Competent Host

Correct answer: A. Vector compatibility and experiment goal

The host should maintain the vector and suit the experiment goal. This is the basis of host choice.

Correct answer: B. Growth of one transformed cell

Each colony can be a population from one transformed cell. Therefore colonies are useful in clone screening.

Correct answer: C. To prevent contamination

Sterile technique is used to keep the transformation experiment free from unwanted microorganisms and foreign DNA. If bacteria or fungi contaminate the culture or agar plate, they may grow as colonies, consume nutrients, or introduce DNA that is unrelated to the intended transformant. This can produce false-positive colonies and make colony counting, selection, and interpretation unreliable. Option C is correct because sterile handling protects the identity of the experimental sample and helps ensure that colonies arose from the intended host and transformation procedure. The other options describe no valid purpose of aseptic technique in molecular biology.

Correct answer: D. Cells are alive and capable of growth

Viability means cells are alive and can grow after transformation. Dead cells do not form colonies.

Correct answer: A. Cells may die

Very harsh conditions can reduce cell viability. Good transformation needs both competence and survival.

Correct answer: B. By selection and screening

Selection chooses transformed cells and screening identifies recombinant clones. Both are important in cloning workflow.

Correct answer: C. Taking vector and forming colonies

The competent host takes the vector and forms colonies whose color is checked in screening. This helps identify recombinants.

Correct answer: D. By selectable marker based growth

Marker based growth gives an initial sign of transformed cells. Separate screening is needed for insert confirmation.

Correct answer: A. It is always a starch-digesting enzyme

A competent host is not an enzyme but a cell capable of DNA uptake. Remember it in transformation context.

Correct answer: B. They are barriers for DNA entry

The bacterial surface acts as a natural barrier. Competence treatment helps reduce this barrier.

Correct answer: C. DNA uptake can be difficult

Because of negative charges DNA and cell surface can repel each other. Calcium ions can help reduce this problem.

Correct answer: D. They can reduce charge effects between DNA and cell surface

Divalent cations such as calcium can make DNA uptake easier. This is a basic idea of chemical competence.

Correct answer: A. Chemical transformation

Chemical transformation commonly uses calcium chloride treatment and heat shock. It is useful for bacterial plasmid uptake.

Correct answer: B. Electroporation

Electrocompetent cells are cells prepared for electroporation. Keeping salt low can be important.

Correct answer: C. Electric arcing may occur

High salt can cause arcing and cell damage in electroporation. Therefore clean low-salt DNA is useful.

Correct answer: D. For correct interpretation of experiment result

A control plate shows whether cells and selection system are working properly. This makes result interpretation safer.

Correct answer: A. To check background growth

A no-plasmid control can show unexpected growth on an antibiotic plate. This can reveal contamination or selection problems.

Correct answer: B. To check cell competence

A positive control with known plasmid shows that competent cells can transform. It helps validate the method.

Correct answer: C. A very large plasmid can make uptake harder

Large plasmids can generally transform less efficiently than small plasmids. Treat this as a practical factor.

Correct answer: D. Impurities can reduce uptake and cell survival

DNA used for transformation should contain as little contaminating protein, salt, solvent, detergent, or degraded material as possible. Such impurities can interfere with the interaction between DNA and the competent cell membrane, reduce the efficiency of DNA entry, or damage and kill sensitive cells. Pure DNA therefore improves the chance that viable cells will receive and maintain the desired plasmid. Option D is correct because contaminants may reduce both uptake and survival, lowering the number of transformant colonies. Purity does not make water, and it is not merely a matter of DNA colour; the claim that impure DNA is always better is also false.

Correct answer: A. Proper selection medium

Selection medium helps maintain vector-containing cells. This can reduce recombinant plasmid loss.

Correct answer: B. By isolating a transformed colony

A transformed colony may contain a recombinant plasmid. Colony isolation is a basic step of clone selection.

Correct answer: C. Colony PCR

Colony PCR can quickly indicate insert presence in a recombinant colony. Final confirmation can be by sequencing.

Correct answer: D. To extract plasmid DNA for confirmation or use

Plasmid can be isolated from transformed host for restriction analysis or sequencing. This helps clone confirmation.

Correct answer: A. A suitable cell that takes DNA and maintains recombinant vector

A competent host is a useful cell for taking external DNA and propagating a vector. Link it with transformation.