Lesson 7: Oxygen Production and Life

Getting Started

In Lesson 6, you learned about three major cycles — water, nitrogen, and carbon. In this lesson, you will look at oxygen and at the role of plant and animal processes that are important for the survival of an ecosystem. Oxygen is located in three reservoirs (places where something is kept in store): the atmosphere (air), all biological matter, and the Earth's crust. While each of these reservoirs is significant, this lesson will focus primarily on oxygen in the atmosphere. The major source of atmospheric oxygen is photosynthesis.

In this lesson, you will begin to see how oxygen, which is necessary for life, is produced at the levels required for all organisms to survive. In order to understand oxygen's significance, you will have to consider two important processes in living organisms — photosynthesis and cellular respiration — which both require oxygen. Respiration requires oxygen to break chemical bonds and release energy. Photosynthesis produces oxygen as a by-product. As you go through this lesson, consider how there always seems to be enough oxygen. Ask this question: if oxygen is constantly being used, how is enough present for all living things?

Stuff You Need

  • Exploring Ecology by Anna Engelke
  • scissors* (Activity 1 - Option 2)

* - denotes an optional material that may or may not be needed

Ideas to Think About

  • How do relationships between living and non-living components of an ecosystem enable the system to sustain itself?
  • How do Earth cycles ensure the survival of an ecosystem?

Things to Know

  • A reservoir is a place where something is kept in store.
  • A depletion is a serious decrease or exhaustion of the abundance or supply of something.
  • Cellular respiration is a process in all living things where stored energy is released by the breaking of chemical bonds to produce energy for survival.
  • Glucose is an energy source produced by the process of photosynthesis. Glucose contains carbon, hydrogen, and oxygen.


  • Know that the major source of atmospheric oxygen is photosynthesis. (S)
  • Know that photosynthesis is a process carried on by green plants and other organisms containing chlorophyll. (S)

Introducing the Lesson

In this lesson, your child will work with the components of photosynthesis either visually or mathematically. The goal of the lesson is to see how important each component of photosynthesis and respiration is and, in an abstract way, learn exactly where the oxygen on the planet goes and where it comes from. Your child has already been exposed to cycles in the Earth's systems, and through today's activity she will be able to take a closer look at how important these cycles are for life.
Reading and Questions
Materials: Exploring Ecology by Anna Engelke
Review pp. 8-10 in the Exploring Ecology booklet. As you read, pay attention to the roles of oxygen and carbon dioxide in photosynthesis. A common idea is that plants are the primary producers of energy. While this is true, plants also release oxygen and water back into the environment. As you read, consider the important role that plants play in releasing oxygen and water into the environments in which they are found.

(If you are using the online version, the pages are the same — pp. 8-10.)
Web Link

  1. By what process do plants utilize carbon dioxide and water and release oxygen?
  2. What will happen if the process of photosynthesis stops in a plant? In all plants?
    Because photosynthesis stores energy and produces the carbohydrates necessary for growth, the plant would no longer have the energy necessary for survival. Also, the plant would stop growing. If one plant stops photosynthesizing, the lack of oxygen production would not be dangerous. If all plants were to stop photosynthesizing, oxygen in the environment would be quickly depleted.
  3. In what way might the release of oxygen back into the environment be harmful to a plant that is found in a dry region (HINT: Consider how a plant produces oxygen)?
    Like all plants, plants found in arid lands produce energy via photosynthesis. This requires water, carbon dioxide, and oxygen. Water is a precious commodity, and if a plant fails to keep the water necessary for producing carbohydrates, a product of photosynthesis, it will eventually die. Also, one of the products of photosynthesis is oxygen, along with water and energy released for the plant to survive. When a plant produces an abundance of oxygen, it is also producing the by-product of water. If this water is also lost, especially in an arid region, the plant may not survive.
  4. Consider the energy pyramid (p. 10). Why do you think it is important that the base of the pyramid (plants) contain the most abundant organisms? How does this relate to the cycling of oxygen?
    Primary consumers depend on producers for food. Due to the energy lost between levels, the primary consumers require a lot of producers to survive. In addition, producers provide oxygen, which organisms at the higher trophic levels (and decomposers) require to survive.