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One Tough Worm [Adapted from the 2002 Gulf of Mexico Expedition]

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One Tough Worm [Adapted from the 2002 Gulf of Mexico Expedition] Expedition to the Deep Slope 2007 One Tough Worm [adapted from the 2002 Gulf of Mexico Expedition] FOCUS group (download from or refer students to http:// Physiological adaptations to toxic and hypoxic asgsb.indstate.edu/bulletins/v13n2/vol13n2p13-24.pdf environments AUDIO/VISUAL MATERIALS GRADE LEVEL None 7-8 (Life Science) TEACHING TIME FOCUS QUESTION One 45-minute class period for first part of activ- How can aerobic organisms cope with environ- ity, plus one-half to one additional 45-minute class ments containing little oxygen and an abundance period for group reports and discussion of respiratory poisons? SEATING ARRANGEMENT LEARNING OBJECTIVES Groups of four students Students will be able to explain the process of chemosynthesis. MAXIMUM NUMBER OF STUDENTS 20 Students will be able to explain the relevance of chemosynthesis to biological communities in the KEY WORDS vicinity of cold seeps. Cold seeps Methane hydrate ice Students will be able to describe three physiologi- Chemosynthesis cal adaptations that enhance an organism’s abil- Brine pool ity to extract oxygen from its environment. Vestimentifera Trophosome Students will be able to describe the problems Fick’s equation posed by hydrogen sulfide for aerobic organisms, Hemoglobin and explain three strategies for dealing with these Hydrogen sulfide problems. Mitochondria Aerobic MATERIALS Anaerobic Copies of “Comparative Functional Gill Characteristics of Polychaete Gills,” one copy for each student group BACKGROUND INFORMATION Copies of “Metazoans in Extreme Cold seeps are areas of the ocean floor where Environments,” one copy for each student gases (such as methane and hydrogen sulfide) 1 Expedition to the Deep Slope 2007 – Grades 7-8 (Life Science) Focus: Physiological adaptations to toxic and hypoxic environments oceanexplorer.noaa.gov and oil seep out of sediments. These areas are (like our own red blood cells). Vestimentiferans commonly found along continental margins, and can grow to more than 10 feet long, sometimes are home to many species of organisms that have in clusters of millions of individuals, and are not been found anywhere else on Earth. Unlike believed to live for more than 100 years. They biological communities in shallow-water ocean do not have a mouth, stomach, or gut. Instead, habitats, cold-seep communities do not depend they have a large organ called a trophosome that upon sunlight as their primary source of energy. contains chemosynthetic bacteria. Hemoglobin in Instead, these communities derive their energy the tubeworm’s blood absorbs hydrogen sulfide from chemicals through a process called chemo- and oxygen from the water around the tentacles, synthesis (in contrast to photosynthesis in which and then transports these raw materials to bac- sunlight is the basic energy source). Some che- teria living in the trophosome (the tentacles also mosynthetic communities have been found near absorb carbon dioxide, which is also transported underwater volcanic hot springs called hydrother- to the bacteria). The bacteria produce organic mal vents, which usually occur along ridges sepa- molecules that provide nutrition to the tubeworm. rating the Earth’s tectonic plates. Visit http://www. Similar relationships are found in clams and mus- pmel.noaa.gov/vents and http://www.divediscover.whoi.edu/vents/ sels that have chemosynthetic bacteria living in index.html for more information and activities on their gills. A variety of other organisms are also hydrothermal vent communities. found in cold-seep communities, and probably use tubeworms, mussels, and bacterial mats as Typical features of the cold seep chemosynthetic sources of food. These include snails, eels, sea communities that have been studied so far include stars, crabs, isopods, sea cucumbers, and fishes. mounds of frozen crystals of methane and water Specific relationships between these organisms called methane hydrate ice that are home to have not been well-studied. polychaete worms. Brine pools, containing water four times saltier than normal seawater, have Recently, increasing attention has been focused also been found. Researchers often find dead fish on cold seeps in the Gulf of Mexico, an area that floating in the brine pool, apparently killed by the produces more petroleum than any other region high salinity. The base of the food chain in cold in the United States. Responsibility for managing seep communities is chemosynthetic bacteria that exploration and development of mineral resources are able to obtain energy from some of the chem- on the Nation’s outer continental shelf is a central icals seeping out of the ocean floor. Bacteria may mission of the U.S. Department of the Interior’s form thick bacterial mats, or may live in close Minerals Management Service (MMS). In addi- association with other organisms. tion to managing the revenues from mineral resources, an integral part of this mission is to One of the most conspicuous associations protect unique and sensitive environments where exists between chemosynthetic bacteria and these resources are found. MMS scientists are large tubeworms that belong to the group particularly interested in finding deep-sea che- Vestimentifera (formerly classified within the phy- mosynthetic communities in the Gulf of Mexico, lum Pogonophora; recently Pogonophora and because these are unique communities that often Vestimentifera have been included in the phylum include species that are new to science and Annelida). Pogonophora means “beard bear- whose potential importance is presently unknown. ing,” and refers to the fact that many species in In addition, the presence of these communities this phylum have one or more tentacles at their often indicates the presence of hydrocarbons at anterior end. Tentacles of vestimentiferans are the surface of the seafloor. bright red because they contain hemoglobin 2 Expedition to the Deep Slope 2007 – Grades 7-8 (Life Science) oceanexplorer.noaa.gov Focus: Physiological adaptations to toxic and hypoxic environments The 2006 Expedition to the Deep Slope was and avoiding the toxic effects of hydrogen sulfide. focused on discovering and studying the sea floor communities found near seeping hydrocarbons There are several strategies that organisms may on hard bottom in the deep Gulf of Mexico. use to improve their ability to obtain oxygen The sites visited by the Expedition were in areas from their surrounding environment. Three of the where energy companies will soon begin to drill most common strategies are anatomical adapta- for oil and gas. A key objective was to provide tions that increase an organism’s surface area in information on the ecology and biodiversity of contact with a source of oxygen, thin membranes these communities to regulatory agencies and between the interior of the organism and an energy companies. Dives by scientists aboard oxygen source, and internal circulatory systems the research submersible ALVIN revealed that that transport oxygen within the organism. These hydrocarbons seepage and chemosynthetic com- strategies are related by Fick’s equation which munities were present at all ten sites visited by the describes the passive diffusion of gas molecules Expedition. The most abundant chemosynthetic across a membrane: organisms seen were mussels and vestimentiferan tubeworms. Expedition to the Deep Slope 2007 F = A • P • c is focused on detailed sampling and mapping of D four key sites visited in 2006, as well as explor- where ing new sites identified from seismic survey data. F = gas flow A = membrane surface area This activity focuses on some of the physiological P = pressure difference on the two sides adaptations that allow cold seep organisms to of the membrane survive conditions that would be deadly to many c = a mathematical constant other species. Polychaete “ice worms” received D = distance over which diffusion takes a lot of attention when they were first discovered place (at the minimum, thickness of at Gulf of Mexico cold seeps in 1997, because the membrane) they were found living inside chunks of frozen methane. Another polychaete belonging to the So, gas flow across a membrane will be family Orbiniidae (previously unknown to sci- increased by increasing the membrane’s surface ence) is often found living among mussel beds area, reducing the membrane’s thickness, and/ that are one of the most conspicuous features of or increasing the pressure difference across the these cold-seep communities. These polychaetes membrane. “Pressure difference” is related to the are aerobic animals, which means they require difference in concentration of a gas on one side oxygen for their metabolism. Yet, these worms live of the membrane compared to the other side. If in areas where oxygen is in extremely short sup- there is no difference, then there will be no net ply, and often can’t be detected in the water at flow of gas (according to Fick’s equation, if P = all. To make matters worse, sediments around the 0 then F = 0). An organism can’t do much about mussel beds contain large quantities of hydrogen the concentration of gas in the external environ- sulfide, which is similar to cyanide in its toxicity. ment, but if it has a way to move gas away from Hydrogen sulfide interferes with cytochrome mole- the membrane as the gas diffuses in, a pressure cules that are essential to aerobic metabolism, as difference can be maintained. A circulatory sys- well as hemoglobin that is used by many organ- tem is a well-known adaptation for maintaining isms to transport oxygen within living tissues. So this kind of pressure difference. If the circulatory our cold-seep polychaete has two big problems: system includes molecules that can bind the gas getting oxygen to support aerobic metabolism, as it diffuses in (like hemoglobin binds oxygen) 3 Expedition to the Deep Slope 2007 – Grades 7-8 (Life Science) Focus: Physiological adaptations to toxic and hypoxic environments oceanexplorer.noaa.gov this also helps maintain the pressure gradient. adaptation in aquatic animals for increasing respiratory surface area (alveoli serve a similar Three major strategies are common among organ- function in lungs of humans and other animals).
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