IB Environmental systems and societies Topic 8: Human Populations and Urban Systems Key Definitions

An age-sex pyramid visually represents the composition of a population by age groups and gender.

Contamination of the indoor or outdoor atmosphere by chemical, physical, or biological agents that modify the natural characteristics of the air.

Biocapacity is the capacity of a biologically productive area to continuously provide renewable resources and assimilate the waste generated by human activities.

Biodiversity refers to the variety of life in an ecosystem, encompassing different levels of biological organization.

A design approach that brings nature into the built environment using features such as living green walls and roofs, water features, and natural light to connect people with natural systems.

A carbon sink is any natural or artificial system that absorbs more carbon than it releases, thus removing CO₂ from the atmosphere.

The circular economy is an economic model that decouples economic growth from resource consumption by keeping materials, products, and resources in use for as long as possible.

The dependency ratio is a measure of the proportion of dependents (people under 15 and over 64) to the working-age population (15–64 years). It is calculated as:

The Doughnut Economics model, proposed by economist Kate Raworth, offers a framework to address these challenges by balancing human needs with planetary boundaries.

An approach to designing cities that treats the urban area as an ecosystem, managing the relationships between living (biotic) and non-living (abiotic) components to support sustainability and quality of life.

Environmental justice is the principle that all people, regardless of race, gender, socioeconomic status, or nationality, have the right to live in a clean, healthy environment and have fair access to natural resources.

Environmental migration refers to the movement of people caused by changes in the environment, which can be either sudden or gradual.

Food security is defined as the physical and economic availability of food, ensuring all individuals can access the balanced diet necessary for a healthy and active life.

Green architecture refers to the design, construction, and operation of buildings in an environmentally responsible and resource-efficient manner throughout their life cycle.

Indicator species are organisms whose presence, absence, or abundance provides information about environmental conditions, particularly pollution levels.

Malnutrition is the condition of having an inadequate or unbalanced diet, including both insufficient intake (undernourishment) and excessive intake (overnourishment).

$NO_x$ refers to a group of gases consisting of nitrogen dioxide ($NO_2$) and nitric oxide ($NO$).

pH measures hydrogen ion concentration, influencing chemical reactions in water.

Photochemical smog is a type of air pollution that forms when primary pollutants, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), undergo chemical reactions in the presence of sunlight, resulting in the creation of harmful secondary pollutants like peroxyacyl nitrates (PANs) and tropospheric ozone.

Population momentum refers to continued population growth even if the fertility rate declines.

Resilience is a system’s ability to resist disturbances, recover, and maintain stability instead of reaching a tipping point that leads to a new equilibrium.

Rural–urban migration is the movement of people from rural areas (countryside) to urban areas (cities and towns) in search of better opportunities.

Social mix refers to creating urban areas where people from different social, economic, and cultural backgrounds live and interact.

Suburbanization is the movement of people from dense urban centers to lower-density areas on the outskirts of cities, known as suburbs.