SC15.6.7

Science (2015) Grade(s): 6

SC15.6.7
Use models to construct explanations of the various biogeochemical cycles of Earth (e.g., water, carbon, nitrogen) and the flow of energy that drives these processes.

Unpacked Content

Scientific and Engineering Practices

Developing and Using Models

Crosscutting Concepts

Stability and Change

Knowledge

Students:

The cycle of atoms between living and non-living things is known as a biogeochemical cycle.
Biogeochemical cycles interact through biotic and abiotic processes.
Biotic involves living or once living things such as plants, animals, and bacteria.
Abiotic involves nonliving things like air, rocks, and water.
Biogeochemical cycles may include, but are not limited to, the water, carbon, and nitrogen cycles.
The water cycle is the continuous process by which water is circulated throughout the earth and the atmosphere.
Water is a chemical compound made up of the elements hydrogen and oxygen.
Global movements of water and its changes in form are propelled by sunlight and gravity.
Energy from the sun drives the movement of water from the Earth (e.g., oceans, landforms, plants) into the atmosphere through transpiration and evaporation.
Water vapor in the atmosphere can cool and condense to form rain or crystallize to form snow or ice, which returns to Earth when pulled down by gravity.
Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land.
Gravity causes water on land to move downhill (e.g., rivers and glaciers) and much of it eventually flows into oceans.
Some liquid and solid water remains on land in the form of bodies of water, glaciers and ice sheets or can be stored below ground in aquifers.
Some water remains in the tissues of plants and other living organisms, and this water is released when the tissues decompose. Water is also released by plants through transpiration and by other living organisms through respiration.
Carbon is an element found in the oceans, air, rocks, soil and all living organisms.
Carbon is the fundamental building block of life and an important component of many chemical processes.
In a process called the carbon cycle, carbon is exchanged among Earth's oceans, atmosphere, ecosystem, and geosphere.
Carbon is present in the atmosphere primarily attached to oxygen in a gas called carbon dioxide (CO2), but is also found in other less abundant but climatically significant gases, such as methane (CH4).
With the help of the Sun, through the process of photosynthesis, carbon dioxide is pulled from the air to make plant food.
Through food chains, the carbon that is in plants moves to the animals that eat them. When an animal eats another animal, the carbon is transferred.
When plants and animals die, their bodies, wood, and leaves decay bringing the carbon into the ground. Some become buried miles underground and will become fossil fuels in millions and millions of years.
Organisms release carbon dioxide gas through a process called respiration.
When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas.
The oceans, and other bodies of water, soak up some carbon from the atmosphere.
Nitrogen is an element found in living things like plants and animals.
Nitrogen is also an important part of non-living things like the air and the soil.
Nitrogen atoms move slowly between living things, dead things, the air, soil and water.
The continuous process by which nitrogen is exchanged between organisms and the environment is called the nitrogen cycle.
Most of the nitrogen on Earth is in the atmosphere as molecules of nitrogen gas (N2).
All plants and animals need nitrogen to make amino acids, proteins, and DNA, but the nitrogen in the atmosphere is not in a form that they can use.
The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes or fires, by certain types of bacteria, or by bacteria associated with bean plants.
Most plants get the nitrogen they need to grow from the soils or water in which they live. Animals get the nitrogen they need by eating plants or other animals that contain nitrogen.
When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water. Bacteria alter the nitrogen into a form that plants are able to use. Other types of bacteria are able to change nitrogen dissolved in waterways into a form that allows it to return to the atmosphere.
Certain actions of humans can cause changes to the nitrogen cycle and the amount of nitrogen that is stored in the land, water, air, and organisms.
The use of nitrogen-rich fertilizers can add too much nitrogen in nearby waterways as the fertilizer washes into streams and ponds. The waste associated with livestock farming also adds large amounts of nitrogen into soil and water. The increased nitrate levels cause plants to grow rapidly until they use up the supply and die. The number of plant-eating animals will increase when the plant supply increases and then the animals are left without any food when the plants die.

Skills

Students are able to:

Use a model of the various biogeochemical cycles and identify the relevant components.
Describe the relationships between components of the model including the flow of energy.
Articulate a statement that relates a given phenomenon to a scientific idea, including the various biogeochemical cycles of Earth and the flow of energy that drives these processes.