Question

Every 15 seconds bacteria double in number. If there are 10 bacteria now, how many will be there in 2 minutes?

Answer 1

Hint: Bacteria are prokaryotic microorganisms that comprise a wide variety of shapes, sizes and also habitats. They are capable of living independently as well as in association with plants and animals.

Complete answer:
In bacteria cell division and cell growth are closely linked to each other. Bacterial growth takes place in four phases- lag phase, log phase, stationary phase and death phase. The lag phase is a period of slow growth during which the bacterial cells are adjusting to their environment, and also synthesize various components required for growth during this phase. This is followed by the log phase or exponential phase where growth occurs at maximum rate. The rate at which the cells grow is known as growth rate and the time taken by the cells to double is known as generation time. The third phase is the stationary phase during which the nutrients start getting limited. This phase is marked by decreased metabolic activity and increase in expression of genes involved in DNA repair and nutrient transport. Finally the last phase is the death where most of the cells die due to depletion of nutrients and accumulation of toxic products. Few cells such as the endospore producing cells that can survive harsh conditions survive.
Generation time=time interval/number of generations(n)
Here generation time =15 seconds and time interval=2 minutes=120 seconds
So, number of generations=120/15=8
To calculate the new number of cells we use the formula n=logN- logN0/log 2, where N is the new number of cells present after 2 minutes and N0 is the number of cells present before 2 minutes.
8=logN-logN0/0.301
log N-log10=2.408
logN=1.408, therefore N=25.58.
So after 2 minutes the number of cells will be 25.
Note: The growth curve of bacteria is affected by external environmental factors such as temperature, pH, water activity, etc. The optimum growth condition varies for different classes of bacteria but is an important factor to obtain maximum growth rate.