The process of accumulation of molecular species at the surface of solid or liquid is called adsorption. It may be physisorption or chemisorption. Low temperature is favourable for physisorption. Amount of gas adsorbed by a solid depends upon nature of gas. Easily liquefiable gases are readily adsorbed. Catalyst increases the rate of reaction. Catalysis may be homogeneous or heterogeneous. Enzymes are biological catalysts. They work at optimum pH and temperature. Solutions are of three types i.e. true solutions, colloids and suspensions. Depending on the interaction between dispersed phase and dispersion medium colloids may be Lyophilic and Lyophobic. Depending on type of particles there may be multimolecular, macro-molecular and associated colloids. Sol, gel, emulsions are also various types of colloids.
The characteristics of enzyme catalysis are:
A. Reactions are fastest at \(pH\) \(9-14\)
B. Human body temperature being \(273 K\) is best suited
C. Enzyme are highly active in presence of activators
D. one enzyme can catalyze many reactions.
E. Poisons interact with active functional groups on enzyme surface
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C and E only
Enzymes are biological catalysts, mostly globular proteins. Their main characteristics: very high efficiency, high specificity, maximum activity at an optimum temperature (298–310 K) and an optimum pH (pH 5–7), increased activity in the presence of activators and co-enzymes, and inhibition by inhibitors and poisons.
(A) Reactions are fastest at \(pH\) \(9-14\) — Incorrect. The rate of an enzyme-catalysed reaction is maximum at the optimum pH, which lies between pH 5 and 7; strongly alkaline solution destroys most enzymes.
(B) Human body temperature being \(273 K\) is best suited — Incorrect. Human body temperature is about 310 K, and it is 310 K that suits enzyme-catalysed reactions; 273 K is the freezing point of water.
(C) Enzyme are highly active in presence of activators — Correct. Activators, usually metal ions such as \( \ce{Na^{+}} \), \( \ce{Mn^{2+}} \), \( \ce{Co^{2+}} \), \( \ce{Cu^{2+}} \), increase the catalytic activity; for example amylase is very active in the presence of \( \ce{Na^{+}} \) ions.
(D) one enzyme can catalyze many reactions. — Incorrect. Enzymes are highly specific: one enzyme catalyses one reaction (e.g. urease catalyses only the hydrolysis of urea).
(E) Poisons interact with active functional groups on enzyme surface — Correct. Inhibitors and poisons interact with the active functional groups on the enzyme surface and reduce or destroy its activity.
NCERT (Pre-rationalised edition, 2022-23):
Characteristics of Enzyme Catalysis – …
