Life Science
What you must understand
Life science questions focus on cells, body systems, heredity, ecosystems, and adaptation. Know that cells are the basic unit of life, that plant cells have cell walls and chloroplasts while animal cells do not, and that multicellular organisms organize from cells to tissues to organs to organ systems. Understand that traits are passed from parents to offspring through genes, and that organisms in a population vary, which is the raw material for natural selection. In ecosystems, trace energy from the Sun through producers to consumers and decomposers, and distinguish a food chain from a food web. Know the roles of competition, predation, and symbiosis in shaping populations.
Traps to watch for
- Energy does not cycle; matter does. Energy flows one way and is lost as heat at each level, so food chains are short.
- Adaptation is not a choice. Individual organisms do not "try" to adapt; populations change over generations because some individuals survive and reproduce more.
- Photosynthesis versus respiration. Photosynthesis stores energy using sunlight, carbon dioxide, and water; respiration releases energy from food. Plants do both.
- Confusing population, community, and ecosystem. A population is one species; a community is all living things; an ecosystem adds the nonliving environment.
Rule of thumb
When a question describes a change in an ecosystem, follow the energy and the population: which organism gains food or space, and which loses it?
Worked example
A pond's algae grow rapidly after fertilizer runoff. Predict one effect. More algae means more food for algae-eating organisms, but when algae die, decomposers use oxygen, which can harm fish. The key is tracing the chain of effects through the food web.