Energy and Matter Exchange in the Biosphere

Energy and Matter Exchange in the Biosphere

Chemosynthesis

• Chemosynthesis is a process where certain organisms, mainly bacteria and archaea, produce food using energy derived from chemical reactions rather than sunlight.

• This process is crucial in environments where sunlight is not available, such as deep-sea hydrothermal vents and cold seeps.

Laws of Thermodynamics and Energy Flow

• First Law of Thermodynamics (Law of Conservation of Energy): Energy cannot be created or destroyed, only transformed from one form to another. In an ecosystem, energy enters as sunlight or chemical energy and is converted into different forms as it flows through trophic levels.

• Second Law of Thermodynamics: Every energy transfer or transformation increases the entropy of the universe. In ecosystems, this means that during energy transfer between trophic levels, some energy is lost as heat, which is a less usable form of energy. This is why energy transfer is never 100% efficient.

  Energy flow is unidirectional and decreases at each successive trophic level due to the loss of energy as heat, in accordance with the second law of thermodynamics.

Terminology for Biotic Components

• Producer (Autotroph): An organism that produces its own food using energy from sunlight (photosynthesis) or chemical reactions (chemosynthesis). Examples include plants, algae, and some bacteria.

• Consumer (Heterotroph): An organism that obtains energy by consuming other organisms. Consumers can be further classified into:

  • Primary Consumers (Herbivores): Feed on producers (e.g., cows, rabbits).

  • Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers (e.g., snakes, foxes).

  • Tertiary Consumers (Carnivores): Feed on secondary consumers (e.g., eagles, sharks).

• Decomposer (Detritivore): An organism that breaks down dead organic matter and waste, releasing nutrients back into the ecosystem. Examples include bacteria and fungi.

Rule of 10 and Trophic Levels

• Rule of 10 (10% Rule): Only about 10% of the energy stored as biomass in one trophic level is passed on to the next trophic level. The remaining 90% is used for metabolic processes or lost as heat.

• Trophic Levels:

  • Primary Producers: Form the base of the food chain (e.g., plants).

  • Primary Consumers: Herbivores that eat primary producers.

  • Secondary Consumers: Carnivores that eat primary consumers.

  • Tertiary Consumers: Carnivores that eat secondary consumers.

Organic vs. Inorganic

• Organic Compounds: Contain carbon and are typically associated with living organisms (e.g., carbohydrates, proteins, lipids, nucleic acids).

• Inorganic Compounds: Do not contain carbon-carbon or carbon-hydrogen bonds (e.g., water, minerals, carbon dioxide).

Ecological Pyramids

• Pyramid of Numbers: Shows the number of individual organisms at each trophic level. Can be inverted in some ecosystems (e.g., a single tree supporting many insects).

• Pyramid of Biomass: Represents the total dry mass of organisms at each trophic level. Can also be inverted in aquatic ecosystems (e.g., phytoplankton with a high turnover rate supporting a larger biomass of zooplankton).

• Pyramid of Energy: Illustrates the energy flow through each trophic level. Always upright because energy decreases as you move up trophic levels due to the second law of thermodynamics.

Biomagnification

• Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each successive trophic level of a food chain or web. Substances like mercury (Hg) and pesticides (DDT) are examples.

Key Biogeochemical Cycles

• Water Cycle (Hydrologic Cycle):

  • Steps: Evaporation, transpiration, condensation, precipitation, runoff, infiltration.

  • Terminology:* Evaporation (liquid to gas), transpiration (water release from plants), condensation (gas to liquid), precipitation (water falling back to Earth), runoff (water flowing over the surface), infiltration (water seeping into the ground).

• Carbon Cycle:

  • Steps: Photosynthesis, respiration, decomposition, combustion, sedimentation, burial.

  • Terminology: Photosynthesis (CO2 to glucose), respiration (glucose to CO2), decomposition (breakdown of organic matter), combustion (burning organic matter), sedimentation (formation of sedimentary rocks), burial (long-term storage of carbon).

• Oxygen Cycle:

  • Closely linked to the carbon cycle through photosynthesis and respiration.

  • Oxygen is produced during photosynthesis and consumed during respiration.

• Nitrogen Cycle:

  • Steps: Nitrogen fixation, ammonification, nitrification, denitrification, assimilation.

  • Terminology: Nitrogen fixation (N2 to ammonia), ammonification (organic N to ammonia), nitrification (ammonia to nitrites/nitrates), denitrification (nitrates to N2), assimilation (uptake of nitrogen compounds by plants).

• Phosphorus cycle:

  • Steps: Weathering, absorption by plants, consumption by animals, decomposition, sedimentation.

  • Terminology: Weathering (release of phosphate from rocks), absorption (uptake by plants), decomposition (release of phosphate from organic matter), sedimentation (formation of phosphate rocks).

Carbon Sources vs. Carbon Sinks

• Carbon Sources: Release more carbon into the atmosphere than they absorb (e.g., burning fossil fuels, deforestation, respiration).

• Carbon Sinks: Absorb more carbon from the atmosphere than they release (e.g., forests, oceans, soil).

Importance of Cycles for Organism Health

• Water: Essential for hydration, nutrient transport, and metabolic processes.

• Carbon: Used to build organic molecules (carbohydrates, lipids, proteins, nucleic acids) necessary for energy storage, structure, and function.

• Oxygen: Required for aerobic respiration, which generates energy for cellular activities.

• Nitrogen: A component of amino acids, proteins, and nucleic acids, essential for growth and genetic information.

• Phosphorus: A component of nucleic acids (DNA, RNA), ATP (energy currency), and phospholipids (cell membranes).

Human Impacts on Cycles

• Global Warming and the Greenhouse Effect: Increased greenhouse gas emissions (CO2, methane) from burning fossil fuels and deforestation trap heat in the atmosphere, leading to global warming.

  • The greenhouse effect is a natural process that keeps the Earth warm, but increased greenhouse gas concentrations enhance this effect, causing climate change.

• Algal Bloom: Excessive nutrient runoff (nitrogen and phosphorus from fertilizers and sewage) into aquatic ecosystems leads to rapid algal growth. When the algae die and decompose, it depletes oxygen, creating dead zones harmful to aquatic life.

• Acid Rain: Burning fossil fuels releases sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere, which react with water to form sulfuric acid and nitric acid, resulting in acid rain. Acid rain damages forests, acidifies lakes and streams, and corrodes buildings.

• Burning Fossil Fuels: Releases large amounts of carbon dioxide into the atmosphere, contributing to global warming and climate change.