IGCSE Biology 75 Views 1 Answers

Sourav PanNovember 15, 2024
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
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
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Sourav PanMay 15, 2025
The sigmoid curve of population growth, also known as the logistic growth curve, illustrates how a population grows in an environment with limited resources. This curve is characterized by four distinct phases: lag phase, exponential (log) phase, stationary phase, and death phase. Here’s a detailed explanation of each phase:
1. Lag Phase
- Description: The lag phase is the initial stage of population growth where the growth rate is slow. During this period, individuals are adapting to their new environment.
- Characteristics:
- Few reproductive individuals are present, leading to minimal reproduction.
- Organisms are metabolically active, increasing in size and preparing for reproduction.
- Environmental conditions are being assessed, and necessary adaptations are occurring.
2. Exponential (Log) Phase
- Description: Following the lag phase, the population enters the exponential growth phase, characterized by rapid population increase.
- Characteristics:
- Resources (such as food and space) are abundant, allowing for high rates of reproduction.
- The number of individuals increases logarithmically, leading to a steep upward slope on the graph.
- Mortality rates are low due to favorable conditions, resulting in a high net growth rate as natality significantly exceeds mortality.
3. Stationary Phase
- Description: As resources become limited and competition increases, the population enters the stationary phase where growth stabilizes.
- Characteristics:
- The birth rate declines as resources become scarce, while mortality rates may rise due to increased competition and limited food supply.
- The population size levels off as natality equals mortality, resulting in a plateau on the graph.
- This phase reflects the carrying capacity (KK) of the environment, where the population oscillates around a stable size.
4. Death Phase
- Description: In some contexts, particularly in microbial studies, a death phase may be identified following the stationary phase.
- Characteristics:
- The death rate exceeds the birth rate due to factors such as resource depletion and accumulation of waste products.
- Population size begins to decline as individuals die off faster than new individuals can be born.
- This phase highlights the consequences of prolonged resource limitation and environmental stress
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