NEET Practice Questions (MCQs) with Answers & Solutions

The text states, 'With very small supply of energy an electron from the valence band can jump to the level $E_A$ and ionise the acceptor negatively.' When an electron leaves the valence band to fill an acceptor level, it leaves behind a hole in the valence band. So, the holes in the valence band are due to acceptance of electrons by acceptor impurities.

The NCERT text states: 'PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro'. This directly describes the fundamental principle of PCR.

The NCERT Figure 9.6 clearly labels the three steps in each PCR cycle as: (i) Denaturation; (ii) Primer annealing; and (iii) Extension of primers. Therefore, the correct order is Denaturation, Annealing, Extension.

From 'BIOTECHNOLOGY AND ITS APPLICATIONS': 'very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR. Can you explain how PCR can detect very low amounts of DNA? PCR is now routinely used to detect HIV in suspected AIDS patients.' This highlights PCR's sensitivity in amplifying small amounts of nucleic acid.

From 'MOLECULAR BASIS OF INHERITANCE': 'The sensitivity of the technique has been increased by use of polymerase chain reaction (PCR– you will study about it in Chapter 9). Consequently, DNA from a single cell is enough to perform DNA fingerprinting analysis.' This emphasizes that PCR amplifies the DNA, reducing the sample requirement.

The text mentions PCR's use in 'early diagnosis' for HIV and its ability to 'detect mutations in genes in suspected cancer patients'. It also introduces PCR as a method to 'synthesise multiple copies of the gene (or DNA) of interest' for recombinant DNA technology. Large-scale production of recombinant proteins involves bioreactors and downstream processing, but PCR itself is for amplifying DNA, not for producing the proteins directly.

The NCERT text states: 'In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro'. 'In vitro' biologically means 'in glass' or, more generally, outside a living organism, typically in a laboratory setting like a test tube.

From 'MOLECULAR BASIS OF INHERITANCE': 'The sensitivity of the technique has been increased by use of polymerase chain reaction (PCR... Consequently, DNA from a single cell is enough to perform DNA fingerprinting analysis.' This clearly indicates that PCR's amplification capability allows the use of very small sample sizes.

The text states: 'very low concentration of a bacteria or virus... can be detected by amplification of their nucleic acid by PCR.' The ability to detect something in low quantities is referred to as sensitivity.

The context mentions 'an amazing range of adaptations to ensure formation of the end products of sexual reproduction, the fruits and seeds.' Post-fertilization events specifically involve the development of the zygote into an embryo (embryogenesis), the primary endosperm nucleus into endosperm, and the ovule into a seed, all contributing to fruit and seed formation.