Discover the Biological Sciences
The introductory information for this site has been contributed as a joint assignment by students in Bio. Sci. 10.
Botany - Bryology
By: Name: Sierra College Bio. Sci. 10
1) Biological field or sub-topic chosen: Botany: Bryology
2) Define field or sub-topic:
According to Wikipedia, the free online encyclopedia, Bryology is defined as “…the branch of botany concerned with the scientific study of bryophytes (mosses, liverworts, and hornworts). (Wikipedia)” Bryophytes are an “ancient and diverse group of non-vascular plants. (Bryology Study)”
“Non-vascular plants is a general term for those plants (including the green algae) without a vascular system (xylem and phloem).” According to Wikipedia, the vascular system of a plant is made up by “all the vascular tissues within a particular plant together.”
Vascular tissue is a defined as a “complex tissue. (Wikipedia)” Complex tissue is found in vascular plants which are “composed of more than one cell type.” There are two components of vascular tissue. One is xylem, a “type of transport tissue.” A common example of this is in wood, and its main function is to “transport water” inside the plant. The other component of vascular tissue is phloem, another tissue that “carries organic nutrients” to parts of the plant where they are needed. Sucrose, a sugar, is the main nutrient being transported in vascular plants. Phloem basically makes sure that glucose and starch are transported that have been made during the plant’s photosynthesis, or the process of turning the sun’s light energy into sugar for the plant to “eat.” Vascular tissue also has different meristems, which are “tissues in all plants consisting of undifferentiated cells (meristematic cells) and found in zones of the plant where growth can take place. (Wikipedia)”
Because xylem and phloem transport water and nutrients through a vascular plant, their form is similar to that of a pipe (Wikipedia). “The individual cells of phloem are connected end-to-end, just as the sections of a pipe might be. As the plant grows, new vascular tissue differentiates in the growing tips of the plant. The new tissue is aligned with existing vascular tissue, maintaining its connection throughout the plant. (Wikipedia)” The vascular tissue in is set in long vascular bundles which include both xylem and phloem, as well as supporting and protective cells (Wikipedia).
This is where the meristem come in. Vascular cambium is a meristem between the xylem and phloem that starts dividing cells to become new xylem and phloem, which makes the plant grow thicker. “As long as the vascular cambium continues to produce new cells, the plant will continue to grow more stout (Wikipedia).”
Bryophytes or non-vascular plants do not have these vascular tissues which transport food and water throughout the plant and enable the plant to grow nice and thick. “Although non-vascular plants lack these particular tissues, a number of non-vascular plants possess tissues specialized for internal transport of water. (Wikipedia)” Interestingly non-vascular plants have no roots, stems, or leaves. This is because those structure contain vascular tissue, which the non-vascular plant does not have (Wikipedia). Liverwort is a bryophyte or non-vascular plant with lobes, or round parts that look a whole lot like leaves but, according to Wikipedia, are not classified as a leaf because of the absence of xylem and phloem. Mosses also do not have these tissues.
3) Describe in more detail the breath and depth of what could be studied or learned within this topic:
Bryology: Study of Bryophytes
There are three kinds of Bryophytes: “Bryophyta (mosses), the Marchantiophyta (liverworts), and the Anthocerotophyta (hornworts)… Because these plants lack the water-conducting tissues, they fail to achieve the structural complexity and size of most vascular plants (Bryology Study).”
According to Bryology Study, “Bryophytes tend to escape people's notice because of their diminutive stature and their tendency to hang around dark and damp cracks and crevices.” Even though bryophytes “thrive in moist and shady habitats,” they can be found in many odd locations such as “sidewalks, tree tops, rocky cliffs, alpine settings, deserts, wetlands, forest floors, lawns, rooftops - just to name a few. (Bryology Study)” Bryophyta or moss will be the focus of this report, but there is more information on liverworts and hornworts at http://www.botany.ubc.ca/bryophyte/index.html
4) Focusing on one major concept, principle, or group of organisms (as appropriate within the topic), describe its importance, relationships, functional aspects, or otherwise explain it in more depth as seems important to you and (potentially) the others in class:
Bryophyta or Mosses
The Gametophyte LifeCycle Stage
The moss lifecycle has two stages. The first is the gametophyte, and the second is the sporophyte. The Bryology Study makes the comparison that in vascular plants, the dominant stage of the lifecycle is the “diploid generation”, however in non-vascular plants like mosses, it is the “haploid generation,” meaning it has only one set of chromosomes. The gameophyte is “all organs and tissues that are part of the haploid generation.” The gameophyte stage can be broken up into two developmental stages: the protonema, and the gametophore.
The first developmental stage of the moss is the protonema. It “develops from the germinating spore (Bryology Study).” “Its filamentous form is remarkably similar to green algae. This photosynthetic colonizer lies flat against its substrate, making it seem as if the rock or tree it grows on is painted green. The protonema will eventually produce leafy shoots called gametophores (Bryology Study).”
The second developmental stage of the moss is the gametophore. This is the “most conspicuous part of the moss (Bryology Study).” “Although these shoots seem to vary from moss to moss, there are many morphological characteristics that are common to most of the mosses. For instance, most mosses have spirally arranged leaves that are one cell layer thick (unistratose) (Bryology Study).”
With rare exceptions, most mosses have “multicellular stems and rhizoids associated with these stems (Bryology Study).” Rhizoids in the mosses are made of more than one cell, but more that one cell is still required to make a rhizoid, “aligned end to end, forming a filament (Bryology Study).” Rhizoids do not absorb water or nutrients from the “substrate”; instead, their main function is to “attach the plant to its substrate. It is thought rhizoids also play a role in water retention and conduction by capillary action (Bryology Study).”
Leaves on mosses are important organs because of how diverse they are. They help tell different spiecies of mosses apart. Moss leaves are almost always photosynthetic and are “composed of a single layer of elongated cells (Bryology Study).” Leaves on mosses are “spirally arranged” and never lobed, which makes them different from leaves in leafy liverworts, another group of bryophytes (Bryology Study). Some useful things to look for in leaves when trying to identify a moss are included in this list provided by (http://www.botany.ubc.ca/bryophyte/index.html)
• Undulations: refers to waves that run perpendicular to the length of the leaf
• Pleats: refers to wrinkles that run along the length of the leaf
• Toothed margins: are sharp extensions of the leaf margins
• Lamellae: photosynthetic cells that form filaments or plates along the lamina or costa of the leaf. They are found in the Polytrichidae
• Incurved margins: margins that are curved upwards and towards the center of leaf
• Recurved margins: margins that are curved downwards and towards the center of the leaf
• Hair point / awn: refers to the extension of the costa beyond the tip of blade, producing a hair or bristle.
• Papillae: refers to bulges of cell wall thickenings of certain cells
• Pits: refers to a perforation or hole in the cell wall of certain cells.
• Hyaline cells: Large, non-photosynthetic, porous cells found in Sphagnum leaves.
• Alar: refers to the basal corner of a leaf where cells are most often larger than the other cells of the leaf.
Another way to identify moss is by its costa, if one is present. A costa is a “midrib of specialized cells that runs lengthwise through the leaf.” Like the stem and leaves, there is a whole lot of differentiation amongst cells of the costa, including: “stereids, guide cells, hydroids and leptoids (Bryology Study).”
Mosses have female and male reproductive organs, called archegonia and antheridia. “The male will produce coiled biflagellated sperm cells that will swim towards the egg that lies within the archegonia. Because water is needed for the sperm cells to reach the egg, this is one of the reasons why moss seem to be more prevalent in wet areas. Once fertilized, the zygote will mature to produce the sporophyte (Bryology Study).” This sporophyte is the second lifecycle phase of a moss.
The Sporophyte LifeCycle Stage
The gametophyte from the first stage is the “haploid mother” of the new sporophyte, which is a diploid (Bryology Study). Diploid means it has two sets of chromosomes. The sporophyte actually remains attached to the gametophyte, as a parasite. This is how it gets its food and water, which passes through “transfer cells” that “lie in the placental layer between the gametophyte and the sporophyte.” Most mosses at this stage have something called a seta, or a “long stem-like organ that connects the sporangium to the gametophyte (Bryology Study),” which is commonly composed of “parenchyma cells, stereids, and many times a well developed conducting strand… The base of the seta is called the foot (Bryology Study).”
The main organ of the sporophyte is called sporangium, where spores are produced. Most sporangium have certain anatomical features: “a sporogenous layer, a columella, peristome teeth, and an operculum (Bryology Study).” To protect the sporangium, there is something called the calyptra in most mosses, which is made of haploid tissue that used to be part of the archegonium, making it gametophytic (Bryology Study). Calyptra can be bald or hairy, depending on the spiecies, and eventually is shed before spore “dispersal” begins (Bryology Study).
4) In studying and discovering more about this topic, what was the most interesting aspect, fact or some other piece of information that you have learned.
I thought it was interesting that the calyptra whose job is to protect the spore making organ, sporophyte, is part of the original moss in stage 1 (gametophyte), which makes it the sporophyte’s “mother,” but the gametophyte is what the sporophyte remains attached to. This was interesting because the sporophyte is parasitic to the gametophyte, its “mother” which is its protector in its young stage. Neat!
6) References provide references used and at least two Web sites with additional information on this topic (or sub-topic) for anyone that would like to learn more:
Bryology Study http://www.botany.ubc.ca/bryophyte/index.html
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