Question

A bacterium divides every 35 minutes. If a culture containing $10^5$ cells per ml is grown for 175 minutes, What will be the cell concentration per ml after 175 minutes?

Answer 1

Bacteria reproduce mainly by asexual method and also show sexual combination. True sexual reproduction is absent. The sexual recombination in bacteria is of primitive type as there is no gamete formation and fusion. However, there is an exchange of genetic material and is therefore called Genetic Recombination.

Complete answer:
Asexual reproduction in bacteria occurs through various asexual spores like sporangiospores, oidia, conidia and endospores. The most common mode of asexual reproduction is binary fission. Under favorable conditions of nutrient availability, moisture and temperature, daughter cells may repeat binary fission a lot of times and may form a large population. Fortunately, such a rapid rate is seldom achieved so the process gradually slows down and ultimately stops because of various reasons like shortage of space, lack of nutrients, accumulation of waste products and development of bacteriophages that kill the bacteria itself.
The binary fission in bacteria involves mainly 3 steps:
Replication of DNA: The bacterial chromosome divides resulting in the formation of circular chromosomes. This mechanism of replication was discovered by Cairn and hence, it is known as Cairn’s theta model.
Mesosome division and membrane formation: The parent chromosome is attached to the mesosome. As a result of the synthesis of the cytoplasmic membrane between the mesosomes, each mesosome is pushed to the middle of a daughter cell.the two daughter chromosomes get properly partitioned into daughter cells.
Cross wall formation: A peripheral ring of plasma membrane invaginates and continues to grow until the two cells are separated. The cell wall materials are also deposited between the membrane completing the division of the cells.The two events, septum and cross wall synthesis, occur simultaneously.
It is given that a bacteria divides every 35 minutes. At zero minute, the culture contains $10^5$ cells/ml.
After 35 minutes, the culture will contain 21 x $10^5$ cells /ml.
Similarly, after 175 minutes, that is after 5 generations the number of cells will be 25 x $10^5$ cells/ml.
This is equal to 32 x $10^5$ cells/ml.

Note:
Cells of certain bacteria for example Bacillus, Clostridium etc. form thick walled, highly resistant bodies within the cell called endospores. Anticoagulant nature of endospores is due to the presence of Ca-dipicolinic acid in the cortex layer of the wall. Endospores are actually the means of perennation and not reproduction.