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Across 3. a thing or event that evokes a specific functional reaction in an organ or tissue. 6. the total quantity or weight of organisms in a given area or volume. 10. the independent variable is the factor that is manipulated or changed by the researcher, acting as the presumed cause, while the dependent variable is the factor that is measured and is expected to change in response to the independent variable, acting as the presumed effect. 11. a systematic process for acquiring knowledge through observation, experimentation, and analysis to test hypotheses and establish facts. 15. a comparison group in an experiment that does not receive the treatment being tested, serving as a baseline to measure the effectiveness of the experimental intervention. 19. the natural home or environment of an animal, plant, or other organism. 20. the living components of an ecosystem, including plants, animals, fungi, bacteria, and other organisms, as well as once-living matter 22. evaluation of scientific, academic, or professional work by others working in the same field. 23. a biological community of interacting organisms and their physical environment. 24. a linear sequence showing how energy and nutrients flow from one organism to another in an ecosystem, 25. the preying of one animal on others. 26. the process of increasing in physical size. 27. an animal that feeds on flesh.

Down 1. a substance that provides nourishment essential for growth and the maintenance of life. 2. a statement that describes an observable phenomenon in nature that appears to always be true under specific conditions, often expressed as a mathematical formula 4. the doctrine that mutual dependence is necessary to social well-being. 5. an animal which feeds on dead organic material, especially plant detritus. 7. the process of converting atmospheric nitrogen gas (N₂) into ammonia (NH₃) or other nitrogen compounds that plants can use. 8. an organism deriving its nutritional requirements from complex organic substances. 9. the independent variable is the factor that is manipulated or changed by the researcher, acting as the presumed cause, while the dependent variable is the factor that is measured and is expected to change in response to the independent variable, acting as the presumed effect. 12. the study of living organisms 13. a conclusion reached on the basis of evidence and reasoning. 14. the tendency toward a relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes. 16. a group of people working together for a common purpose 17. a supposition or proposed explanation made on the basis of limited evidence as a starting point for further investigation. 18. the practice of living as a parasite in or on another organism. 21. a verbal or written answer. 22. all the inhabitants of a particular town, area, or country. a particular section, group, or type of people or animals living in an area or country. 23. the branch of biology that deals with the relations of organisms to one another and to their physical surroundings.