1. Section 15.1 Learning Goals
Trace the pathways by which elements are recycled in nature.
Identify specific processes associated with chemical cycles.
Discover how living organisms within ecosystems are affected by or interact with Earth’s chemical cycles.

2. 15.1 Chemical Cycles
The Earth’s elements essential for living things are called nutrients.
Living things need macronutrients in large quantities while micronutrients are needed in small quantities.

3. 15.1 Chemical Cycles
Over time, these elements are transported through the living and nonliving parts of our planet in sets of processes called chemical cycles.

4. 15.1 Chemical Cycles Examples of these cycles include the:
oxygen cycle,
carbon cycle,
nitrogen cycle, and
phosphorus cycle.
Even before life appeared on Earth millions of years ago, elements were recycled.

5. 15.1 How living organisms affect cycles
An ecosystem consists of a group of living things and their physical surroundings.
The Sun is the main energy source for ecosystems.
Can you list some living and nonliving parts in this tropical rainforest ecosystem?

6. 15.1 Photosynthesis
Photosynthesis is the process by which plants and some other organisms convert the Sun’s energy to chemical energy.

8. 15.1 Living parts of an ecosystem
A producer is a living thing, like a plant, that can take the Sun’s energy and store it as food.

9. 15.1 Living parts of an ecosystem
A consumer must feed on other living things to get food and energy.
An herbivore is a consumer that eats only plants.
A carnivore is a consumer that eats only animals.
A consumer that eats both plants and animals is called an omnivore.

10. 15.1 Living parts of an ecosystem
A decomposer is a living thing that consumes waste and dead organisms to get energy.
Decompose means “to break down”.

11. 15.1 Living parts of an ecosystem
A food chain shows how each member of an ecosystem gets its food.
A simple food chain links a producer, an herbivore, and one or more carnivores.
Which is the herbivore?

12. 15.1 Pollution in ecosystems
Mercury from power plants falls to Earth with rain and ends up in lakes and oceans.
As toxic mercury is concentrated up the food chain, it can accumulate to dangerous levels if ingested by humans.

13. 15.1 The water and oxygen cycles
Living things need water and sunlight.
Nature allows water to recycle so it can be used in many ecosystems.
Water supply depends on the water cycle.

14. 15.1 The water and oxygen cycles
Like water, oxygen is essential for living things.
During photosynthesis, plants release oxygen into the atmosphere.
During respiration, plants or animals use oxygen to store energy.

15. 15.1 The carbon cycle
Trace the pathways through which carbon is released and absorbed in the diagram below:

16. 15.1 The nitrogen cycle
Nitrogen is important to living things because it is used to make amino acids, the building blocks of all proteins.
Nitrogen must be changed or “fixed” into NO3- & NH4+ to be usable by plants.
Note the importance of bacteria in this cycle!

17. 15.1 The phosphorus cycle
Phosphorus is essential for cell replication, metabolism, and structures.
Phosphorus from minerals is absorbed by the roots for use by the plant.
Animals obtain phosphorus by eating plants.

18. 15.1 Cycles interconnect
Cycles do not have beginning or ending points.
Because organisms are not 100% efficient at using what they consume, they release heat energy as they metabolize nutrients.