Food Webs

In this lesson, students develop a model to analyze how energy flows through a food web in the Pantanal wetlands of South America. They trace the flow of energy from the sun to producers and then consumers and decomposers, and evaluate how living things are part of all ecosystems, and depend on one another and their environment for survival.  

• The Pantanal is the world’s largest freshwater wetland system and is located in South America.  
• Ecosystems are communities of different organisms that depend on interacting with each other and their physical environment for survival.
• Ecosystems are made up of different living things, as well as air, water, sunlight, and Earth materials (rocks, soil, etc.).
• Ecosystems cannot survive without plants because plants capture the sun’s energy and turn it into energy they need for growth and development.  
• All ecosystems have consumers as well as producers. Consumers are organisms that get energy by eating other living things.
• Decomposers are an important part of all food chains and food webs. They are organisms that break down organic material and feed on the nutrients.
  
  

• How do Earth’s systems interact in the wetlands?
• Why are nonliving parts important in an ecosystem?
• How are plants able to make food from sunlight?
• Why do all ecosystems need producers?
• How are plants different from animals?
• How do herbivores get energy when they eat plants? How do carnivores get energy since they don’t eat plants?  
• How do decomposers get energy?
• Why are decomposers important in a food chain (the path that energy travels as one organism eats another)?  
• Why do the arrows in a food chain go from the producers to the consumers, even though the consumers are eating the producers?  
• Why do all food webs have the same parts (producers, consumers, and decomposers)?

Misconception: The organisms in an ecosystem are not part of a larger whole, but instead are just a collection of living things surviving independently of one another and their environment.

Fact: Ecosystems are systems, made up of smaller interacting parts. Both the living and nonliving parts of an ecosystem influence the overall ecosystem.

Misconception: An organism is not a system.

Fact: All organisms are systems because they are made up of smaller structures that have a specific function and work together to help the organism survive.

Animal: a living thing that eats other organisms for energy, breathes oxygen, and undergoes growth and reproduction

Change: to make something different from what it is now

Consumer: an organism that eats other organisms

Decomposer:  an organism that breaks down organic material and feeds on the nutrients

Ecosystem: a community of different organisms that depend on interacting with each other and their physical environment for survival

Food chain: the path that energy travels as one organism eats another

Food web: a visual that shows the network of food chains in an ecosystem

Function: the normal action of something or how something works

Photosynthesis: the process of turning sunlight, carbon dioxide, and water into glucose and oxygen

Plant: a living thing that captures energy from sunlight for growth and development

Producer: an organism that captures energy from sunlight through a process called photosynthesis

Why Wetlands Are Important

Wetlands play an important role in the water cycle. They help to refill groundwater. This is possible because wetlands can store water, acting as natural sponges. They slowly release this water into aquifers.

Wetlands also improve water quality because they act as natural filters. For example, some plants take pollutants into their roots and change them into less harmful substances. By the time water has moved through wetlands, many pollutants have been removed. The roots of the plants also help to slow flood waters and reduce the amount of erosion that takes place.Because of this, all of Earth’s systems are connected in wetlands. All wetlands have the ability to hold water, which is the hydrosphere. They also have moist or wet soil, which connects the hydrosphere and geosphere. Finally, they are home to water plants and other living things, connecting the hydrosphere, geosphere, and biosphere.

Wetlands Ecosystems

The wetlands ecosystem is unique because of its position between water and land. An ecosystem is a community of different organisms that depend on interacting with each other and their physical environment for survival. All ecosystems include living things; oxygen and carbon dioxide from the atmosphere; water; and energy from the sun.

The seasonal flooding during the rainy season in the Pantanal is caused by heavy precipitation that causes rivers to overflow their banks. This flooding carries with it many nutrients. These nutrients allow many different kinds of organisms to flourish in the wetlands ecosystem.

Because of their nutrients, wetlands have been called “biological supermarkets.” For example, the Pantanal is home to the most wildlife in all of South America. There are 3,500 different kinds of plants, 656 kinds of birds, 325 kinds of fish, 159 kinds of mammals, 53 kinds of amphibians, and 98 kinds of reptiles.

The Pantanal Food Web

Different wetlands are home to different kinds of organisms. For example, the kinds of organisms in an Arctic wetlands ecosystem are unlike the organisms in the Pantanal because the climate is so much colder in the Arctic.

However, no matter where they live, all organisms need energy and nutrients to survive, grow, and reproduce. Without energy, living things cannot survive. The path that energy travels as one organism eats another is called a food chain. A food web is a visual that shows the network of food chains. It shows the complex set of relationships between organisms that are linked by the flow of energy.

Energy Begins with the Sun

All energy on Earth begins with the sun. As the sun shines, it produces light energy. When the light energy reaches a plant, the plant captures the energy and turns it into food. Plants are living things that capture energy from sunlight for growth and development.

Plants can do this because they are producers. Producers are organisms that capture energy from sunlight through a process called photosynthesis [foh-toh-sin-thuh-sis]. Plants are able to do photosynthesis because they have internal structures in their leaves that collect the sun’s energy. These internal structures are called chloroplasts [klawr-uh-plasts].

After chloroplasts collect the sun’s energy, they turn that energy, along with water and carbon dioxide, into oxygen and a sugar called glucose. Glucose is food for the plant. Glucose contains chemical energy. It gives the plant energy to grow. Plants store extra glucose in their leaves and other parts.

In this lesson, students develop a model of a tropical wetlands food web that shows the relationships among the living parts of an ecosystem: producers, consumers, and decomposers.

Students identify the evidence from their model food webs that supports the idea that all energy begins with the sun, and it must move through producers before consumers and decomposers can access that energy to grow and develop.