Tag: the world of microbes

The contractile vacuole is a structure found in many marine organisms. It functions as an organelle to eliminate the excess water which may have stored in the cell because of osmotic conditions.

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).

• Eukaryotic cilia and flagella have similar organization-
• They possess a central bundle of microtubules called the axoneme which contain nine outer doublet microtubules surrounded by a central pair of singlet microtubules.
• This characteristic 9 + 2 arrangement of microtubules is seen when the axoneme of eukaryotic flagella.
  
• The correct answer is OPTION B.

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.

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.

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.