Chapter 19, Problem 9STP

Summary Introduction

To analyze : 

The parts of the bacterium, along with their functions.

Introduction :

Bacteria belong to a group of prokaryotes that is characterized by the presence of a peptidoglycan wall, a naked DNA with attached mesosomes, and reserve food. Ribosomes are the 70S in nature. They multiply through binary fission.

Explanation of Solution

  

Functions of the parts of the given bacterium: -

1. Flagella − Bacterial flagella are involved in locomotion. They are made up of three parts, the basal body, hook, and filament. The basal body is inserted in the cell envelope. The hook connects the basal body to the filament. The filament is a tubular structure responsible for causing turbulence in the liquid medium. Flagella perform to move the bacteria forward by performing rotation type movement that pushes water backward. 
2. Pili − Pilus is not involved in bacterial locomotion. They are longer, and thicker outgrowths that are developed in response to the fertility factor in Gram-negative bacteria. They help in the attachment of the recipient cell and formation of the conjugation tube.
3. Plasma membrane − Plasma membrane forms the innermost component of the cell envelops. It is semipermeable and separated the cytoplasm from the surroundings. It allows selective movement of substances in and out of the bacterial cell. The receptors present on its surface detect and respond to the chemicals present in the surroundings. It also takes part in respiration, lipid synthesis, and synthesis of cell wall components.
4. Chromosome − Nucleoid consists of a single circular strand of DNA duplex in a highly coiled form. It is considered as naked because it is not associated with histone proteins, and the nuclear envelope is absent around it. The single chromosome contains genes that code for proteins. It also transfers the traits to the daughter cells.
5. Cell wall − Cell wall is a rigid covering that provides structural support to the cell. It prevents bacterial cells against bursting when present in a hypotonic medium. 
6. Capsule − It is the outermost covering of bacteria that is made up of non cellulosic polysaccharides (in some cases, proteins are also present). It is thick and tough and prevents bacterial cells from phagocytes, toxic chemicals, drugs and some viruses such as bacteriophage. In some cases, it also helps bacteria to attach on different membranes or cells and virulence.

Conclusion

A bacterial cell is one of the most primitive forms of life. All the structures of a bacterial cell help it to thrive and reproduce in a wide variety of environments.