Cycling of Matter

Cycling of Matter

Middle School

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Learning Objectives

• Describe the law of conservation of mass.

• Define the roles of producers, consumers, and decomposers in an ecosystem.

• Explain how food webs model the transfer of matter and flow of energy.

• Explain how carbon, water, nitrogen, and oxygen cycle through ecosystems.

• Analyze the relationship between the carbon and oxygen cycles.

Key Vocabulary

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Matter

Matter is anything that has mass and takes up space in the universe.

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Conservation of Mass

This law states that matter is never created or destroyed, but only changes its form.

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Ecosystem

An ecosystem is a biological community of interacting organisms and their physical environment.

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Producer

A producer is an organism that creates its own food from simple non-living matter.

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Consumer

A consumer is an organism that gets its energy and matter by eating other living things.

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Decomposer

A decomposer is an organism that breaks down dead organic material, returning nutrients to the soil.

Key Vocabulary

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Food Web

A food web is a model that clearly shows how matter and energy are transferred within an ecosystem.

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Carbon Cycle

The carbon cycle describes the continuous movement of carbon atoms through the Earth's different systems, like the atmosphere.

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Water Cycle

The water cycle illustrates the constant movement of water on, above, and even below the Earth's surface.

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Nitrogen Cycle

The nitrogen cycle is the natural process by which essential nitrogen is converted and moved through the environment.

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Oxygen Cycle

The oxygen cycle details the important movement of oxygen through the atmosphere, living things, and the Earth's crust.

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Nitrogen Fixation

Nitrogen fixation is the essential process of changing atmospheric nitrogen gas into a form that plants can use.

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What Is Matter Cycling?

• Unlike energy that flows one way, matter is reused in cycles.

• ​Matter changes form but is never created or destroyed.

• This is known as the law of conservation of mass.

• Atoms cycle between living and nonliving parts of an ecosystem.

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Multiple Choice

What does the law of conservation of mass state?

• Matter flows in one direction through an ecosystem.

• Matter is not created or destroyed, it only changes form.

• Living things create the new matter they need to survive.

• Matter can only cycle between the living parts of an ecosystem.

Multiple Choice

How is the movement of matter in an ecosystem different from the flow of energy?

• Matter flows in one direction, while energy is cycled and reused.

• Matter is cycled and reused, while energy flows in one direction.

• Both matter and energy are destroyed as they move through an ecosystem.

• Energy is used by living things, but matter is only found in nonliving things.

Multiple Choice

When a tree dies and decomposes in a forest, what is the most likely fate of the atoms that made up the tree?

• The atoms are destroyed as the log breaks down.

• The atoms are converted into energy for other organisms.

• The atoms are returned to the environment to be used by other organisms.

• The atoms are permanently locked in the soil and cannot be used again.

Roles in an Ecosystem

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Producers

• Organisms like plants that are able to produce their own food.

• They use the sun's energy to convert nonliving matter into food.

• For example, they use carbon dioxide, water, and other minerals.

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Consumers

• Organisms like animals that get their energy by eating other organisms.

• A rabbit eats grass, and then a fox might eat the rabbit.

• This is how energy is transferred through the food chain.

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Decomposers

• Organisms like bacteria and fungi break down dead plant and animal matter.

• This process helps them to get the energy they need to live.

• It also recycles nutrients back into the soil for producers to use.

Multiple Choice

What is the primary characteristic used to classify organisms as producers, consumers, or decomposers?

• By how they get energy for survival.

• By the type of environment they live in.

• By whether they are a plant or an animal.

• By the size of their population.

Multiple Choice

What is the relationship between decomposers and producers in an ecosystem?

• Decomposers recycle nutrients from dead organisms that producers then use.

• Producers convert sunlight into food, which decomposers eat directly.

• Decomposers protect producers from being eaten by consumers.

• Producers and decomposers compete for the same food source.

Multiple Choice

Based on the roles described, what would be the most likely long-term consequence if decomposers were removed from an ecosystem?

• Nutrients would not be recycled into the soil, limiting plant growth.

• Consumers would have an unlimited food supply.

• Producers would create food more efficiently.

• Energy would be transferred directly from consumers to producers.

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Modeling Matter and Energy in Food Webs

• Food webs model how energy and matter move through an ecosystem.

• When one organism is eaten, its atoms are transferred to the other.

• This matter cycles between organisms and the physical environment at every level.

• Decomposers return atoms to the soil and air, completing the cycle.

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Multiple Choice

What is the main purpose of a food web model?

• To show how energy and matter move through an ecosystem

• To list all the animals that live in a habitat

• To explain how decomposers create new energy

• To show how individual organisms grow and reproduce

Multiple Choice

What is the specific role of decomposers in the cycling of matter?

• They create new matter for producers to use.

• They transfer energy directly from the sun to consumers.

• They return atoms from dead organisms back to the soil and air.

• They are the main source of food for all other organisms.

Multiple Choice

What would most likely happen to the atoms in an ecosystem if all the decomposers were suddenly removed?

• The atoms would be transferred to producers more quickly.

• The atoms would be destroyed and disappear from the ecosystem.

• The atoms would be converted directly into energy for other animals.

• The atoms would be trapped in dead organisms and not returned to the environment.

The Carbon Cycle

• Plants take in carbon dioxide (CO₂) from the atmosphere during photosynthesis.

• Animals consume plants and other organisms to obtain carbon.

• Carbon returns to the environment through respiration, decomposition, and burning fossil fuels.

Multiple Choice

How do plants first get the carbon they need to live?

• By absorbing it through their roots from the soil

• By taking in carbon dioxide from the atmosphere

• By drinking water that contains carbon

• By breaking down other dead organisms

Multiple Choice

What is the primary way carbon moves from plants to animals in the carbon cycle?

• Animals create their own carbon through respiration.

• Carbon is transferred from plants to the animals that eat them.

• Plants release carbon for animals to breathe in.

• Animals absorb carbon directly from the atmosphere.

Multiple Choice

If a large forest fire burned down most of the trees in an area, what would be the most likely immediate effect on the carbon cycle?

• Atmospheric carbon dioxide would decrease because animals would have less to eat.

• Atmospheric carbon dioxide would increase because less would be removed by plants.

• The amount of carbon would stay the same due to decomposition.

• Animals would start getting their carbon from the air instead.

The Water Cycle

• Evaporation turns liquid water into a gas called water vapor.

• Condensation changes water vapor back into liquid, forming clouds.

• Precipitation is water, like rain or snow, falling from clouds.

Multiple Choice

What is the process by which liquid water turns into a gas called water vapor?

• Evaporation

• Condensation

• Precipitation

• Collection

Multiple Choice

What happens to water vapor during the process of condensation?

• It changes from a gas back to a liquid.

• It changes from a liquid to a solid.

• It falls from clouds as rain or snow.

• It is absorbed by plants.

Multiple Choice

A puddle on a sunny sidewalk disappears, and later that day, clouds form and it rains. What is the correct sequence of events that occurred?

• Evaporation, followed by condensation, then precipitation.

• Condensation, followed by precipitation, then evaporation.

• Precipitation, followed by evaporation, then condensation.

• Evaporation, followed by precipitation, then condensation.

The Nitrogen Cycle

• All living organisms need nitrogen to make proteins for survival.

• Bacteria in the soil convert nitrogen gas into a usable form for plants.

• Nitrogen moves from plants to animals and is returned to the soil by decomposers.

Multiple Choice

What is the primary reason all living organisms require nitrogen?

• To make the proteins they need to survive

• To provide them with energy for daily activities

• To help them absorb water from the soil

• To protect them from diseases in the environment

Multiple Choice

What is the specific function of bacteria in making nitrogen available to an ecosystem?

• They convert nitrogen gas into a form that plants can absorb.

• They transfer nitrogen directly from animals to other animals.

• They help plants release nitrogen gas into the air.

• They break down proteins to create oxygen for the soil.

Multiple Choice

If all decomposers were removed from an ecosystem, what would be the most likely consequence for the nitrogen cycle?

• The nitrogen from dead plants and animals would not be returned to the soil.

• Bacteria would no longer be able to convert nitrogen gas for plants.

• Animals would stop receiving nitrogen from eating plants.

• Plants would start absorbing nitrogen directly from the air.

The Oxygen Cycle and Its Connection to Carbon

• Photosynthesis is the main source of Earth's oxygen.

• Living things take in oxygen for cellular respiration to get energy.

• They release carbon dioxide, which links to the carbon cycle.

Multiple Choice

What is the main process that creates the oxygen found in Earth's atmosphere?

• Photosynthesis

• Cellular respiration

• Water evaporation

• Volcanic eruptions

Multiple Choice

What is the relationship between oxygen and energy for living things?

• Living things use oxygen during cellular respiration to get energy.

• Living things convert energy directly into oxygen.

• Energy is required for living things to breathe in oxygen.

• Oxygen and energy are both produced during photosynthesis.

Multiple Choice

How does the process of cellular respiration in living things provide a link between the oxygen and carbon cycles?

• It uses oxygen and releases carbon dioxide.

• It uses carbon dioxide and releases oxygen.

• It uses both oxygen and carbon dioxide.

• It releases both oxygen and carbon dioxide.

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A Closer Look: The Greenhouse Effect

• The greenhouse effect is a natural process that warms the Earth for life.

• ​Greenhouse gases absorb the Sun's energy, preventing it from escaping back into space.

• Burning fossil fuels increases gases like carbon dioxide (CO₂) in the atmosphere.

• This increase in greenhouse gases traps more heat and warms the planet further.

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Multiple Choice

What is the primary role of the natural greenhouse effect?

• It is a natural process that warms the Earth, making it suitable for life.

• It is a process that cools the Earth by reflecting sunlight.

• It is a cycle that creates clouds in the atmosphere.

• It is a process that only occurs over the Earth's oceans.

Multiple Choice

What is the relationship between burning fossil fuels and the Earth's temperature?

• Burning fossil fuels releases more greenhouse gases, which trap more heat.

• Burning fossil fuels absorbs greenhouse gases, which cools the planet.

• Burning fossil fuels creates a layer that reflects the Sun's energy.

• Burning fossil fuels has no significant effect on the atmosphere.

Multiple Choice

Based on the process described, what would be the most likely outcome if humans significantly reduced the burning of fossil fuels?

• The rate of planetary warming would decrease because less heat would be trapped.

• The planet would cool down immediately to its original temperature.

• The amount of greenhouse gases in the atmosphere would not change.

• The Earth would stop being warmed by the Sun's energy altogether.

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Common Misconceptions

Misconception	Correction
Energy is cycled in an ecosystem.	Energy flows through an ecosystem, while matter is what gets cycled.
Matter is destroyed during decomposition.	Matter only changes form; it is conserved and not destroyed.
Plants get their food from the soil.	Plants get mass from carbon dioxide (CO2) in the air.
The greenhouse effect is entirely bad.	The greenhouse effect is a natural process that keeps Earth warm.

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Summary

• Matter cycles through ecosystems, while energy flows in one direction.

• Producers make food, consumers eat organisms, and decomposers recycle nutrients.

• Food webs model how matter is conserved and cycles through an ecosystem.

• Photosynthesis, respiration, and nitrogen fixation are key processes in nutrient cycles.

Poll

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