Plants and animals have structures for respiration, digestion, waste disposal, and transport of materials.

All Earth’s organisms either consist of single cells or of many cells that work together. The first cells appeared about 500 million years after Earth formed. For most of Earth’s history, the only living things were single-celled organisms. It took about 3,000 million years for the first multicellular animal to evolve from these single-celled ancestors.

This long period of time testifies to the difficult challenge of having different cells specialize to perform tasks for the whole organism, and of coordinating these specialized cells so they function as a unified whole. Part of the solution is to have cells organize into structures that are larger than cells but smaller than the whole organism. This set of standards explores some of the structures that multicellular organisms possess in order to digest food, burn sugars for energy, move materials to different parts of the organism, and excrete wastes.

While not directly mentioned, the concept of systems underlies these standards. Almost any interesting aspect of our world can be analyzed as a system that is made of parts that join together to form the whole system. An animal’s circulatory system is made of parts such as the heart, veins, arteries, and blood cells. The heart, a part of the circulatory system, is also a system made of parts. Its parts include muscle cells, nerve cells, and valves.

Another way to understand this major concept is to trace how cells come together to form tissues that come together to form organs that work with other organs to form a body system such as the digestive or circulatory system.

The Grade 5 Physical Science standards also illustrate the principle that parts come together to form systems that have qualitatively different properties than those of the parts. Water has properties that are very different from oxygen and hydrogen. Similarly, the circulatory system as a whole has properties much greater than the heart or the veins or the arteries by themselves. Each of us is a system that is much more than our circulatory system or our digestive system.

This set of standards also directly focus on another very big idea, the connection between photosynthesis and respiration. From the point of view of life, these are two of the most important chemical reactions occurring on Earth. By capturing energy from sunlight and packaging it in chemical form, photosynthesis forms the basis of almost all Earth’s ecosystems. It also provides the oxygen in our atmosphere. Respiration is the main way that cells release the chemical energy stored in food to be used in life processes. These two chemical reactions are mirror images of each other.

As in all the strands, these standards can be taught in many ways and in many sequences. The order in which they were written does not imply that they are supposed to be taught in that sequence. 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 47 of the book "Making Connections" available from the California Science Teachers Association (CSTA).]