Energy and Matter Cycles Study Guide

1.2 Energy and Matter Cycles (Bio.1.2)

Explore this Phenomenon

Each of the ecosystems pictured looks quite different, but they all have some things in common.

1. Use the pictures to identify patterns in ecosystems. What are some things that all of the ecosystems have in common?
2. What questions could you investigate to understand what causes the patterns we see across ecosystems?
3. Explain some of the patterns you identified. For example, why do ecosystems tend to have more plants than animals?

Bio.1.2 Energy and Matter Cycles

Develop and use a model to explain cycling of matter and flow of energy among organisms in an ecosystem. Emphasize the movement of matter and energy through the different living organisms in an ecosystem. Examples of models could include food chains, food webs, energy pyramids or pyramids of biomass. (LS2.B)

As you read this chapter, pay attention to the way that matter and energy move through the ecosystem. Look for similarities and differences in the way that matter and energy move through the biotic factors in the ecosystem.

Energy Flows Through Ecosystems

Where do these flowers get the energy they need to grow and reproduce?

The Sun supports most of Earth's ecosystems. Plants create chemical energy from abiotic factors that include solar energy. The food energy created by producers is passed through the food chain.

How Energy Flows Through Ecosystems

All living things need energy. They need it to power the processes of life. For example, it takes  energy to grow. It also takes energy to produce offspring. In fact, it takes energy just to stay alive. Remember that energy can’t be created or destroyed. It can only change form. Energy changes form as it moves through ecosystems.

Most ecosystems get their energy from the Sun. Only producers can use sunlight to make usable energy. Producers are organisms like plants and algae that can convert the sunlight into chemical energy or food. Producers form the base of all food chains. Consumers get some of that energy when they eat producers. They also pass some of the energy on to other consumers when they are eaten. In this way, energy flows from one living thing to another.

Food Chains

A food chain is a simple diagram that shows the path energy takes as it flows from one part of an ecosystem to the next. Pictured below is an example of a food chain. In this example, the grass and flower are the producers that convert light energy from the sun into chemical energy. The snail gets energy from the plants. The small bird gets energy from eating the snail, and the large bird gets energy when it eats the small bird.

At each level of a food chain, a lot of energy is lost. Only about ten percent of the energy passes to the next level. Where does that energy go? Some energy is given off as heat. Some energy goes into animal wastes. Energy also goes into growing things that another consumer can't eat, like fur. It's because so much energy is lost that most food chains have just a few levels. There’s not enough energy left for higher levels.

Watch this video on food chains:

https://www.youtube.com/watch?v=5Z8rKhXUYAg

Food Webs

Food chains are too simple to represent the real world. They don’t show all the ways that energy flows through an ecosystem. A more complex diagram is called a food web. Food webs more accurately represent the flow of energy through the ecosystem.

A food web consists of many overlapping food chains. Can you identify the food chains in the figure? How many food chains include the mouse? Food webs also overlap. For example, an eagle is part of a land food web, but it might go to the sea to catch and eat a fish. That fish is part of a marine food web.

Matter Cycles Through Ecosystems

What happens when you don't get enough of a nutrient?

Millions of sailors in the 15th through 18th centuries died mysteriously. They developed a disease called scurvy. The scurvy, it turns out, was due to the lack of vitamin C in their diets. It wasn't until 1932 that the link between scurvy and vitamin C was made. Without the right types and amounts of matter, or nutrients, you can get sick or even die. Other animals and plants also need the right nutrients to live. Where does the matter organisms need to survive come from?

How Matter Moves Through Ecosystems

Living things need matter as well as energy. What do you think matter is used for? It's used to build bodies. It's also needed to carry out the processes of life. Matter that living things need are called nutrients. Carbon and nitrogen are examples of nutrients. Unlike energy, matter is recycled in ecosystems. For example, decomposers break down dead organisms, and release the matter in the organisms. The matter is then taken up by plants through their roots. When an animal eats the plant, the matter passes to the animal. When living things die, the matter that makes up their bodies is released by decomposers, and they cycling of matter starts over.

Can you explain how the movement of matter and energy through ecosystems is the same? How is the movement of matter and energy different? Use the model below to compare and contrast the movement of energy and matter in ecosystems.

Energy and Biomass Pyramids

The way that matter and energy move through ecosystems affects the structure of the system. Each step of the food chain is called a trophic level. Most of the energy at one trophic level is lost and not available to the organisms in the next trophic level. How will the decreasing amount of available energy affect the amount of matter at each level of the food chain?

Because there is less energy at higher trophic levels, there are usually fewer organisms as well. Organisms tend to be larger in size at higher trophic levels, but their smaller numbers still result in less biomass. Biomass is the total mass of organisms in a trophic level (or other grouping of organisms). The ecological pyramid shows how the available energy and amount of biomass changes from first to higher trophic levels in a food chain.

Ecological Pyramid. This pyramid shows how energy and biomass decrease from lower to higher trophic levels. Assume that producers in this pyramid have 1,000,000 kilocalories of energy. How much energy is available to primary consumers?

Only about 10% of the energy available at one trophic level will be passed up to the next trophic level. If the producers in the ecological pyramid have 1,000,000 kilocalories of energy, how much energy will be available to the primary consumers?

The materials in dead organisms and wastes at all trophic levels are broken down by decomposers. Organisms such as detritivores and saprotrophs return needed elements to the ecosystem and use up most remaining energy. Because of the reduction in energy at each trophic level, virtually no energy remains. Therefore, energy must be continuously added to ecosystems by producers.

Putting It Together

Each of the ecosystems pictured looks quite different, but they all have some things in common.

1. Use the pictures to identify patterns in ecosystems. What new patterns can you identify now that you know about the way energy and matter move through ecosystems?
2. Use what you learned about the movement of matter and energy to explain the patterns you identified. Try creating a model that can explain the patterns.