Study Notes
A population is a group of organisms of one species living in the same area at the same time. Community refers to all populations of different species in an ecosystem. Ecosystem is a unit containing the community of organisms and their environment interacting together.
- Population — a group of organisms of one species living in the same area at the same time Example: A herd of elephants in a savannah
- Community — all of the populations of different species in an ecosystem Example: Fish, plants, and microorganisms in a pond
- Ecosystem — a unit containing the community of organisms and their environment interacting together Example: A forest with trees, animals, and soil
- Sigmoid Growth Curve — a graph showing population growth with four phases: lag, log, stationary, and death Example: Bacteria growing in a petri dish
- Lag Phase — organisms adapt to the environment before reproducing Example: Bacteria adjusting to a new nutrient medium
- Log Phase — rapid population growth due to abundant resources Example: Rapid increase in bacteria when food is plentiful
- Stationary Phase — population levels out as resources become limited Example: Bacteria growth stabilizes when nutrients are limited
- Death Phase — population decreases as death rate exceeds birth rate Example: Bacteria die off when waste accumulates
- Exponential Growth — rapid increase in population size Example: Human population growth over the last 150 years
Exam Tips
Key Definitions to Remember
- Population: a group of organisms of one species living in the same area at the same time
- Community: all of the populations of different species in an ecosystem
- Ecosystem: a unit containing the community of organisms and their environment interacting together
- Sigmoid Growth Curve: a graph showing population growth with four phases
Common Confusions
- Confusing community with ecosystem
- Misunderstanding the phases of the sigmoid growth curve
Typical Exam Questions
- What is a population? A group of organisms of one species living in the same area at the same time
- Describe the log phase of population growth. Rapid population growth due to abundant resources
- What factors affect population growth? Food supply, predation, and disease
What Examiners Usually Test
- Understanding of the sigmoid growth curve phases
- Ability to identify factors affecting population growth
- Interpretation of population growth graphs