Which of the following statements is incorrect for antibiotics?
- An antibiotic must be a product of metabolism.
- An antibiotic should be effective in low concentrations.
- An antibiotic is a synthetic substance produced as a structural analogue of naturally occurring antibiotic.
- An antibiotic should promote the growth or survival of microorganisms.
The Correct Option is D
Solution and Explanation
1. (1): Correct. Antibiotics are often products of microbial metabolism (e.g., penicillin from Penicillium species).
2. (2): Correct. Many antibiotics are synthetic analogues (e.g., sulfonamides).
3. (3): Correct. Antibiotics are effective at low concentrations due to their high specificity.
4. (4): Incorrect. Antibiotics inhibit the growth or kill microorganisms; they do not promote their survival.
Antibiotics are agents that inhibit the growth of or kill microorganisms. They do not promote survival and are effective at low concentrations.
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Concepts Used:
Unit Cells
The smallest portion of a crystal lattice which repeats in different directions to form the entire lattice is known as Unit cell.
The characteristics of a unit cell are:
- The dimensions are measured along the three edges, a, b and c. These edges can form different angles, they may be mutually perpendicular or may not.
- The angles held by the edges are α (between b and c) β (between a and c) and γ (between a and b).
Therefore, a unit cell is characterised by six parameters such as a, b, c and α, β, γ.
Types of Unit Cell:
Numerous unit cells together make a crystal lattice. Constituent particles like atoms, molecules are also present. Each lattice point is occupied by one such particle.
- Primitive Unit Cells: In a primitive unit cell constituent particles are present only on the corner positions of a unit cell.
- Centred Unit Cells: A centred unit cell contains one or more constituent particles which are present at positions besides the corners.
- Body-Centered Unit Cell: Such a unit cell contains one constituent particle (atom, molecule or ion) at its body-centre as well as its every corners.
- Face Centered Unit Cell: Such a unit cell contains one constituent particle present at the centre of each face, as well as its corners.
- End-Centred Unit Cells: In such a unit cell, one constituent particle is present at the centre of any two opposite faces, as well as its corners.