All organisms need energy and matter to live and grow.
Living organisms depend on one another and on their environment for survival.

These standards relate to two huge science ideas: interdependence and systems. All organisms depend on other organisms for their existence. As noted in Standard 2a, all animals ultimately depend on plants for matter and energy.

Plants therefore play the role of the producers in the vast majority of ecosystems. Ecosystems are a kind of system. Whenever we analyze something in our world in terms of systems, we encounter a phenomenon called “nested systems” or “systems within systems within systems.” A human being can be considered a system that has parts that define it. Some of these parts are known as the circulatory system, the nervous system, and the digestive system. Each of these body systems is made of parts. The circulatory system is made of the heart, veins, arteries, and capillaries. The heart, for example, can be considered as a system that is made of muscle and nerve cells. Thus, we have systems within systems within systems.

Ecosystems also have this characteristic of systems within systems. The California Sierra Nevada mountains can be considered a very large ecosystem that stretches most of the length of the state. Yosemite National Park is an ecosystem within the Sierra Nevadas. Mariposa Grove is an ecosystem within Yosemite that is dominated by giant Sequoia Redwood trees. A decaying fallen redwood tree is an ecosystem within Mariposa Grove. Each of these ecosystems within ecosystems within ecosystems is defined by its physical setting and the organisms that live there.

All ecosystems with their food chains and food webs ultimately rely on a class of organisms called producers who capture the energy that sustains the entire ecosystem. In essentially all the familiar ecosystems, organisms in the plant kingdom play this role. Through the process of photosynthesis, plants ranging from redwood trees to grasses to microscopic plankton in the ocean capture the energy of sunlight and package this energy in chemical form in sugars.

Photosynthesis not only captures energy, but it also takes carbon dioxide gas from the air and makes organic molecules from this inorganic form of carbon. Initially these organic molecules are sugars, but these sugars are then built into the proteins, DNA, carbohydrates, and fats that make up living organisms. When you pick up a dry log, almost 90% of the weight of that log came from carbon dioxide gas that the tree made into sugar through photosynthesis! Thus, the producers in an ecosystem provide not only the energy but also the very substance of the bodies of the organisms in that ecosystem.

The order in which the standards were written does not imply that they are supposed to be taught in that sequence. As in all the strands, these standards can be taught in many ways and in many sequences. The concept map below provides one way to organize these standards. The wording of some of the standards has been slightly changed for space reasons and to emphasize a particular conceptual flow.

[A different concept map for these standards is on page 43 of the book "Making Connections" available from the California Science Teachers Association (CSTA).]