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Unlock This CourseLife on Earth depends on the constant recycling of nutrients. When organisms die, their bodies don't just disappear - they're broken down and their nutrients are returned to the environment. This process, called decomposition, is essential for keeping ecosystems healthy and productive. At the same time, combustion (burning) also plays a role in how nutrients move around our planet.
Key Definitions:
When a leaf falls from a tree or an animal dies, decomposer organisms immediately get to work. Bacteria and fungi secrete enzymes that break down complex organic molecules into simpler compounds. This process releases nutrients like nitrogen, phosphorus and carbon back into the soil and atmosphere, where they can be used by living plants and animals again.
Carbon is one of the most important elements for life. It forms the backbone of all organic molecules, from the proteins in your muscles to the cellulose in plant cell walls. The carbon cycle shows how this vital element moves between the atmosphere, living organisms and the Earth's surface.
Carbon dioxide in the atmosphere is absorbed by plants during photosynthesis. Plants use this carbon to build glucose and other organic compounds. When animals eat plants, the carbon becomes part of their bodies. Eventually, when organisms die, decomposers break down their remains, releasing carbon dioxide back into the atmosphere.
Plants absorb CO₂ from the atmosphere and convert it into glucose using sunlight energy. This removes carbon from the air and stores it in plant tissues.
All living organisms release CO₂ when they break down glucose for energy. This returns carbon to the atmosphere.
When organisms die, decomposers break down their remains, releasing stored carbon as CO₂ back into the atmosphere.
In a healthy forest, the carbon cycle is perfectly balanced. Trees absorb massive amounts of CO₂ during photosynthesis, storing carbon in their wood, leaves and roots. When leaves fall and trees die, decomposers slowly break them down, releasing CO₂ back to the atmosphere over several years. This creates a natural carbon storage system that helps regulate Earth's climate.
Nitrogen makes up about 78% of our atmosphere, but most organisms can't use it in this form. The nitrogen cycle shows how this essential element is converted into forms that plants and animals can actually use to build proteins and DNA.
Special bacteria in soil and plant roots can convert atmospheric nitrogen into ammonia and nitrates - forms that plants can absorb through their roots. When organisms die, decomposers break down their proteins, releasing nitrogen compounds back into the soil where they can be used again.
Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃). Some of these bacteria live in special root nodules on legume plants like peas and beans, creating a mutually beneficial relationship.
Plants absorb nitrogen compounds from soil through their roots. They use this nitrogen to make amino acids, which are then assembled into proteins needed for growth and development.
Combustion - the process of burning - has a significant impact on nutrient cycles. When organic matter burns, it rapidly releases stored carbon, nitrogen and other elements into the atmosphere, often much faster than natural decomposition would.
Forest fires are a natural part of many ecosystems, quickly releasing nutrients stored in dead wood and leaf litter. However, human activities like burning fossil fuels and clearing forests for agriculture have dramatically increased the amount of combustion happening worldwide.
Natural fires clear dead material and release nutrients quickly. Many plants have adapted to benefit from periodic fires, which help their seeds germinate.
Burning coal, oil and gas releases carbon that was stored underground for millions of years, adding extra CO₂ to the atmosphere.
Farmers sometimes burn crop residues, which quickly releases nutrients but can also contribute to air pollution and soil degradation.
The Amazon rainforest demonstrates both natural decomposition and human-caused combustion. In undisturbed areas, fallen trees and leaves decompose slowly, keeping carbon stored in the forest ecosystem. However, when areas are cleared and burned for agriculture, decades of stored carbon are released into the atmosphere in just a few hours, contributing to climate change.
Human activities have significantly altered natural nutrient cycles. We've increased the rate of combustion through fossil fuel use, changed decomposition patterns through land use changes and added artificial fertilisers that affect nitrogen cycling.
When we burn fossil fuels, we're adding carbon to the atmosphere that was locked away for millions of years. When we use nitrogen fertilisers, we're adding extra nitrogen to ecosystems that can cause problems like water pollution and algal blooms.
Excess CO₂ from combustion is causing global warming. This affects decomposition rates - warmer temperatures speed up bacterial activity, potentially releasing even more stored carbon from soils.
Excess nitrogen from fertilisers can wash into rivers and lakes, causing eutrophication - explosive algae growth that uses up oxygen and kills fish.
Understanding nutrient cycles helps us make better decisions about how we manage ecosystems. By working with natural processes rather than against them, we can maintain healthy environments that continue to provide the services we depend on.
Composting organic waste mimics natural decomposition, returning nutrients to soil. Reducing fossil fuel use decreases excess carbon emissions. Protecting forests maintains natural carbon storage and cycling systems.
Home composting is a perfect example of working with natural decomposition. Kitchen scraps and garden waste are broken down by bacteria and fungi, creating nutrient-rich compost that can improve soil health. This reduces waste going to landfill and provides a sustainable source of nutrients for gardens, completing a local nutrient cycle.
Decomposition and combustion are two key processes that drive nutrient cycles on Earth. Decomposition slowly breaks down organic matter, returning nutrients to ecosystems in a sustainable way. Combustion rapidly releases stored nutrients, which can be beneficial in natural systems but problematic when human activities increase it beyond natural levels. Understanding these processes helps us appreciate the delicate balance of ecosystems and make informed decisions about environmental management.