Pre-IB Grade 9 Science Practice Exam

An ecosystem is the integrated system of living organisms and their physical environment, interacting and exchanging energy and matter. The description that emphasizes a community of organisms together with their abiotic surroundings captures this interconnected system most fully. Energy from the sun flows through producers, consumers, and decomposers, while nutrients cycle between living things and their environment, all linked by relationships such as predation, decomposition, and symbiosis. The other options miss essential features: a non-living system lacks living interactions; a collection of unrelated individuals has no interactions; a single species with no interactions excludes the network of relationships that define ecosystems.