Download Lab 4: Mosses Fern

Lab #4: Nonvascular and Seedless Vascular Plants
Objectives:
 Become familiar with the alternation of generations.
 Describe the life cycle of a typical bryophyte; distinguish between the gametophyte and
sporophyte generations.
 Describe the life cycle of a typical fern; distinguish between the gametophyte and sporophyte
generations.
 Understand the changes in the alternation of generation that occurred over time, moving from
the bryophytes to the vascular plants.
 Distinguish between rhizoids, rhizomes and roots.
General Procedures
Examine the slides and live materials for the organisms in each section.
For the slides:
 start with a low magnification and make a drawing of the overall structure
 increase the magnification and make close-up drawings of the “structures to identify” as noted in
each section.
For the live material:
 make drawings of the organism as a whole
 use a dissecting scope/or hand lens to make close-ups of important structures.
Label all drawings with the name of the organism, the magnification used and the names of the
structures. Also include color, texture, shape, size or any other notes that would help you identify the
organism and its structures.
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You may work individually or in groups of two but all students will complete their own notebook
drawings and questions.
There are often limits to the number of slides/specimens available. Please take only the
slides/specimens to your desk that you are currently working on and leave the rest for other students.
Use the pictures in the photo atlas and your textbook to guide you through the slides and specimens.
Some of these slides may be difficult to interpret. Do your best and ask me if you have
questions.
Clean up instructions - Do not put in notebook
For prepared slides:
 Return to the slide box. Please take care to make sure the slides are placed in the correct box and
properly aligned!
For slides you prepare:
 Put cover slip in broken glass jar
 Put samples in the garbage
 Rinse slide clean, wipe dry with a tissue and return to the slide box. Please take care to make
sure the slides are properly aligned.
General
 Return all materials to cart or bench where you got them and wipe down your bench.
General Introduction
Plants are generally defined as multicellular, photosynthetic eukaryotes. Plant cells have cell
walls composed of cellulose and store surplus carbohydrates as starch. They utilize two photosystems in
photosynthesis with two forms of chlorophyll (a and b).This list of characteristics is not mutually
exclusive to the Plant Kingdom, however, as several phyla of algae also fit the description. Therefore,
the definition of plants can be refined to include the fact that plants enclose their embryos in parental
tissue. This is true whether looking at mosses or ferns where the embryos grow directly on the parental
(haploid) gametophyte, or looking at seed plants where the embryos are enclosed by parental tissue in
the seed. The plants are sometimes referred to as “embryophytes” for this reason. Plants also show
adaptations to a terrestrial life cycle as most live on land. Aquatic plants are generally viewed as
secondarily aquatic.
The plant life cycle is referred to as “alternation of generations”. The key to this life cycle is that
both the haploid stage (gametophyte) and the diploid stage (sporophyte) are multicellular. The
gametophyte produces haploid gametes through mitosis and the sporophyte stage produces haploid
spores through meiosis. As we examine the Plant Kingdom, you should notice a shift in the alternation
of generations from a gametophyte dominant life cycle (mosses and liverworts) to a sporophyte
dominant life cycle (ferns, conifers, and flowering plants). Importantly, remember that all the plants still
exhibit a true alternation of generations.
We will examine the Plant Kingdom through a series of four evolutionary stages. The nonvascular or nontracheophytes (mosses and liverworts) exhibit the first stage: embryos wrapped in
parental tissue. The second stage, formation of vascular tissue, is displayed in the vascular seedless
plants (ferns and horsetails). The evolution of seeds will be examined in the gymnosperms and the
evolution of flowers in the angiosperms.
1) Nonvascular plants “Bryophytes” (Phylum Bryophyta and Phylum Hepaticophyta)
The nonvascular plants represent the earliest group of terrestrial plants. Materials are still
transported through the plant body, but the vascular cells of later plants are not evident. Consequently,
the nonvascular plants are generally low-lying, mat-like plants in which water is absorbed as much
through the “leaf-like” structures as it is through the rhizoids. Rhizoids are small, root-like structures
used by the gametophyte for attachment and some water absorption. The alternation of generations life
cycle is very evident as both the multicellular haploid gametophyte and the multicellular diploid
sporophyte are visible and will be viewed macroscopically in this lab.
Phylum Bryophyta (mosses)
Examine and sketch the live moss specimens. Review Fig. 29.8 The life cycle of a moss from
your textbook and use it to help you identify the structures. The main body is the haploid gametophyte
generation. Rhizoids may be visible. The diploid sporophytes are visible as stalks (seta) with
capsules (sporangium) rising from the main gametophyte body. Inside the capsule is the sporangium,
which produces spores via meiosis. Use the slide below to examine the sporophyte capsule in more
detail.
Demo Live specimens: Various species
Choose one live specimen to draw and label.
Structures to Identify: gametophyte, sporophyte, stalk (seta), capsule (sporangium), rhizoids
Slides: Mnium sp. capsule
Structures to Identify: capsule, spores
Lab# 4 Nonvascular and Seedless Vascular Plants
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The spores are released and when they germinate they grow into the gametophyte generation. Most
species of moss produce separate male and female gametophytes. The female gametophyte produces the
female gamete (egg) in an archegonium. The male gametophyte produces the male gamete (sperm) in an
antheridium. The archegonium and antheridium are not easily apparent on the live specimen. Use the
slides below to examine them in detail.
Slides: Mnium sp. antheridia
Structures to Identify: antheridium, sperm (visible in some slides)
Slides: Mnium sp. archegonia
Structures to Identify: archegonium, egg (visible in some slides)
The sperm is released and travels to the archegonia in water droplets, and once there, fertilizes
the egg. The diploid zygote (embryo) grows into a diploid sporophyte which grows from the main body
of the gametophyte. It will remain attached and get nourishment from the gametophyte. The cycle
begins again when spores are released from the sporophyte.
Phylum Hepatophyta (liverworts)
Examine and sketch the live specimens of Marchantia sp. Use Fig. 6.6 Life cycle of a
thalloid liverwort, Marchantia from the photo atlas to help you identify the structures. The most visible
structures will be part of the haploid gametophyte generation. The gametes are produced in specialized
structures that rise above the main gametophyte body. The female structure, the archegoniophore
(palm-tree like), produces eggs inside archegonia. The male structure, the antheridiophore (more flat
topped), produces sperm inside antheridia. Use the slides below to take a more detailed look at these
structures.
Demo Live specimens: Various species
You may need to draw more than one live specimen to identify all the structures.
Structures to Identify: gametophyte, sporophyte, archegoniophore, antheridiophore, sporophyte
Slides: Marchantia sp. antheridiophore
Structures to Identify: antheridiophore, antheridia
Slides: Marchantia sp. archegoniophore
Structures to Identify: archegoniophore, archegonia, egg (visible in some slides)
Sperm travel to the archegonia in water droplets, and once there, fertilizes the egg. The diploid
zygote grows into a diploid sporophyte which remains as a small structure attached to the
archegoniophore. Use the slide below to view maturing sporophytes. The sporophyte will produce spores
that will grow into the gametophyte.
Slides: Marchantia sp. mature sporophyte
Structures to Identify: sporophyte, sporangium, seta (stalk), foot, spores
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Liverworts also reproduce asexually through the use of gemmae cups; cup-like areas on the
surface of the gametophyte that contains small pieces of tissue (gemmae). If rain knocks the gemmae
out of the cup and onto a suitable habitat, a new gametophyte will grow. Look for gemmae cups on the
live specimen. Use the slide below to see a cross section of a gemmae cup.
Demo Live specimens: Various species
Choose one live specimen to draw and label.
Structures to Identify: gemmae cups
Slides: Marchantia sp. gemmae cup
Structures to Identify: gemmae cup, gemmae
2) Seedless vascular plants
Vascular tissue is composed of cells joined into tubes transporting water and nutrients throughout
the plant body. Xylem tissue is the water-transport tissue carrying water from the roots up the plant
body, and phloem tissue is the food-transport tissue carrying phloem sap (food nutrients) from food
sources (leaves or food storage organs) to food sinks (growing non-photosynthetic structures or food
storage organs). The bodies of the vascular plants are divided into an aerial shoot system (stems, leaves,
and reproductive structures), and an underground root system. True leaves, stems, and roots all contain
true vascular transport tissue. The development of vascular tissue allowed the vascular plants to grow
much taller than the non-vascular plants. These plants are seedless. Ferns often have rhizomes, modified
stems that grow horizontally underground or just above the ground.
Phylum Pterophyta: (ferns)
Examine and sketch the live specimens of the ferns. Review Fig. 29.13 The life cycle of a
fern from your textbook and use it to help you identify the structures.
Begin with the mature sporophyte, the diploid structure which we know of as the “fern”.
Identify leaves, rhizomes (if present), and sori (groups of sporangium produced on the underside of the
fern leaf). Haploid spores are produced within the sporangium via meiosis and then released. Once the
spores have found a good environment, they will germinate and grow into haploid gametophytes. In
the fern, there is a female gametophyte, which is larger and heart shaped, and a male gametophyte,
which is smaller, not heart shaped, and looks like it is covered in small round cells with dots in them.
The round structures are the antheridia, which produce sperm. The female gametophyte produces eggs
in archegonia, which are small bulges (hard to identify) that tend to be clustered at the cleft of the
“heart”. There are also hermaphroditic gametophytes, which look like a female, but also have antheridia.
Rhizoids should also be visible.
Demo Live specimens: Various species
Choose one live specimen to draw and label.
Structures to Identify: mature sporophyte, leaves, rhizomes, sori (sporangium)
Slides: Fern antheridia/archegonia
Structures to Identify: male gametophyte, antheridium w/sperm, female gametophyte,
archegonium, rhizoids
Once the sperm is released, it swims through the water, following a trail of attractants released by
the female gametophyte. The sperm swim to the archegonia and fertilize the eggs. A zygote is formed,
which then grows into a diploid sporophyte, growing from the gametophyte. The sporophyte is not
dependent on the gametophyte for food and eventually the gametophyte dies. The sporophyte grows,
becomes sexually mature, produces spores, and the cycle begins again.
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Phylum Pterophyta, Genus Equisetum (horsetail)
Examine and sketch the live specimen of the mature sporophyte of Equisetum sp.,
commonly known as “horsetail”. Review Fig. 7.26 Life cycle of the horsetail, Equisetum from the
photo atlas and use it to help you identify the structures. The prominent bumps on the stem are nodes,
areas where leaves and stems connect. The leaves are very small, and look like a thin, fringed sheath
that wraps around the node. More stems arise from the nodes (often mistaken for leaves). Rhizomes
may be visible, as well as true roots.
Equisetum sends up separate reproductive stems, which hold the strobilus (cone-like structure).
The strobili hold many sporangia on specialized structures called sporangiophores and produce spores
via meiosis. The spores germinate and grow into gametophytes, which then produce the gametes, which
fuse together in fertilization to become a new sporophyte generation. Depending on the season, a live
specimen with a strobilus may not be available. Use the slide below to examine the strobilus in more
detail.
Demo Live specimens: Various species
Draw both the vegetative stem and the reproductive stem
Structures to Identify: nodes, leaves, rhizomes, roots, strobilus
Slides: Equisetum sp. mature strobilus
Structures to Identify: strobilus, sporangiophore, sporangia, spores
Questions for your lab notebook
1. Are the “leafy” (photosynthetic) portions of the moss of the sporophyte or gametophyte generation?
2. What type of gamete is produced by an antheridial head? By an archegonial head?
3. How does the sporophyte generation of the moss acquire nutrients?
4. What is the difference between a rhizoid and a rhizome? a rhizome and a root?
5. What features do you look for to classify a plant as vascular?
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