Unit 3: Matter & Energy Flow on Earth

Transcription

1 Unit 3: Matter & Energy Flow on Earth Objectives: E2.3c - Explain how the nitrogen cycle is part of the Earth system. E2.3d - Explain how carbon moves through the Earth system and how it may benefit or harm society.

2 Nitrogen Cycling Nitrogen is an important element that is part of the DNA molecule, which is responsible for the replication of living cells. Nitrogen is also an important component of protein molecules. Approximately 5% of the human body is composed of nitrogen. The source of nitrogen for the world s ecosystems is the atmosphere. Earth s atmosphere is composed of 78% nitrogen. The nitrogen gas that fills the atmosphere is in a diatomic form (N 2 ), which means it is composed of two atoms of nitrogen bonded together.

3 Nitrogen Cycle* The Nitrogen Cycle begins when microscopic bacteria located in the soil and in the root systems of specialized plants combine atmospheric nitrogen with other atoms to form nitrogen compounds. This process is called nitrification, and it produces nitrogen-containing molecules such as nitrites, nitrates and ammonia.

4 Nitrogen compounds can then be taken up by the root system of plants to be used to make proteins. The plants that harbor these specialized bacteria in their root systems are called legumes. Common legumes include clover, beans, peanuts, and alfalfa. Legumes are often used in agriculture to add nitrogen to the soil, and they act as natural fertilizers. Nitrogen Cycle

5 Carbon Cycling Carbon molecules form the base for all life (at least here on Earth), making the availability of carbon to living things essential. Most carbon that finds its way into living organisms comes from the atmosphere. Approximately 19% of the human body is composed of the element carbon. All of this carbon was derived from eating food.

6 Carbon Cycle* Carbon dioxide gas (CO 2 ) present in the Earth s atmosphere is used by green plants and algae for photosynthesis. Photosynthesis uses solar energy to take carbon dioxide from the atmosphere and combines it with water to form sugars. A common form of sugar that is a product of photosynthesis is glucose (C 6 H 12 O 6 ). Carbon dioxide + water + sunlight = sugar + oxygen

7 Respiration breaks down sugars and starches in the presence of oxygen and produces carbon dioxide as a by-product. Every time humans and animals exhale air out of their lungs, they are removing carbon dioxide from their bodies and returning it to the atmosphere. Carbon Cycle*

8 Carbon Cycle* Another path carbon can take in the food chain is to be eliminated from an organism in its waste. The waste becomes part of the nonliving soil environment. Once there, the organic molecules that are in waste can be used by decomposers such as fungi or bacteria. Eventually this carbon is also returned to the atmosphere as carbon dioxide.

9 Carbon Cycle Sometimes the bodies of plants and animals are buried deep in the Earth for millions of years. These carbon-containing organisms are then exposed to the great heat and pressure below the Earth s surface. This causes chemical changes that transform the long-dead organisms into what we call fossil fuels. Common fossil fuels include oil and coal.

10 When fossil fuels are burned, the carbon that was locked in the Earth for millions of years is released back into the atmosphere as carbon dioxide gas. In the past 100 years, the burning of fossil fuels as an energy source is causing an imbalance of carbon dioxide in the Earth s atmosphere. Carbon Cycle

11 Carbon Cycle Part of the carbon cycle also involves the creation of methane gas (CH 4 ). Methane is a molecule produced by anaerobic bacteria. Anaerobic means without oxygen. Anaerobic bacteria survive only without the presence of oxygen. Examples include methane gas that is created as a by-product as cows and sheep digest tough grasses, from the mud of rice paddies found in Asia, and from human sewage and garbage waste.