Question

Upon inoculation into a new nutrient medium, the bacteria shows four distinct phases of growth (Lag phase, Log phase, Stationary phase and Phase of decline). Choose the correct option with respect to proportion of viable bacteria over a period of time in various phases.
(A). Lag phase: Total number of metabolically active (but not dividing) bacteria is low.
(B). Log phase: Total number of bacteria is high in which number of dying cells is higher than number of dividing cells.
(C). Stationary phase: Total number of bacteria is constant in which number of dividing cells is equal to the number of dying cells.
(D). Phase of decline: Total number of bacteria may be high in which number of dying cells is higher than number of dividing cells.
Choose the correct answer from the options given below:

• A. (B) and (D) only
• B. (A) and (C) only
• C. (C) and (D) only
• D. (B), (C) and (D) only

Hint:

To remember the biological dynamics of each growth phase:
- Lag: Adaptation occurs; cell division is zero.
- Log: Growth and division far exceed death.
- Stationary: Growth and division are equal to death.
- Decline: Death exceeds growth and division.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question deals with bacterial growth kinetics in a closed system (batch culture).
When bacteria are inoculated into a finite volume of nutrient medium, they undergo a characteristic, predictable pattern of growth over time.
This pattern is represented graphically by the bacterial growth curve, which is divided into four distinct physiological phases: the lag phase, the log (exponential) phase, the stationary phase, and the decline (death) phase.

Step 2: Detailed Explanation:
Let us analyze each statement to determine its biological accuracy:
- Statement (A): "Lag phase: Total number of metabolically active (but not dividing) bacteria is low."
This statement is incorrect.
During the lag phase, bacteria are undergoing intense metabolic activity as they adapt to their new environment.
They are actively synthesizing proteins, enzymes, RNA, and other macromolecules, but physical cell division is absent or negligible.
The absolute number of metabolically active bacteria is determined by the size of the initial inoculum and is not necessarily "low."
The key feature of the lag phase is that the net change in cell number is zero, not that the number of active cells is low.
- Statement (B): "Log phase: Total number of bacteria is high in which number of dying cells is higher than number of dividing cells."
This statement is incorrect.
In the log (exponential) phase, bacterial cells are dividing at their maximum rate permitted by the environment.
Generation time is constant, and the rate of cell division far exceeds the rate of cell death.
This results in a rapid, exponential increase in the viable bacterial population, which is the opposite of the statement's claim.
- Statement (C): "Stationary phase: Total number of bacteria is constant in which number of dividing cells is equal to the number of dying cells."
This statement is correct.
As nutrients are depleted and toxic metabolic waste products accumulate, the growth rate slows down.
The rate of new cell division becomes approximately equal to the rate of cell death.
Consequently, the net number of viable (living) bacteria remains constant, representing a plateau on the growth curve.
- Statement (D): "Phase of decline: Total number of bacteria may be high in which number of dying cells is higher than number of dividing cells."
This statement is correct.
During the phase of decline (death phase), environmental conditions become highly unfavorable, causing the rate of cell death to exceed the rate of any new cell division.
While the total cumulative physical count of bacteria (including dead cells) may remain high initially, the number of viable, living bacteria decreases progressively because death exceeds division.
Therefore, statements (C) and (D) are correct, while statements (A) and (B) are incorrect.

Step 3: Final Answer:
The correct set of statements is (C) and (D) only.
Therefore, the correct choice is Option (C).