Biology 20 Energy and Matter Exchange in the Biosphere

The Cycling of Matter in the Biosphere  The earth is a closed system, so although energy from the sun can come into the system and heat energy can leave, matter cannot.  Food molecules become cellular structures that become tissues and organisms.  Eventually, those tissues and organisms become food for other organisms or decompose becoming part of the soil. The cycling of matter is a necessary part of all living things.

Water  Water is required by all living things. It is important for a variety of reasons:  it absorbs and releases thermal energy  most metabolic reactions take place in water solutions  it exists as a solid, liquid or a gas in earth’s atmosphere

The Hydrologic Cycle

 Transpiration – is the loss of water to the atmosphere through the leaves of plants.  Percolation – is the movement of water through porous soil.

Carbon  On earth, all organic substances are compounds of carbon, including those that make up living things.  Carbon is also found in inorganic forms such as CO 2 and carbonates.  Combustion, decomposition and cellular respiration all produce inorganic carbon dioxide.  Photosynthesis is required to capture inorganic carbon and convert it to organic carbon.

The Carbon Cycle

Nitrogen  Nitrogen is an important building block of proteins and nucleic acids.  Nitrogen gas is abundant on our planet and accounts for 79% of the atmosphere.  To be useful to organisms, however, nitrogen must be in a more useable form like nitrate.

The Nitrogen Cycle Nitrogen fixation is the process by which atmospheric nitrogen is converted to a useable form, nitrates. This is done by lightening and nitrogen fixing bacteria. Nitrification - Ammonium is converted into nitrates by nitrifying bacteria. Denitrification is the process where nitrifying bacteria convert nitrates to nitrites, which in turn will be used as nitrogen gas in the atmosphere. Ammonification is the process where decomposers break down organic nitrogen from dead plants and animals into ammonia. Bacteria in turn, change the ammonia into useable nitrates.

The Nitrogen Cycle

Phosphorus  Phosphorus is required in cell membranes, ATP, DNA and in bone formation.  Phosphorus cycles though the earth’s crust and through living organisms.

The Phosphorus Cycle