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

2026-2028 syllabus, in our words

What the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).

  1. Describe Describe a population: all the members of one species found in a particular area at a particular time.
  2. Describe Describe a community: every population of every species within an ecosystem.
  3. Describe Describe an ecosystem: a unit made up of a community of organisms together with their environment, with the two interacting.
  4. Identify Identify and state what affects how quickly an organism's population grows, limited to disease, predation, competition and food supply.
  5. Identify Identify the four phases of the sigmoid population growth curve (lag, exponential or log, stationary, death) for a population growing with limited resources.
  6. Interpret Interpret diagrams and graphs showing population growth.
  7. Explain Explain what causes each phase of the sigmoid population growth curve, referring where relevant to the part played by 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

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