Energy & Biogeochemical Cycles

Topics 1.3 to 1.11 of the AP Outline

Carbon sources

Places where carbon is released into the atmosphere, often in the form of carbon dioxide (CO2).

Carbon sinks

A system that absorbs more carbon from the atmosphere than it releases, storing the excess carbon in solid or liquid form.

Photosynthesis

The process plants and other organisms use to convert sunlight, water, and carbon dioxide into glucose (sugar) and oxygen.

Cellular respiration

The process most organisms use to break down glucose (sugar) and oxygen to release energy, producing carbon dioxide and water as byproducts.

Decomposition

The process of breaking down dead organisms and other organic matter into simpler substances, often releasing carbon dioxide into the atmosphere.

Fossil fuels

Natural fuels formed from the remains of plants and animals that lived millions of years ago, such as coal, oil, and natural gas.

Atmospheric carbon sink

Carbon stored in the Earth's atmosphere, primarily as carbon dioxide.

Terrestrial carbon sink

Carbon stored on land, including in living things, soils, and rocks.

Aquatic carbon sink

Carbon stored in the oceans, lakes, and rivers, including in dissolved carbon dioxide and marine organisms.

Nitrogen sources

Substances or processes that provide nitrogen to the environment. Examples include atmospheric nitrogen, nitrogen-fixing bacteria, and fertilizers.

Nitrogen sinks

Processes or components that remove nitrogen from the environment. Examples include denitrification, plant uptake, and sedimentation in aquatic ecosystems.

Atmospheric nitrogen

Nitrogen gas (N₂) that makes up about 78% of the Earth's atmosphere. It is relatively inert and not directly usable by most organisms.

Nitrates

A common form of nitrogen in the environment, often found in soil and water. Nitrates are essential for plant growth but can be harmful in excess.

Uptake (Nitrogen Cycle)

The process by which plants or other organisms absorb nitrogen from the environment, typically nitrate or ammonium.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into a usable form by organisms or non-biological processes.

Ammonification

Decomposition of organic nitrogen compounds into ammonia by microorganisms.

Nitrification

Oxidation of ammonia to nitrite and then nitrate by bacteria.

Denitrification

Reduction of nitrate to nitrogen gas by bacteria under anaerobic conditions.

Assimilation (Nitrogen Cycle)

Uptake and incorporation of nitrogen by plants into organic compounds.

Weathering (Phosphorus Cycle)

The breakdown of rocks and minerals, releasing phosphorus into the environment.

Phosphorus sinks

Processes or components that remove phosphorus from the environment. Most phosphorus is found in sediments, mineral compounds, and rocks.

Erosion

The process of wearing away soil and rock by wind, water, or ice.

Eutrophication

The excessive growth of algae in a water body due to nutrient pollution, often caused by excess phosphorus.

Sedimentation

The settling of phosphorus-containing particles at the bottom of water bodies.

Evaporation

The process of liquid water turning into water vapor, typically due to heat from the sun.

Condensation

The process of water vapor cooling and changing back into a liquid or solid state, often forming clouds.

Precipitation

Water that falls from the sky as rain, snow, sleet, or hail.

Infiltration

The process of water sinking into the ground.

Runoff

Water that flows over the land surface, often into rivers, lakes, or oceans.

Transpiration

The process of plants releasing water vapor into the atmosphere through their leaves.

Aquifer

A layer of rock or soil that can hold water.

Groundwater

Water that is stored underground in aquifers.

Water Table

The upper limit of the zone of saturation in an aquifer.

Hydrosphere

The part of the Earth that is composed of water.

Watershed

Geographical area where all water flows to a common point, such as a river, lake, or ocean.

Divide (Watershed)

The boundary that separates one watershed from another.

Mouth (River)

The point where a river or stream flows into a larger body of water.

Tributary

A smaller stream or river that flows into a larger one.

Headwaters

The source of a river or stream.

Primary productivity

The rate at which organic matter is produced by autotrophs (organisms that can produce their own food, such as plants).

Gross Primary Productivity (GPP)

The total rate at which organic matter is produced by autotrophs.

Net Primary Productivity (NPP)

The rate at which organic matter is produced by autotrophs after accounting for respiration.

Terrestrial Primary Producers

Plants, trees, and grasses.

Aquatic Primary Producers

Phytoplankton (microscopic algae) and aquatic plants.

Trophic Level

The position of an organism in a food chain.

Producer

Organisms that produce their food through photosynthesis or chemosynthesis.

Consumer

Organisms that obtain energy by consuming other organisms.

Decomposer

Organisms that break down dead organisms and waste products.

Primary Consumer

Organisms that consume producers directly.

Secondary Consumer

Organisms that consume primary consumers.

Tertiary Consumer

Organisms that consume secondary consumers.

Quaternary Consumer

Organisms that consume tertiary consumers (often the top predators).

Pyramid of Numbers

A pyramid showing the number of organisms at each trophic level.

Pyramid of Biomass

A pyramid showing the total mass of organisms at each trophic level.

Pyramid of Energy

A pyramid showing the energy available at each trophic level.

Energy Flow

The movement of energy through an ecosystem, typically from producers to consumers.

10% Rule

A general rule stating that only about 10% of the energy at one trophic level is transferred to the next higher trophic level.

Energy Loss

The loss of energy that occurs at each trophic level due to factors such as heat, respiration, and waste.

Solar Energy

The most common source of energy for most ecosystems. Plants, algae, and other photosynthetic organisms capture sunlight and convert it into chemical energy through the process of photosynthesis.

Chemosynthetic Energy

A less common source of energy, primarily found in deep-sea hydrothermal vents and other environments where sunlight is unavailable.

Chemosynthetic organisms

Organisms that obtain energy by oxidizing inorganic compounds (like hydrogen sulfide or methane) to produce organic matter.

Food Chain

A linear sequence showing the transfer of energy from one organism to another.

Food Web

A complex network of interconnected food chains showing how multiple organisms interact.

Omnivore

An organism that eats both plants and animals.

Carnivore

An organism that eats primarily meat.

Herbivore

An organism that eats primarily plants.

Detritivore

An animal that feeds on dead organic material, especially plant detritus.