The food chain describes who eats whom in the wild. Every living thing—from one-celled algae to giant blue whales—needs food to survive. Each food chain is a possible pathway that energy and nutrients can follow through the ecosystem. For example, grass produces its own food from sunlight. A rabbit eats the grass. A fox eats the rabbit. When the fox dies, bacteria break down its body, returning it to the soil where it provides nutrients for plants like grass. Of course, many different animals eat grass, and rabbits can eat other plants besides grass. Foxes, in turn, can eat many types of animals and plants. Each of these living things can be a part of multiple food chains. All of the interconnected and overlapping food chains in an ecosystem make up a food web. Trophic Levels Organisms in food chains are grouped into categories called trophic levels. Roughly speaking, these levels are divided into producers (first trophic level), consumers (second, third, and fourth trophic levels), and decomposers. Producers, also known as autotrophs, make their own food. They make up the first level of every food chain. Autotrophs are usually plants or one-celled organisms. Nearly all autotrophs use a process called photosynthesis to create “food” (a nutrient called glucose) from sunlight, carbon dioxide, and water. Plants are the most familiar type of autotroph, but there are many other kinds. Algae, whose larger forms are known as seaweed, are autotrophic. Phytoplankton, tiny organisms that live in the ocean, are also autotrophs. Some types of bacteria are autotrophs. For example, bacteria living in active volcanoes use sulfur compounds to produce their own food. This process is called chemosynthesis. The second trophic level consists of organisms that eat the producers. These are called primary consumers, or herbivores. Deer, turtles, and many types of birds are herbivores. Secondary consumers eat the herbivores. Tertiary consumers eat the secondary consumers. There may be more levels of consumers before a chain finally reaches its top predator. Top predators, also called apex predators, eat other consumers. Consumers can be carnivores (animals that eat other animals) or omnivores (animals that eat both plants and animals). Omnivores, like people, consume many types of foods. People eat plants, such as vegetables and fruits. We also eat animals and animal products, such as meat, milk, and eggs. We eat fungi, such as mushrooms. We also eat algae, in edible seaweeds like nori (used to wrap sushi rolls) and sea lettuce (used in salads). Detritivores and decomposers are the final part of food chains. Detritivores are organisms that eat nonliving plant and animal remains. For example, scavengers such as vultures eat dead animals. Dung beetles eat animal feces. Decomposers like fungi and bacteria complete the food chain. They turn organic wastes, such as decaying plants, into inorganic materials, such as nutrient-rich soil. Decomposers complete the cycle of life, returning nutrients to the soil or oceans for use by autotrophs. This starts a whole new food chain. Food Chains Different habitats and ecosystems provide many possible food chains that make up a food web. In one marine food chain, single-celled organisms called phytoplankton provide food for tiny shrimp called krill. Krill provide the main food source for the blue whale, an animal on the third trophic level. In a grassland ecosystem, a grasshopper might eat grass, a producer. The grasshopper might get eaten by a rat, which in turn is consumed by a snake. Finally, a hawk—an apex predator—swoops down and snatches up the snake. In a pond, the autotroph might be algae. A mosquito larva eats the algae, and then perhaps a dragonfly larva eats the young mosquito. The dragonfly larva becomes food for a fish, which provides a tasty meal for a raccoon.
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 The amount of energy at each trophic level decreases as it moves through an ecosystem. As little as 10 percent of the energy at any trophic level is transferred to the next level; the rest is lost largely through metabolic processes as heat. If a grassland ecosystem has 10,000 kilocalories (kcal) of energy concentrated in vegetation, only about 1,000 kcal will be transferred to primary consumers, and very little (only 10 kcal) will make it to the tertiary level. Energy pyramids such as this help to explain the trophic structure of an ecosystem: the number of consumer trophic levels that can be supported is dependent on the size and energy richness of the producer level. © Encyclopædia Britannica, Inc.
A team of ecologists observed feeding patterns of several populations in the desert. The energy pyramid shown below depicts the feeding patterns the ecologist observed. Which of the following best explains the difference in the amount of available energy in the trophic levels of the desert ecosystem? A. There is less energy available in the producers because their tissues are less dense than those at higher trophic levels. B. There is more energy available in the second trophic level because less energy is needed for hunting compared to the higher trophic levels. C. There is more available energy in the birds of prey because they have greater muscle mass for storing energy than organisms in lower trophic levels have. D. There is less available energy in the fourth trophic level because of the loss of energy through metabolism in each of the lower trophic levels. CLICK HERE FOR ANSWER
A diagram of a food web is shown below. Which organism receives the least amount of energy from the producers? A. Hawk B. Rabbit C. Grasshopper D. Mouse CLICK HERE FOR ANSWER
The diagram below shows the cycling of nutrients in an ecosystem. The removal of which of the following groups would cause an immediate decrease in the amount of energy flowing through the system? A. Producers B. Consumers C. Decomposers D. Inorganic nutrients CLICK HERE FOR ANSWER
Complete burning of plant material returns carbon primarily to the A. herbivores. B. water. C. vegetation. D. atmosphere. CLICK HERE FOR ANSWER
Which of these organisms would most likely be found at the top of an energy pyramid? A. clams - a primary consumer B. sardines - a primary consumer C. sharks - a secondary consumer D. kelp - a primary producer CLICK HERE FOR ANSWER
The diagram below shows the flow of carbon in a terrestrial ecosystem. Which will most likely happen if the decomposers are removed from the carbon cycle? A. The amount of carbon dioxide in the atmosphere will increase. B. The amount of carbon dioxide in the atmosphere will decrease. C. The amount of carbon dioxide used by producers will increase. D. The amount of carbon dioxide needed by consumers will decrease. CLICK HERE FOR ANSWER
In a process called transpiration, plants get rid of excess water through pores in the leaves called stomata. This excess water is then released into the atmosphere as part of the water cycle. Which of the following terms best describes how the released water enters the atmosphere? A. condensation B. precipitation C. evaporation D. capillary action CLICK HERE FOR ANSWER
The framework of organic molecules essential to all organisms is composed mainly of carbon atoms. Which processes are involved in the cycling of carbon within an environment? A. photosynthesis and respiration B. evaporation and condensation C. transcription and translation D. diffusion and transpiration CLICK HERE FOR ANSWER
Which of the following statements is true about natural systems? A. Consumers form the bottom levels of both the energy pyramid and the biomass pyramid. B. Producers are at the bottom level of both the energy pyramid and the biomass pyramid. C. Producers are at the bottom of the energy pyramid, but at the top of the biomass pyramid. D. Consumers are at the bottom of the energy pyramid, but at the top of the biomass pyramid. CLICK HERE FOR ANSWER
Water & carbon Cycles
Ecosystem Ecology
Trophic Levels
Energy Transfers in Ecosystems
Global Carbon Cycle
General Biology - Sections 13.3-13.6, pgs. 406-419 Honors Biology - Sections 3.2-3.4, pgs. 60-73
Web Game: Food Webs and Energy Transfer - Glencoe |
Which of the following best explains the difference in the amount of available energy in the trophic levels of the desert ecosystem group of answer choices?
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