National Entrance Screening Test (NEST) Previous Papers

Total Marks: 200
Time: 3 hours

General instructions

1. This question booklet contains 5 sections, with mark distribution as follows.

Section 1 General 60 marks Compulsory

Section 2 Biology 70 marks Choose any two sections

Section 3 Chemistry 70 marks
Section 4 Mathematics 70 marks
Section 5 Physics 70 marks

Total = 60 + 2 X 70 = 200 marks
2. Section 1 is a General section and is compulsory.
3. Sections 2 to 5 are subject sections (Biology, Chemistry, Mathematics and Physics). Choose any two. That is, omit any two of the four subject sections.
4. Carefully read and follow the instructions given in each section.
5. Answers to the questions are to be marked in the Answer Sheet provided.
6. Ensure that you have received Answer Sheet A.
7. Rough work should be done on the sheets provided.
8. Return the Answer Sheet to the invigilator at the end of the examination.
9. Calculators, log tables, cell phones, etc. are not permitted in the examination hall.
Instructions for writing on Answer Sheet
1. Read and follow the instructions given on the Answer Sheet.
2. Write your name, roll number and other required information with ball point pen in the appropriate boxes provided. Sign your name with ball point pen in the box provided.
3. Your roll number (given on the admit card) must be entered correctly. If entered wrongly or not entered, the Answer Sheet may not be graded.
4. In the remaining part of Answer Sheet use HB pencil only as instructed. Make sure that the bubbles are lled properly (as shown in Answer Sheet).
5. Each question has four options. Fill the appropriate bubble(s). Some questions (as speci ed in the question paper) have more than one correct option.
6. Ensure that you are lling up the bubbles corresponding to correct sections.
7. Fill in the answers only when you are sure that you do not need to change the answer. As far as possible, avoid erasing the answer. In case you have to erase the answer, do so properly so that there is no black spot inside the bubble.

Section 1: GENERAL
Marks for Section 1: 60
This section contains 22 questions.
For each question, only one of the 4 options is a correct answer. For questions 1.1 to 1.16, a correct answer will earn 3 marks. For questions 1.17 to 1.22, a correct answer will earn 2 marks. For this section, a wrong answer or an unattempted question will earn 0 mark.

Read the following passage carefully and answer questions 1.1 to 1.3.

Metabolism and Life Living systems are open, non-equilibrium systems which continually exchange energy and mat- ter with their surroundings through the process of metabolism. The metabolic network of a living organism consists of a large number of pathways. Each pathway consists of a number of biochemical reactions. The pathways are integrated with/linked to other pathways to various extents. There are no stand-alone pathways. A metabolite is a molecule in a metabolic network. A precursor is a metabolite in a pathway from which other metabolites are synthesised either in a single step or in multiple steps. An end-product is a metabolite that is at the dead end of a pathway. Some steps of a metabolic pathway are committed steps for that pathway (i.e., they are not reversible). Metabolic pathways are regulated. \Repression” is one type of regulatory mechanism where the synthesis of the enzyme from DNA is inhibited, i.e., no new molecules of the enzyme which is under inhibition are synthesised. \Feedback inhibition” is another type where the existing enzyme molecules are prevented from catalysing the reaction.
In the \common feedback inhibition” mechanism, the end-product of a pathway inhibits the committed step.
A \sequential feedback inhibition” mechanism is seen in branched pathways. In this mecha- nism, the intermediate before the branch point inhibits the committed step. In the \cumulative feedback inhibition” mechanism, multiple end-products partially inhibit a committed step
1.1 Suppose all the reactions in a unicellular organism have come to equilibrium. This
(A) signals the birth of the organism.
(B) happens when the organism is at rest.
(C) is true at all the times.
(D) leads to death.

1.2 P, Q, R, S, T and U are metabolites. Within this set of metabolites, P is the precursor of all others. T and U are the only end-products. Q is the precursor of R and S. R is the precursor of T. Both the metabolites T and U partially inhibit the synthesis of Q. This is an example of
(A) common feedback inhibition.
(B) cumulative feedback inhibition.
(C) repression.
(D) sequential feedback inhibition.
1.3 In its natural environment, a bacterium E. coli can digest lactose by synthesising -galactosidase enzyme. If the medium contains minimal lactose, a speci c protein binds to the nearby region of the gene and inhibits enzyme synthesis. This is an example of
(A) common feedback inhibition.
(B) cumulative feedback inhibition.
(C) repression.
(D) sequential feedback inhibition.
Read the following passage carefully and answer questions 1.4 to 1.6.

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