Ib Study Guide: Communities and Ecosystems

  1. Define species, habitat, population, community, ecosystem, and ecology. Species – A species is a group of organisms with similar characteristics, which can interbreed and produce viable, 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 together and interacting with each other in an area. Ecosystem – An ecosystem is a community and its abiotic environment. Ecology – Ecology is the study of relationships in ecosystems – both relationships between organisms and between organisms and their environment.
  2. Distinguish between autotroph and heterotroph. Autotrophs are organisms that synthesize their own organic molecules (food) from simple inorganic substances. More commonly known as producers, autotrophs make their own food. In most communities these producers create their own food through the process of photosynthesis. Meanwhile heterotrophs are organisms that obtain organic molecules (food) from other organisms. There are three different types of heterotrophs. The heterotrophs are represented by the consumers in a community, and can be found on the top of the food chain with the tertiary consumers.
  3. Distinguish between consumers, detrivores, and saprotrophs. There are three types of heterotrophs including consumers, detrivores, and saprotrophs. Consumers are organisms that ingest organic matter that is living or recently killed. Consumers are also split into three categories: primary, secondary, and tertiary consumers. Primary consumers directly ingest producers. Secondary consumers consume primary consumers as well as producers. Tertiary consumers are at the top of the food web and can consume any other consumers or producers. Detrivores ingest dead organic matter. And saprotrophs live on or in dead organic matter, secreting enzymes into it and absorbing the products of digestion.
  4. Describe what is meant by food chain, giving three examples, each with at least three linkages (four organisms). A food chain is visual representation of sequences of trophic relationships, where each member in the sequence feeds on the previous one. Trophic relationships are very important – where one population of organism feeds on another population. Example: Producer Primary consumer Secondary consumer Tertiary consumer.
  5. Describe what is meant by a food web. A food web is a diagram of all the feeding relationships in a community. The arrows indicate the direction of flow of energy.
  6. Define trophic level. Trophic level – The trophic level of an organism is its position in the food chain. Examples of this are producers, primary consumers, secondary consumers, and tertiary consumers.
  7. Deduce the trophic level of an organism in a food chain or food web. Photosynthetic organisms including plants, or all autotrophs, are producers in a food web. Primary consumers are organisms that eat only the producers. Secondary consumers then eat the primary consumers. And in turn the tertiary consumers eat the secondary consumers.
  8. State that light is the initial energy source in all communities. In almost all communities the producers make organic matter through the process of photosynthesis. This making light is the initial energy source for the whole community. Producers convert light energy into the chemical energy of sugars and other organic compounds.
  9. Explain the energy flow in a food chain. Sunlight gives energy in organic matter to producers through the process of photosynthesis. When the primary consumers eat the producers, the energy is organic matter is transferred to them. About ten percent of the energy from the producers is transferred to the primary consumers. Then the secondary consumers eat the primary consumers and quire that energy though organic matter. About ten percent of the energy from the primary consumers is transferred to the secondary consumers and so on to the tertiary consumers. It is important to realize that energy is lost through the movement through each trophic level and this energy is released in heat. This energy release occurs through cellular respiration for use in the producer then lost as heat. In addition, as energy passes through the trophic levels not all the food is digested and then is lost in organic matter through feces. The feces as well as death of producers also gives energy to the detrivores and saprotrophs when they digest the producers.
  10. State that energy transformations are never 100% efficient. A large amount of the energy that is absorbed by an organism is released is cellular respiration. This energy that is ATP is then used in processes such as active transport or muscle contractions. These processes require energy transformations which are never 100% efficient. Some of this energy is converted into heat. 10-20% is a typical efficiency level. Most of the energy released by cell respiration is lost from the organism as heat.
  11. Explain the reasons for the shape of pyramids of energy. Pyramids of energy are always pyramid shaped because less energy flows through each successive trophic level. Energy is lost at each trophic level, through heat, so less remains available for the next level. In addition, mass is lost as well as energy, so the energy content per gram of the tissues of each successive trophic level is not lower.
  12. Explain that energy enters and leaves ecosystems, but nutrients must be recycled. Unlike nutrients, energy is not recycled. It is constantly being supplied from light to be used for photosynthesis by producers and then passed through all trophic levels. Energy can leave the ecosystem through the form of heat in saprotrophs and detrivores. This means that there needs to be a constant supply of energy entering the environment to ensure that the environment can transfer energy between trophic levels. Nutrients however, need to be recycled showing the interaction between living organisms and the abiotic environment they live in. Carbon, nitrogen, phosphorous, and all other necessary nutrients must be recycled because there is a limited supply of them. They are absorbed from the environment, used by living organisms and then returned to the environment. This is known as the carbon cycle. They are absorbed by the environment, used by living organisms, and then returned to the environment.
  13. State that saprotrophic bacteria and fungi (decomposers) recycle nutrients. Saprotrophic bacteria and fungi are essential in nutrient cycles because they release nutrients from dead organic matter and provide other organisms with these nutrients. They feed by secreting an enzyme into the dead organic matter which gradually breaks down the organic matter and the nutrients are released. The saprotrophs absorb the substances that they need from digested organic matter.

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Ib Study Guide: Communities and Ecosystems. (2016, Dec 17). Retrieved from https://graduateway.com/ib-study-guide-1-communities-and-ecosystems/