British Columbia PLO’s:
- Grade 7 Life Sciences: Ecosystems
An ecosystem is a network of interactions that link the living and non-living parts of an environment. The living parts of the ecosystem include the organisms, such as the plants and animals that live within the environment. Each different type of organism is known as a species. All the members of one particular species in a give area are called a population. When two or more populations of different species live in the same area, they form a community. The non-living parts of the ecosystem include elements such as sunlight, rain and snow, sediment, rock, and temperature.
2. Energy Sources: Photosynthesis and Chemosynthesis
All living things need energy. People and other animals get their energy from the food they eat. However, neither the plants on land nor the microbes that live around hydrothermal vents eat food. Instead, they make their own food. Organisms that make their own food are called producers.
Producers such as plants, seaweeds, and phytoplankton harness energy from the sun to make sugars. This process is called photosynthesis. Organisms that are photosynthetic use the sun’s energy to produce simple sugars from carbon dioxide and water, releasing oxygen in the process.
C02 + H2O + sunlight (energy) » sugar (C6H12O6) + O2
One of the major scientific discoveries of the last 100 years is the presence of complex deep-sea communities that do not depend upon sunlight as their primary source of energy. Hot vent communities like the one found at the Endeavour Ridge Node, and methane seep communities like the ones found at the Barkley Canyon Node are two examples of undersea ecosystems that thrive without sunlight. Instead, these communities get their energy from chemicals through a process called chemosynthesis. Organisms that are chemosynthetic use chemicals as the energy source to produce sugars from carbon dioxide, oxygen, and water.
For example, hydrogen sulfide is abundant in the water erupting from hydrothermal vents, and is used by microbes to produce sugars that are the base of the vent community food chain. These bacteria get their energy by oxidizing hydrogen sulfide to sulfur:
C02 + O2 + H2S (energy) » sugar (CH2O) + S + H2O
Put into words, carbon dioxide plus oxygen plus hydrogen sulfide makes organic carbon in the form of CH2O, sulfur, and water. Chemosynthetic bacteria grow on and below the seafloor at hydrothermal hot vent sites, and are even found growing within other animals found at the vents, such as tubeworms.
Just like hydrothermal hot vents, chemosynthetic bacteria are also the bottom of the food web in cold seep communities like the one found at the Barkley Canyon Node. Cold seeps are generally found along continental margins, where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. Cold seeps are home to many species of organisms that have not been found anywhere else on Earth. Similar to the bacteria found at the hot vent sites of Endeavour Ridge, the bacteria that live at Barkley Canyon process sulfides and methane through chemosynthesis. The bacteria here form thick bacterial mats, or live in close association with other organisms.
Figure 2. Folger Passage Pinnacle food web
Instead of photosynthesis, vent ecosystems derive their energy from chemicals in a process called “chemosynthesis.” To produce sugars, both methods involve
Image courtesy Woods Hole Oceanographic Institution.
- an energy source
- carbon dioxide
- Photosynthesis gives off oxygen gas as a byproduct, while chemosynthesis produces sulfur
Text from Ocean Explorer
The chemistry of a “black smoker.” After seawater seeps into the crust (1), oxygen and potassium (2) and then calcium, sulfate, and magnesium (3) are removed from the water. As the water begins to heat up (4), sodium, potassium, and calcium dissolve from the crust. Magma superheats the water, dissolving iron, zinc, copper, and sulfur (5). The water then rises back to the surface (6), where it mixes with the cold seawater, forming black metal-sulfide compounds (7).
Image courtesy of Woods Hole Oceanographic Institution.
Text from Ocean Explorer
3. Exploring Symbiosis
If you have poked around in a tide pool, you have probably seen bright green sea anemones that look more like flowers than animals. The anemone is green because it has an algal partner (or symbiont) that is green! These giant green anemones, Anthopleura xanthogrammica, are an example of symbiosis. The anemone provides a secure home for the algae, and the algae make sugars by photosynthesis for the anemone.
There are three different ways in which organisms can engage in a symbiotic relationship. Mutualism is a close relationship between two organisms in which both organisms benefit. Parasitism is a relationship between two organisms in which one is harmed and the other benefits, and commensalism is a relationship in which two organisms live together where one benefits while the other is unaffected.
In the deep-sea there are many relationships among organisms that may seem strange and unusual to you. At hot vents and cold seeps, unique food chains were discovered completely reliant on chemosynthesis. When worms found at hot vents like the Giant Tubeworm, Riftia, were looked at, biologists found that this worm was “gutless”. It took a while, but what they discovered was a unique chamber inside the animal, called a trophosome. The trophosome contains microbes that need sulfide compounds to produce sugars. These sugars are then consumed by the tubeworm. The Giant Tubeworm and the microbes are so interconnected that they cannot survive without each other. When hydrothermal venting stops and the tubeworm can no longer provide chemicals to the bacteria, both organisms die.
Similar symbiotic relationships between tubeworms and microbes, and between clams and microbes exist at cold seeps like the one found in Barkley Canyon.. Deep-sea clams farm methane-munching microbes in their guts providing the microbes with methane. The clams then harvest the sugars made by the microbes, showing another example of producers and consumers living together to meet their survival needs. Other clams, such as “V” clams (“Vesicomyid Clams”) commonly seen in vent fields and at cold seeps, live by sucking sulfide through their foot from the mud. Sulfide travels through the V-clam’s body to the gills where gizzillions of microbes live. The gills absorb oxygen, carbon dioxide and water giving the bacteria all of the chemical elements they need to produce sugars. For more information on Cold Seeps and V-clams, check out College of Marine Science: Project Oceanography (Cold Seeps and V-Clams.doc)
These are just three examples of symbiosis. In the sea and on land, there are thousands of animals that have symbiotic relationships.
4. The Needs of Living Things
All organisms must have their basic needs met in order to survive. Organisms live successfully in ecosystems that supply them with their basic needs, such as food, water, and suitable living conditions. In general, the survival needs of organisms include an energy source, oxygen, water, and shelter.
The physical space where an organism lives is called its habitat. We have researched the habitats of three of the NEPTUNE Canada Nodes sites in Lesson One (Folger Passage, Barkley Canyon, and Endeavour Rideg). For this lesson, we will examine some of the organisms that live in each of the ecosystems, and assess how their survival needs are met.
Begin by reviewing the key concepts found in this lesson (organism, species, population, community, ecosystem), giving examples for each. Having the vocabulary list on the board or as an individual handout for reference during the lesson will be very helpful.
- Lead a discussion about the essential needs for life. Get them to think about all living things, from the smallest microbe to their own needs for survival.
- Using the board, brainstorm with the class to create a concept map outlining their survival needs. What provides each of the needs? Are their needs inter-connected?
- Focus on energy source. Introduce photosynthesis, and the importance of organisms that can make their own food. Ask the class if they can think of any ecosystems that thrive without sunlight as the energy source.
- Introduce chemosynthesis, and the idea that ecosystems can exist without sunlight. In these ecosystems, the organisms that provide the rest of the food web with energy use chemicals as the energy source to make sugars rather than sunlight. Ensure that the students understand this process on a basic level.
- Use the Dive and Discover Website http://www.divediscover.whoi.edu/vents/light.html to compare and contrast Photosynthesis versus Chemosynthesis. This interactive animation is a great tool to help your students understand these processes. You can use a computer linked to a LCD projector at the front of the classroom to go through the steps (1-4) all together, or alternatively get the students to go through the steps on their own or in small groups at the computer.
- Task the students to complete the Photosynthesis vs Chemosynthesis Worksheet
- Re-visit the site characteristics of each of the NEPTUNE Canada Nodes the students researched in the previous lesson, and explain that both the Endeavour Ridge Node and the Barkley Canyon Node are examples of two under-sea habitats that support ecosystems that thrive without sunlight. The Folger Passage Node is found at much shallower depths, and therefore has photosynthetic organisms at the base of the food web, like the ones we are familiar with.
- Using the Background Information on Exploring Symbiosis given above, go over what symbiosis means with your students, explaining the three ways in which these symbiotic relationships exists.
Optional: Symbiotic Relationships Activity (Reference: Adapted from Ohio Department of Education
Re-visit the topic of survival needs of living things. In general, the survival needs of organisms include an energy source, oxygen, water, and shelter.
Divide the class into three groups. Each group should be assigned to one of the NEPTUNE Canada Nodes (you could use the same groups from the discussion in Lesson One, or form new groups).
Provide each group with a list of organisms found at their underwater ecosystem (download Organism Lists). This copy is for the teacher only, as an aid to help with the creation of the Critter Cards. Only provide the students with the name of the organism.
Get each student to choose one organism from the list, ensuring that there are no duplicate organisms, and each trophic level (producer, secondary consumer, and tertiary consumer) is appropriately represented.
Using the SOLE Website and other resources on the Web, task the students to go on a quest to discover the following information about their organism:
- Task the students to complete the Pre-Assignment, the Activity, and the Post-Assignment, or
- Chose the activities that are most appropriate for you students
- Pictures of the organism
- Common Name
- Scientific Name
- How the organism gets the basic requirements for life: energy, shelter, oxygen, and water
Students should make rough notes and sketches in their notebooks as their research progresses.
Hint: In the underwater ecosystems that we’ve been studying, all the organisms get their need for oxygen from the water (dissolved). Also, since the organisms are already in water, get the students to figure out what temperature (hot, cold etc.) and chemical make-up of water they require.
Give each student a copy of the Critter Card Template. The students should work on completing a Critter Card for their organism, including a colour drawing on the front.
Follow-up this activity with a discussion of ways in which these unique underwater ecosystems are able to meet the needs of the organisms that live there.
Inform the student that they will be learning about Food Webs and Trophic Levels in the final lesson (Lesson Three), and adding to their Critter Card. Therefore, they need to keep their Critter Cards safe from harm until then!
- Open discussion about the ways in which these unique underwater ecosystems are able to meet the needs of the organisms that live there, include topics such as biotic and abiotic factors, limiting factors, depth, light, oxygen levels, sulfur levels, metals, energy source, symbiosis, competition, predator-prey relationships, and reproduction.
- Hold a round-table discussion and/or debate based on what students learned in this lesson using the following statement: Some scientists believe in the possibility that Earth itself might have started in the sulfurous cauldron around hot vents. Vent environments minimize oxygen and radiation, which can damage primitive molecules. They believe that many of the primordial molecules needed to jump-start life could have formed in the subsurface of the ocean floor from the interaction of rock and circulating hot water driven by hydro¬thermal systems (Source: OceanExplorer).
Extension 1: ART – engage the students to draw and colour a picture that describes themselves and their relationship to the ecosystems they live in. Include the elements that they believe are needed for their own survival.
For more information on Cold Seeps and V-clams, check out College of Marine Science: Project Oceanography
B.C. Science PROBE 7 Textbook, Nelson (2005)
Dive and Discover (Wood’s Hole Oceanographic Institute): http://divediscover.whoi.edu/
NEPTUNE Canada: http://www.neptunecanada.ca (up to date, not as student-friendly)
Wood’s Hole Oceanographic Institute: http://www.whoi.edu/
College of Marine Science: Project Oceanography http://www.marine.usf.edu/pjocean/packets/sp02/sp02u2p4.pdf-
Ohio Department of Education http://www.edquest.ca/pdf/7final03key.pdf