IB Environmental systems and societies 2.1 Individuals, Populations, Communities and Ecosystems Key Definitions

Abiotic factors are the non-living physical and chemical elements, such as temperature, sunlight, and soil composition.

Body structures that look or work alike in different species but evolved independently under similar pressures, not from a common ancestor. They are not evidence of close relationship.

Bioaccumulation refers to the process by which the concentration of non-biodegradable pollutants increases in an organism over time.

Biomagnification refers to the process by which the concentration of non-biodegradable pollutants increases as you move up trophic levels in a food chain or food web.

Biomass is the total mass of living organisms in a given area or volume.

The biosphere is the global ecological system that includes all living organisms and their interactions with the atmosphere, hydrosphere, and lithosphere.

Biotic factors are the living components of an ecosystem, such as plants, animals, and microorganisms, as well as their interactions.

Species with traits between r-strategists and K-strategists, combining fairly rapid reproduction with moderate parental care and competitive ability. They often dominate mid-successional stages.

Carrying capacity is the maximum number of individuals of a species that an environment can sustainably support over time.

A clade is a group of organisms that includes a common ancestor and all its descendants.

Cladistics is the branch of biology that classifies organisms according to their evolutionary relationships, not just physical similarities.

Classification is the systematic arrangement of organisms into groups based on shared characteristics.

A community is a collection of interacting populations of different species living in the same area and at the same time.

Competition occurs when two or more organisms require the same limited resource, resulting in a negative effect on all participants’ growth, survival, or reproduction.

If two species compete for exactly the same limited resources, one will always be the better competitor, so the two cannot occupy the same niche indefinitely. The weaker competitor is eliminated from that niche.

Density-dependent factors are biotic elements that intensify as population density increases.

Density-independent factors are usually abiotic events, such as drought, fire, hurricanes, or volcanic eruptions, that affect a population by the same proportion regardless of how dense it is.

The Dichotomous Key is a step-by-step decision-making tool that helps classify an organism based on observable characteristics.

Disease is a biological interaction in which a pathogen (virus, bacterium, fungus, or protozoan) infects a host organism, causing harm or death.

Dissolved Oxygen is the amount of oxygen dissolved in water, essential for aquatic organisms.

An ecological footprint is the measure of the amount of land and water area required to provide all resources a population consumes and absorb waste and emissions (e.g., CO₂ absorption by forests)

An ecological niche is the unique set of abiotic and biotic conditions and resources that a species requires to survive, grow, and reproduce.

Ecosystem is a geographic area where plants, animals and other organisms, as well as weather and landscape, work together to form a bubble of life

Endocrine disruptor is a chemical that interferes with the hormonal system, causing developmental, reproductive, or immune problems.