Energy and Matter in Food Webs

Once students understand how plants capture energy and nutrients from the environment, they focus on how that energy and matter move through a food web. Specifically, in this lesson, they model the flow of energy and the cycling of matter between the environment and organisms in a temperate forest ecosystem.

• An ecosystem is a community of different organisms that depend on interacting with each other and their physical environment for survival. 
• All ecosystems are made up of different living things, as well as air, water, sunlight, and Earth materials (rocks, soil, etc.). 
• All ecosystems depend on the sun for energy.  
• Matter is constantly cycling between the living and nonliving parts of an ecosystem.
• Animals are consumers because they eat other living things. When animals eat plants, they absorb some of the energy from the plant.
• Animals breathe in oxygen and breathe out carbon dioxide. Plants take in carbon dioxide and release oxygen. This exchange of oxygen is called the oxygen cycle.
• When organisms eat one another, nutrients that are stored get passed along. When decomposers eat the remains of other living things, they break down the nutrients and return them to the soil. Plants access those nutrients, and the cycle begins again.
  
  

• How do ecosystems provide evidence that all of Earth’s systems are connected to one another?
• Why are nonliving parts important in an ecosystem?
• Why is the sun important for all life?
• Why do all ecosystems need producers?
• How can animals get energy since they can’t directly access energy from the sun?
• What is the relationship between primary, secondary, tertiary consumers?
• What happens to the energy when plants and animals die?
• How is energy different from nutrients?
• How can oxygen and carbon dioxide cycle through an ecosystem?
• How do other nutrients cycle through a food chain?
  
  

Misconception: An organism is not a system.

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

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

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

Consumer : an organism that eats other organisms

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

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

Function :  the normal action of something or how something works

Inorganic :  anything that is not living and never was living (e.g., water and rocks)

Organic :  anything that is living or was once living (e.g., fallen leaves and animal remains)

Organism :  a complete living thing

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

Structure :  the way in which parts are put together to form a whole

Energy Moves Through Ecosystems

The need for energy also connects all living things in an ecosystem. When plants capture the sun’s energy and turn it into chemical energy stored in glucose through photosynthesis, they are performing an important function. That energy will get passed between organisms as they eat one another. The path that energy travels as one organism eats another is called a food chain.

Food chains always begin with energy from the sun and then move to plants and other producers. Producers are organisms that capture energy from sunlight through photosynthesis. When organisms eat one another, some of that energy that started with the sun gets passed along.

Eating for Energy

When squirrels eat nuts, they get some of the tree’s energy. Squirrels are consumers because they must eat other organisms for energy and nutrients. All animals are consumers. Food also gives animals the materials they need for body repair and growth. For example, when animals eat plants, they absorb some of the plants’ glucose. They also absorb some of the carbon atoms that the plant had stored for its growth and development.

There are different kinds of consumers, depending on what an organism eats. Any animal that eats producers is called a primary consumer. Butterflies are primary consumers that eat the nectar of plants. Primary consumers are also called herbivores.

Carnivores eat only other animals. Coyotes are common carnivores that eat many different kinds of animals. Coyotes eat deer, sheep, rabbits, rodents (like squirrels), snakes, and fish.

Other animals eat both plants and animals. These are called omnivores. Squirrels are omnivores. They eat nuts, fruits, and seeds, which are all plants. They also eat insects and caterpillars, which are other animals.

Any organism that eats primary consumers is called a secondary consumer. Any organism that eats a secondary consumer is called a tertiary consumer. Omnivores and carnivores can be either secondary or tertiary consumers, depending on what they eat.

When animals and plants die, living things called decomposers will eat their remains. Decomposers are organisms that break down organic material and feed on the nutrients. They put nutrients (matter) back into the ground. Plants will then use those nutrients to grow. Bacteria, worms, and fungi are common decomposers in a food web.

As energy flows from the sun to producers and then to consumers and decomposers, it always moves in one direction. A food web is a visual that shows the network of food chains in an ecosystem. It shows the complex set of relationships between organisms that are linked by the flow of energy. Because energy flows in one direction, life requires a constant supply of energy from the sun.

Matter Cycles Through Ecosystems

In contrast to energy, matter is always cycling through ecosystems. Most of the matter that is on Earth today has been around since the planet first formed. Matter is transferred and recycled at every level of a food web. All organisms need to take in new matter to keep their cells healthy and functioning. The nutrients an organism takes in help the organism grow, develop, and reproduce.

Water is also cycled throughout an ecosystem. Plants absorb water through their roots. They release some of that water back to the environment through transpiration. Animals drink water, and then release some of the water back into the environment as part of their waste.

In this lesson, students develop models to figure out and analyze how the phenomena of drought conditions affect the flow of energy and cycling of matter in a temperate forest ecosystem. Students investigate how prolonged drought could affect a forest ecosystem over time, using their models to support their claims about how the effects of a drought are related to the flow of energy from the sun to plants and then to animals, and that matter moves between plants, animals, decomposers, and the environment. Students use information from their models to communicate their analysis about how energy and matter connect the different parts in all ecosystems, and how a change to one part of an ecosystem (resulting from a drought) will impact the entire ecosystem.