Chapter 5, lesson 2

How is Energy Passed through an Ecosystem?

Pg. 160, Energy Transfer

What is an ecosystem?

All living and nonliving things interacting in an area make up an ecosystem.

How do living things interact with one another in an ecosystem?

They may eat one another, compete for space, or share homes.

Give examples of how living and nonliving things interact in an environment.

Living things drink water, breathe air, and make homes. Weather, soil, and pollution affect living things. Plants anchor the soil and keep it from blowing away.

Pg. 161

Look at the pictures on pages 160 and 161 to respond to the following questions.

How does the moss make energy?

It converts and stores energy through photosynthesis.

Do the caribou and wolf make their own energy? How do they acquire energy?

Animals can’t make their own energy, so they get it by eating plants or plant-eating animals.

What do consumers and decomposers have in common?

They must acquire energy from other organisms.

How are nutrients returned to the ecosystem?

Decomposers break down the moss, caribou, and wolf when they die.

Many trees drop their leaves in the fall. How does this action fit into a food chain?

Trees are producers. Decomposers break down fallen leaves to extract energy and return nutrients to the soil.

What can happen next to food energy taken in by a second-level consumer?

It can be transferred to a third-level consumer or be broken down by decomposers.

Pg. 162, Food Webs

What non-living parts of the environment affect the plants, animals, and decomposers you see in the picture on pg. 162?

Sunlight, rain (or drought), wind, or soil conditions all affect the environment.

Humans live on the prairie, too. Where do they fit into the food web?

Native Americans and early settlers on the prairie survived on naturally available foods such as squirrels, snakes, and bison. Today, humans get their energy from the cattle that feed on the grasses and also grain crops, such as wheat.

Pg. 163

Humans are part of the pond food web, too. Where do they fit into the pond food web?

Humans take food such as fish and ducks from the pond. Humans may also affect the ecosystem by adding new species or pollution that impacts the ecosystem. They may also disturb habitats where plants grow or animals make their homes.

If all the mosquitoes in a pond died, what might happen next?

The carnivores that feed on mosquitoes would starve or eat more of another kind of food. Either change would upset the balance of the food web.

How do carnivores help keep an ecosystem in balance?

Higher-level consumers help control the sizes of populations at lower levels of the food web. Without them, demand on an ecosystem’s resources – energy, space, and materials – could be too great.

Pg. 164, Energy Pyramid

It is possible, but rare, for an animal to be a fourth level consumer. Why?

There is very little energy remaining for a fourth level of a food chain.

What percent of the energy they make do producers pass on to first level consumers?

Producers use about 90% of the energy they make to survive. They store and pass on about 10% of the energy to the first level consumers that eat them.

What percent of their energy do first-level consumers pass on to second-level consumers?

About 10% of energy is passed on at each level.

Suppose the grasses at the base the energy pyramid pictured on pg. 164 produce 100,000 kilocalories of energy. How many kilocalories would be passed to each of the other levels?

The plant would pass 10,000 kilocalories to the locusts. The locusts would pass 1,000 kilocalories to the snakes. The snakes would pass 100 kilocalories to the owl.

Pg. 165

What can happen to a food chain if the number of second-level consumers increases?

The second-level consumers may eat more of the first-level consumers, wiping them out. Eventually, the second-level consumers starve because there are not enough first-level consumers for them to eat.

Pg. 166, Natural Cycles

What nonliving materials are important to living things?

Water, nitrogen, oxygen, and carbon are important to all living things.

How does the movement of energy through an ecosystem differ from the movement of materials?

Energy is used for life processes and is lost to the system, so the sun must continually provide a new source of energy. Materials and nutrients are recycled and used repeatedly.

What would happen in an ecosystem if decomposers didn’t break down wastes?

Materials, such as nitrogen, would get locked up in wastes and not be able to support new life. Living things and their ecosystems would die out.

What part do decomposers play in the nitrogen cycle?

Decomposers release nitrogen back into the soil.