Moss

external image GREEN-carpet-of-MOSS.jpg
Green Carpet of Moss


Classification/Diagnostic Characteristics

Moss is a nonvascular land plant that lacks fluid-conducting cells called tracheids. Moss lack true leaves, stems and roots. [1] Bryophytes have erect stems and tiny leaves. [2] Individual moss plants are very small and are often found in large clusters occasionally described as "cushions". A carpet of moss in a forest can be seen in the photograph above. These "cushions" of moss are always very wet because the moss need moist environments in order to survive due to the absence of a proper cuticle that allows for efficient water retention. [3]

Relationship to Humans

Many gardeners mix moss with their soil in order to improve the water-holding capacity of soil. The most important Moss to humans is Sphagnum because of its many diverse uses. [4] Westerns also use moss to create moss gardens, due to the little to no maintenance that is required for moss to grow. The most famous moss garden is located in Japan, know as the Koke-dera as show in the image below. [5]
external image Saihouji-kokedera02.jpg
Koke-dera

Some more extreme humans also may ingest different mosses, as some are not harmful to the body and are a great source of carbohydrates. They may cause an upset stomach due to their acidity, but for the most part are a valid source of carbs. [6] Moss is also commonly used in biotechnology, having potential for crop improvement and human health, such as the production of biopharmaceuticals. [7]

File:Bioreaktor quer2.jpg
File:Bioreaktor quer2.jpg
Moss Bioreactor

A common use of moss to humans is to be a bioindicator, or simply a gage as to how successful/ healthy an ecosystem is working. Moss are bioindicators of conditions such as water pollution, air pollution and acid rain damage, both two factors that can greatly affect the land in which humans live on. [8]

Habitat and Niche

Moss is found in almost every terrestrial environment. Moss is often to be found on cool, damp grounds in large mats. Moss can also live on the soil and on vascular plants. This plant can also grow on rocks, dead or fallen tree trunks and on buildings. [1] Since moss gametophytes have no vascular system to transport water through the plant or waterproofing systems to prevent tissue water from evaporating, they must have a damp environment in which to grow, and a surrounding of liquid water to reproduce. Since mosses are autotrophic they require enough sunlight to conduct photosynthesis.[16] Shade tolerance varies by species, just as it does with higher plants. In most areas, mosses grow chiefly in areas of dampness and shade, such as wooded areas and at the edges of streams; but they can grow anywhere in cool damp cloudy climates, and some species are adapted to sunny, seasonally dry areas like alpine rocks or stabilized sand dunes. [9]

Predator Avoidance

Moss avoid their predators by camouflaging themselves with the environment they are in. This disguises themselves and makes them harder for predators to detect. Also, moss sometimes contain spikes and other poisonous materials on them which make them dangerous for predators to eat. [10]

Nutrient Acquisition

Minerals are distributed through their bodies by diffusion. Mosses absorb water and nutrients through their leaves. They use photosynthesis to create fuel from the sunlight.

Some mosses are able to take up nutrients from water flowing over them because they have a very effective absorptive surface. Other mosses obtain nutrients directly from the soil or substrate on which they are growing, and transfer the nutrients to the growing leaves.

Since mosses lack a complex vascular system which includes xylem and phloem, mosses must absorb nutrients through their leaves or the soil which is why they must stay close to the ground. This form of nutrient absorption also keeps mosses from overexposure to sunlight, causing the plants to dehydrate.

Moss can more efficiently absorb water when there is more CO2 present in the atmosphere. A study was done in the UK where moss water absorbance levels were observed during different parts of the day, being dependent on weather, ex. dew, and it's affect on carbon dioxide levels.

Reproduction and Life Cycle

Moss goes through both haploid (one set of chromosomes) and diploid (two sets of chromosomes) phases. First, the sporophyte, which is the multicellular, diploid part of the plant, makes the unicellular spores, through the process of meiosis. The haploid spores are produced within the sporangium. A gametophyte, which is the multicellular, haploid part of the plant, forms when the spore germinates. The cells of the gametophyte have chloroplasts and are photosynthetic. Eventually, gametes will form within the gametangia, the specialized sex organs. The female sex organ is called the archegonium and is multicellular, flask-shaped, with a long neck and a wide base. In the archegonium, one egg is produced. The male sex organ is called the antheridium. In the antheridium, sperm are made in large quantities. Each individual moss has both the archegonium and the antheridium. Because these reproductive structures are next to each other, moss often fertilize each other's gametes. Once the sperm is released from the antheridium, the sperm must swim or be carried over by rain to the archegonium. The sperm then are helped by chemical attractants, which are chemical compounds that help the sperm swim toward the archegonium. Certain cells in the neck of the archegonium must break-down to open a passage filled with water, so that the sperm can swim through to the egg. Once the sperm arrives at the egg, the nucleus of the sperm fuses with the nucleus of the egg, which forms a diploid zygote. The zygote will then go through mitosis and the zygote produces a multicellular, diploid sporophyte embryo. The sporophyte then grows and produces a sporangium, where meiosis occurs and spores are made and the cycle repeats again. [1]


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Life Cycle of Moss {Alexander Soloviev)


Growth and Development

Due to moss lacking a vascular system, moss growth is limited as nutrients could not travel to all parts of the plant if it was any taller. [11]

Integument

Moss has layers of maternal tissue that protect their embryos from drying out. [1]

Movement

Moss is incapable of movement as it is a plant. The way it spreads is through spores which are dispersed by the wind. In some cases the acceleration of the spores can exceed 36000 times the acceleration of gravity. [12/13]

Sensing the Environment

Moss, like most green-plants, are autotrophic organisms. To sustain this sort of lifestyle, they require a pigment called chlorophyll which absorbs the sunlight needed to conduct photosynthesis. This relates back to why moss needs to grow in areas that are both damp and sunlight-abundant, because they manufacture their own food and lack vascular transportation for water. (Prashant)

Gas Exchange

Moss have stomata that is important in gas exchange. [1] The stomata (plural, stoma) are pores through which carbon dioxide, oxygen, and water vapor are taken in and out of the moss. The stoma are surrounded by guard cells that open and close it. The guard cells coordinate the amount of gas lost and gained from the plant since they controls the stoma. [14]

Waste Removal


Environmental Physiology (Temperature, Water and Salt Regulation)

Because of their structure, water can move through the mats of moss through capillary action. Stomata play an important role in the water retention of moss. Some moss gametophytes are too big and as a result cannot transport enough water to the whole body by diffusion. Both the gametophyte and sporophyte mosses have a type of cell, called a hydroid, which dies and then leaves a small channel, so that water can travel through. The rhizoids, a root like support structure at the base of moss, can conduct water externally using capillary action; not absorbing water internally, they can bunch together to form tubes for water transport. [1]

Internal Circulation

Mosses have no vascular system or circulatory system. They can, however, have structures called hydroids, which die in order to leave behind a channel in which water can travel. Hydroids, in a sense, give moss a kind of primitive vascular system, but not one complex enough to knock moss out of the nonvascular category of land plants. [1]

Chemical Control (i.e. Endocrine System)


Review Questions:

1. In general, where is the sporophyte positioned in relation to the gametophyte in bryophytes? How does the sporophyte obtain nutrients?
2. How do the sporophyte and gametophyte of moss compare to those of other species of plants?
3. Why does moss need to live in cool, damp places and how does this affect the environmental physiology system of moss?

References

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.
2. http://www.rbge.org.uk/science/cryptogamic-plants-and-fungi/bryology
3. http://www.houseandhome.org/moss-facts
4. http://science.jrank.org/pages/4460/Moss-Importance-humans.html
5. http://www.rothteien.com/landing/plants/moss.htm
6. http://www.survivalistboards.com/showthread.php?t=9409
7. Eva L. Decker and Ralf Reski(2007): Moss bioreactors producing improved biopharmaceuticals. Current Opinion in Biotechnology 18, 393-398.
8. http://bryophytes.science.oregonstate.edu/page3.htm#anchor30816
9. http://en.wikipedia.org/wiki/Moss#Habitat
10. http://www.elkhornslough.org/sloughlife/birds/snowy_plover-mudstomp.htm
11. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/M/Mosses.html
12.http://www.wisegeek.com/how-can-i-grow-moss.htm
13.https://en.wikipedia.org/wiki/Moss
14. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GasExchange.html
http://www.anbg.gov.au/bryophyte/what-is-moss.html