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Across 1. the lessening of the productivity of land due to human activity 7. no longer exists 8. a natural fuel formed in the geological past from the remains of living organisms 9. the accumulation of substances such as pesticides in an organism 10. defined by climate, flora and fauna 11. expansion of deserts due to overgrazing, erosion, drought 13. the process of carbon being exchanged between organisms and the environment 14. release of any hazardous substance into the environment 15. the physical environment plants and animals live in

Down 2. atmospheric effect keeping the surface temperature at 15 degrees C 3. the total surroundings 4. inability to meet basic needs for food, clothing and shelter 5. the variety of all life forms 6. rise in temperature caused by heat-absorbing gases in the atmosphere 12. the relationship between living things and their physical environment