Ecology:

The study of how organisms interact with each other and their environment.

Biosphere:

The global sum of all ecosystems—essentially Earth’s living system.

Ecosystem:

A community of organisms plus their physical environment, interacting as a system.

Population:

A group of individuals of the same species living in a given area.

Community:

All the populations of different species living and interacting in an area.

Evolution:

Change in heritable traits of populations over generations.

Adaptations:

Traits shaped by natural selection that increase survival or reproduction.

Thermodynamics:

The study of energy and heat transfer; in ecology, applies to how energy flows through organisms and ecosystems.

Hypothesis:

A testable explanation for a phenomenon, based on observations.

Model:

A representation (conceptual, mathematical, or physical) of a system used to study processes and make predictions.

Osmotic potential

The potential of water to move into a solution due to solute concentration (lower potential = more solutes).

Ammonia (NH₃):

A nitrogen compound produced during protein metabolism and nitrogen fixation; toxic but can be converted to usable forms.

Photic zone:

The upper layer of water (in lakes or oceans) where enough light penetrates for photosynthesis.

Bundle sheath:

A layer of cells surrounding leaf veins; important in C4 photosynthesis for concentrating CO₂.

Anaerobic / Anoxic:

Conditions without oxygen (anaerobic = lacking oxygen, anoxic = totally oxygen-free).

Thermophilic:

Heat-loving organisms (e.g., some bacteria in hot springs).

Conduction:

Direct transfer of heat through physical contact.

Convection:

Heat transfer via movement of fluids (air or water).

Transpiration:

Evaporation of water from plant leaves through stomata.

Evaporation:

Process of liquid water turning into vapor.

Evapotranspiration:

Combined water loss from evaporation (soil, surfaces) and transpiration (plants).

Specific heat:

The amount of energy required to raise the temperature of a substance (water has a high specific heat, moderating climate).

Viscosity

Resistance of a fluid to flow; water’s viscosity affects organism movement.

Thermocline:

A steep temperature gradient in a body of water separating warm upper layers from cold deep water.

Epilimnion:

Warm, well-mixed surface layer in stratified lakes.

Diffusion:

Passive movement of molecules from high to low concentration.

Upwelling:

Deep, nutrient-rich water rising to the surface, supporting high productivity.

Spring and fall overturn:

Seasonal mixing in lakes when surface and bottom water reach similar temperatures, redistributing nutrients and oxygen.

Photosynthesis:

Process plants and some microbes use to convert light energy, CO₂, and water into sugars and oxygen.

Light reactions:

First stage of photosynthesis; capture light to produce ATP and NADPH.

Rubisco:

Enzyme that fixes CO₂ during the Calvin cycle; also reacts with O₂ (photorespiration).

Respiration:

Breakdown of sugars to release energy (ATP), releasing CO₂ and water.

Water-use efficiency (WUE):

Ratio of carbon gained in photosynthesis to water lost via transpiration.

C3 pathway:

Most common photosynthetic pathway; directly fixes CO₂ with rubisco.

C4 pathway:

Adaptation to hot, dry climates; CO₂ is concentrated in bundle sheath cells before fixation.

CAM pathway (Crassulacean Acid Metabolism):

Plants (like cacti) open stomata at night to store CO₂, reducing water loss.

Photosynthetically active radiation (PAR):

Range of light (400–700 nm) usable for photosynthesis.

Saturated soil:

Soil pores completely filled with water.

Wilting point

Soil moisture level where plants can no longer extract water and wilt.

Available water capacity:

Water held in soil between field capacity and wilting point (usable by plants).

Cation exchange capacity (CEC)

Soil’s ability to hold and exchange positively charged ions (nutrients).

Homeotherms:

Animals that maintain a constant internal body temperature (e.g., mammals, birds).

Ectotherms:

Animals whose body temperature varies with the environment (e.g., reptiles, fish)

Weather:

Short-term atmospheric conditions (temperature, rain, wind).

Climate

Long-term average weather patterns over time and space.

Greenhouse effect:

Warming of Earth’s surface by atmospheric gases trapping outgoing infrared radiation.

Summer solstice:

Point when Earth’s tilt is most toward the sun; longest day in the Northern Hemisphere (~June 21).

Relative humidity:

Ratio of actual water vapor to the maximum amount air can hold at that temperature.

Dew point:

Temperature at which air becomes saturated and water condenses.

Intertropical convergence zone (ITCZ)

Region near the equator where trade winds converge, causing rising moist air and rainfall.

El Niño:

Periodic warming of eastern Pacific Ocean, altering weather patterns globally.

La Niña:

Opposite of El Niño; stronger trade winds push warm water west, cooling eastern Pacific.

Infiltration:

Water soaking into soil from precipitation.

Rain shadow:

Dry area on leeward side of mountains, caused by moist air losing water on windward slopes.

Adiabatic cooling

Air cools as it rises and expands without exchanging heat with surroundings.

Solar equator:

Latitude where the sun is directly overhead at solar noon.

Hadley cells:

Tropical convection cells driving equatorial rainfall and subtropical deserts.

Ferrel cells

Mid-latitude atmospheric cells between Hadley and Polar cells.

Polar cells:

High-latitude convection cells driving cold, dry circulation.

Coriolis effect:

Apparent deflection of moving air/water due to Earth’s rotation (right in N hemisphere, left in S).

Intertropical convergence:

Same as ITCZ; where warm trade winds meet and rise.

Ocean upwelling:

Cold, nutrient-rich water rising to the surface (similar to earlier definition).

Thermohaline circulation:

Global “conveyor belt” of ocean currents driven by temperature (thermo) and salinity (haline).

Thermocline:

Already covered; in oceans, it separates warm surface from cold deep water.