19.4

Populations

12 flashcards to master Populations

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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.

About Populations (19.4)

These 12 flashcards cover everything you need to know about Populations for your Cambridge IGCSE Biology (0610) exam. Each card is designed based on the official syllabus requirements.

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