What is the Nutrient Cycle? - Definition & Steps Video

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  • 0:03 What Are Nutrient Cycles?
  • 0:41 Carbon Cycle
  • 1:32 Oxygen & Water Cycles
  • 2:38 Nitrogen Cycle
  • 3:48 Phosphorus & Sulfur Cycles
  • 5:42 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
In this lesson, we'll be exploring types of nutrient cycles. First we'll review what nutrient cycles are and why they are important. Then, we'll look at the details of carbon, oxygen, water, nitrogen, phosphorus and sulfur cycles.

What Are Nutrient Cycles?

Every living thing needs nutrients, right? They give our bodies energy and help our cells function. However, you might be surprised to learn that nutrients aren't just in living things. Nutrients move between living things, into the Earth, and into the atmosphere. This process is called a nutrient cycle. Things we need to survive like carbon-containing compounds such as sugar, micronutrients like nitrogen, phosphorus, and sulfur, and water, move through living things and our environment. Today we're going to look at the nutrient cycle for each of these important compounds.

Carbon Cycle

One of the most important scientific issues currently is the carbon cycle. You probably have heard of global warming or climate change in the news. This increase in global temperature is due to changes in the carbon cycle. The carbon cycle moves carbon between living things, the Earth, and the atmosphere. Trees take in carbon dioxide to grow and form new structures. Animals eat plants and assimilate the carbon. When living things decay, the carbon cycles back into the Earth and oceans. Eventually the carbon is compressed by geological activity and forms reservoirs of fossil fuels, such as coal.

The carbon cycle
carbon cycle

One of the main problems today is that humans are digging up fossil fuels faster than they're being replaced. When we burn them to generate energy, we release carbon dioxide into the atmosphere, which is causing global warming.

Oxygen and Water Cycles

Plants and animals both play a role in cycling oxygen through the atmosphere. As you know, oxygen is crucial for many animals, including humans. We breathe in oxygen, and our bodies use it to make energy during a process called cellular respiration. This process releases carbon dioxide as a waste product, which is what we breathe out. Plants take in carbon dioxide during photosynthesis, in which they make food and oxygen. The oxygen is released, and the cycle starts again.

The most important criteria for life is water. Like the carbon cycle, the water cycle is the process of moving water between living things, the Earth, and the atmosphere. Water evaporates from bodies of water on Earth, like lakes, rivers, and oceans. The water vapor condenses in the clouds and forms precipitation that returns water to Earth. On Earth, some of the water returns to the lakes and oceans it originated from, and some soaks into the ground, forming groundwater. Living organisms, like plants and animals, consume water. The water evaporates again, continuing the cycle.

The water cycle creates precipitation
water cycle

Nitrogen Cycle

Although we don't hear as much about nitrogen, it's a very important part of living things. Nitrogen is needed to build our proteins that form body structures, such as muscles. Nitrogen atoms are even used to make our DNA, the blueprints for all living things. Although our air is mostly made of nitrogen gas, it's not a form living things can use. Bacteria in the soil help convert nitrogen into usable forms for living things, called nitrification. Soil bacteria first convert atmospheric nitrogen to ammonium, the same chemical you might find in some of your cleaning products. Other bacteria convert the ammonium to nitrites and finally nitrates, which can be taken up by the roots of plants. Animals consume the plants to get nitrogen. Unfortunately, like the carbon cycle, humans are disrupting the nitrogen cycle.

Since plants need nitrogen to grow, farmers often apply fertilizers rich in nitrogen to their crops. Nitrogen runs off into local streams and lakes, causing problems in their ecosystems. Any time humans add a nutrient in excess, or take away a nutrient from the cycle, ecological problems occur.

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