• Energy is continually transferred from one object to another and transformed between various forms.
  • As matter and energy flow through different organizational levels of living systems, chemical elements are recombined to form different products.
  • The result of these chemical reactions is that energy is transferred from one system of interacting molecules to another.

Photosynthesis

• Some organisms obtain energy for life processes by storing energy from the sun in chemical bonds. This process is called photosynthesis.
• Photosynthesizing organisms, including green plants, algae, and phytoplankton, produce their own food (sugar), and are called producers.
• No process is more important for life on Earth than photosynthesis. Producers are the foundation of virtually all food webs.




• Sustaining life processes requires substantial energy and matter inputs.
• Two organelles—chloroplasts and mitochondria—act as change agents within the cells of living things to make energy available for life processes
• The organelles, cells, tissues, organs, and organ systems of plants work as a system to obtain the raw materials (sunlight, water, and carbon dioxide) and produce the products (sugars and oxygen) in photosynthesis
• Chloroplasts, organelles found in some plant cells, convert radiant energy from sunlight into chemical energy. Chloroplasts do this with the help of the pigment chlorophyll.
• Chlorophyll aids in the energy transformation of sunlight (radiant energy) to chemical energy in sugar
• The sugar molecules produced from photosynthesis can be used immediately by plants and animals for energy, stored for later use, or rearranged into other compounds to carry out life processes

Cellular Respiration

• Cellular respiration occurs in the mitochondria of all cells (including plant cells).
• In this process, sugar molecules combine with oxygen to release energy in a form that cells can more easily use
• Although they occur in different organelles, photosynthesis and cellular respiration are interdependent processes.
  • The products of one process are the reactants for the other process and vice versa
• Matter and energy are conserved in chemical processes. This is true of all biological systems, from individual cells to ecosystems
• Living things are composed of systems which are dynamic and change in response to inputs and outflows of energy and matter.
• The availability of raw materials and other factors can affect the life processes of living things, including the rate of photosynthesis and cellular respiration.
  • Factors affecting the rate of photosynthesis are light intensity, carbon dioxide concentration, and temperature.
• Cellular respiration also releases the energy needed to maintain body temperature, despite ongoing energy loss to the surrounding environment.

Students should :
• understand the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.
• understand why producers are the foundation of food webs 
• know the raw materials (reactants) used and products generated in photosynthesis and cellular respiration
• the cellular organelles involved in photosynthesis and cellular respiration
• how energy from photosynthesis is used
• explain how cellular respiration is the reverse of photosynthesis