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Across 3. neither the subject nor the investigators know which participants are receiving an experimental treatment 7. measure of how likely something is 9. The nodules on the roots of this plant contain bacteria that help convert nitrogen in the soil to a form the plant can utilize. 11. occurs when a majority of scientists accept that the old explanation no longer explains new observations very well 13. species that play essential community roles (examples: mycorrhizae, giant kelp) 16. the smallest particle that exhibits the characteristics of an element 18. changes in an individual organism due to non-permanent physiological modifications 19. the circumstances and conditions that surround an organism or a group of organisms 22. an overarching model of the world that guide our interpretation of events 24. the number of individuals of a species in an area 26. stored energy that is latent but available for use 27. the systematic study of our environment and our place in it 29. catalysts that speed up the rate of chemical reactions in living systems 30. the energy contained in moving object

Down 1. progress in human well-being that we can extend or prolong over many generations, rather than just a few years 2. basic unit of matter which cannot be subdivided chemically into smaller units 4. the point where there is maximum population of species due to the presence of outstanding or ideal conditons 5. a conditional explanation that can be verified or falsified 6. a form of predation where one species benefits and the other is harmed 8. proposed that the single environmental factor in shortest supply relative to demand is the critical determinant in species distribution 10. gradual changes in a species due to changes in genetic material and competition 12. conducted so investigators do not know which is the control and which is the experimental group, until after data have been gathered and analyzed 14. the role played by a species in a biological community 15. a molecule made up of two or more kinds of atoms held together by chemical bonds 17. the study of an organism or organisms, the impact of the environment on them, and their impact on the environment 20. formed when one atom gives up an electron to another atom 21. the number of different species in an area 23. everything that takes up space and has mass 25. the place or set of environmental conditions in which a particular organism lives 28. the capacity to do work