Bacteria - introduction, shape and structure - class-XI

Pili are hair-like appendages found on the surface of many bacteria that help them attach to surfaces or other cells.

Bacteria are prokaryotes grouped in Kingdom Monera. Prokaryotes have a pro or primitive karyon. Thus the true nucleus is absent in bacteria. The chromosome, a single, continuous strand of DNA, is localized, but not contained, in a region of the cell called the nucleoid. All the other cellular components are scattered throughout the cytoplasm.

Nucleic acids constitute the genetic material and help in cellular expressions in bacteria, while proteins are important for constitutive activities in the bacterial cells. 15% of bacterial cell is protein, while 7% nucleic acids (DNA and RNA).
So answer is -'nucleic acid and proteins'.

The mucilage capsule present in bacteria serving as an extra covering is present outside the cell because it is a temporary layer surrounding the cell wall and protects the bacteria from antibiotics and dessication.

Bacterial genome as that of a bacteria E.coli consists of Double-stranded DNA (ds DNA) which is circular which means it doesn't have ends like eukaryotic chromosomes. E.coli consists of 4.6 x 10$^6$ base pairs(bp).

Peptidoglycans (or mucopeptide or glycopeptide or murein) are the structural elements of almost all bacterial cell walls. They constitute as much as 95% of the cell wall in some Gram positive bacteria to as little as 5 to 10% in Gram negative bacteria. Peptidoglycans are made up of a polysaccharide backbone consisting of alternating muramic acid and glucose amine residues in equal amounts.

Bacteroids are the differentiated, non-motile form of Rhizobium bacteria found within the root nodules of legumes, where they fix nitrogen.

Membrane bound organelles are absent in prokaryotes. As compared to a eukaryotic cell, the only comparable organelles present in prokaryotes are ribosomes which are naked nucleoprotein particles. Plasmodium is a unicellular eukaryotic organism which belongs to Kingdom Protista. Saccharomyces is also a unicellular eukaryotic organism which belongs to Kingdom Mycota or Fungi. Streptococcus is a unicellular prokaryotic organism which belongs to Kingdom Monera. Chlamydomonas is a unicellular eukaryotic organism, previously classified under Kingdom Plantae as Chlorophyceae but has now been moved to Kingdom Protista. Of the given options only Streptococcus is a prokaryotic organism. Hence, membrane bound cell organelles are missing in Streptococcus.

  E. coli , a gram negative rod shaped bacteria has since the time of discovery have been commonly used for biological lab experiment and research. The simple cell structured E. coli has one circular chromosome and a ds circular DNA molecule with 4.6 million base pairs in length and 4288 protein coding genes.

The cell walls of bacteria are composed of a macromolecule peptidoglycan which is a repeating framework of long glycan chains having alternate N-acetyl glucosamine and N-acetyl muramic acid; these glycan chains are cross-linked by short peptide fragments to provide a strong but flexible support framework. This makes option A correct. The green algal cell wall is composed mainly of cellulose which makes option B incorrect. Chitin is common constituent of cell walls of all type of fungi; option C is incorrect. The yeast cell wall itself is mainly composed of glucans ($\beta$$-glucans), mannoproteins and chitin; option D is incorrect. Thus, the correct answer is option A.

Cocci that remain in pains after dividing are called diplococci. Cocci that remain in chains after dividing are called streptococci.

Microorganisms are the organisms that we cannot see by our naked eyes. It can be prokaryotic unicellular like bacteria, eukaryotic unicellular like protozoa, eukaryotic multicellular like fungi and algae and even acellular like viruses.

Thus, the correct answer is option C.

Pili are minute hair like appendages, that emerges from suface of Gram -ve bacteria. They have similar structure as flagella and often involved in attachment to surface and making of biofilm. They also help in DNA exchange. They are involved in conjugation which results in transfer or exchange of genetic material. 

Escherichia coli is a rod-shaped, gram-negative bacterium that is typically 1-3 micrometers in length.

Rhodospirillum bacteria is facultative aerobic Photo - autotrophic bacteria use non-sulphur aliphatic organic  compound as donor of $H _{2}$  go,. Propyl alcohol .

$6CO _{2}+12CH _{3}CHOHCH _{3}\overset{Light}{\rightarrow}$

$C _{6}H _{12}O _{6}+12CH _{3}COH _{3}+6H _{2}O$

Some bacteria, such as cyanobacteria, are photosynthetic and contain chlorophyll, which led to their historical classification as plants.

In bacteria the site for respiratory activity is found in mesosomes. Mesosomes are folded invaginations in the cell membrane of bacteria. They increases the surface area required for respiration. They contain respiratory enzymes. It is the site of respiratory activity.

F-factor is also called as fertility factor. It is the sex factor of bacteria. It allows the transfers of genes from one bacterium carrying the factor to another bacterium lacking the factor by the process of conjugation. It is found in some bacteria only.

The bacterial cell wall is made up of Peptidoglycan or murein. It is a polymer that is made up of sugars and amino acids. The sugar component is made up of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). NAM is then attached to an amino acid chain of L-alanine, D-glutamic acid, diaminopimelic acid (DAP) and D-alanine. 

Bacteria is a unicellular prokaryotic organism. It has a cell wall around the cell membrane. The bacterial cell membrane is made up of proteins and phospholipids. the proteins in are randomly distributed in the phospholipid bilayer of the cell membrane.

Teichoic acids are characteristic components of the cell wall of Gram-positive bacteria. Pneumococcus is a well-known Gram-positive bacterium, whereas the others listed do not possess this specific cell wall structure.

Some bacteria have a capsule outside cell wall. It is made up of mucopolysaccharide. The functions of mucopolysaccharide are;

• Bacterial capsule usually consists of a polysaccharide layer that lies outside the cell envelope. The capsule is found in both gram-positive and gram-negative bacterium.
• The capsule is considered as virulence factor because it enhances the ability of bacteria to cause disease. It protects the bacterial cell from engulfment by macrophages.
• Capsules also contain water which protects the bacterium from desiccation.

Bacterial ribosomes are 70S, consisting of 30S and 50S subunits. The statement claiming they are 30 nm by 50 nm is incorrect as these numbers refer to the Svedberg units of the subunits, not the physical dimensions in nanometers.

• Mesosomes are absent in eukaryotes.
• Mesosomes refers to the folded invaginations in the plasma membrane of prokaryotes or bacterial cells.
  
• Its main function is to increase the surface area of the plasma membrane. 
• When the surface area of the membrane is increased it helps to carry out the cellular respiration more efficiently.
  
• So, the correct answer is 'Mesosome'.

Escherichia coli is a Gram-negative, facultatively anaerobic bacteria. It is found in the intestine of warm-blooded organisms. It has one circular chromosome. The chromosome contains double-stranded DNA. It may contain some circular plasmids as well as extrachromosomal material.

• Mitochondria are absent in bacteria and blue-green algae.
  
• A prokaryotic cell lacks membrane-bound cell organelles and nucleus whereas, a eukaryotic cell consists of membrane-bound cellular organelles and well-defined nucleus.
  
• Red algae, green algae and brown algae have eukaryotic cells (well-defined nucleus and cellular organelles).
• So, the correct answer is 'Bacteria'.

A. Amphitrichous bacteria have flagella (single or multiple) extending from both ends of the cell.

Amphitrichous bacteria possess a single flagellum or a tuft of flagella at both poles of the cell. This distinguishes them from peritrichous (all over) or lophotrichous (tuft at one end) arrangements.

Agrobacterium radiobacter strain K84 is used for the biological control of crown gall disease. It produces a bacteriocin called agrocin 84, which inhibits the growth of pathogenic Agrobacterium tumefaciens.

Peritrichous flagellation is found in E. coli (A-L). Ginkgo is a living fossil (B-J). Selaginella has rhizophore (C-M). Wolffia is the smallest flowering plant (D-N). Macrocystes is a large perennial alga (E-K).

Carl Woese proposed the three-domain system based on ribosomal RNA sequences, which serves as a measure of genetic relatedness (phylogeny) among organisms.

Rhodopseudomonas and Rhodospirillum are photosynthetic bacteria that belong to the group of purple non-sulphur bacteria, which use organic compounds as electron donors.

Cell division is the process in which a parent cell divides into two or more daughter cells. The unicellular organism divides and results in the formation of daughter cells and hence, cell division is a type of reproduction in unicellular organisms. Thus, the correct answer is option A.

Bacteria have three mechanism for genetic information transfer without undergoing reproduction-
1. Transformation- take up free fragment of DNA floating in medium. 
2. Transduction- transfer of DNA by a virus bacteriophage.
3. Conjugation- direct cell to cell transfer of DNA mediated by plasmid. So, option C is correct, all other options depend on reproduction for exchange of genetic material.

Glycocalyx is the outermost layer of the cell envelope. Cell wall lies between plasma membrane and glycocalyx.

Superbugs is a term used to describe strains of bacteria that are resistant to the majority of antibiotics commonly used today. These resistant bacteria can cause pneumonia, urinary tract infections, skin infections and many other diseases that are difficult to treat and may be fatal.

An anaerobic organism or anaerobic bacteria is any organism that does not require oxygen for growth. It may react negatively or even die if oxygen is present. Mitochondria, Golgi body and ER are organelles of eukaryotic organisms. Since anaerobic bacteria is prokaryotic, they are absent in anaerobic bacteria.

Denitrifying bacteria convert nitrates in the soil to free atmospheric nitrogen, nitrogen-fixing bacteria are heterotrophs.