Showing posts with label water-related life. Show all posts
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1:13 AM
Marine Agriculture
Marine Agriculture

Marine agriculture uses techniques of artificial cultivation, such as growing, managing, and harvesting, and applies them to marine plants and animals. The products are then used for human consumption.

Marine agriculture is also known as mariculture or aquaculture, although aquaculture is a more general term referring to both freshwater and marine farming of organisms. The world’s oceans cover approximately three-fourths of the globe, including vast regions of unexplored life and landforms.

The potential for exploiting the oceans agriculturally is great but currently meets significant obstacles. Because of the expense of equipment and personnel involved, most marine species are not cultivated.


Coastal pollution, habitat destruction, competition for land use, and economics all limit mariculture programs. Nevertheless, mariculture does offer several food, medical, and other products that are currently being marketed.

Food

Seaweeds are edible, especially the red and brown algae. The three most common types of seaweeds are known by their Japanese names: nori (Porphyra), a red seaweed high in vitamin C and digestible protein; kombu (Laminaria); and wakame (Undaria), high in calcium.

They are eaten raw, cooked, or dried and have several vitamins and minerals as well as protein. Seaweeds are low in fats, and 35 to 50 percent of the dry weight of red seaweeds is protein.

Seaweeds can be used to add taste and variety to foods. They are used as a hot vegetable, boiled and formed into cakes and fried, in salads, and in preparing desserts, breads, soups, casseroles, sandwiches, teas, and candy.

The world’s yearly harvest of seaweeds is approximately 8.4 million tons of green seaweed, 2.8 million tons of brown seaweed, and 1.2 million tons of red seaweed. The total seaweed market in 1998 was worth more than $5 billion, with $600 million deriving from food additives alone.

China is the leading harvester and the world’s biggest seaweed consumer. Japan is the leading seaweed importer and, at the end of the twentieth century, employed more than thirty-five thousand people in the industry. Harvesting and marketing edible seaweed is a growing business in the United States, especially on the West Coast.

Seaweeds
Seaweeds

Seaweeds produce several types of phycocolloids, starchlike chemicals used in food processing and manufacturing. An important type called algin, which makes up alginic acid and alginates, is used inmanufacturing dairy products such as ice cream, cheese, and toppings as well as to prevent frostings and pies from desiccation.

Another extract is agar, used to form jellies and protect fish and meats during canning. Agar is also used in low-calorie foods and as a thickener. Red algae is a source of the agglutinant carrageenan, which is used in many food products as an emulsifier to give body to dairy products and other processed foods, including instant puddings. Additionally, seaweed-based food additives are common in prepared and fast foods, including hamburgers and yogurt.

Kelp farming is a major livelihood in the eastern Pacific, with approximately 140,000 tons harvested each year for the extraction of alginates used in food and food additives. Kelp is a good source of calcium, potassium, iron, iodine, bromine, and zinc. It is also low-fat, has some protein, and is a natural tenderizer. Kelp flakes are used as a low-sodium salt substitute.

Medicine

The use of marine plants inmedicine is still in the early stages of exploration and faces many challenges, including identification of useful chemicals and the cultivation of significant quantities.

Dinoflagellates and other microalgae are being investigated for compounds that might fight cancerous tumors. Diluted algae toxins from red tides can be used to inhibit the growth of most bacteria. Green algae has halosphaerin, a strong antibiotic.

Seaweed is used in wound dressings in hospitals and as a source of iodine, A, B, D, and E vitamins, calcium, magnesium, potassium, sodium, sulfur, and trace antioxidants such as selenium and zinc. The seaweed extract agar is used in laxatives and as a medium to grow bacteria and molds.

Kelp is rich in chlorophyll, which can help detoxify the body, fight inflammations, and increase the formation of oxygen-carrying red blood cells. Chlorophyll is also used to fight bad breath and as an ingredient in deodorants.

Kelp is used to reduce cholesterol, treat gastrointestinal, respiratory, and genitourinary disorders, and lower blood pressure. The alginic acid produced by kelp can rid the body of radioactive strontium, the most dangerous to humans of all components in the fallout from atomic explosions.

Other Uses

Marine plants are used for a variety of other purposes. Seaweed is used as a component of many fertilizers, as a food additive in animal feed, and to reduce soil acidity.

Research on cattle and swine has revealed that the addition of seaweed to animal feed can enhance the immune system and makes the meat a more desirable color. It can also save cattle from the effects of fungus-infected grass.

Seaweed is used as an ingredient in cosmetics as well as to nourish, revitalize, condition, and improve the skin, hair, and body. It is used in cleansers, toners, moisturizers, scrubs, body lotions, and hair and bath products.


The giant kelp (Macrocystis) is a major source of algin for commercial uses, as is the brown algae Laminaria, which is harvested in the north Atlantic. Algin is used in shampoos, shaving cream, plastics, pesticides, rubber products, paper, paints, and cosmetics.

Additionally, kelp is used in emulsifiers for toothpastes and printing inks. Kelp has even been used to make fishing lines. Some research has been done on using kelp as a fuel to produce a clean-burning methane gas. Kelp can be used to ferment human waste and garbage, which can then be sold as fertilizers.
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1:34 AM
Algae
Algae
Algae comprise a diverse group of (with few exceptions) photosynthetic oxygen-producing organisms, ranging in size from microscopic single cells to gigantic seaweeds.

The study of algae is known as phycology (in Greek, phycos means "algae"). Currently, most authors place eukaryotic algae in the kingdom Protista (domain Eukarya) and prokaryotic algae in the domain Bacteria.

In the past algae were considered to be lower plants because some forms look like plants. As in plants, the primary photosynthetic pigment in algae is chlorophyll a, and oxygen is produced during photosynthesis.

What Are Algae?

Algae can be found nearly everywhere on earth: oceans, rivers, lakes, in the snow of mountaintops, on forest and desert soils, on rocks, on plants and animals (such as within the hollow hair of the polar bear), or even on other algae. They are involved in diverse interactions with other organisms, including symbiosis, parasitism, and epiphytism.


Lichens are symbiotic associations between algae (blue-green algae, or cyanobacteria) and fungi. Atmospheric nitrogen-fixing cyanobacteria occur in symbiotic associations with plants such as bryophytes, water ferns, gymnosperms (such as cycads), and the angiosperms.

The aquatic fern Azolla, commonly used as a biofertilizer in rice fields in Asian countries, harbors the symbiotic cyanobacterium Anabaena azollae. Gunnera, the only flowering plant to house symbiotic cyanobacterium Nostoc, is widely distributed in the tropics.

Symbiotic dinoflagellates known as zooxanthellae livewithin the tissues of corals. Corals get their colors and obtain energy from their photosynthetic symbionts. About 15 percent of red algae occur as parasites of other red algae. Parasitic algae may even transfer nuclei into host cells and transform them.

After transformation, the reproductive cells of the host algae carry the parasite’s genes. Various algae live on the surfaces of plants and other algae as epiphytes. Sometimes algae can be found in strange places—the pink color of flamingos originates, for example, comes from a pigment in the algae consumed by these birds.

Algal Structure and Properties

Algal cells are bounded by a cell wall. Algal cells are either prokaryotic or eukaryotic. All prokaryotic algae belong to Cyanophyta (cyanobacteria) and lack both a nucleus and complex membrane-bound organelles, such as chloroplasts and mitochondria.

Photosynthesis occurs in cyanobacteria in thylakoid membranes similar to those of plants. However, there is no double membrane surrounding the thylakoids of cyanobacteria.

All other algal groups are eukaryotic. Eukaryotic algae differ from cyanobacteria in that they possess chloroplasts and flagella with associated structures and in their cellwall composition. According to the endosymbiont hypothesis, some eukaryotic algae (red and green algae) obtained their chloroplasts by acquiring symbiotic prokaryotic cyanobacteria. This is known as primary endosymbiosis.

types of alga
types of alga

Other eukaryotic algae probably obtained their chloroplasts by taking up eukaryotic endosymbiotic algae, a process known as secondary endosymbiosis. The existence of secondary endosymbiosis is indicated by the occurrence of more than two membranes around the chloroplasts of some algae, such as haptophytes, euglenophytes, dinoflagellates, and cryptomonads.

Pigments found in algae include chlorophylls, phycobilins, and carotenoids. All algae contain chlorophyll a. Accessory pigments vary among different algal groups.

Photoautotrophy is the principal mode of nutrition in algae; in other words, they are "self-feeders", using light energy and a photosynthetic apparatus to produce their own food (organic carbon) from carbon dioxide and water. The majority of algal groups contain heterotrophic species, which obtain their organic food molecules by consuming other organisms.

Numerous algae are mixotrophs; that is, they use different modes of nutrition (such as autotrophy and heterotrophy), depending on the availability of resources. The molecules used as food reserves differ among and are characteristic for algal groups. Food reserve molecules are polymers of glucose with different links between monomers.

Many algae are capable of movement. Movement is accomplished by means of flagellar action and by extrusion of mucilage. There are also peristaltic and amoeba-like algal movement. Within algal cells, movement of the cytoplasm, plastids, and nucleus also occurs.

Advantages conferred by mobility include achieving optimal light conditions for photosynthesis, avoiding damage caused by excess light, and obtaining inorganic nutrients.

Algal Reproduction and Life Cycles

Algae may reproduce either asexually or sexually. Asexual reproduction among algae includes production of unicellular spores that germinate without fusing with other cells, fragmentation of filamentous forms, and cell division by splitting.

In sexual reproduction, parent cells release gametes, which then fuse to form a zygote. Zygotes may either develop into new filaments or produce haploid spores by meiotic division.

Algae exhibit different types of life cycles. Some algal life cycles are characterized by an alteration of generations similar to that of plants. Two phases occur: sporophyte (usually diploid) and gametophyte (usually haploid).

The sporophyte produces haploid spores through meiosis, and the haploid gametophyte produces male or female gametes by mitosis. Gametophyte and sporophyte may be structurally identical or dissimilar, depending on the algal group.

Roles of Algae

Algae have played significant roles in the earth’s ecosystems since the origin of cyanobacteria (also known as blue-green algae)more than three billion years ago. Early cyanobacteria were responsible for the development of significant amounts of free oxygen in the atmosphere, which then made aerobic respiration possible.

More than 70 percent of all photosynthetic activity on earth is carried out by phytoplankton—floating microscopic algae—rather than plants. Phytoplankton recharge the atmosphere with oxygen and simultaneously absorb carbon dioxide, helping to support the complex web of aquatic biota.

Algae are also very important in the global cycling of other elements, such as carbon, nitrogen, phosphorus, and silicon. Several algal groups—such as cyanobacteria, green algae, red algae, and the haptophyte algae—are able to generate calcium carbonate.

Sedimented algae are the major contributors to deep-sea carbonate deposits (sand), which cover about half of the world’s ocean floor. Calcified coralline red algae contribute to coral reefs in tropical waters. Silica sediments in oceans (sand) are based on abundant growth of another algal group, the diatoms, which contain silica in their cell walls.

Some algae (cyanobacteria) are able to fix atmospheric nitrogen and convert it to ammonia. Ammonia, in turn, can be a nitrogen source for plants and animals. On the other hand, high levels of nitrogen and phosphorus in rivers and lakes owing to pollution can cause the rapid and uncontrollable growth of algae, known as algal blooms.

A bloom of algae is a threat to human and marine health, both directly and indirectly. It clogs fishes’ gills, interferes with water filters, and ruins recreation sites. More than 50 percent of algal blooms produce toxins.

Cases of human respiratory, skin, and gastrointestinal disorders associated with algal toxins have been reported. Certain blooms of algae are called red tides. The water appears to be red or brown because of the color of algal bodies, mainly dinoflagellates that contain the pigment xanthophyll.

Technological Applications

Algae can be grown and turned into biofuel - an ethanol that can power homes and cars.
Technological Applications

Algae have been used as food, medicine, and fertilizer for centuries. The earliest known reference to the use of algae as food occurs in Chinese poetic literature dated about 600 b.c.e. More recently, algae have begun to play important roles in certain biotechnological processes.

Several algae, including reds, browns, greens, and cyanobacteria, are used for food in Pacific and Asian countries, especially Japan. The annual harvest of the red alga Porphyra worldwide is worth several billion dollars. Porphyra (Japanese nori, Chinese zicai) is used as a wrapper for sushi or may be eaten alone. Another edible alga with a high iodine content is the brown alga Laminaria (Japanese kombu). The cyanobacterium Spirulina, with a protein level of 50 to 70 percent, was cultivated for centuries by indigenous Central Americans at Lake Texcoco near modern-day Mexico City for use as human food.

Several gelling agents are produced from red and brown algae. Agar from red algae is used as a medium for culturing microorganisms including algae, as a food gel, and in pharmaceutical capsules. Red algal carrageenan is used in toothpaste, cosmetics, and food such as ice creamand chocolate milk.

Alginates from brown algae have extensive applications in the cosmetics, soap, and detergent industries. Sources of alginates are Laminaria, some Fucus species, and the giant kelp Macrocystis,which can grow to more than 60 meters long. Algae are also used as feed in the culture of commercially important fish and shrimp.

Mass cultivation of algae (microalgae)—in open ponds and photobioreactors for production of fuels (such as biomass) and biochemicals (such as carotenoids, amino acids, and carbohydrates) and for water purification—is a rapidly developing area based on the use of solar energy as energy source. The green alga Dunaliella is used in the industrial production of carotene. In wastewater treatment plants, algae are used to remove nutrients and heavy metals and to add oxygen to the water.

Algae are used worldwide as indicators (biomonitors) of water quality, helping to detect the presence of toxic compounds in water samples. Several fast-growing algae are used, including the green alga Selenastrum capricornutum.

Many algae are widely employed as research tools because they are easy to culture and manipulate. Danish biologist Joachim Hammerling’s experiments with the green alga Acetabularia identified the nucleus as the likely storage site of hereditary information.

Diversity

Taxonomists believe that there are between thirty-six thousand and tenmillion species of algae. Molecular comparisons using nucleotide sequences in ribosomal RNA (ribonucleic acid) suggest that algae do not fall within a single group linked by a common ancestor but that they evolved independently.

The algae are divided into ninemajor phyla, which differ in their photosynthetic pigments, food reserves, cell structure, and reproduction. These groups include euglenoids, cryptomonads, dinoflagellates, haptophytes, and red algae.

Phylum Euglenophyta contains mostly unicellular formswith one or two flagella. Only one-third of this group possess chlorophyll-containing chloroplasts. Other euglenoids are strictly heterotrophic.

The phylum contains more than nine hundred, mostly freshwater, species. The food reserve is the carbohydrate paramylon, a polymer of glucose. Euglenophytes have chlorophyll a and b as well as carotenoids as their photosynthetic pigments. There is no cell wall.

Cells have several small chloroplasts; each is surrounded by three membranes. A close relative of euglenophytes is the protozoan Trypanosoma, which causes the human disease African sleeping sickness. Reproduction in the euglenophytes occurs by division of cells. Sexual reproduction is unknown.

Phylum Cryptophyta includes unicellular biflagellates. In addition to chlorophyll a, chloroplasts can contain chlorophyll c, carotenoids, and phycobilins. The carotenoid pigment alloxanthin is unique to Cryptophyta. Four membranes surround each chloroplast.

Chloroplast endoplasmic reticulum borders the chloroplasts. The principal food reserve is starch. Instead of a typical cell wall, a periplast composed of protein plates occurs beneath the cell membrane. There are about two hundred freshwater and marine species. Reproduction is primarily asexual.

Members of the phylum Dinophyta, or dinoflagellates, have unicellular forms with two different flagella. There are between two thousand and four thousand marine species and about two hundred freshwater forms. Many have chlorophylls a and c as well as the unique carotenoid peridinin. Some members of Dinophyta have fucoxanthin.

Chloroplasts have three closely associated membranes. The primary food reserve is starch, but lipids are also important storage molecules. A dinoflagellate cell is not surrounded by a cell wall but has a theca (a sort of armor) made of cellulose. Dinoflagellates can reproduce asexually and sexually.

Phylum Haptophyta includes primarily marine unicellular biflagellated algae. A haptophyte cell also has a flagellum-like haptonema, used to capture food. There are about three hundred species. The photosynthetic pigments include chlorophyll a and accessory pigments chlorophyll c and the carotenoid fucoxanthin.

Each chloroplast has four membranes. The food reserve is chrysolaminarin, which is a polymer of glucose. Several layers of scales, or coccoliths, composed primarily of calcium carbonate may cover the haptophyte cell. Asexual and sexual reproduction is widespread.

Phylum Rhodophyta, or the red algae, has between four thousand and six thousand species. Red algae lack any flagellated stages. The photosynthetic pigments include chlorophyll a as well as accessory phycobilins and carotenoids. Two membranes surround each chloroplast.

The food reserve is a floridean starch. A red algal cell is encircled by a wall composed of cellulose. Asexual and sexual re production, as well as alteration of generations, are widespread among Rhodophyta. A triphasic life cycle is unique for this group of algae.
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2:47 AM
Aquatic Plants
Aquatic Plants
Aquatic plants are any "true" plants, members of the kingdom Plantae, that are able to thrive and complete their life cycle while in water, on the surface of water, or on hydric soils.

Hydric soils developwhen the ground is flooded or ponded long enough during the growing season to become anaerobic (depleted of oxygen) in the rooting zone. These soils include organic (peats and mucks) and inorganic (mineral) sediments.

Aquatic plants grow in fresh, brackish, and salt water but are most common in fresh water. Their habitats include flowing waters (rivers, streams, brooks), standing waters (lakes, ponds), and wetlands (bogs, fens, marshes, swamps), which are categorized as riverine, lacustrine, and palustrine communities, respectively.

Wetland plants are sometimes referred to as helophytes. Marshes are dominated (that is, more than half covered) by herbaceous species and swamps by woody species. Bog plants are aquatics that grow in acidic organic soils. Fen plants occur in alkaline organic soils.


Aquatic plants (also known as hydrophytes, macrophytes, and water plants) occur throughout the plant kingdom. The term "macrophyte" distinguishes them from microscopic aquatic algae, which are not true plants. Aquatic plants have evolved repeatedly, having more than 250 independent origins by some estimates.

They occur occasionally in spore-producing plants such as ferns, liverworts, lycopods, and mosses but are relatively rare among nonflowering seed plants (gymnosperms), with bald cypress (Taxodium) a notable exception.

Flowering plants (angiosperms) contain the greatest hydrophyte diversity, with more species proportionally in monocotyledons than in dicotyledons. Nevertheless, fewer than 2 percent of flowering plant species are aquatic.

Life-Forms

Regardless of their taxonomic affinities, aquatic plants are often classified ecologically by their lifeforms. Categories include the following:
  • Floating (acropleustophytes), with stems and leaves floating completely on the water surface and stems not rooted in the bottom, such as duckweed (Lemna) and water hyacinths (Eichhornia).
  • Emergent (hyperhydrates), with stems and leaves extending mainly above the water surface and stems rooted in the bottom, such as cattails (Typha) and reeds.
  • Phragmites (planmergents or ephydrates), floating-leaved, with some or all leaves floating on the water surface and stems rooted in the bottom, such as floating-leaved pondweed (Potamogeton natans), water chestnut (Trapa natans), and water lily (Nymphaea).
  • Submersed (hyphydrates), with stems and leaves completely under water and stems rooted in the bottom, such as Eurasian water milfoil (Myriophyllum spicatum) and wild celery (Vallisneria).
  • Suspended (mesopleustophytes), with stems and leaves completely under water and stems not rooted in the bottom, such as the bladderwort (Utricularia vulgaris) and the coontail (Ceratophyllum).

Benthophyte and pleustophyte are used respectively to differentiate between forms that are either rooted in the substrate or unrooted. Species with elongate, leafy stems are termed vittate or caulescent (such as coontail).

Those with leaves clustered in a basal rosette are rosulate (such as wild celery), and those not clearly differentiated into stems and leaves are thalloid (such as duckweed). Species whose floating or emergent leaves differ morphologically from their submersed leaves are heterophyllous (such as floating-leaved pondweed).

Adaptations

Watermeal (Wolffia)
Watermeal (Wolffia)
Water plants are anatomically and structurally reduced. Watermeal (Wolffia), the world’s smallest angiosperm, contains plants only 0.4 millimeter long. Submersed species often lack water conducting tissue (xylem), mechanical tissue (sclerenchyma), and cuticle.

Some lack roots entirely. Support and floatation of underwater stems are accommodated by buoyant tissue (aerenchyma) and extensive air spaces (lacunae) which also transport oxygen throughout the plant.

Submersed plants usually possess either highly dissected (compound) or thin, ribbonlike leaves. Some leaves become fenestrate, that is, lacking tissue between the veins. Such leaf shapes increase surface area-to-volume ratios for more efficient nutrient uptake and to reduce damage from water currents.

Floating leaves are normally flat and circular, with stomata on their upper surfaces. They may reach 2.5 meters in diameter (such as Victoria). For stability, the stalks (petioles) of most floating leaves are positioned centrally by emargination of the base, as in the water lily, or are peltate by complete fusion of leaf lobes, as in the water shield (Brasenia) and Victoria. Physiological adaptations enable aquatic plants to tolerate deleterious effects of anaerobic hydric soils.

Reproduction

Most aquatic plants are perennials that reproduce vegetatively (asexually). Species survive winters or other unfavorable periods as intact plants, by dying back to dormant stem apices, by means of modified stems (rhizomes, stolons, tubers), or by use of specialized dormant structures (hibernacula) in the sediment.

"Winter buds" are a kind of hibernaculum; buds are insulated by normal foliage leaves on shortened internodes. They usually remain attached to the plant. Turions are specialized hibernacula that produce modified, morphologically distinct leaves to protect the enclosed buds.

Turions always detach from the plant and function as propagules for dispersal. Water plants also disperse vegetatively by fragmentation of stems, which are characteristically brittle, due to the lack of mechanical tissue. Detached stems can establish themselves by production of adventitious roots.

The few aquatic plants that are annuals produce seeds as their dormant stage. Some aquatic annuals also multiply vegetatively by fragmentation during the growing season. Generally, sexual reproduction is rare in submersed species, more common in floating-leaved species, and quite common in emergent species (and annuals).

Pollination in water plants is facilitated by insects (entomophily), wind (anemophily), and water (hydrophily). Most aquatics are insect-pollinated; about one-third of them are wind-pollinated.

Less than 5 percent of aquatic species are hydrophilous, with pollen transported on the water surface (ephydrophily) or under the water surface (hyphydrophily). Most marine angiosperms (seagrasses) are hydrophilous.

Seeds, fruits, and vegetative propagules are dispersed locally by water currents and more widely by waterfowl. Waterfowl transport propagules in plumage, in mud adhering to their feet, and by excretion of seeds consumed as food. Many water plants are distributed broadly, with some species achieving worldwide distributions.

Uses

Aquatic plants are important economically. Foods include rice (Oryza sativa), which sustains more human life than any other plant on earth. Aquatic plants are important horticulturally as aquarium and water-garden ornamentals.

Some aquatic plants, such as the water hyacinth, are invasive weeds that interfere with shipping, irrigation, or recreation and cost millions of dollars to eradicate. The beauty of many water plants, especially water lilies, has inspired art and religion since ancient times.
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8:17 PM
Bioluminesence
Bioluminesence
Bioluminesence is the production of light by living organisms, including algae and phytoplankton in the oceans and fungi on land.

Bioluminescence is a specific form of chemiluminescence in which the chemical energy that is produced in a chemical reaction is converted into radiant energy. In bioluminescence the reaction originates in a wide variety of living organisms, including a small number of plants. It should not be confused with fluorescence or phosphorescence, both of which do not involve a chemical reaction.

In either of the former cases the energy from a source of light, not from a chemical reaction, is basically absorbed and then re-emitted in some form of another photon. The chemical reactions that lead to bioluminescence release energy in the form of light.

Unlike the light bulb, in which electrical energy is converted into light, with some of this energy lost in the form of heat, a bioluminescent reaction is 100 percent efficient and converts all the emitted energy into light. Because there is no heat released, bioluminescence is also known as "cold light."

Species and Habitats

Bioluminescence is primarily marine in nature and is the only source of light in the deep ocean, which is the largest habitable biome of the earth. The phenomenon rarely occurs in any source of fresh water. Bioluminescent organisms include ctenophores, annelid worms, mollusks, insects, and fish.

Species and Habitats
Species and Habitats
The most common manifestation of this phenomenon on land is seen as a glowing fungus on wood or in the few families of luminous insects. This property can be used as ameans of species recognition in the darkness as well as for courtship, preying, and mating.

There are several bioluminescent fungi that are not marine in nature, occurring primarily in the tropics. These fungi appear in different colors. The most common is Panellus stiptucus,which is a small decay fungus that is mostly restricted to North America. The jack-o’-lantern mushroom (Omphalotus olearius) glows brightly, especially when fresh. A few Armillaria species are also reported to glow mildly. No luminous tree or plant is known, however.

Mechanisms of Bioluminescence

Bioluminescence occurs only when two different species are in contact and, almost exclusively, when oxygen is present. The two species are luciferin, which produces the light, and luciferase, a protein that triggers and catalyzes the reaction. The mechanism involves the loss of two electrons, also known as oxidation, by luciferin, a process achieved only through the intervention of luciferase to yield oxyluciferin.

Occasionally luciferin, luciferase, and a cofactor such as oxygen are bound together in a single moiety called photoprotein, which leads to light formation upon contact with a positively charged species, such as the calcium cation. The mechanism appears to involve a peroxide decomposition with free radical intervention.

Dinoflagellates

Dinoflagellates known as Pyrrhophyta, or fire plants, are the most common sources of bioluminescence at the surface of the ocean. They are a group of marine algae that produce light upon mechanical, chemical, or temperature changes. The phenomenon was first observed in the genus Noctiluca in the nineteenth century and has since been observed to occur within other species.

Generally, three types of stimuli can cause bioluminescence in dinoflagellates: mechanical, chemical, and temperature stimulation.

Dinoflagellates
Dinoflagellates
Mechanical forms of stimulation, such as the stirring of water from a moving boat, a swimming fish, or a breaking wave, are prevalent in many Pyrrhophyta. The light appears to serve as a "burglar alarm" against grazing predators, which are then being seen through the flash by a larger second predator.

For example, as a copepod approaches the dinoflagellate, agitation of the seawater stimulates light flashes which a small fish, the secondary predator, uses to pinpoint the position of the copepod and eventually consume it. It appears that the mechanical stimulation deforms the cell membrane to create a short flash as little as one one-hundredth of a second.

Dinoflagellate luciferin is thought to derive from the similarly structured chlorophyll, which is found in most plants. The molecule is protected from luciferase at slightly basic medium by a luciferin-binding protein. However, once the acidity increases, the free luciferin reacts, and light is emitted.

The light produced by a single dinoflagellate is only six to eight photons in energy, and the flashing may last only one-tenth of a second. Larger organisms, such as jellyfish, provide flashes that may last up to tens of seconds. Temperature lowering in some dinoflagellate species also creates bioluminescence.

Purpose and Applications

The disappearance of the flash, once oxygen is consumed, has suggested that the bioluminescent reaction was originally used to remove toxic oxygen from primitive types of bacteria that developed at a time when oxygen was not available.

Bioluminescence has also played a crucial role in the direct studies of several cellular and biochemical processes, such as in the formation of ultimate carcinogens from benzoapyrene. The phenomenon has served scientists in many ways.

Calcium levels are monitored via the jellyfish biochemical system, adenosine triphosphate (ATP) measurements are achieved through the firefly, and the gene activity of organisms can be detected by splicing known bioluminescent proteins.
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10:14 PM
Seaweeds that are brown to olive-green in color belong to the phylum Phaeophyta, or brown algae, which includes between fifteen hundred and two thousand species.

Brown algae (phylum Phaeophyta) are familiar to most people as brown or dark green seaweeds. Some brown algae are microscopic in size, but many are relatively large: One giant kelp measured 710 feet in length. All brown algae are multicellular.

Appearance and Distribution

Brown algae have a body, called a thallus, which is a fairly simple, undifferentiated structure. Some thalli consist of simple branched filaments. Some brown algae have more complex structures called pseudoparenchyma because they superficially resemble the more complex tissues of higher plants.

Giant kelp have a thallus that is differentiated into a holdfast, a stipe, and one or more flattened, leaflike blades. The holdfast functions as the name implies, and holds the rest of the organism to the substrate.


It is a tough, sinewy structure resembling a mass of intertwined roots. The stalk that constitutes the stipe is often hollow, with a meristem (a zone of growing tissue) either at its base or at the blade junctions. Because the meristem produces new tissue at the base, the oldest parts of the blades are at the tips.

The blades, which, like most of the rest of the giant kelp body, are photosynthetic, may have gasfilled floats called bladders toward their bases, which may contain carbon monoxide gas. The function of this particular gas has not yet been determined.

The vast majority of species are marine, living in cold, shallow ocean waters, and may be the dominant plant life on rocky coastlines. The giant kelp can be found in waters around 100 feet deep. Only 4 of the 260 identified genera occur in fresh water. Brown algae of the order Fucales are commonly called rockweeds; kelp belong to the order Laminariales.

Brown algae are less common in tropical and subtropical areas. However, in the Caribbean region, sargassum (large masses of brown algae having a branching thallus with lateral outgrowths differentiated into leafy segments, air bladders, or spore-bearing structures) make up large floating mats; they gave their name to the Sargasso Sea.

Pigments and Food Reserves

The color of the brown algae can vary from light yellow-brown to almost black. Its color reflects the presence of varying amounts of the brown xanthophyll pigment fucoxanthin, a carotenoid pigment, in addition to chlorophylls a and c. The main food reserve is a carbohydrate called laminarin, although giant kelp can also translocate mannitol. Algin (alginic acid) can be found in or on the cell walls and may comprise as much as 40 percent of the dry weight of some kelps.

Reproduction

Reproductive cells of brown algae are unusual in that their two flagella are located laterally, instead of at the ends. The only motile cells in the brown algae are the gametes or reproductive cells. In the common genus Fucus, separate male and female thalli are produced. Fertile areas called receptacles develop at the tips of the lobes of the thallus. Each receptacle has pores on the surface.

These pores open into special spherical, hollow chambers called conceptacles, in which the gametes are formed. Eight eggs are produced in the female structure, while sixty-four sperm cells are produced in the male structure. Eventually, both eggs and sperm are released into the water, where fertilization takes place and the resulting zygotes develop into mature thalli.

Economic Uses

Brown algae have several uses and applications for humans. Giant kelp is eaten, and one species found in the Pacific Ocean has been used, in chopped-up form, as a poultice applied to cuts.

Algin, a colloidal substance produced by brown algae, is used as a thickener or stabilizer in commercially produced ice cream, salad dressing, beer, jelly beans, latex paint, penicillin suspensions, paper, textiles, toothpastes, and floor polish. Brown algae, with its high concentration of the element iodine, has been used to treat goiter, an iodine-deficiency disease. Kelp, also high in nitrogen and potassium, has been used as fertilizer and as livestock feed.

Some types of brown algae, such as Fucus, contain either phenols or terpenes. Botanists believe these substances may discourage herbivory. These substances also have been shown to possess microbe- and cancer-fighting properties. Brown algae is the subject of continuing research in these areas of medicine.
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12:45 AM
Cellular Slime Molds
Cellular Slime Molds
Cellular slime molds, or dictyostelids, were originally considered to be fungi. These microscopic, multicellular organisms are easily mistaken for some of the microfungi that commonly occur as contaminants in laboratory cultures. However, cellular slime molds are more closely related to the protozoans than to fungi.

Although once thought to be fungi, the protists of the phylum Dictyosteliomycota actually have more in common with the paramecium or amoeba that can be observed in a drop of pond water when viewed under the microscope than they do with mushrooms and toadstools.

Cellular slime molds are essentially microscopic throughout their entire life cycle, and only rarely can they be observed directly in nature, as is the case for the plasmodial slime molds. Cellular slime molds must therefore be grown under controlled laboratory conditions in order to be studied.

Life Cycle

Since their discovery in the late nineteenth century, cellular slimemolds have intrigued biologists. Their life cycle exhibits a curious alternative to the way in which most other creatures on earth grow, develop, and become multicellular, with different specialized tissues produced as a result of the process.


Most plants and animals begin life as a single cell (called a zygote) that is the product of the fusion of an egg cell and sperm cell. Shortly after the two cells fuse (through a process termed fertilization), the zygote divides into two cells that stick together.

Life Cycle
Life Cycle

These cells soon divide again to produce a cluster of four cells that in turn divide, and so on. Within hours or days (depending upon the particular plant or animal), clusters of dozens to thousands of cells form an embryo. Specialized cells begin to take form, and the basic shape of the body of the organism begins to become apparent.

Cellular slimemolds approach reproduction differently. Like fungi and plasmodial slime molds, they produce spores as reproductive structures. When a spore germinates (no fusion of cells is required), it releases a single amoeboid cell that begins to engulf and digest bacteria in soil and decaying plant debris, the usual habitats for cellular slime molds.

When the amoeboid cell divides, the two cells produced separate and become completely independent of each other, with each continuing to feed and undergo additional divisions for a number of hours or days. Only after the growing population of amoeboid cells depletes the local supply of bacteria is there any indication that a multicellular structure will be produced.

In response to the production of chemical attractants, thousands of amoeboid cells that have been operating as individual single-celled organisms begin tomove, either singly or in streaming masses, to form multicellular clumps, or aggregations.

Shortly thereafter, one or more cigar-shaped structures called pseudoplasmodia emerge from each aggregation. Apseudoplasmodiumis a unifiedcollection of thousands of what had once been separate, independent amoeboid cells.The cells remain distinct in the pseudoplasmodium but no longer act independently.

Instead, they cooperate as parts of a multicellular entity. Remarkably, when amoeboid cells of two or more different species of cellular slimemolds are grown together, the amoeboid cells of the different species can recognize each other, so that the cells that form any one aggregation are all of a single species rather than a mixture.

Immediately, or perhaps after the entire structure has migrated a short distance toward a light source, cells of the pseudoplasmodium begin to display different patterns of specialization. Cells that happen to have been positioned near the anterior end of the moving “cigar” begin to secrete a wall consisting of cellulose.

These cells bind together to form a slender stalk that grows upward from the surface of the substrate upon which the pseudoplasmodium occurs. Other cells, those that happened to have been nearer the posterior end of the pseudoplasmodium, are liftedoff the surface on the end of the extending stalk.

These cells begin to become encapsulated and specialized as spores. Only the latter live on and produce another generation of amoeboid cells to feed on soil bacteria. The cells that produced the stalk in order to elevate the spore cluster above the substrate eventually die, dry up, and decay.

Reproduction

Reproduction
Reproduction
It appears that cellular slime molds reproduce asexuallymost of the time, at least under laboratory conditions. All of the cells that originate from the same spore are basically genetically identical to one another and collectively represent a genetic clone.

As is the case for asexual reproduction in other lifeforms, finding a “mate” is not necessary to perpetuate the species. If amoeboid cells are equipped with the genetic characteristics necessary to survive long enough to produce spores, the same gene combinations will be passed faithfully to all offspring, thus providing the same qualities for survival.

However, a method of sexual reproduction, with its potential of introducing genetic variability, also seems to exist in cellular slime molds. Occasionally in laboratory cultures, a number of large, thick walled cells are found that are quite different from spores or encysted amoeboid cells.

These giant cells are called macrocysts. Macrocysts appear to form when several amoeboid cells (sometimes described as being of compatible “mating types”) fuse together and rearrange their genetic libraries and those of other amoeboid cells that may be engulfed.

When macrocysts germinate, the amoeboid cells that emerge seem to have different combinations of genetic information than the cells that initially formed the macrocysts. This mixing up of genetic information, along with the genetic changes resulting from mutations, provides cellular slime molds with an ability to cope with changing environments.

Distribution and Ecology

Distribution and Ecology
Distribution and Ecology
Most of what is known about cellular slime molds has been acquired from studying these organisms in laboratory culture. What about the biology of “wild” slimemolds in nature? In natural ecosystems, it is quite likely that cellular slime molds play a significant role in controlling the size of bacterial populations in soil and decaying litter.

Nutrients that are taken up from decaying plants and animals by bacteria are transferred to cellular slime cells when the latter feed upon these bacteria. The cellular slime molds, in turn, become food for soil protozoans, nematode worms, microscopic arthropods such as mites, and other small invertebrate animals. Because of this, cellular slime molds play an essential role in patterns of energy flow and nutrient cycles within terrestrial ecosystems.

There are about seventy-five described species of cellular slime molds. These have been assigned to one of three genera: Dictyostelium, Polysphondylium, and Acytostelium. Some species of cellular slime molds have been found in almost all parts of the world. Two good examples are Dictyostelium mucoroides and Polysphondylium pallidum.

Numbers of species of cellular slime molds appear to be highest in the American tropics, which suggests that this region represents a center of evolutionary diversification of the group. More than thirty-five different species have been found in the small area around the Mayan ruins at Tikal in Guatemala. In general, numbers of species of cellular slime molds decrease with increasing elevation and with increasing latitude.

Some species have restricted habitat associations. One species (Dictyostelium caveatum) has been found only in a single cave systemin Arkansas. Another species (Dictyostelium rosarium), known from a number of localities worldwide but rarely above ground, also seems to have an affinity for the type of conditions found in caves. Of the thirty-five species that occur at Tikal, many appear to be restricted to tropical or subtropical locations.

Dictyostelium discoideum is the most intensively studied cellular slime mold and the one most widely used in research on developmental biology and genetics. Any search for information about cellular slime molds would probably turn up numerous references to this particular form.

Dispersal of Spores

Unlike most spore-producing organisms (including plasmodial slime molds), cellular slime molds produce spores that do not seem to be carried appreciable distances by wind. Instead, dispersal of cellular slime mold spores seems to depend more upon their accidental transport on the body surface or within the digestive tract of some animal.

Viable spores of cellular slime molds have been recovered from the droppings of a number of animals, including rodents, amphibians, bats, and even migratory birds that travel great distances between winter and summer homes. In tropical forests, many living plants and considerable amounts of organic material are found high above the ground in the forest canopy.

Cellular slime molds have been isolated from the mass of organic material (literally a “canopy soil”) found at the bases of epiphytic plants growing on the trunks and branches of trees in these forests. It seems likely that they are introduced to such habitats by being carried up from the ground by birds, insects, or other animals that move between the forest floor and the canopy above it.
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7:31 AM
Charophyceae
Charophyceae
It is almost impossible not to see Spirogyra floating on the surface of a pond on a hot summer day, but most people dismiss it as pond scum. Few realize that what they are looking at is a member of the Charophyceae, a class in the phylum Chlorophyta, or green algae, and a cousin of the ancestor of the Embryophyta, or bryophytes and vascular plants.

Most Charophyceae, like Spirogyra, live in freshwater habitats, but some also occur in moist soil in terrestrial habitats. Charophyceae can live as single cells, colonies, or branched and unbranched filaments and come in a variety of shapes.

The characteristics that unite members of the class—and which link them with the embryophytes—include flagellated cells (similar to sperm cells in vascular plants), a nuclear envelope that breaks down during mitosis, mitotic spindles that persist as phragmoplasts (a type of cytoskeletal scaffolding) through cell division either by furrowing or by forming a cell plate, the presence of chlorophylls a and b and phytochrome, and the storage of starch inside plastids.


Charophytes possess decay-resistant cell walls made of phenolic compounds as well as lignins or ligninlike compounds. Cell walls made of similar compounds are found in bryophytes and vascular plants as well.

Likewise, all three groups of plants also contain sporopollenin, the substance in the walls of spores and pollen grains that makes them virtually indestructible.

Communication channels between cells are similar, too. Plasmodesmata similar to that seen in embryophyte cells allow between-cell communications in charophytes and embryophytes.

Life Cycle

Life Cycle
Charophytes have a two-stage life cycle involving a dominant haploid stage, upon which develops the sex organs; antheridia, which produce sperm cells; and oogonia, which produce egg cells. Typically, individual charophytes produce both antheridia and oogonia, but in some species an individual will produce only one or the other.

Fertilization—which in one group, the Zygnematales, takes place via conjugation—produces a diploid zygote, which quickly undergoes meiosis. If the environment is unfavorable, the zygote will go dormant and remain so for a long period of time. Dormancy ends when the environment improves.

Classification

Genetic analysis supports the recognition of six orders within the Charophyceae: the Mesostigmatales, Chlorokybales, Klebsormidiales, Zygnematales, Coleochaetales, and Charales.

Of these, the most abundant group is the Zygnematales, a large order which consists of more than three thousand species, including Spirogyra and the desmids, a group of mostly single-celled organisms with a constriction across the middle which nearly divides the cells in two.

Zygnematales live primarily in freshwater habitats as phytoplankton, as benthic dwellers, or attached to other aquatic plants. Some species live on snow and ice.

The Charales, commonly called stoneworts or brittleworts, are a large group of filamentous charophytes that feature complex branching patterns. Some can reach lengths of more than a meter. The branching pattern—branches reach out from nodes along the filament—is similar to that of higher plants.

Charales reside primarily in freshwater habitats, but some can be found in brackish water as well as on land. The stems of stoneworts and brittleworts can be encrusted with calcium and magnesium carbonates.

As a result, their hard bodies are well known from the fossil record. The lineage extends back to more than 400 million years ago. Two current genera, Chara and Nitella, date back about 200 million years.

The Coleochaetales are a small group of complex, microscopic filamentous algae that can be found only in freshwater habitats. Klebsormidiales are a small group of unbranched, filamentous charophytes that occur in both freshwater and terrestrial environments.

Mesostigmatales and Chlorokybales are two groups of rare algae. The Coleochaetales and Charales are more closely related to bryophytes and vascular plants than the other groups.

Evolutionary Significance

For decades, structural similarities led plant biologists to suspect that the Embryophyta evolved from charophytes. Recently, cladistic analyses of chemical, structural, and genetic characteristics have opened up research on the topic.

In cladistics, characteristics among a number of organisms are analyzed statistically in the hopes of developing a classification system for the group which will reveal evolutionary relationships. Cladistic analyses support the notion that embryophytes are monophyletic; in other words, bryophytes and vascular plants descend from a common ancestor.


Furthermore, several recent analyses support the notion that a member of the Charophyceae gave rise to embryophytes. Cladistic analyses were somewhat unclear, however, about the relationships of the charophyte orders with one another and with other green algae (Chlorophyta), bryophytes, and land plants.

One of the latest analyses of mitochondrial, chloroplast, and nuclear genes helps resolve some of the confusion. The research indicates that the Mesostigmatales were probably the most ancient group of charophytes, followed by the Chlorokybales, Klebsormidiales, Zygnematales, Coleochaetales, and Charales.

The work also supports earlier suggestions that the Charales are the closest living relatives to extant embryophytes and that the charophytes descended from other green algae.
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9:02 PM
Chlorophyceae
Chlorophyceae
Chlorophyceae (from the Greek word chloros, meaning “green”) make up an extremely large and important class of green algae. Members may be unicellular, colonial, or filamentous. Cells of unicellular and colonial chlorophyceans may have two or more flagella.

There are about 2,650 living species of chlorophyceans. The main features of the class (and most plants) are the use of starch as the principal food reserve and the green chloroplasts with chlorophylls a and b. In spite of plant characteristics, this algal group is not directly related to early land plants.

Chlorophyceans are almost entirely restricted to freshwater and terrestrial habitats. Some members of this class have adapted to life on snow as snow algae. Snow algae cause snow to appear red-burgundy or orange in color because of high levels of unusual carotenoid pigments within the algal cells.


There are a variety of asexual and sexual reproduction modes among members of this class. Sexual reproduction is characterized by the formation of a zygote produced by gametic fusion.

Chlorophyceans show differences during cell division compared to other green algal groups. For example, they produce a set of microtubules, the phycoplast, that is parallel to the plane of cell division.

Diversity

Diversity
Diversity
The Chlorophyceae include some familiar green algae. Perhaps the most famous chlorophyceans are Chlamydomonas (from the Greek word chlamys, meaning “cloth”) and Volvox (from the Latin volvo, meaning “to roll”).

Both are important research models in laboratories. Chlorophyceans fall into several orders, including Volvocales, Chlorococcales, Chaetophorales, and Oedogoniales.

Volvocales

Members of the order Volvocales include both unicellular organisms, such as those in the genus Chlamydomonas with their two equal flagella, and colonial forms. The Chlamydomonas are a large genus of chlorophyceans.

More than six hundred species have been described worldwide. The Chlamydomonas probably represent the most primitive structure among chlorophyceans. Nevertheless, their basic cell features may be found among other representatives of this order.

A cell wall made of glycoproteins, rather than cellulose, surrounds each Chlamydomonas cell. Inside the cell, there is a single large chloroplast and a pyrenoid, which forms starch.

Other cytoplasmic structures include the contractile vacuole rather than a central vacuole. The contractile vacuole is responsible for the removal of water from the cell. Cells of Chlamydomonas are capable of phototaxis: They swim toward moderate light but away from high-intensity light.

Rhodopsin-like pigment is their primary lightsensing photoreceptor. Under dry conditions, Chlamydomonas form a palmelloid stage, in which nonflagellate cells are held together by common mucilage.

Chlamydomonas reproduce asexually via cell division. Also, cells of this alga can become gametes. In most species of Chlamydomonas, the male and female gametes appear the same; they are designated (+) and (–).

Colonial flagellates of the order Volvocales range from simple colonies of Gonium to visible-without-magnification spheres of Volvox with up to several thousands of cells and some sort of cellular specialization.

Volvox are one of the most structurally advanced colonial forms of green algae.Only specialized cells participate in reproduction. During asexual reproduction, some cells of Volvox divide and bulge inward, forming new daughter colonies, which are held for some time within the parent colony. Volvox are also capable of sexual reproduction. They produce gametes that differentiate into sperm and eggs.

Chlorococcales

Members of the order Chlorococcales include nonmotile unicellular and colonial algae. Typical representatives of the unicellular nonmotile form are found in Chlorococcum. They occur as spherical single cells or cell aggregates and produce flagellated zoospores.

Examples of colonial representatives of Chlorococcales are Hydrodictyon, commonly known as the “water net”; Pediastrum, famous for their distinctive, starlike shape; and Scenedesmus, wide-spread inhabitants of the freshwater phytoplankton.

The order Chlorococcales has now been divided on the basis of small subunit ribosomal ribonucleic acid (RNA) sequence data into several groups, including the Sphaeropleales, Tetracystis clade, and Dunaliella clade.

Chaetophorales and Oedogoniales

Chaetophorales and Oedogoniales
Chaetophorales and Oedogoniales
The most complex of the class Chlorophyceae are the filamentous members in orders Chaetophorales and Oedogoniales, some of which exhibit features that are observed primarily in plants. The chaetophoralean green algae have plantlike bodies with a system of primary and secondary branches.

The Draparnaldia (named for Jacques Phillipe Raymond Draparnaud, a French naturalist) from order Chaetophorales have a main filamentous axis with relatively large cells, primary branches with smaller cells, and secondary branches with even smaller cells.

One representative of Oedogoniales, the green alga Oedogonium (from the Greek oidos, meaning “swelling”), has been a subject of intense study for its unusual cell division technique.

The entire contents of an Oedogonium cell may be used in the for mation of one large zoospore with multiple flagella. Members of Bulbochaete (from the Greek bolbos, meaning “bulb”) resemble Oedogonium in cell division but differ in being branched and having a distinctive hair cell at the end of each branch.

Technological Uses

A few chlorophycean green algae have commercial value. These algae are good candidates for the industrial production of hydrogen gas because they are able to release the gas from water using solar energy. Hydrogen gas is an environmentally desirable fuel because the burning of hydrogen produces water, and it can be converted effectively to electricity.

Another “commercial” organismis Dunaliella salina, a saltwater alga that accumulates massive amounts of beta-carotene, a vital antioxidant also used in food coloring and in pharmaceuticals.

Selenastrumcapricornutum are the most widely used algal biomonitors in the detection of water pollution. Chlorophyceans are used in freshwater aquaculture systems as food for fish.One alga with possible potential for salmon feeds is Haematococcus.

Algae contain large amounts of the pigment astaxanthin, which is responsible for the red coloration typical of salmon flesh. Chlorella (formerly classified in the order Chlorococcales) are famous both as the experimental systems in the discovery of the photosynthetic Calvin cycle and as health food in Asia.
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