Ecosystems and Energy Flow

Ecosystems and Energy Flow

• An ecosystem includes all living organisms and abiotic factors in a given area
• The sun is the ultimate energy source for all life on Earth
• Only a small fraction (less than 1%) of the sun's energy is used by living organisms
• Photosynthesis is the process by which green plants (and some others) convert water and carbon dioxide into glucose using sunlight
• Autotrophs are organisms capable of producing their own food through photosynthesis, including green plants, algae, some bacteria, and some protists
• Autotrophs are also called producers
• Heterotrophs are organisms that cannot produce their own food and obtain energy from consuming other organisms; these are also called consumers
• Herbivores eat only plants
• Carnivores eat only other animals
• Omnivores eat both plants and animals
• Detritivores feed on dead organic matter
• Decomposers break down organic matter, releasing nutrients
• Energy flows through an ecosystem in a one-way path, from the sun to producers, then to consumers

Feeding Relationships

• A food chain depicts a series of steps in which organisms transfer energy by eating and being eaten
• All food chains start with an autotroph
• A food web is a network of multiple food chains

Trophic Levels

• Each step in a food chain is a trophic level
• Producers form the first trophic level
• Herbivores (primary consumers) form the second trophic level
• Predators of herbivores (secondary consumers) form the third level
• Predators of secondary consumers (tertiary consumers) form the fourth level
• Transfer of energy between trophic levels is inefficient, with only about 10% of energy transferred to the next level.

Ecosystem Productivity

• Gross primary productivity (GPP) is the rate at which producers convert light energy to chemical energy through photosynthesis
• Net primary productivity (NPP) is the GPP minus the energy used by the producers for respiration
• The amount of net primary productivity varies greatly between ecosystems, with factors such as light, temperature, and rainfall contributing to the amount of productivity
• Biomass is the total mass of organic matter in an ecosystem

Ecosystem Recycling

• Energy flows in one direction within an ecosystem
• Matter is recycled within and between ecosystems through biogeochemical cycles
• Biogeochemical cycles involve the biological, geological, and chemical aspects of the biosphere
• Key biogeochemical cycles include the water, carbon, nitrogen, and phosphorus cycles

Water Cycle

• Evaporation of water from bodies of water, living organisms (transpiration), and the atmosphere is a driving force of the water cycle.
• Condensation forms clouds and causes precipitation, which returns water to Earth.
• Water moves between ground, air, and living organisms

Carbon Cycle

• Photosynthesis removes carbon dioxide from the atmosphere.
• Cellular respiration and decomposition release carbon dioxide back to the atmosphere.
• Cycles are driven by respiration and decomposition, with human activities significantly affecting current levels.

Nitrogen Cycle

• Nitrogen fixation converts atmospheric nitrogen into a usable form for plants.
• Plants use nitrogen to build proteins and other essential compounds
• Ammonification converts waste and dead organisms into ammonia
• Nitrification converts ammonia to nitrates (forms usable by plants)
• Denitrification converts nitrates back to atmospheric nitrogen
• Various soil bacteria play crucial roles in each step of this cycle

Phosphorus Cycle

• Phosphates are found in rocks and soil and are crucial for energy transfer processes
• Plants assimilate phosphorus into their organic compounds
• Phosphorus is essential for DNA and ATP synthesis
• Cycles primarily among organisms and the land, with less significant atmospheric movement.

Nutrient Limitation

• A limiting nutrient is a single nutrient that limits the growth of organisms in an ecosystem
• Nitrogen or phosphorus can be limiting nutrients in many areas