19.4

Populations

Cambridge IGCSE Biology (0610)  · Unit 19: Organisms and their environment  · 12 flashcards

Populations is topic 19.4 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 19 — Organisms and their environment , alongside Energy flow, Food chains and food webs and Nutrient cycles.  In one line: A population is a group of organisms belonging to the same species, inhabiting the same area, and existing at the same time.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 12 flashcards — 3 definitions and 9 key concepts — covering the precise wording mark schemes reward.  Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

'population' in ecological terms

A population is a group of organisms belonging to the same species, inhabiting the same area, and existing at the same time.

Example: a population of deer in a forest or a school of tuna in the ocean.

What the Cambridge 0610 syllabus says

Official 2026-2028 spec

These are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.

  1. Describe Describe a population as a group of organisms of one species, living in the same area, at the same time
  2. Describe Describe a community as all of the populations of different species in an ecosystem
  3. Describe Describe an ecosystem as a unit containing the community of organisms and their environment, interacting together
  4. Identify Identify and state the factors affecting the rate of population growth for a population of an organism, limited to food supply, competition, predation and disease
  5. Identify Identify the lag, exponential (log), stationary and death phases in the sigmoid curve of population growth for a population growing in an environment with limited resources
  6. Interpret Interpret graphs and diagrams of population growth
  7. Explain Explain the factors that lead to each phase in the sigmoid curve of population growth, making reference, where appropriate, to the role of limiting factors Supplement
Definition Flip

Define 'population' in ecological terms.

Answer Flip

A population is a group of organisms belonging to the same species, inhabiting the same area, and existing at the same time.

Example: a population of deer in a forest or a school of tuna in the ocean.
Definition Flip

What is a 'community' in the context of ecology?

Answer Flip

A community encompasses all the different populations of various species living and interacting within a specific ecosystem. An example is a forest community containing trees, insects, birds, fungi, and mammals.

Definition Flip

Describe an 'ecosystem'.

Answer Flip

An ecosystem is a functional unit consisting of a community of organisms and their physical environment, all interacting as a system.

Example: A lake ecosystem including fish, plants, algae, and the water chemistry, or a desert ecosystem.
Key Concept Flip

List four key factors that affect population growth rate.

Answer Flip

Four key factors influencing population growth are food supply, competition (for resources), predation, and disease. These factors can limit or promote population increase.

Key Concept Flip

Name the four phases of the sigmoid (S-shaped) population growth curve.

Answer Flip

The four phases are: the lag phase (slow growth), the exponential (log) phase (rapid growth), the stationary phase (stable population size), and the death phase (population decline). These phases occur when a population is growing in an environment with limited resources.

Key Concept Flip

What is the 'lag phase' in population growth and what causes it?

Answer Flip

The lag phase is the initial period of slow population growth as organisms adjust to their environment. This is due to factors such as small initial population size and the time needed for individuals to mature and reproduce.

Example: Bacteria introduced to fresh nutrient broth.
Key Concept Flip

Explain the 'exponential (log) phase' of population growth.

Answer Flip

The exponential phase is a period of rapid population increase, occurring when resources are abundant and limiting factors are minimal. Reproduction rates are high, and mortality rates are low, leading to a steep increase in population size.

Example: Algae bloom in a pond.
Key Concept Flip

Describe the 'stationary phase' of population growth.

Answer Flip

The stationary phase is reached when population growth levels off and stabilizes. Birth and death rates are approximately equal, usually because the carrying capacity of the environment is reached, and resources become limited.

Example: A deer population reaching the limit of food available.
Key Concept Flip

Explain what occurs during the 'death phase' of population growth.

Answer Flip

The death phase, or decline phase, occurs when the death rate exceeds the birth rate, leading to a decrease in population size. This happens when resources are depleted, waste products accumulate, or disease spreads rapidly.

Example: Yeast cells dying due to alcohol toxicity after fermentation.
Key Concept Flip

What are 'limiting factors' and how do they affect population growth?

Answer Flip

Limiting factors are environmental resources or conditions that restrict population growth. These can be density-dependent (

Example: competition, disease) or density-independent (. natural disasters). They ultimately determine the carrying capacity of an environment.
Key Concept Flip

Describe how competition can act as a limiting factor on population growth.

Answer Flip

Competition for resources (food, water, shelter, mates) increases as population density rises. This leads to reduced survival and reproduction rates, ultimately slowing or stopping population growth.

Example: Lions competing for prey.
Key Concept Flip

Explain how predation can affect population growth.

Answer Flip

Predation directly influences the population size of the prey species. An increase in predator population can decrease the prey population.

Example: A rise in fox numbers reducing the rabbit population.

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19.3 Nutrient cycles 20.1 Food supply

Key Questions: Populations

Define 'population' in ecological terms.

A population is a group of organisms belonging to the same species, inhabiting the same area, and existing at the same time.

Example: a population of deer in a forest or a school of tuna in the ocean.
What is a 'community' in the context of ecology?

A community encompasses all the different populations of various species living and interacting within a specific ecosystem. An example is a forest community containing trees, insects, birds, fungi, and mammals.

Describe an 'ecosystem'.

An ecosystem is a functional unit consisting of a community of organisms and their physical environment, all interacting as a system.

Example: A lake ecosystem including fish, plants, algae, and the water chemistry, or a desert ecosystem.

More topics in Unit 19 — Organisms and their environment

Populations sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

19.1 Energy flow

10 flashcards
19.2 Food chains and food webs

10 flashcards
19.3 Nutrient cycles

12 flashcards

Key terms covered in this Populations deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

'population' in ecological terms
'community' in the context of ecology
Describe an 'ecosystem'

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How to study this Populations deck

Start in Study Mode, attempt each card before flipping, then rate Hard, Okay or Easy. Cards you rate Hard come back within a day; cards you rate Easy push out to weeks. Your progress is saved in your browser, so come back daily for 5–10 minute reviews until every card reads Mastered.