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Test: Enzymes (NCERT) - NEET MCQ


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15 Questions MCQ Test Biology Class 11 - Test: Enzymes (NCERT)

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Test: Enzymes (NCERT) - Question 1

What is denoted by X and Y in the given graph?

Detailed Solution for Test: Enzymes (NCERT) - Question 1

Most reactions do not start automatically because the reactions have an energy barrier which may be due to hydrogen bonding, absence of precise collisions due to small reactive site, mutual repulsion, etc. External supply of energy needed to overcome this barrier is known as activation energy. The enzyme lowers the activation energy of the reaction and allows a large number of molecules to react at a time.

Fig. Lowering of activation energy by enzyme in the energy relations of a chemical reaction

Test: Enzymes (NCERT) - Question 2

Enzymes are regarded as the:

Detailed Solution for Test: Enzymes (NCERT) - Question 2
  • Enzymes are regarded as the biocatalysts.
  • Enzymes are proteins made from amino acids. 
  • It is made up of hundreds and thousands of amino acids stringed together in a very specific and unique order. 
  • Any chemical reaction inside a cell or any work that goes on inside a cell is the handiwork of enzymes inside the cell. 
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Test: Enzymes (NCERT) - Question 3

What is meant by feedback inhibition?

Detailed Solution for Test: Enzymes (NCERT) - Question 3

Inhibition of an enzyme controlling an early stage of a series of biochemical reactions by the end product when it reaches a critical concentration.

Test: Enzymes (NCERT) - Question 4

Lanolin or wool fat is a/an:

Detailed Solution for Test: Enzymes (NCERT) - Question 4
  • Lanolin or wool fat is a wax secreted by the sebaceous glands of wool-bearing animals.
  • Lanolin used by humans comes from domestic sheep breeds that are raised specifically for their wool.
Test: Enzymes (NCERT) - Question 5

Read the given statements and select the correct options.
Statement 1:
Low temperature destroys enzymes by causing their denaturation.
Statement 2: High temperature preserves the enzymes in their inactive stages.

Detailed Solution for Test: Enzymes (NCERT) - Question 5

Low temperature preserves the enzymes in their inactive state. Therefore it is used in preservation of foods inside cold storage. Low temperature present inside cold storage prevents spoilage of food.

High temperature destroys enzymes by causing their denaturation, This occurs at 50oC or so. In between the minimum and maximum temperature the reaction velocity doubles for every 10oC in temperature (general rule of thumb).

Test: Enzymes (NCERT) - Question 6

Select the right option regarding the given graph.

Detailed Solution for Test: Enzymes (NCERT) - Question 6

The variable with which we have to find the relation should always have to be on the y axis and the variable which does not show variation and will always increase will be on the x-axis.

Test: Enzymes (NCERT) - Question 7

Feedback inhibition of enzyme is influenced by

Detailed Solution for Test: Enzymes (NCERT) - Question 7

In feedback inhibition, product of a reaction inhibits the enzyme catalysing that reaction. It is a type of control mechanism at the enzyme level. If the product is produced in sufficient amount, in inhibits the enzyme to stop the further production.


 

Test: Enzymes (NCERT) - Question 8

The inhibitor which does not resemble the substrate in structure and binds to the enzyme at site other than the active site is called

Detailed Solution for Test: Enzymes (NCERT) - Question 8

In non-competitve inhibition, the inhibitor binds at a site other than the active site ob the enzyme surface. This binding impairs the enzyme function. The inhibitor has no structural resemblance with the sunstrate. It does not interfere with the enzyme-substrate binding but the catalysis is prevented, possibly due to a distortion in the enzyme conformation. Non-competitive inhibition is usually irreversible because it cannot be overcome by increasing the substrate concentration. The inhibitor (l) generally binds with the enzyme as well as the ES complex. The overall relation in non.competitve inhibition is represented as :

Test: Enzymes (NCERT) - Question 9

Michaelis Menten Constant (Km​) is equal to

Detailed Solution for Test: Enzymes (NCERT) - Question 9

Km  or the Michaelis-Menten constant is defined as the substrate concentration (expressed in moles/l) at which half-maximum velocity in an enzyme catalysed reaction is achieved. It indicates that half of the enzyme molecules (i.e. 50%) are bound with the substrate molecules when the substrate concentration equals the Km value. It was given by Leonor Michaelis and Maud Menten (1913). Km value is a characteristic feature of a given enzyme. It is a representative for measuring the strength of ES complex. A low Km value indicates a strong affinity between enzyme and substrate, whereas a high Km value reflects a weak affinity between them. For majority of enzymes, the Km values are in the range of 10−5 to 10−2 moles.

Test: Enzymes (NCERT) - Question 10

Dihydroxyacetone-3-phosphate and glyceraldehyde-3- phosphate are interconvertible. The enzyme responsible for this interconversion belongs to the cateogry of

Detailed Solution for Test: Enzymes (NCERT) - Question 10

Isomerases catalyse the change of a substrate into a related isomeric form by rearrangement of molecules.

Test: Enzymes (NCERT) - Question 11

Holoenzyme is the complete enzyme consisting of an apoenzyme and a co-factor. Select the option that correctly identifies the nature of apoenzyme and co-factor.

Detailed Solution for Test: Enzymes (NCERT) - Question 11

Enzyme may be broadly classified into two types depending on their chemical composition-simple enzymes and conjugated enzymes are wholly made up of proteins and any additional substance or group is absent, e.g., pepsin, trypsin, etc. Conjugated enzymes (or holoenzymes) are formed of two parts -a protein part called apoenzyme and a non-protein part named co-factor. The complete conjugated enzyme consisting of an apoenzyme and a co-factor is called holoenzyme. Holoenzyme is the functional unit of enzyme.

Co-factor may be inorgainc or roganic in nature. Catalytic activity is lost when co-factor is removed from the enzyme which indicates that it plays a crucial role in catalytic activity of enzymes.

Test: Enzymes (NCERT) - Question 12

Which of the following graphs shows the relationship between the rate of an enzymatic activity and substrate concentration (S)?

Detailed Solution for Test: Enzymes (NCERT) - Question 12

Increase in substrate concentration increases the rate of reaction due to two factors: (i) occupation of more and more active sites by the substrate molecules, (ii) higher number of collisions between substrate molecules. The rise in velocity is quite high in the beginning but it decreases progressively with the increase in substate concentration. If a graph is plotted for substrate concentration versus reaction velocity, it appears as a hyperbolic curve. A stage is reached where velocity is maximum. It does not increase further by increasing the substrate concentration. At this stage the anzyme molecule becomes fully saturated and no active site is left free to bind additional substrate molecules.

Test: Enzymes (NCERT) - Question 13

An enzyme extract, when subjected to electric field, separates into two fractions, each catalysing the same reaction. These fractions are:

Detailed Solution for Test: Enzymes (NCERT) - Question 13
  • Isoenzymes (also called isozymes) are alternative forms of the same enzyme activity that exist in different proportions in different tissues.
  • Isoenzymes differ in amino acid composition and sequence and multimeric quaternary structure; mostly, but not always, they have similar (conserved) structures.
Test: Enzymes (NCERT) - Question 14

Which of the following statements about enzymes are correct?
(i) Enzymes do not alter the overall change in free energy for a reaction.
(ii) Enzymes are proteins whose three dimensional shape is key to their functions.
(iii) Enzymes speed up reactions by lowering activation energy.
(iv) Enzymes are highly specific for reactions.
(v) The energy input needed to start a chemical reaction is called activation energy.

Detailed Solution for Test: Enzymes (NCERT) - Question 14

Enzymes are biological catalysts that facilitate chemical reactions in living organisms. Let's go through each statement and determine if it is correct or not:
(i) Enzymes do not alter the overall change in free energy for a reaction.
This statement is incorrect. Enzymes lower the activation energy required for a reaction, which in turn affects the overall change in free energy. Enzymes do not change the equilibrium constant or the final energy state, but they do accelerate the rate of reaction.
(ii) Enzymes are proteins whose three-dimensional shape is key to their functions.
This statement is correct. Enzymes are typically proteins, and their three-dimensional shape, also known as their conformation, is crucial for their biological activity. The active site of the enzyme, where the substrate binds and the reaction occurs, is determined by its specific three-dimensional shape.
(iii) Enzymes speed up reactions by lowering activation energy.
This statement is correct. Enzymes function by providing an alternative reaction pathway with a lower activation energy. By lowering the activation energy, enzymes increase the rate of reaction without being consumed or permanently altered in the process.
(iv) Enzymes are highly specific for reactions.
This statement is correct. Enzymes are highly specific for the reactions they catalyze. Each enzyme has a specific substrate or set of substrates that it binds to and acts upon. This specificity is due to the complementary shape and chemical properties of the enzyme's active site and the substrate.
(v) The energy input needed to start a chemical reaction is called activation energy.
This statement is correct. Activation energy is the energy required to initiate a chemical reaction by breaking bonds in the reactant molecules. It is the energy barrier that must be overcome for the reaction to proceed.
Therefore, the correct answer is (D) - All of these.
Test: Enzymes (NCERT) - Question 15

Which of the following is an example of isozyme?

Detailed Solution for Test: Enzymes (NCERT) - Question 15

The multiple molecular forms of an enzyme occuring in the same organism and having a similar substrate activity are called isoenymes or isozymes. They have similar properties but different molecular weights and locations. Over 100 enzymes are known to have isoenzymes. α-amylase of wheat endosperm has 16 isozymes, lactate dehydrogenase has 5 isozymes. Glucokinase is an isozyme of hexokinase.

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