| A | B | 
| community | all the populations of organisms living together within the same area | 
| consumers | organisms within a community which cannot make their own food and therefore depend on other organisms for their food | 
| decomposer | an organism that obtains energy from dead organisms and waste material | 
| food chain | a producer and a series of consumers through which energy is transferred when one individual eats another | 
| food web | summary of known food chains in a community | 
| herbivores | animals which eat only producers | 
| niche | includes all the roles of an organism in the ecosystem | 
| photosynthesis | process by which plants and other producers capture the light energy of the sun and transform it into chemical energy in food | 
| predator | an organism that catches and eats other organisms | 
| prey | living organisms that are caught and eaten by other organisms | 
| producers | organisms which make food by the process of photosynthesis | 
| trophic level | a feeding level in a food chain | 
| carnivore | consumer that eats only animals | 
| energy pyramid | compares energy available at each level of the food chain | 
| population | made of organisms of one species living together | 
| ecosystem | community interacting with the abiotic parts of the environment | 
| biosphere | all the parts of Earth where life is found | 
| carrying capacity | largest number of individuals an environment can support | 
| population density | number of organisms in a certain area | 
| symbiosis | close relationship between two different species | 
| parasitism | relationship in which two organisms live together and one is benefited and the other is harmed | 
| mutualism | a relationship in which two organisms live together and both benefit | 
| commensalism | relationship in which two organisms live together and one is benefited and the other is not affected | 
| competition | use of the same limited resource by different species | 
| biotic factors | living things in the environment | 
| abiotic factors | nonliving things in the environment | 
| limiting factor | any biotic or abiotic factor that restricts the number of individuals in a population | 
| ecology | the study of interactions that take place between organisms and their nonliving environment | 
| habitat | the place where an organism lives in a community | 
| omnivore | consumers that eat both plants and animals | 
| organism | an individual living thing of a certain species | 
| population size | number of individuals in a population | 
| water cycle | evaporation , condensation, precipitation | 
| nitrogen | important material needed by living things to make proteins | 
| nitrogen cycle | the transfer of nitrogen from the atmosphere to plants and back |