Imagine for a moment that you stay after school one day to clean up the classroom. While cleaning, you move some plants away from the sunny windows. A week later, you remember to move the plants back. You notice something strange has happened. Instead of standing upright, the plants appear to be leaning toward the windows! Why? Plants need sunlight to survive. If a plant is moved away from sunlight, then special cells in the plant help it turn toward the Sun. The Sun s energy allows plants to produce their own food. Plants then use this food energy to grow and reproduce. However, not all organisms can make their own food. How do those other organisms get their food energy? Do they get it from the Sun? Where do all food chains and food webs get their energy? All of the food energy that passes between organisms comes from the Sun. You might be wondering how this is possible. After all, humans can t eat sunlight! Plants and other organisms that use sunlight absorb it and then use that energy to make their own food. That energy passes to other organisms that eat the plants. For example, grass uses sunlight to make food. A deer gets energy by eating the grass. After that, a wolf gets energy by eating the deer. The movement of food energy from one organism to another is called a food chain. Take a look at the food chain on the right. The arrows show how food energy is passed from one organism to the other. The plants use energy from the Sun to make their own food. Both antelopes and squirrels get energy by eating plants. The hawk gets energy by eating the squirrels. Mountain lions and coyotes get energy from eating the antelopes. A simple food web showing multiple food chains. You might think the arrows in a food chain show which organism is eating another organism. The arrows actually show how energy is moving through the food chain. 1
Matter and Energy Transfer What are the different parts of a food web? A group of overlapping or connected food chains is called a food web. A food web can be big or small. It can contain many different types of plants and animals or just a few. Whether a food web is big or small, the organisms fall into one of two categories: producers or consumers. Producers: Producers are organisms that get their energy directly from the Sun. Their cells are able to turn sunlight into food through a process called photosynthesis. In photosynthesis, producers combine carbon dioxide, water, and sunlight to produce oxygen and sugar (their food). carbon dioxide: a type of gas found in Earth s atmosphere Other organisms get energy by eating producers. Have you ever eaten lettuce or any other vegetable? If so, you have eaten a producer! The lettuce plant converts sunlight into food your body uses as fuel. Producers are very important to life on Earth. Without them, other organisms would not survive. Consumers: A bald eagle is an example of a consumer. It cannot directly use the Sun s energy to make food. As a consumer, it has to eat or, consume other organisms for energy. A consumer may eat producers (such as a deer eating grass) or other consumers (such as a bald eagle eating a fish). Animals, fungi, and some bacteria are types of consumers. Consumers that eat only plants are called herbivores. Consumers that eat only animals are called carnivores. If a consumer eats both plants and animals, then it is called an omnivore. Some consumers live off of dead plants and animals. Mushrooms and vultures are examples of decomposers. Decomposers get their energy from their food, just like other consumers. 2
What do organisms use energy for? Organisms use energy for a variety of functions. Cells make up all living organisms. Cells need energy to stay alive. Cells need more energy if they divide to make the body grow larger. They also divide to help the body recover from an injury. Both plants and animals use energy to stay alive and to grow. cells: the basic units of all living things organisms: living things Some animals such as sea stars and lizards can regrow whole limbs. The oriental garden lizard shown in the picture was probably attacked by a predator. The lizard escaped but now has to regrow its tail. How do you think their food consumption changes while this process is happening? This lizard is replacing its tail. Human bodies cannot regrow limbs, but many people experience serious injuries. Healing from a serious injury or illness also requires extra energy. Maintaining body temperature also requires energy Warm-blooded animals, including humans, maintain a nearly constant body temperature. The body temperature of coldblooded animals changes based on the temperature of the environment. Warm-blooded animals have to use a lot of the energy from food they eat just to stay warm. The advantage they have over cold-blooded animals is that they can move and live in colder climate. Comparison of the energy used by warm-blooded and cold-blooded animals. Suppose a dust storm blocked sunlight in your town for several weeks. What do you think would happen to the plants in the area? What would happen to the organisms that depend on the plants for food? Why? 3
Motion requires energy. Organisms use energy to move. Animals that spend a lot of their time moving will expend a lot more energy. Animals that have to escape predators frequently also expend energy. In general, plants don t move and, therefore, don t expend a lot of their energy on motion. Plants do require energy to stay alive, grow, and repair themselves. Real Life Science: Inability to use energy can cause human disease People with multiple sclerosis (MS) often have weakness in their arms or legs, difficulty seeing, and difficulty thinking. In MS, cells in the brain and spinal cord become sick and die. Cells in the brain and spinal cord need a lot of energy to function. Scientists hypothesize that inability to use energy well is one of the things that makes these cells sick. People with MS are told to get plenty of rest to help with their symptoms. Doctors also use medicines to treat other symptoms of MS. What Do You Know? Study the images in the chart on the next page. Then, decide if the organism in each image is a producer or consumer. Write your answer in the first column of the chart. If the organism is a consumer, decide if it is a carnivore, herbivore, or omnivore. Write your answer in the second column of the chart. Finally, think about how each organism gets its food energy. Write your answer in the last column of the chart. The first row s answers have been completed for you. 4
Organism Is the organism a producer or a consumer? Is the organism a carnivore, herbivore, or omnivore? How does the organism get food energy? Strawberry Bush Producer Not a consumer Directly from the sun Deer Eating Grass Snake Eating a Frog Raccoon Eating Plants and Animals from a Trash Can 5
Exploring energy transfer using food To explore energy balance, gather the containers for five different foods your child eats. The amount of energy per serving is listed as calories or kcal. Next, look up how much energy your child s favorite activity consumes. Discuss with your child how many servings of a given food your child needs to eat to replenish the energy used during a particular activity. Remember that energy is also used to maintain body temperature, among other things, so the amount of food needed to keep you child healthy is actually higher. 6