1. All ecological pyramids have ___________________________________ at their base.
 
2. Impurities added to the environment that cause an undesirable change are called ____________________________.
 
3. A __________________ pyramid can be inverted.
 
4. The total of all species populations in an area forms a ___________________________.
 
5. The speed at which an ecosystem returns to its former state following a disturbance is ___________________________.
 
5. Ecological ________________________ is a progression of communities appearing on a site over time.
 
6. Gaseous biogeochemical cycles involve elements that have their major reservoir in the _______________________.
 
7. The Earth's water cycle is driven by ____________________________.
 
8. Evaporation of water from plant leaves is called ________________________.
 
9. Nitrogen-fixing bacteria live on the roots of ________________________.
 
10. Photosynthesis removes __________________ from the air and adds ____________________.
 
11. The _________________ carbon cycle involves the fossil fuels.
 
12. The capacity of an ecosystem to remain relatively unchanged when confronted by a disturbance is called ___________________________.
 
13. __________________ communities accumulate biomass, causing rapid change.
 
14. ___________________ succession occurs on sites where no community has previously existed.
 
15. ___________________ plants are the first to grow in a disturbed area.
 
16. The first green things to grow in a pond are ______________________.
 
17. _________________plants are rooted to the bottom of a pond and their stems and leaves extend above the surface.
 
18. After a pond disappears, __________________ mark where the edge of the pond used to be.
 
19. Biogeochemical cycles show the movement of __________________________ from the atmosphere or soil into organisms and back again.
 
20. Oxygen and nitrogen can be combined in the air to form nitrate ions by _______________________.