Energy for Life
What Is Energy and How Does It Contribute to Maintaining Life on Earth?
Living Organisms and Energy
Teacher Note: Connections
In this concept, students will understand the role that energy plays in living systems. They will learn about energy changes in a system. They also will learn that energy cannot be created nor destroyed. As students learn about energy, have them summarize the information using the Journals strategy. The Journals strategy is found on the Professional Learning tab. Click on Strategies & Resources, then click on Spotlight on Strategies (SOS). Now click on Vocabulary Development, then click on Spotlight on Strategies: Journals.
As students read and comprehend complex texts, view the videos, and complete the interactives, labs, and other Hands-On Activities, have them summarize and obtain scientific and technical information. Students will use this evidence to support their initial ideas on how to answer the Explain Question or their own question they generated during Engage. Have students record their evidence using “My Notebook.”
All living organisms require energyglossary term (opens in a new window) to perform essential cellular processes. Growth and reproduction are complex processes that need energy. Building larger molecules from smaller ones requires the input of energy; these larger molecules can also be used to store energy for later use. Moving molecules from low to high concentrations requires the input of energy. Organisms also need energy for a variety of other tasks such as movement and sending electrical signals in the nervous system. Without energy, none of the processes of life are possible.
Ultimately, the energy for most organisms on Earth comes from the sun. Photosynthetic organisms such as plants, algae, and some bacteria and archaea can convert solar energy into chemical energyglossary term (opens in a new window), which is energy stored in chemical bonds. Other organisms such as animals and fungi must acquire their energy from the photosynthetic organisms. When an animal ingests food, the food molecules are broken down, and the energy within is released. Some single-celled organisms are able to use inorganic molecules such as compounds containing sulfur as an energy source.
Teacher Note: Misconception
Students may believe that cells make energy. In fact, cells can only convert energy from one form into another.
Defining Energy
All organisms require a source of energy, but what is energy? Energy is the ability to do work or cause change. The processes of living organisms such as moving and building molecules are examples of work that can be accomplished using energy. To do this work, cells convert energy from one form to another. Energy cannot be created or destroyed, but it can be transformed into different forms. Kinetic energy is the energy of motion, thermal energyglossary term (opens in a new window) is heat generated by the kinetic energy of atoms or molecules, and potential energyglossary term (opens in a new window) is stored energy. Chemical potential energy, commonly called chemical energy, is a form of potential energy that is stored in chemical bonds. It is the conversion of energy among these forms that keeps living organisms alive.
Measuring Energy
Energy can be measured using a number of different techniques. Energy is defined as the ability to do work, and work is defined as the force used to move an object for a certain distance (work = force x distance). The standard unit of measurement for energy is the joule (J), which is defined as 1 newton of force used to move an object 1 meter; 1 joule = 1 newton*meter.
A watt is defined as the use of 1 J/second. This measurement is often used to measure power expenditure in electrical equipment.
The energy in food is often measured in calories. A calorie (cal) is the amount of thermal energy needed to raise the temperature of 1 g of water by 1° C. The calories listed on food labels are kilocalories (1000 calories). On food labels, kilocalories are designated as Calories with a capital letter C.
Energy can also be measured in ergs, which are defined as the kinetic energy of 2 g moving at a velocity of 1 cm/sec. These measures of energy relate to each other with the following conversions:
In biology, the calorie is the most commonly used unit of energy.
Teacher Note: Connections
In this item, students will analyze different life processes to match them with descriptions of the way energy flows into, through, and within that system. The energy uses of each process may not be obvious to students at first. Review with them other concepts that they have learned in Biology, including DNA replication, digestion, respiration, and the nervous system to help them recall how energy is used in each of these processes. Have small groups write tweets to summarize how each system uses energy using the strategy Tweet, Tweet! Access this strategy on Techbook by clicking the Professional Learning tab. Click on Strategies & Resources, then Spotlight on Strategies (SOS). Tweet, Tweet! is found underneath “Summarizing.”
