Microbiology

Cryopreservation is a technique used to preserve cells, tissues, or any biological constructs by cooling them to extremely low temperatures. The commonly used temperature for this process is: This is the boiling point of liquid nitrogen, which is widely used as the cryogenic medium for storage.
At this temperature, all metabolic and biochemical processes are effectively halted, thereby preserving the biological sample without damage for extended periods.
- is absolute zero — not practically achievable.
- and are cold but not standard for long-term cryopreservation.

The assertion is correct because methanogens are indeed present in the rumen of cattle and help in breaking down cellulose. However, the reason provided (about nutrition of cattle) is not a correct explanation of the assertion, as methanogens help in the fermentation process but not directly in providing nutrition.

Lactic acid bacteria used in the fermentation process of curd production can increase the vitamin B12 content of milk.

Step 1: Analyze Statement I.
"Conjugation is a conservative process because donor bacteria donot retain copy of genetic material."
Bacterial conjugation is a process where genetic material (usually a plasmid) is transferred from a donor bacterium to a recipient bacterium through direct contact. In this process, the donor bacterium \textit{does} retain a copy of the genetic material. The plasmid replicates during transfer, so the donor remains F+ (if it's an F plasmid transfer), and the recipient becomes F+. Therefore, it is \textit{not} conservative in the sense described. Statement I is False. Step 2: Analyze Statement II.
"In Bacterial transformation, genetic information is expressed in recipient cell."
Bacterial transformation is the process by which bacteria take up naked DNA from their environment. Once the foreign DNA is incorporated into the recipient cell's genome, it can be expressed, leading to the acquisition of new traits. For the transformation to be successful and for the genetic information to have an effect, it must be expressed. Statement II is True. Step 3: Analyze Statement III.
"\textit{Salmonella typhimurium} is a transformation bacteria." \textit{Salmonella typhimurium} is a well-known bacterium, often studied for its pathogenicity. While some bacteria are naturally competent for transformation (e.g., \textit{Bacillus subtilis}, \textit{Streptococcus pneumoniae}, \textit{Haemophilus influenzae}), \textit{Salmonella typhimurium} is primarily known for its ability to undergo transduction (gene transfer via bacteriophages) and conjugation, rather than being a naturally competent transformation bacterium. While it can be made competent artificially in a lab, it's not typically classified as a "transformation bacteria" in the natural sense compared to those known for natural competence. More importantly, it is commonly used in the Ames test for mutagenicity, which involves its ability to acquire mutations, not necessarily natural transformation. Therefore, Statement III is False. Step 4: Analyze Statement IV.
"Biologically active toxic pollutant can be detected by Biosensors." Biosensors are analytical devices that combine a biological component (like enzymes, antibodies, DNA, or whole cells) with a physicochemical detector. They are designed to detect specific substances (analytes), including toxins, pollutants, and other biologically active molecules, with high sensitivity and specificity. Many biosensors are developed specifically for environmental monitoring and detection of toxic pollutants. Statement IV is True. Step 5: Identify the correct combination of statements. From the analysis: \begin{itemize} \item Statement I: False \item Statement II: True \item Statement III: False \item Statement IV: True \end{itemize} The correct combination is II and IV. The final answer is .

A) Enrich nutrient quality — Bio fertilizers (III)
B) Kill insect pest — Bio pesticides (IV)
C) Dung to gas — Biogas (II)
D) Microbial scale growth — Bioreactor (I)

A) Complementary receptor site — Tail fibres (III)
B) Two identical RNA molecules — Retroviridae (II)
C) Viral enzyme — Lysozyme (IV)
D) Proteinaceous infectious particle — Prions (I)

Lactobacillus bacteria help ferment milk to produce curd and also enhance its vitamin B₁₂ content, improving its nutritional quality.

Pleomorphic bacteria can alter shape and size in response to environmental conditions.
Acetobacter shows pleomorphism.