Grade 7:  Cycling of Energy and Matter

7.LS1.6 Construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.

7.LS1.7 Develop a model to describe how food molecules in plants and animals are broken down and rearranged through chemical reactions to form new molecules that support growth and/or release energy as matter moves through an organism.

7.LS2.3 Develop a model to describe the cycling of matter and flow of energy among living and nonliving parts of an ecosystem. 

In a Nutshell

Matter and energy cycle through both living and nonliving parts of ecosystems. Almost all energy that drives the cycling of matter comes from the sun, whether it is the cycling of energy in photosynthesis or cellular respiration. Students can construct explanations based on evidence to describe the roles of these processes in the cycling of matter and flow of energy into and out of organisms. Student-developed models can describe how energy stored within food molecules is released as the molecules are broken apart and rearranged into new molecules, supporting organisms growth and energy needs. Student models can include illustrations of energy flows and matter cycles through both living and nonliving parts of ecosystems. A change in a living or nonliving component of an ecosystem can result in the rest of the components in the system being impacted.

Student Actions

Teacher Actions 

• Gather evidence to construct an explanation that in order for plants, algae, and phytoplankton to produce complex food molecules, energy from the sun, carbon dioxide from the atmosphere, and water are required. 

• Construct an explanation based on evidence that photosynthesis in plants, algae, and phytoplankton uses the flow of sunlight energy to drive the cycling of matter from the environment into sugars (food molecules) and oxygen that is released into the environment.  

• Analyze and interpret data to construct an explanation that food molecules made during the process of photosynthesis can be used immediately by plants for energy, or stored for growth, and other necessary functions like repair and seed production.  

• Develop a model that describes how food molecules taken in by an organism are broken down then rearranged to form molecules that are used for growth or repair of the organism.  

• Develop a model that describes how as food molecules are rearranged through chemical reactions, energy is released to support other processes within the organism.  

• Develop a model of a food web to describe how matter and energy are transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem. 

• Develop a model to describe how decomposers recycle matter from dead plant or animal matter back into the soil or water and use the energy released from rearranging those molecules for growth and development. 

• Develop a model to demonstrate an understanding that the atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem. 

• Support students in gathering evidence and developing explanations for the role photosynthesis has in cycling of matter and energy into and out of organisms.

• Assist students in developing and using models to explain how food used by organisms is broken down during a series of chemical reactions and rearranged to form new molecules that support growth or release energy.

• Pose meaningful questions to help students develop a model to describe that energy flows and matter cycles through living and nonliving parts of ecosystems.

Key Concepts 

Misconceptions 

Organization for Matter and Energy Flow in Organisms

• Plants, algae (including phytoplankton), and many microorganisms use the energy from light to make sugars (food) from carbon dioxide from the atmosphere and water through the process of photosynthesis, which also releases oxygen. These sugars can be used immediately or stored for growth or later use.

• Within an individual organism, food moves through a series of chemical reactions in which it is broken down and rearranged to form new molecules, to support growth, or release energy.

Energy in Chemical Processes and Everyday Life

• The chemical reaction by which plants produce complex food molecules (sugars) requires an energy input (i.e., from sunlight) to occur.

• In this reaction, carbon dioxide and water combine to form carbon-based organic molecules and release oxygen.

• Cellular respiration in plants and animals involves chemical reactions with oxygen that release stored energy. In these processes, complex molecules containing carbon react with oxygen to produce carbon dioxide and other materials.

Cycle of Matter and Energy Transfer in Ecosystems

• Food webs are models that demonstrate how matter and energy are transferred between producers, consumers, and decomposers as the three groups interact within an ecosystem.

• Transfers of matter into and out of the physical environment occur at every level.

• Decomposers recycle nutrients from dead plant or animal matter back to the soil in terrestrial environments or to the water in aquatic environments.

• The atoms that make up the organisms in an ecosystem are cycled repeatedly between the living and nonliving parts of the ecosystem. 

• Plants get energy from multiple food sources including the soil, water, and carbon dioxide.

• Plants take in all substances needed to grow through their roots. 

• Plants use oxygen during photosynthesis.

• Energy is created during the process of cellular respiration.  

• Cellular respiration is different in plants and animals.  

• Food and fuel are energy rather than sources of energy. 

• Many students believe that energy is always released when a chemical reaction occurs. They relate chemical reactions to the use of fossil fuels as energy stores in the world. 

• If a population in a food web is disturbed, there will be little or no effect on populations that are outside the linear sequence in the food web. 

Instructional Resources 

Unit 3: Cycling of Energy and Matter