List of top Questions asked in NEST

In an experiment, bacteria were grown for 500 generations in a medium containing $^{14}\text{N}$ (light isotope), then transferred to a medium with $^{15}\text{N}$ (heavy isotope) for one generation, and finally transferred back to the $^{14}\text{N}$ medium for one more generation. Assuming all cells divide synchronously and replication is semi-conservative, the ratio of $^{14}\text{N}^{15}\text{N}$ to $^{14}\text{N}^{14}\text{N}$ double-stranded DNA at the end of the experiment is:

Bacteria have cell wall made of a polymer of N-acetylglucosamine and N-acetylmuramic acid connected by $\beta$-1,4 glycosidic bonds. Lysozyme, an enzyme, cleaves the glycosidic bond and disrupts the cell wall structure. In an experiment, Gram-positive and Gram-negative bacteria, which differ in terms of cell envelope and peptidoglycan thickness, are treated with lysozyme and subsequently placed in a hypotonic solution. The correct statement about the effect of the treatment is:

The fate of a cell in which pyruvate dehydrogenase is completely inhibited will be:

Two spherical unicellular organisms, X and Y, have the same cytoplasmic composition, metabolic pathways, and live in identical nutrient-rich aerobic conditions. The diameters of X and Y are, respectively, 10 and 20 $\mu\text{m}$. When nutrients are not limiting, the ratio of total oxygen consumption per hour per cell of organisms Y to X is:

Mendel's law of independent assortment implies that

Covishield is a vaccine used to create immunological memory against COVID-19 infection. It is made by inserting the gene coding for the SARS-CoV-2 spike protein into an adenovirus vector. When injected into the human body, the vector releases the gene into human cells, which then produce the spike protein. However, the adenovirus vector is not able to replicate itself because:

Negatively charged monodentate strong field ligand \(X^-\) and weak field ligand \(Y^-\) form the complexes \[ [MnX_6]^{4-} \quad \text{and} \quad [MnY_6]^{4-} \] respectively. Under certain reaction conditions, let the crystal field splitting energies for \[ [MnX_6]^{4-} \quad \text{and} \quad [MnY_6]^{4-} \] be \(\Delta_{o1}\) and \(\Delta_{o2}\), respectively. Which of the following statements is/are correct?

Which one of the following statements about DNA replication is incorrect?

Genomic DNA is digested with Alu I restriction enzyme that is a 4-base pair cutter. Assuming a random distribution of bases in the genome, what is the frequency with which it will cut the DNA?

Once upon a time there lived a population of mammals \(X\). Due to continental drift, the population got separated into two groups and continued to live independently for a long period of time. After approximately \(1\) lakh years, researchers attempted to interbreed the two populations, but they were unable to produce fertile offspring. This type of speciation has probably occurred due to:

Consider the following reaction: \[ xMnO_4^- + yI^- + zH^+ \rightarrow pMn^{2+} + qIO_3^- + rH_2O \] The correct ratio \(x:y\) in the balanced equation is:

Evaluate \[ \int_{0}^{\sqrt{\pi}} x\sin^{2}(x^{2})\,dx \]

For \(x \in \mathbb{R}\), define \[ \langle x \rangle = x-[x] \] where \([x]\) denotes the greatest integer less than or equal to \(x\). Then for any arbitrary pair of real numbers \(x,y \in \mathbb{R}\), which of the following is always true?

Let \(S\) be the set of all rational numbers \(r\) such that if \[ r=\frac{p}{q} \] with \(p,q\in\mathbb{Z}\), \(q\neq0\), then the two roots of the quadratic equation \[ x^{2}+2px+q^{2}=0 \] are equal. Then the number of elements in \(S\) is:

Consider a metal cylinder of heat capacity \(C\), thermal conductivity \(K\), mass \(m\) and radius \(r\). The combination that will have the dimension of time is:

Let \(\theta \neq \dfrac{(2n+1)\pi}{2}\), for \(n\in\mathbb{Z}\). Consider the system of equations \[ x\cos\theta+y\sec\theta=0 \] \[ x\sin\theta+y\tan\theta=0 \] This system does not have a unique solution if and only if \(\theta\) belongs to:

Three positive and two negative charges each of magnitude \(q\) are placed at five of the six vertices of a regular hexagon of side \(R\). The work done to bring a negative charge \(-q\) from infinity to the centre of the hexagon is:

The Balmer series of hydrogenic spectral lines refers to an electron transitioning from \(n\geq 3\) to \(n=2\). A hydrogenic atom with atomic number \(Z=24\) undergoes a Balmer transition of the largest possible wavelength. The emitted photon has energy \(E_0\). Another hydrogenic atom with atomic number \(Z=25\) undergoes a similar Balmer transition with emitted photon energy \(E_1\). Then \(|E_1-E_0|\), in eV, is closest to:

In the 2024 Olympics, two runners, Noah Lyles and Kishane Thompson, finished the 100.00 m race in 9.784 s and 9.789 s respectively. Assuming that they move with constant speed throughout the race, the distance between the two runners when Noah Lyles touched the finishing line would be closest to: