Topic 5.1 Communities and Ecosystems IBSL Biology S. Dosman • 5.1.1 - Define species, habitat, population, community, ecosystem and ecology. • 5.1.2 - Distinguish between autotroph and heterotroph. • 5.1.3 - Distinguish between consumers, detritivores and saprotrophs. • 5.1.6 - Define trophic level. Species • A species can be defined as a group of organisms which can interbreed and produce fertile offspring. Habitat • A habitat is the environment in which a species normally lives or the location of a living organism. Population • A population is a group of organisms of the same species who live in the same area at the same time. Community • A community is a group of populations living and interacting with each other in an area. Ecosystem • An ecosystem can be defined as a community and its abiotic environment Ecology • Ecology is the study of relationships between living organisms and between organisms and their environment. Autotroph • An autotroph is an organism that can produce its own food. • They synthesize organic molecules from simple inorganic substances. • The process used is often photosynthesis but chemosynthesis may be used also. • Due to the fact that they make their own food they are often referred to as producers. Heterotroph • A heterotroph is an organism that cannot make their own food so they must obtain their organic matter (nutrients) from other organisms. • Heterotrophs consume autotrophs and other heterotrophs to obtain needed nutrients. This is why they are often referred to as consumers. Consumer • A consumer is an organism that ingests other organic matter that is living or recently killed. Detritivore • A detritivore is an organism that consumes or eats non-living organic matter. • They eat dead leaves, feces or carcasses and some examples are earthworms, woodlice, and dung beetles. Saprotroph • Saprotrophs are organisms that live on or in non-living organic matter. • They secrete digestive enzymes into the organic matter and absorb the products of digestion. • This group is composed mainly of fungi and bacteria and are often referred to as decomposers. Trophic Level • The position of an organism on a food chain is its trophic level. • Trophic levels are another way of classifying organisms based on their feeding relationships with other organisms in the same ecosystem. • The first trophic level in a food chain is always the producer. The next organism is the primary consumer and so on. 5.1.4 - Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms). • A food chain is a sequence which shows the feeding relationships and energy flow between species. Food chains answer the question “Who eats whom?” • Arrows are used in food chains to show the direction the energy flows through the chain. • The first organism in the food chain is the producer and the other organisms are all consumers. They are known as the primary, secondary and tertiary consumers depending on their position in the food chain. • The following are some examples of food chains from three different ecosystems: Grassland ecosystem Grass →grasshoppers → toad → hognose snake → hawk River Ecosystem Algae → mayfly larva → juvenile trout → kingfisher Marine Ecosystem Diatoms → copepods → herring → seal → great white shark 5.1.5 - Describe what is meant by a food web. • A food web can be defined as a series of interconnecting food chains. • Food webs are useful because an organism does not often only eat one source of food so food chains do not tell the whole story for each organism. • Food webs can show the complex and complete network of trophic relationships in a community. • Once again the arrows indicate the direction of energy flow within the web. • Due to the fact that some organisms may be food for more than one predator and some organisms feed on more than one type of food, food webs can have more than one arrow that emanates from or arrives at more than one organism. 5.1.7 - Deduce the trophic level of organisms in a food chain and a food web. • Use the handout given to you in class to deduce the trophic level of organisms. • The producer is always the first trophic level. • It is important to note that in a food web, an organism may occupy one or more different trophic levels depending on the food chain you follow in that food web. 5.1.8 - Construct a food web containing up to 10 organisms, using appropriate information. • This will be student specific. • It is important to remember the direction of arrows in a food web. 5.1.9 - State that light is the initial energy source for almost all communities. • Light is the initial energy source in all communities because it is absorbed by the photosynthetic organisms (producers) and converted to chemical energy. • The producers are the most important trophic level in the food chain because they provide the initial food for the consumers. They also absorb the sunlight which is the energy that drives food chains. • All food in a community contains energy that can be traced back to sunlight. 5.1.10 - Explain the energy flow in a food chain. • After the initial energy enters a food chain in the form of radiant energy (sunlight) the producers convert it into chemical energy in the form of organic molecules. • The energy is transferred from one organism to the next or one trophic level to the next when the carbohydrates, lipids and proteins are digested. • For example, the energy in grass is transferred to a cow when it eats the grass. Inside the cow cellular respiration releases the chemical energy and some energy is lost to the environment in the form of heat. • If the cow dies it is eaten by another consumer and the chemical energy stored in the cow is transferred to the next trophic level. If the cow dies and is not eaten, the detritivores and decomposers will use the available energy. 5.1.10 - Explain the energy flow in a food chain. • The decomposers and detritivores also perform cellular respiration and heat produced will be lost to the environment. • The chemical energy in a food chain can be passed from one trophic level to the next. Energy from the food chain is constantly being lost to the environment as heat. 5.1.11 - State that energy transformations are never 100% efficient. • As mentioned in AS 5.1.10, only chemical energy can be used by the next trophic level and a consumer can only convert a small amount of energy it absorbs into chemical energy. • No organism can convert or utilize 100% of the energy present in the organic molecules they consume. They commonly only utilize about 10-20% of the energy from the previous trophic level. • The reasons the energy transformations are so inefficient is due to energy being lost as heat, organisms dying before they can be consumed by the next trophic level, not all food is swallowed or some that is swallowed cannot be used by that organism. 5.1.12 - Explain reasons for the shape of pyramids of energy. • An energy pyramid is designed to show how much and how fast energy flows from one trophic level to the next. An energy pyramid considers time or the rate of energy production along with the quantity of energy produced. • The energy is measured in kilojoules per square metre per year or (kJ m-2 yr-1). 5.1.12 - Explain reasons for the shape of pyramids of energy. • Due to the fact that energy is always lost from one trophic level to the next, each level of the pyramid is smaller than the previous level. 5.1.13 - Explain that energy enters and leaves ecosystems, but nutrients must be recycled. • All nutrients within ecosystems must be continuously recycled to meet the needs of the biosphere. • All of the elements necessary for life such as carbon, nitrogen, phosphorus and other elements and compounds must be recycled and used over and over. • Every time an organism consumes nutrients from the environment they must be returned to the environment at some point. Some nutrients will be temporarily “locked up” within the organism as structural components but will eventually be returned once that organism is eaten or decomposes. 5.1.14 - State that saprotrophic bacteria and fungi (decomposers) recycle nutrients. • The saprotrophic bacteria and fungi play an essential role in releasing the nutrients that were temporarily locked up inside of the cells of plants and animals. • When plants and animals die the decomposers release digestive enzymes that break down the dead organic matter and release the nutrients which can then be used for themselves or by other organisms. • Without these important organisms, nutrients could not be released from dead organic matter and there would soon be a nutrient shortage.
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