Summary and Exam Tips for Populations
Populations is a subtopic of Organisms and their Environment, which falls under the subject Biology in the Cambridge IGCSE curriculum. A population is defined as a group of organisms of one species living in the same area at the same time. In contrast, a community includes all populations of different species within an ecosystem, which is a unit containing these communities and their environment interacting together.
Factors Affecting Population Growth: Population growth is influenced by food supply, predation, and disease. Organisms compete for resources, and those best adapted tend to increase their populations. Human population growth has been exponential over the last 150 years due to improved technology, medicine, and healthcare.
Growth Curves: Population growth can be represented by a sigmoid growth curve with four phases:
- Lag Phase: Organisms adapt to the environment; reproduction is minimal.
- Log Phase: Rapid growth due to abundant resources; birth rate exceeds death rate.
- Stationary Phase: Growth stabilizes as resources become limited; birth and death rates equalize.
- Death Phase: Population declines as death rate surpasses birth rate due to resource scarcity or toxic waste accumulation.
In natural environments, population growth may not follow a perfect sigmoid curve due to factors like temperature changes, predation, disease, immigration, and emigration.
Exam Tips
- Understand Key Definitions: Be clear on the definitions of population, community, and ecosystem.
- Identify Growth Phases: Be able to identify and explain the lag, log, stationary, and death phases in a sigmoid growth curve.
- Factors Influencing Growth: Know the factors affecting population growth, such as food supply, predation, and disease.
- Graph Interpretation: Practice interpreting graphs and diagrams related to population growth.
- Tailor Your Answers: Always read the exam questions carefully and tailor your responses to the specific organism or scenario presented.
