19: Organisms and Their Environment Vocabulary

50 vocabulary flashcards covering all key terms from CAIE Biology IGCSE Topic 19: Organisms and Their Environment.

Biomass

Total mass of organic material in a specific area over a set period.

Carbon cycle

Process through which carbon dioxide moves between living organisms and the environment via respiration, photosynthesis, feeding, combustion, decomposition and fossilisation.

Carnivore

Animal that feeds on other animals.

Combustion

Scientific term for burning a substance.

Community

All the populations of different species living together in a habitat.

Condensation

Water vapour cooling and forming water droplets, producing clouds in the water cycle.

Consumers

Organisms that obtain energy by feeding on other organisms.

Deamination

Removal of the amino group from amino acids in the liver to produce ammonia, later converted to urea.

Death phase

Population period where mortality rate exceeds reproduction rate, causing numbers to fall.

Decomposers

Organisms that break down dead plant and animal material into simpler organic matter for energy.

Decomposition

Breakdown of dead materials into simpler organic matter.

Deforestation

Removal of trees from land later used for crops or cattle.

Denitrification

Conversion of nitrate ions to nitrogen gas by denitrifying bacteria.

Denitrifying bacteria

Microorganisms that convert nitrate ions into nitrogen gas.

Ecosystem

Community of organisms and their non-living environment plus all interactions.

Evaporation

Transformation of liquid water to water vapour.

Food chain

Sequence showing feeding relationships and biomass transfer: producer → primary consumer → secondary consumer → tertiary consumer.

Food web

Diagram displaying how different food chains interconnect.

Fossil

Remains of organisms preserved in rocks millions of years old.

Fossil fuel

Fuel such as coal, oil or natural gas formed from compressed remains of plants or animals over millions of years.

Fossilisation

Process by which a fossil is formed.

Herbivore

Animal that feeds on plants.

Ingestion

Intake of food and drink through the mouth; mechanism of energy transfer in a food chain.

Lag phase

Period of slow population growth at the start of a growth curve.

Light energy

Solar energy trapped by photosynthetic organisms and converted to chemical energy.

Log phase

Period of rapid, exponential population growth where birth rate exceeds death rate.

Nitrification

Two-step oxidation of ammonium ions to nitrite and then nitrate ions by nitrifying bacteria.

Nitrifying bacteria

Soil microorganisms that convert ammonium ions to nitrite and nitrate ions.

Nitrogen cycle

Movement of nitrogen between organisms and the environment involving decomposers, nitrifying, nitrogen-fixing and denitrifying bacteria.

Nitrogen fixation

Conversion of atmospheric nitrogen gas into ammonia by nitrogen-fixing bacteria or lightning.

Nitrogen-fixing bacteria

Microorganisms that convert atmospheric nitrogen gas into nitrogen-containing compounds; may be free-living or in legume root nodules.

Over-harvesting

Excessive harvesting of a species causing population decline and risk of endangerment or extinction.

Photosynthesis

Reaction in photosynthetic organisms that uses light energy to manufacture carbohydrates from raw materials.

Population

All individuals of the same species living in a particular habitat at the same time.

Population growth curve

Sigmoidal graph showing how population size changes over time in an environment with limited resources.

Precipitation

Release of water from clouds as rain or snow in the water cycle.

Predators

Consumers that hunt and eat other animals.

Prey

Animals that are eaten by predators.

Primary consumers

Herbivores at trophic level 2 that feed on producers.

Producers

Photosynthetic organisms at the start of a food chain that provide biomass for all living things.

Pyramid of biomass

Diagram/table showing dry mass of living material at each trophic level, forming a pyramid shape.

Pyramid of numbers

Diagram showing number of individual organisms at each trophic level of a food chain.

Quaternary consumers

Carnivores at the top of a food chain.

Respiration

Cellular reaction that releases energy from nutrient molecules.

Secondary consumers

Carnivores at trophic level 3 that eat herbivores.

Stationary phase

Stage in population growth where numbers stay approximately constant.

Tertiary consumers

Carnivores at trophic level 4 that feed on other carnivores.

Transpiration

Loss of water vapour from plant leaves and shoots via diffusion and evaporation.

Trophic level

Position an organism occupies in a food chain, web, or pyramid of numbers or biomass.

Water cycle

Movement of water between organisms and environment involving evaporation, transpiration, condensation and precipitation.