Question

Microbes at exponential growth phase will have

• A. Rate of growth is inversely proportional to division
• B. Rate of growth and division is constant and maximal
• C. Population is not uniform in terms of chemical and physical properties during this phase
• D. Population is uniform but not in terms of chemical and physical properties during this phase

Hint:

• Phases of Microbial Growth in Batch Culture: Lag phase \(\rightarrow\) Exponential (Log) phase \(\rightarrow\) Stationary phase \(\rightarrow\) Death (Decline) phase.
• Exponential Phase: Cells divide at a constant, maximum rate. Population increases exponentially. Cells are generally most uniform and metabolically active.

Answer 1

The Correct Option is B

The exponential growth phase (also known as the logarithmic or log phase) is a period in a microbial batch culture where cells are actively dividing at a constant and maximal rate under the given conditions (e.g., nutrient availability, temperature). Characteristics of the exponential phase:

• Constant and Maximal Growth Rate: The rate of increase in cell number (or biomass) per unit time is constant, and cell division occurs at the maximum rate possible for that organism in that specific medium and environment. This leads to an exponential increase in population size.
• Balanced Growth: Cells are typically in a state of balanced growth, meaning that all cellular components are synthesized at constant rates relative to each other. This results in a relatively uniform population in terms of size, chemical composition, and metabolic activity.
• High Metabolic Activity: Cells are metabolically very active.

Let's analyze the options: (a) "Rate of growth is inversely proportional to division": This is incorrect. Higher division rate means higher growth rate. (b) "Rate of growth and division is constant and maximal": This correctly describes the exponential phase. The specific growth rate (\(\mu\)) and division rate are constant and at their peak. (c) "Population is not uniform in terms of chemical and physical properties during this phase": This is generally false. During balanced exponential growth, the population is usually most uniform. Non-uniformity is more characteristic of lag phase or stationary phase. (d) "Population is uniform but not in terms of chemical and physical properties during this phase": This is contradictory and incorrect. If it's uniform, it's generally in terms of these properties during balanced growth. Therefore, option (b) is the correct statement. \[ \boxed{\text{Rate of growth and division is constant and maximal}} \]