Stages of Growth Curve for Bacteria:

The growth curve of bacteria represents the pattern of bacterial population growth over time. It consists of four distinct phases: Lag phase, Log phase, Stationary phase, and Decline phase. The correct sequence of these stages is option 'A': Lag, log, stationary, decline phase.

1. Lag Phase:
During the lag phase, bacteria do not show significant growth in population. This phase occurs when bacteria are introduced into a new environment or when the conditions for growth change. Bacteria in the lag phase are adapting to the new environment, synthesizing necessary enzymes, and preparing for rapid growth. The duration of the lag phase varies depending on the species of bacteria and the conditions they are exposed to.

2. Log Phase:
The log phase, also known as the exponential phase, is characterized by rapid and exponential growth of the bacterial population. During this phase, bacteria reproduce at their maximum potential rate, doubling their population size with each generation. The growth rate in the log phase is influenced by factors such as nutrient availability, pH, temperature, and oxygen levels. This phase is of great interest to researchers as it represents the period of active growth and replication.

3. Stationary Phase:
The stationary phase occurs when the growth rate of bacteria equals the death rate, resulting in a stable population size. During this phase, the availability of nutrients becomes limited, waste products accumulate, and the environment becomes less favorable for bacterial growth. As a result, bacterial reproduction slows down, and the number of viable cells remains constant. Bacteria in the stationary phase may enter a dormant state or form protective structures such as spores to survive adverse conditions.

4. Decline Phase:
The decline phase, also known as the death phase, is characterized by a decrease in the number of viable cells. This phase occurs when the death rate of bacteria exceeds the growth rate. The decline phase can be attributed to the depletion of nutrients, accumulation of toxic waste products, and the occurrence of cell death. Some bacteria may enter a viable but non-culturable state during this phase, where they are alive but unable to grow on standard laboratory media.

Conclusion:
The correct sequence of stages in the growth curve for bacteria is Lag, log, stationary, decline phase (option 'A'). It is important to understand these stages to study and manipulate bacterial growth in various fields such as microbiology, biotechnology, and medicine.