1. Cycles in Nature
13.2

2. A. Water Cycle
Evaporation – takes place when water changes into water vapor, which is a gas, and enters the atmosphere

3. B. Types of Evaporation
water evaporates from the surface of lakes, streams, puddles and oceans
water vapor enters the atmosphere from plant leaves in a process known as transpiration
animals release water vapor into the air when they exhale
water also returns to the environment from animal wastes

4. C. Condensation
Condensation – the process of changing from a gas to a liquid
Water vapor that has been released into the atmosphere comes in contact with colder air
Temperature of the water vapor drops
Water will eventually cool enough to change back into liquid water (which is called condensation)
Example: Cold drink sweating like a soda

5. Water vapor condenses on particles of dust in the air, forming tiny droplets
At first, the droplets clump together to form a cloud
When they become large and heavy enough, they fall to the ground as rain or other precipitation

7. D. Water Use
The amount of water people take from reservoirs, rivers, and lakes for use in households, businesses, agriculture, and power production reduce the amount of water that evaporates into the atmosphere
Why would this be a concern?
Because the less water that there is to evaporate, the less water there is to create rain and come back to the earth. It also takes away water for plants and animals in nature.

8. E. Nitrogen Cycle Nitrogen is a necessary ingredient of proteins
Proteins are required for the life processes that take place in the cells of all organisms
Nitrogen is also an important part of the DNA in organisms

9. Nitrogen is the most available gas in the atmosphere (78% of the air), but most organisms cannot use nitrogen directly from the air
For plants, nitrogen must be combined with other elements to form nitrogen compounds
Nitrogen fixation – a process in which some types of soil bacteria can form the nitrogen compounds that plants need
Plants absorb the nitrogen compound through their roots

10. Animals obtain nitrogen they need by eating plants or other animals
When dead organisms decay, the nitrogen in their bodies returns to the soil or to the atmosphere
Nitrogen cycle – the transfer of nitrogen from the atmosphere to the soil, to living organisms, and back to the atmosphere

11. F. Soil Nitrogen The nitrogen cycle can be affected by humans
When farmers grow crops, the plants take in the nitrogen from the ground, but the plants don’t decay in the same place so the nitrogen is moved to a different location
If the nitrogen compounds are not replaced, the soil could become infertile

12. Fertilizers can be used to replace soil nitrogen in crop fields, lawns, and gardens
Compost and animal manure also contain nitrogen compounds that plants can use and be added to improve fertility

13. Farmers will also grow nitrogen-fixing crops such as peas, clover, and beans like soybeans
These plants have nitrogen-fixing bacteria that grow on their roots
The nitrogen compounds are supplied to the plants and the soil

14. G. The Carbon Cycle
Carbon cycle – describes how carbon molecules move between the living and nonliving world
Carbon atoms are found in the molecules that make up living organisms
Carbon is an important part of soil humus and it’s found in the atmosphere as carbon dioxide gas

15. Carbon cycle starts when producers remove carbon dioxide from the air during photosynthesis
They use carbon dioxide, water, and sunlight to produce energy rich sugar molecules and energy is released from these molecules during respiration

16. Respiration uses oxygen and releases carbon dioxide
Photosynthesis uses carbon dioxide and releases oxygen
These two processes help recycle carbon on Earth

17. H. Harmful Carbon Dioxide Release
Human activities also release carbon dioxide into the atmosphere
Using fossil fuels as gasoline, coal, and heating oil
These fuels are made up energy-rich, carbon-based molecules
When these are burned, carbon dioxide is released into the atmosphere as a waste product

18. Wood is used for building or burning and this wood comes from trees that can no longer remove carbon dioxide from the atmosphere
This causes an increase of carbon dioxide not being removed as quickly as it is being created. More heat is trapped in the atmosphere, helping to cause Global Warming

19. Review
1. Why is evaporation an important process? 2. How do animals release water vapor? 3. What is an unusual way water vapor is released into the atmosphere? 4. How does the process of condensation work?

20. 5. How is a cloud formed? 6. What are ways that people take Earth’s water? 7. Why do people need to be careful how quickly and how much water is used on Earth? 8. What is a necessary ingredient for proteins? 9. Why are proteins important?

21. 10. How do plants get the necessary nitrogen compound to survive. 11
10. How do plants get the necessary nitrogen compound to survive? 11. How is nitrogen used and returned back to the earth? 12. How can the nitrogen cycle be affected by humans? 13. What would happen if nitrogen compounds are not returned back to the earth?

22. 14. What are the 3 ways that humans can replace nitrogen compounds back to Earth? 15. How can planting certain crops help replace nitrogen compounds to the earth? 16. Where are carbon atoms found? 17. How does the carbon cycle start? 18. What two processes help replace carbon on Earth?

23. 19. How are humans causing Global Warming. 20
19. How are humans causing Global Warming? 20. Why is Global Warming dangerous?