Download PLANTS: NONVASCULAR, VASCULAR, SEED AND SEEDLESS

BIO170 General Biology Freeman/Mac Leod FMCC
PLANTS: NONVASCULAR, VASCULAR, SEED AND SEEDLESS
LAB 1 of 3
Objective: After completing this series of labs, you should be able to do the following:
 Describe adaptations that allowed Plants to colonize terrestrial habitats
 Describe the Alternation of Generations life cycle in plants using appropriate terminology
 Recognize and identify representative members of the Bryophyta, Hepaticophyta,
Pteridophyta and Lycophyta
 Identify basic morphological structures (and their functions) of representatives of the
Bryophyta, Hepaticophyta, Pteridophyta and Lycophyta
 Recognize and identify representative members of the Gymnosperms and Angiosperms.
 Describe the life cycle of the Gymnosperms and Angiosperms.
 Identify basic morphological structures (and their functions) of representatives of the
Gymnosperms and Angiosperms.
 Summarize major trends in the evolution of land plants and provide evidence from your
laboratory investigations.
Introduction
Among the seven major lineages of the domain Eukaryota is the lineage Plantae. Plantae consists
of the algae and the green plants. Green plants dominate terrestrial and freshwater habitats.
Although green algae have traditionally been considered protists, it is logical to study green
algae along with land plants for two reasons: (1) they are the closest living relatives to land
plants and (2) the transition
from aquatic to terrestrial life
occurred when land plants
evolved from green algae.
Land plants were the first
organisms that could thrive
with their tissues completely
exposed to the air instead of
being partially or completely
submerged in water. The most
ancient groups in the lineage
are dependent on wet habitats,
while the more recently
evolved groups can live and
reproduce in dry – or even
desert – conditions. The
phylogenetic tree in Figure1
reflects a recent phylogeny
that has emerged from
laboratories around the world.
Figure 1. A phylogeny of Plantae
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In order for the transition to land to be successful four key adaptive steps occurred (figure 2):
1) Land plants had to
prevent water loss.
This was accomplished
by the formation of a
waxy cuticle that
covers the aboveground
parts of plants. To allow
for gas exchange stoma
evolved. Stomata
consist of an opening
surrounded by
specialized guard cells.
The ability to open and
close the stomata
provides the plant with
a way to regulate gas
exchange (figure 3).
2) Land plants had to
protect themselves from
UV light. This was
accomplished by
forming UV-absorbing
compounds called
flavonoids.
3) Land plants had to
move water from tissue
in direct contact with
water to areas without
access to water. This
was accomplished by
means of specialized
cells composing
vascular tissue.
4) Land plants had to
Figure 2: A series of evolutionary Innovations Allowed
protect their gametes
Plants to Adapt to Life on Land.
from desiccation. This
was accomplished through:
a. The formation of spores, highly protected structures that contain the gametes.
b. The development of the gametangium, a multicellular reproduction organ that
produces and protects gametes. A gametangium that produces sperm is called an
antheridium and a gametangium producing eggs is called an archegonium.
Land plants reproduce undergoing a process called alternation of generations.
Individuals exist as a multicellular haploid organism (a gametophyte) or a
multicellular diploid organism (a sporophyte). As their names imply,
gametophytes produce gametes and sporophytes produce spores (figure 4).
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BIO170 General Biology Freeman/Mac Leod FMCC
stoma
Figure 3. Structure of a leaf
Figure 4. Alternation of
Generations in Land Plants
Based on morphology land plants are traditionally
clustered into three broad categories:
 Nonvascular plants which lack vascular tissue.
 Seedless vascular plants which have vascular tissue but do not make seeds. Instead, they
make spores that are carried by wind to a new habitat.
 Seed plants which have vascular tissue and produce seeds.
During this lab we will investigate the microanatomy of nonvascular and vascular plants
(including both seedless and seed plants). In the following 2 labs, you will investigate the
macro-anatomy of these organisms in the field. You must bring this lab with you as a reference
for the following 2 labs.
A. NONVASCULAR PLANTS (BRYOPHYTES)
The nonvascular plants are composed of three groups that share some key characteristics: mosses
(Bryophyta), liverworts (Hepaticophyta) and hornworts (Anthocerophyta). These are small
plants generally lacking a true vascular tissue (xylem and phloem). In fact, they do not have true
roots, stems or leaves. Because of this, we refer to the plant body as a thallus. Nonvascular
plants have a cuticle but generally lack stomata.
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BIO170 General Biology Freeman/Mac Leod FMCC
Because they are nonvascular, these plants are restricted to moist habitats for their reproductive
cycle and have never attained the size of most land plants. The gametophytes remain close to the
ground, enabling the motile sperm to swim from the antheridium (male reproductive structure)
to the archegonium (female reproductive structure) in order to fertilize the egg. Unlike other
land plants, the nonvascular plants are characterized by a dominant gametophyte and a small,
short-lived sporophyte that is dependent on the gametophyte (figures 5 and 6). Since the
gametophyte produces sperm (male gametophyte) or egg (female gametophyte), self-fertilization
does not occur. Asexual reproduction can occur by fragmentation of the gametophyte.
Figure 5: Mosses Life Cycle
Figure 6: Liverwort Life Cycle
Procedure for the Bryophyta:
1. Refer to page 45 and 46 in your photo atlas.
2. Obtain a compound microscope, prepared slides of Mnium antheridia, archegonia and
capsule (sporangium).
3. Draw and label the following terms in your notebook: antheridial head, antheridia,
archegonial head, archegonia, sporangium, and spores.
4. Review the life cycle of mosses.
5. Fill in the Bryophyta information on the summary table for plants and include this table in
your notebook. (you can do this as homework)
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BIO170 General Biology Freeman/Mac Leod FMCC
Procedure for the Hepaticophyta:
1. Refer to pages 41 through 43 in your photo atlas.
2. Obtain a compound microscope, prepared slides of Marchantia male gametophyte and
female gametophyte.
3. Draw and label the following terms in your notebook: thallus, rhizoid, antheridiophore,
antheridia, archegoniophore, archegonia, sporophyte
4. Review the life cycle of liverworts.
5. Fill in the Hepaticophyta information on the summary table for plants and include this
table in your notebook. (you can do this as homework)
B. SEEDLESS VASCULAR PLANTS
Seedless vascular plants consist of the Lycophyta (club mosses), Psilotophyta (whisk ferns),
Pteridophyta (ferns) and Equisetophyta (horsetails). Seedless vascular plants are analogous to
the first terrestrial vertebrate animals,
amphibians, in their dependence on water
for external fertilization and development
of the unprotected, free-living embryo.
Because of that, they are well suited for
swampy areas.
The first green plants possessed a
cellulose-based cell wall that also
contained lignin. Lignin provided firm
structural support and the condition for
evolution of tracheids. Tracheids are
long, thin, tapered vascular cells that have
a lignin containing secondary cell wall in
addition to the cellulose-based primary
cell wall. The cell wall contains pits that
allow for water and nutrients transport.
Today, all vascular plants contain
tracheids.
The life cycle is a variation of alternation
of generations in which the sporophyte is
the dominant plant while the gametophyte
is much reduced. The sporophyte is still
dependent on the gametophyte for early
development. Eventually, the gametophyte is
Figure 7. Fern Life Cycle
Figure 7. Fern Life Cycle
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totally consumed by the sporophyte (figure 7). These plants generally have well-developed
roots, stems, and leaves. The specialized leaf that bears the sporangia is called a sporophyll.
Procedure the Pteridophyta:
1. Refer to pages 51-53 in your photo atlas.
2. Obtain a compound microscope and prepared slides of fern gametophyte and sori.
3. Draw and label the following terms in your notebook: gametophyte, archegonia,
antheridia, rhizoids, sorus, pinna, sporangium
4. Review the life cycle of ferns.
5. Fill in the Pteridophyta information on the summary table for plants and include this table
in your notebook. (you can do this as homework)
Procedure the Lycophyta:
1. Refer to page 48 in your photo atlas
2. Obtain a compound microscope and prepared slides of Lycopodium strobilus.
3. Draw and label the following terms in your notebook: sporophyll, sporangium, spores
4. Based on what you know about the life cycle of plants in general and the life cycle of
seedless vascular plants specifically, draw a picture of a proposed life cycle of club mosses
in your notebook. (you can do this as homework)
5. Complete table 1 (Summary of structures and functions involved with the life cycle of
plants) and put a copy in your notebook. (you can do this as homework)
6. Fill in the Lycophyta information on the summary table for plants and include this table in
your notebook. (you can do this as homework)
C. SEED PLANTS: GYMNOSPERMS AND ANGIOSPERMS
Seed-producing plants are probably the most familiar plants to most people because, unlike
mosses, liverworts, horsetails, and most other seedless plants, which are overlooked because of
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BIO170 General Biology Freeman/Mac Leod FMCC
their size or
inconspicuous
appearance, most seed
plants are large or
showy. Gymnosperms
include pines, firs, yew,
redwood, and many other
large trees. Angiosperms
include plants whose
flowers are showy as
well as many plants with
reduced flowers, such as
the oaks, grasses, and
palms.
Figure 8. Life
Cycle of
Pinophyta
The seed plants are the
monophyletic group
consisting of the gymnosperms
and angiosperms. The group is
defined by two key
synapomorphies: the production
of pollen and seeds.
In the life cycle of these plants
(Figures 8 and 9), the
gametophyte have been greatly
reduced. The male gametophyte
is a multinucleated pollen grain.
The female gametophyte is small
and retained within the
sporangium in the ovule of the
sporophyte generation.
Figure 9.
Angiosperm life
cycle
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BIO170 General Biology Freeman/Mac Leod FMCC
The pollen grain is desiccation resistant and
adapted for pollination, removing the
necessity for fertilization in a watery medium.
The pollen grain grows a pollen tube to
convey the sperm nucleus to an egg cell. The
resulting zygote develops into an embryonic
sporophyte which develops within the
gametophyte tissue that is itself protected by
the sporophyte generation.
The seed includes three primary regions: the
embryo, nutritive tissue, and seed coat
(Figure 10). The embryo is the young
sporophyte plant. This is what will grow into
the new tree, shrub, vine, etc. The embryo is
surrounded by nutritive tissue which will feed
it during its early growth; until it can establish
its own root system and leaves to support
itself. Nutrients in the tissue are absorbed into
Figure 10. Anatomy of a bean seed
the developing embryo by specially modified
leaves called cotyledons. In some plants, the cotyledons may absorb all the nutrients before the
seed is even dispersed, storing the food inside them.
Around the whole seed is a layer called the seed coat. This layer may be thick or thin, depending
on the species, but it often contains light-sensitive chemicals. When the environment has
appropriate light and water the seed coat may trigger germination of the seed.
The seed develops from structures called ovules. The ovule is an immature seed, which does not
yet contain a viable embryo. It is only after the egg cell inside the ovule is fertilized by sperm
that the ovule is called a seed. The ovule is surrounded by integument tissues that produce the
seed coat. The resulting seed is not only protected from environmental extremes but also is
packed with nutritive materials and can be dispersed away from the parent plant.
1. GYMNOSPERMS
150 million years ago Earth became warmer and drier and the swamp forests declined. The
landscape became dominated by a great variety of seed-bearing plants called gymnosperms
(“naked seed plants”). Gymnosperms were the first to gain reproductive independence from
water through the development of internal fertilization via pollen. Unlike the angiosperms,
gymnosperms do not produce flowers that attract pollinators. They rely on wind pollination.
Gymnosperms do not produce flowers. Gymnosperms consist of Ginkgophyta (Ginkgoes),
Cycadophyta (Cycads), Cupressophyta (Redwood, Junipers, and Yews), Pinophyta (Pines,
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Spruces, Firs) and Gnetophyta (Gnetophytes). In this exercise we will closely observe examples
of the Pinophyta.
Procedure for the Pinophyta:
1. Refer to pages 55-57 in your photo atlas.
2. Observe a prepared slide of Pinus female gametophyte using a compound microscope
3. Draw and label the following terms in your notebook: ovuliferous scale, ovule,
megasporangium, megaspore, micropyle, integument.
4. Observe a prepared slide of a Pinus male gametophyte using a compound microscope.
5. Draw and label the following terms in your notebook: microsporophyll, microsporangium,
pollen grains.
6. Review the pine life cycle.
7. Fill in the Gymnosperm information on the summary table for plants and include this
table in your notebook. (you can do this as homework)
2. ANGIOSPERMS
Angiosperms occupy well over 90% of the vegetated surface of Earth and contribute virtually
100% of our agricultural food plants. The evolution of the flower resulted in enormous advances
in the efficient transfer and reception of pollen. Whereas gymnosperms are all wind-pollinated,
producing enormous amounts of pollen that reach appropriate species by chance, the process of
the flower pollination is mediated by specific agents – insects, birds, and bats – in addition to
water and wind.
Angiosperm reproduction (Figure 9) follows the trend for reduction in the size of the
gametophyte. Flowers contain two key reproductive structures: the stamen and the carpel
(pistil). The stamen includes an anther, where microsporangia develop. Meiosis occurs inside
the microsporangia, forming microspores. Microspores divide by mitosis to form pollen grains.
The carpel contains a protective structure called an ovary where the ovules are found. As in
gymnosperms, ovules contain the megasporangia. A cell inside the megasporangium divides by
meiosis to form the megaspore, which then divides by mitoses to form the female gametophyte
(embryo sac). When a pollen grain lands on the stigma, it germinates, grows a pollen tube to
the embryo sac and release 2 sperm. A double fertilization follows producing a zygote that will
develop into the embryo and the endosperm nucleus which will develop into nutritive
endosperm tissue. The ovule and its contents will develop into the seed. The ovary or other
tissue surrounding the ovule will develop into another unique feature of angiosperms: fruit.
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BIO170 General Biology Freeman/Mac Leod FMCC
Procedure for the Magnoliophyta:
1. Refer to pages 59-62 in your photo atlas.
2. Use a compound microscope to observe a slide of a cross section through a lily anther.
3. Draw and label the following terms in your notebook: pollen grain, microsporangium,
anther
4. Use a compound microscope to observe a slide of a cross section through a lily ovary.
5. Draw and label the following terms in your notebook: ovary, carpel, ovule, embryo sac
6. Fill in the Angiosperm information on the summary table for plants and include this table
in your notebook. (you can do this as homework)
Writing Assignment (see syllabus for due date):
Complete this assignment in Google Docs.
Describe the alternation of generations life cycle. Using that description, compare and contrast
the life cycle of the nonvascular, seedless vascular and seed vascular plants. Be sure to use
appropriate terminology and to use the examples you observed in class as examples throughout.
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BIO170 General Biology Freeman/Mac Leod FMCC
Complete the table and place it in your notebook.
Table 1 Summary of structures and functions involved with the life cycle of plants
Structure
Function
Haploid or diploid?
Produced by mitosis
or meiosis?
Examples of organisms
that have this
Antheridium
Archegonium
Spore
Gamete
Sporangium
Gametophyte
Sporophyte
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