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MCAT Official Prep (AAMC)
Biology Question Pack, Vol 2. Question 119
Section Bank B/B Section Passage 5 Question 34
Practice Exam 4 B/B Section Question 48
Bacterial growth represents an exponential increase in the number of bacteria; It is a series of four different phases, namely lag phase, exponential or log phase, stationary phase, and death phase.
Bacteria reproduce via binary fission, this means that all of the bacteria are genetically identical, and no bacteria will divide faster than the others. Bacteria are said to grow in a series of four different phases: lag phase, exponential or log phase, stationary phase, and death phase.
During the lag phase, bacteria adapt themselves to growth conditions. It is the period where the individual bacteria are maturing and not yet dividing. As the bacteria adapt, growth increases, causing a cell doubling or an exponential increase in the number of bacteria during the exponential phase, which can sometimes be called the log phase. As the bacteria grows exponentially, the medium is soon depleted of nutrients and enriched with wastes that result in the stationary phase. Bacteria will soon run out of nutrients and die. This occurs during the death phase.
Bacterial Growth Curve: This chart shows the logarithmic growth of bacteria. Note the Y-axis scale is logarithmic meaning that the number represents doubling. The phases of growth are labeled on top.
Practice Questions
Key Points
• Exponential growth can be modeled with four different phases namely lag phase, exponential or log phase, stationary phase, and death phase.
• During lag phase, cells initially adjust to the new medium until they can start dividing regularly by the process of binary fission (exponential phase); when the growth becomes limited, the cells stop dividing (stationary phase), until no more nutrients are available and cells die (death phase).
Key Terms
Bacterial growth: the division of one bacterium into two daughter cells in a process called binary fission
Lag phase: the period of bacterial growth in which bacteria adapt themselves to growth conditions; the individual bacteria are maturing and not yet able to divide
Logarithmic: forming a straight line when plotted on a logarithmic scale; exponential
Binary fission: the process whereby a cell divides asexually to produce two daughter cells
Exponential: to describe a quantity increasing over time rapidly
Exponential phase: is a period characterized by cell doubling in a population
Stationary phase: the size of a population of bacteria remains constant, even though some cells continue to divide and others begin to die
Death phase: period that begins when cells in culture exhaust their nutrient supply and begin to die
