Download 432

CHAPTER 37: VEGETATIVE PLANT DEVELOPMENT
WHERE DOES IT ALL FIT IN?
Chapter 37 is a follow-up of Chapter and 36 builds up the general information on green plants
provided in Chapter 30. A quick summary of Chapter 36 is essential for success at covering Chapter
37. In addition, students should be encouraged to recall the principles of eukaryotic cell structure and
evolution associated with the particular features of plants.
SYNOPSIS
The basic body plan of a plant is established while it is still an embryo. Only a portion of it is formed
when it first emerges from the soil, and differentiation and development continue throughout its life
cycle. Shape and form come about through regulation of the amount and pattern of cell division. The
first division results in two different cells types. Early on, cells can give rise to various cell and organ
types, but as development proceeds, cells with multiple potentials are restricted to meristematic
regions. Apical meristems are involved in growth and differentiation of root and shoot tips during
embryogenesis, and help establish the three basic tissues: dermal, ground, and vascular.
Concurrently, food supplies for the embryo are formed differently, in angiosperms and
gymnosperms, and differentiation of ovule tissue forms protective coverings around the embryos,
indicating the end of embryogenesis. Germination will occur when appropriate environmental and
hormonal signals contribute to the breaking of seed dormancy, which can last for many years.
The first embryonic cell division is asymmetric, producing one small cell that is destined to become
the embryo while the other becomes the suspensor that connects the embryo to the food supply in the
seed. Cells near the suspensor form the root while those at the other end form the shoot. Tissues
differentiate when the embryo is in the globular stage, but shoot and root apical meristems are
controlled independently. The outermost cell layer, the protoderm, becomes protective dermal tissue.
The ground tissue forms the bulk of the embryo interior and functions in food and water storage.
Procambium forms at the core of the embryo and forms the future vascular tissue. Knowledge of
plant development has been advanced greatly with the examination of the small, mustard-related
Arabidopsis thaliana. This plant has a short generation time and is able to produce thousands of
offspring in only two months. Many gene mutations affecting pattern formation are known, helping
elucidate the mechanisms of early plant development. A heart-shaped embryo forms from divisions
in the globular stage. Embryonic cells, not meristematic cells, give rise to cotyledons (seed leaves),
initiating morphogenesis during which rates and planes of cell division bring about the 3-D form of a
plant body. Microtubules and actin, as well as hormones and other factors are involved. Food
reserves especially starch, lipids, and proteins are produced during embryogenesis. In fact, these
proteins are so abundant that molecular biologists used them during early gene-cloning research.
Food reserves in seeds reflect the evolutionary trend toward enhancement of embryo survival.
Angiosperm embryos develop within fruit, mature ovaries, also called carpels that exhibit a great
variety of adaptations that facilitate dispersal. Fruits may be dry and hard, soft and fleshy, small,
large, winged, or hooked, among many other forms. They may disperse by simply dropping, or
floating on wind and water, or passing through animals that consume them, or otherwise adhering to
them or to other moving objects. Plant colonization of new areas is part of succession.
283
Embryo development ceases, generally, following the differentiation of meristems and cotyledons,
and resumes when environmental conditions are favorable for plant growth. Various adaptations
provide for timely germination of different species. When environmental conditions signal
germination, the seed absorbs water, enzymes and hormones including gibberellic acid become
activated, and metabolism including protein synthesis in the embryo resumes. Environmental signals
may involve certain intensities and wavelengths of light, and temperatures, sometimes for long
periods of time. Using its food reserves, the seed resumes growth orienting itself so the root grows
downward and the shoot grows upward. Grains possess a single cotyledon that forms a scutellum that
conveys nutrients from the endosperm to the embryo. The emergence of root and shoot is quite
variable. In peas and corn, the cotyledons remain underground. In beans, radishes, and onions, they
emerge above ground and become photosynthetic. Most young seedlings are very susceptible to
stress, especially pathogens and drought, during this period.
LEARNING OUTCOMES








Explain how the basic body plan of a plant is formed during the plant’s embryonic state.
Know the locations and functions of the three tissues found in a plant embryo.
Explain the roles of apical and lateral meristems.
Describe the development of the root-shoot axis, and the differentiation of stem and root tissues.
Know the functional and adaptive features of the seed, seed dormancy, and germination.
Explain the value of fruit to plant reproduction and dispersal. How does fruit form?
Describe the variability in cotyledon activity among different types of plants.
Explain why seedlings are susceptible to stress.
COMMON STUDENT MISCONCEPTIONS
There is ample evidence in the educational literature that student misconceptions of information
will inhibit the learning of concepts related to the misinformation. The following concepts
covered in Chapter 37 are commonly the subject of student misconceptions. This information on
“bioliteracy” was collected from faculty and the science education literature.











Students are unaware that plants develop environmental adaptations
Students believe that plants lack tissues and organs
Students do not equate pollination with sexual reproduction
Students think pollen are one and the same as sperm
Students are unaware that plants produce eggs
Students are unaware that plants undergo embryological development
Students are unaware of all of the functions of roots
Students are unaware of all of the functions of stems
Students are not sure of the definition and characterization of fruits
Student believe that only leaves can carry out photosynthesis
Students believe that the reproductive structure of all plants are flowers
284




Students believe all plants produce seeds
Students confuse spores with pollen
Students believe that all flowers are insect pollinated
Students believe that the pollen of any plant can be found in the wind
INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE
Morphogenesis in plant embryos, regulated by the amount and pattern of cell division, is as
exciting and as complex as morphogenesis in animal zygotes. In fact, comparing the two is a
productive exercise. Note that cell differentiation in plants does not exhibit any movement of
cells, and that patterns of development are not affected by chemical signals in the egg. The egg
tissue is nutrition for the embryo when it begins developing. More specifically, in angiosperms,
double fertilization produces endosperm for the food supply while the megagametophyte is the
food source in gymnosperms. Food reserves in seeds reflect the evolutionary trend that benefits
embryo survival. Seeds, seed dormancy, and the breaking of seed dormancy are marvelous
adaptations to discuss in lively fashion. Living plant cells retain the ability to divide.
Plant morphogenesis, however, is not easy to explain to a general audience. Emphasize the apical
meristems that form the three ground tissues, and then explain what develops from the ground
tissues. Have students sketch, or otherwise study, comparisons of embryonic roots and stems,
then more mature roots and stems. Discuss the recent plant development knowledge that comes
from genetic work with Arabidopsis. Involvement of actin and microtubules, in addition to
hormones, adds another level of intrigue, and that embryonic cells, not meristem cells, give rise
to cotyledons.
This chapter may help a typical pre-med student gain insight about how cool plants are. If your
arm is chopped off, a new one will not grow. My bushes keep sprouting new branches no matter
how many times I prune them back. Higher animals typically lack the abilities provided by
meristems and seeds, as well as other plant adaptations.
HIGHER LEVEL ASSESSMENT
Higher level assessment measures a student’s ability to use terms and concepts learned from the
lecture and the textbook. A complete understanding of biology content provides students with the
tools to synthesize new hypotheses and knowledge using the facts they have learned. The
following table provides examples of assessing a student’s ability to apply, analyze, synthesize,
and evaluate information from Chapter 37.
Application

Have students describe how differentiation is important in determining the
characteristics of different plant structures.

Have students explain relationship between the location of meristem and a
plants ability to repair damaged parts.

Ask students to explain the possible habitat of a plant whose seed is
stimulated to germinate by temperature but is not affected by the duration
285
or quality of light exposure.
Analysis
Synthesis
Evaluation

Have students explain the impact of mutations that significantly alter fruit
formation.

Have students explain how mutations to genes that affect hormone
regulation would impact embryological development of a plant.

Ask students to explain the benefits and limitations provided by seed
coats

Ask students to explain why ground tissue is important to researchers who
genetically modify plants for agricultural and commercial purposes.

Have students hypothesize the agricultural value of a technique that
permits the regulation of cotyledon development.

Ask the students to design an experiment that tests the relative
effectiveness of seed coat thickness on the survival of seeds.

Ask students evaluate the possible consequences of global climate change
of plant development.

Ask students to evaluate the safety of a drug sprayed on carrots and
potatoes that reduces meristem growth.

Ask students to evaluate benefits and risks of breeding crops that develop
only under very strict environmental conditions.
VISUAL RESOURCES
Transparencies, slides, and videos are essential in presenting this chapter.
IN-CLASS CONCEPTUAL DEMONSTRATIONS
A. Barley Germination Model.
Introduction
This demonstration permits faculty to show the process of seed germination using a
virtual animated sequence that can be discussed with students.
Materials


Computer with Media Player and Internet access
LCD hooked up to computer
286

Web browser linked to Virtual Plant Animations at
http://www.indiana.edu/~oso/animations/An12.html
Procedure & Inquiry
1.
2.
3.
4.
Explain to the class that you will be showing an animated sequence of barley germination.
Load up the website and show go to the Barley Seed Germination image
Ask the students to identify the parts of the seed shown in the image
Click on the image and ask the students what they are observing with first two steps and
then have them answer the questions associated with the following steps.
5. Ask the students to briefly review and explain the steps of the animation.
USEFUL INTERNET RESOURCES
1. Fruit images are valuable teaching resources for supplementing a lecture on the material
covered in Chapter 37. The Agricultural Research Service has a website with many
agricultural fruit images that can be downloaded for educational use. The site is available
at http://www.ars.usda.gov/is/graphics/photos/fruitsimages.new.htm.
2. A brief mention of plant conservation is critical for the reinforcing the need for
maintaining plant biodiversity. The Center for Plant Conversation has a valuable website
for gaining resources about protecting plant biodiversity. The website is available at
http://www.centerforplantconservation.org/
3. Seed germination conditions and times can be valuable information to gardeners and
people involved in environmental conservations. Students can also use the information to
better understand the evolutionary adaptations of plants. The Virtual Seed “Seed
Germination Database” has germination information on many common types of garden
plants. This website is located at http://www.virtualseeds.com/Germination.html.
4. Classical botanical illustrations show students the incredible detail that went in to earlier
plant anatomy studies. The Smithsonian Catalog of Botanical Illustrations has
anatomical illustrations of various plant structures that can be projected or run off as hand
outs for the class. The website can be found at http://ravenel.si.edu/botany/botart/.
LABORATORY IDEAS
A. Fruit and Seed Adaptations
This activity asks students to use the characteristics of different types of fruits and seeds
to understand their evolutionary adaptations.
a. Mention to students that most plants need to have an efficient way to disperse their seeds
so more plants will grow. Also mention that there are many different ways that seeds can
travel.
b. Tell students that they will be for looking at various fruit and seeds to determine their
means of dispersal.
c. Instruct that you want them to record the properties of the fruits or seeds that characterize
287
their means of dispersal.
d. Provide students with the following materials to be distributed into research teams who
dissect one animal:
a. Various fruits available from the grocery store, garden centers, or biological
supply companies:
i. Strawberry
ii. Apple
iii. Maple
iv. Acorn (oak)
v. String bean
vi. Burdock
vii. Marigold
viii. Oxalis
ix. Burdock
x. Coconut
e. Instruct to share their conclusions with the class justifying each mechanism of dispersal
by justify how the fruit structure is “designed” for that dispersal mechanism.
LEARNING THROUGH SERVICE
Service learning is a strategy of teaching, learning and reflective assessment that merges the
academic curriculum with meaningful community service. As a teaching methodology, it falls
under the category of experiential education. It is a way students can carry out volunteer projects
in the community for public agencies, nonprofit agencies, civic groups, charitable organizations,
and governmental organizations. It encourages critical thinking and reinforces many of the
concepts learned in a course.
1. Have students assist a garden club set up a “food garden” for the community.
2. Have students tutor high school students learning plant development.
3. Have students volunteer on environmental restoration projects with a local conservation
group.
4. Have students volunteer at botanical garden or nature center.
288