DNA Uptake and Bacterial Competence — NEET Biology

Correct answer: A — S1 and S5 only

The core concept involves different methods of introducing recombinant DNA into host cells. S1: Incorrect. NCERT states, "In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell." It is not into the cytoplasm of plant cells. S2: Correct. NCERT states, "In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as biolistics or gene gun." S3: Correct. NCERT explains, "bacterial cells must first be made ‘competent’ to take up DNA. This is done by treating them with a specific concentration of a divalent cation, such as calcium... followed by placing them briefly at 420C (heat shock)." S4: Correct. NCERT states, "Similarly, retroviruses have also been disarmed and are now used to deliver desirable genes into animal cells." S5: Incorrect. NCERT states, "Since DNA is a hydrophilic molecule, it cannot pass through cell membranes." Therefore, special treatments are required. Based on the analysis, S1 and S5 are the statements that are NOT correct. Option A is correct as S1 and S5 are the incorrect statements. Option B is incorrect because S3 and S4 are correct. Option C is incorrect because S2 is correct. Option D is incorrect because S2 is correct. This question tests the understanding of various DNA delivery methods and their specific applications.