm tall,
select three seedlings that are equivalent in
height. Mark them and leave them in the
tray. Remove the other three. This is Day 1
of your investigation.
5. Join another group so that two trays are
available. Prepare two labels, one for each
tray: “GA YES” (meaning treat with
gibberellic acid) and “GA NO” (meaning do
not treat with gibberellic acid). Prepare an
observation chart in your notebook like the
one shown on the next page.
conducted experiments to try to explain the nature
of this observation. In 1926, Frits Went performed a
series of experiments that showed there was a
chemical messenger in the grass seedlings. This
chemical could enhance plant growth. He named
the substance auxin, from the Greek work auxein,
which means “to increase”.
Other discoveries about plant hormones came as
a result of people noticing unusual growth in
plants. For example, observers noticed that a rice
plant infected with the fungus Gibberella fujikoroi
grew abnormally tall. In 1935, researchers were
finally able to isolate the chemical compound that
caused the accelerated growth, and named it
Average height of seedlings in cm over several days
Tray
Day 1
Day 2
Day 3
Day 4
Day 5
GA No
GA Yes
6. Measure the height of each individual
seedling. Calculate the average height for the
seedlings in each tray and record your
results in the Day 1 column.
7. Treat the plants in the “GA YES” tray by
placing one drop of gibberellic acid on the
shoot tip of each seedling.
8. Repeat Steps 6 and 7 for up to 5 days,
recording your results in the appropriate
column. Be sure all seedlings receive the
same amount of light, warmth, and water
each day.
9. Watch for any obvious difference in growth
between the two trays. Note when this
difference becomes apparent.
gibberellic acid. They discovered that applying
artificially-manufactured gibberellic acid to a plant
not infected by the fungus caused the plant to grow
abnormally tall.
Scientists and researchers continued to search
for other plant hormones that might affect growth
and development. They discovered two types of
plant growth hormones: promoter hormones, which
are hormones that cause growth, and inhibitor
hormones, which are hormones that block growth.
2. Based on your observations, how does
gibberellic acid affect the growth of the bean
seedlings? How soon after the first
application can this effect be observed?
3. What would you expect to observe if the
gibberellic acid were applied to the base of
the stem rather than to the tip of the shoot?
Conclude and Apply
4. What medium did your plants grow in?
Where did you place the drops of gibberellic
acid? Do you think gibberellic acid would
make a good additive for impoverished soil?
Explain why or why not.
5. Look at this sketch of a normal rice plant.
Sketch the probable appearance of a rice
plant infected with the fungus Gibberella
fujikuroi. How would you know the
infection is present?
10. Use the data in your observation chart to
create a graph. Plot height vs. time for both
trays on the same piece of graph paper.
Label the curves appropriately.
Post-lab Questions
1. What variable were you testing? Which tray
was the experimental group? Which tray was
the control group? What variables were you
controlling in both trays?
Using Plants • MHR
559
Table 15.1
Naturally occurring plant growth hormones
I
Class
Auxins
II
Example
III
Molecular structure
β -indoleacetic acid
CH 2 COOH
N
H
Cytokinins
H
6-furfurylaminopurine
CH 2
N
Figure 15.6 As auxin concentrations decrease, the
deciduous trees begin to shed their leaves.
The Classes of Hormones
The different classes of plant hormones and their
molecular structure are summarized in Table 15.1.
A full summary of the type and function of all of
the plant hormones is given in Table 15.2 on the
next page. Auxins are a class of hormone that is
produced in the apical meristem of shoots. There
are both natural and synthetic auxins that promote
cell elongation, the development of vascular tissue,
and trigger the development of above-ground stems,
which help support the plant. These hormones also
cause leaves to drop after they are no longer
needed. The stimulation of cell elongation occurs
because auxin increases the plasticity of the plant
cell wall. The more plastic the cell wall is, the
more it can stretch during active cell growth. This
process is shown in Figure 15.7.
N
N
H
Gibberellins
Gibberellic acid (GA3)
O
HO
C
O
OH
CH 2
CH 3
Abscisic acid
COOH
Abscisic acid (ABA)
CH 3 CH
3
O
Ethylene
Ethylene gas
CH 3
CH
C
OH CH
CH
CH 3
COOH
H
H
C
H
cell wall
H+
ATP ATP
H+
O
N
N
C
H
Note: Three of the hormone classes listed in column I are
shown as plurals. Each of these classes includes two or
more chemical compounds with similar functions but
different structures or formulas. Only the most common
example of each is shown in column II.
ATP
H+
ATP
auxin
ATP
H+
Figure 15.7 Auxin stimulates an H+ pump so that hydrogen ions
H+
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MHR • Plants: Anatomy, Growth, and Functions
(H+ ) are transported out of the cytoplasm of the cell. The resulting
acidity causes the cell wall to weaken, and solutes enter the cell.
Water follows by osmosis and the cell elongates.
Gibberellins are also produced in the apical
meristem and act to increase stem length. As well,
gibberellins increase the uptake of starch in the
embryo of germinating seeds and stimulate the
development of vascular tissue. The effects of
gibberellins include taller and stronger plants,
plants that flower early, or genetically dwarf plants
that grow to normal heights. Gibberellins are used
in commercial crops to increase fruit size, and
cluster size in grapes. As well, they can delay the
ripening of citrus fruits and speed up the flowering
of strawberries.
Cytokinins promote cell division and cell
differentiation. Cell differentiation occurs when
specialized cells are needed to perform certain
functions. They also delay the aging of leaves
and fruit. Cytokinins work by influencing the
synthesis and activation of proteins that are
required for mitosis.
Oligosaccharins are a recently discovered class
of growth promoters. They stimulate plants to
manufacture antibiotics in response to attack by
fungi or bacteria. This allows the plant to grow to
its full potential because the negative influences of
pests are diminished.
In addition to hormones that promote plant
growth, plants produce hormones that inhibit
growth. There are two classes of hormone growth
inhibitors. The first is abscisic acid (ABA), which
is synthesized mainly in mature green leaves,
fruits, and root caps. This hormone inhibits the
germination of seeds, 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.
Ethylene, the second inhibitor, is a gaseous
hydrocarbon. It occurs as a natural plant hormone.
It stimulates the aging of plant tissues, the ripening
and sweetening of fruit, and can also speed up the
dropping of leaves from trees. The production of
ethylene gas by plants can stimulate other plants to
ripen. This was initially noted when bananas
ripened quickly if they were left near oranges. The
ripening action of ethylene has led to its use in
agriculture. For example, tomatoes may be picked
while green and then ripened artifically by the
application of ethylene.
Table 15.2
Summary of plant growth hormones and their actions
Growth promoters
Auxins act to
promote cell elongation
suppress the growth of
lateral branches
trigger the growth of
prop roots that grow
from aboveground
stems
suppress leaf drop
before leaf ages;
promote leaf drop
afterward
Gibberellins act to
promote cell
enlargement
promote uptake of
starch tissue by the
embryos in germinating
seeds
reverse genetic
dwarfism
stimulate the vascular
cambium to produce
secondary phloem in
woody plants
promote “bolting,” the
rapid elongation of the
flower stem in plants
such as cabbage
Cytokinins act to
promote cell division
(recall that cytokinesis is
the process of cell
division after mitosis)
stimulate formation of
adventitious buds
delay senescence
(ageing) of leaves by
maintaining chlorophyll
content
reverse suppression by
auxin
Growth inhibitors
Abscisic acid (ABA)
acts to
block intake of carbon
dioxide by causing the
closure of leaf stomata
inhibit seed germination
inhibit active growth of
axillary lateral buds
block the action of
growth-promoting
hormones
promote abscission of
leaves and fruits
Ethylene acts to
stimulate fruits to ripen
stimulate other effects
associated with tissue
ageing
trigger its own
production through
positive feedback (its
presence promotes the
production of still more
ethylene, so ethylene
levels build up rapidly)
Using Plants • MHR
561
Plant Tropisms
Plants exhibit the ability to orient themselves in
response to external stimuli such as light. A
directional growth response to unequal stimulation
from the external environment is called a tropism,
and it controls the growth pattern of the plant.
Various external stimuli affect the production of
plant hormones. This results in the directional
growth of a plant. In tropism, the plant may grow
either toward or away from the stimulus. Growth
toward the stimulus is a positive tropism. Growth
away from the stimulus is a negative tropism.
There are three major kinds of plant tropisms that
are affected by light, gravity, and touch.
Phototropism occurs when the growth of a plant
is affected by light. In general, plants are positively
phototropic, that is, they grow toward light. Roots
are negatively phototropic and grow away from
light. The growth is caused by differing amounts of
auxin produced on the light and dark sides of the
stem. Auxin accumulates on the shaded side of the
stem, which causes the cells there to elongate. This
causes the stem bend toward the light, as shown in
Figure 15.8. Turning the plant around will cause
the stem to bend in the other direction however, it
will not change the original curve in the stem
because it is the result of growth. Figure 15.9
demonstrates the experimental procedure that led
to the discovery of phototropism.
light
source
elongated cells
Figure 15.8 Tropisms result when external stimulation is
unequal. For example, the stem of this plant is receiving
much more light on its right surface than on its left surface.
Figure 15.9 Oat seedlings,
After tips are placed on agar,
agar is cut into blocks.
Coleoptile tip
is intact.
MINI
Coleoptile tip
is removed.
Cell elongation
occurs only
beneath block.
LAB
How Plants Respond to Light
The flowering heads of sunflowers can be seen to turn in
response to the movement of the Sun as it moves across
the sky. This is one example of phototropism.
Plant some bean, tomato, or other vegetable seeds or
acquire some seedlings. When the plants are a few inches
high, place them in a room where the only light comes from
one light source. (For example, place them on a window
ledge with a cardboard box blocking out the light from the
classroom.) Examine the plants daily and record what
you see.
562
Block is placed
to one side of
coleoptile.
shown here, are protected
by a hollow sheath called a
coleoptile. After a tip is
removed and placed on a
block of agar, a block of
that agar placed on one
side of the coleoptile can
cause it to curve even in
the absence of light. The
agar blocks contain the
hormone produced by the
original coleoptile.
MHR • Plants: Anatomy, Growth, and Functions
Analyze
1. How long does it take to see
any bending of the stems?
2. How could you get the plant
to straighten out?
3. Where would you expect the
auxin to be produced in
these plants?
Gravitropism is a plant’s response to gravity.
This tropism causes roots to grow downwards
(positive gravitropism) and shoots and stems to
grow upward (negative gravitropism). This benefits
the plant, because shoots that grow upward will
receive light and roots that grow downward will
receive nutrients from the soil.
Thigmotropism is the response of plants to
touch. This behaviour is a caused by specialized
cells in the epidermis of the plant. Vining plants
demonstrate a strong positive thigmatropism, as
shown in Figure 15.10. The vines grow toward the
object touching them causing them to coil around
the object. Other plants demonstrate a negative
thigmotropism.
Figure 15.10 Vining plants such as bindweed demonstrate
thigmotropism.
PAUSE
RECORD
Record how you would expect the primary root of a
germinating seed to respond to light and to gravity. Name
these tropisms. Repeat for the stem of a germinating seed.
Write a brief explanation of why you would expect these
responses.
Nastic Responses in Plants
Another type of response, called nastic movements,
are caused by a stimulus that is not directional. For
example, the leaves on a mimosa plant fold up when
the plant is touched, as shown in Figure 15.11.
This response might seem to illustrate a negative
thigmotropism, however, it is neither directional
nor permanent. The leaflets fold downward in the
same way regardless of the direction of the
stimulus. These movements are not a result of
growth, but rather a change in turgor pressure in
the cells at the base of each leaflet. A sudden drop
in pressure causes the cells to become limp and the
leaflets fold down. Once the stimulus has ceased,
the turgor pressure in the cells rises once again and
the leaflets open. Another example of a nastic
response is shown in Figure 15.3 on page 555,
where you can see the hinged leaf of a Venus’sflytrap. The movement of an insect on the leaf
triggers the hinged leaf to close, trapping the insect
between the leaves.
Commercial Use of
Growth Regulators
Over the past century, scientists have learned much
about plant growth hormones. Horticulturists and
other agricultural scientists use this knowledge of
plant growth regulators to influence the growth and
development of crops and ornamental plants. Most
growth regulating hormones used for commercial
purposes are synthetically produced rather than
extracted from plants. For example, there appears
to be only one naturally occuring auxin, but many
more synthetic auxin-like growth regulators exist.
Although these synthetically produced hormones
are not identical to natural auxins, their chemical
action is similar, and the plants respond as they
would to naturally occurring auxin. Commercial
uses of several types of plant growth regulators are
listed in Table 15.3 on the next page.
Figure 15.11 Mimosa is sometimes called the sensitive
plant. When it is touched, it folds its leaves in less than
one-tenth of a second.
Using Plants • MHR
563
Table 15.3
Some uses for commercial plant growth regulators
Plant growth regulators
Auxin-like growth regulators
Commercial uses
stimulate rooting
act as a herbicide for dicots
prevent sprouts in pruned trees
prevent fruit from dropping too soon
Cytokinin-like regulators
promote axillary bud growth in orchids and
daylilies (results in more flowers)
prevent browning in cut salads
increase fruit size
Gibberellic acid-like regulators
increase flower size (for example, camellias)
increase grape size
stimulate separation of berries from stalks
stimulate seed germination
Gibberellic acid-like inhibitors
control (restrict) height in flowerpot plants
(lilies, orchids)
control height of bedding plants
Ethylene-like regulators
stimulate flowering
stimulate ripening (bananas, tomatoes)
accelerate colour development in tomatoes and
citrus fruits
stimulate separation of cherry stems from
branches (for mechanical harvesting machines)
Ethylene inhibitors
allow long-term, controlled storage of apples
allow hypobaric (low-pressure) storage of many
fruits, vegetables, and flowers
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MHR • Plants: Anatomy, Growth, and Functions
A large industry is based on the manufacture of
artificial plant growth regulating hormones. Some
of the growth regulating hormones that are
produced can be very specialized For example, a
chemical treatment can be applied to ornamental
trees to prevent them from growing too tall and
interfering with utility lines. From the ground, the
trees look normal, but the tops look as if they have
been pruned flat. Table 15.3 outlines more of the
commercial uses of plant growth regulators.
Chemical Look-alikes:
Commercial Growth Regulators
Over the past century, scientists have built up an
impressive body of knowledge about plant growth
hormones. As in any branch of science, there is
more to be learned and research is ongoing.
However, horticulturists are already taking
advantage of our present knowledge by applying
plant growth regulators to influence the growth and
development of crops and ornamental plants.
PAUSE
RECORD
What have you learned about growth regulators? Do you
think there should be more public awareness of these
chemicals? Suggest how public awareness of plant growth
technology could be improved. List two reasons to support
your position.
SECTION
REVIEW
1.
K/U Both plants and animals depend on hormones
to regulate growth and development. Name three of
these hormones and describe their effects.
2.
K/U Which plant growth hormone is gaseous? What
is its function?
3.
C How does a plant growth regulator differ from a
plant growth hormone? Explain what the two have in
common.
4.
I Your uncle buys two unripe pears. He puts the
first in a plastic bag by itself and puts the second in a
plastic bag with a ripe banana. The second pear
becomes edible much faster than the first. Develop a
hypothesis to explain why this happens. Give reasons
for your answer.
5.
K/U Which of the following effects would you expect
to observe if the tip of a shoot is cut off? Support
your answer.
The plant will become taller because the
production of gibberellins will be increased.
6.
C Where is meristem tissue located? Explain how
meristem tissue works. Draw a labelled diagram of
apical or lateral meristem tissue to support your
answer.
7.
MC Plant growth regulators are involved in the
cultivation, processing, and storage of many
commercially grown fruits and vegetables. Yet, few
shoppers are aware of this. Should supermarkets
post signs identifying produce treated with plant
growth regulators? Give reasons for your answer.
8.
I A researcher is investigating how an auxincytokinin mixture affects the development of
meristematic tissue. When the mixture contains a
higher concentration of auxin, the meristematic tissue
develops into organized root tissue. When the
cytokinen is more concentrated, the meristematic
tissue develops buds. What would you expect to
observe if the mixture contained equal mixtures of the
two hormones? Explain your reasoning.
The leaves will fall off because the tip will release
ethylene.
Using Plants • MHR
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