GATE 2021 BT – Question 26

General Biology · Microbiology: History, bacterial classification and diversity, cell wall, Gram positive and negative bacteria, archaea, methods · 1 mark · Multiple choice

Which statement about microbial growth medium is correct?

Luria-Bertani broth is synthetic
Nutrient broth is defined
Sabouraud dextrose agar is differential
Trypticase soy agar is complex

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Correct answer: (D) Trypticase soy agar is complex

Explanation

A **complex medium** contains ingredients of unknown or variable chemical composition, such as digests of protein, yeast extract or meat extract. A **defined (synthetic) medium** has every component known exactly. A **selective** medium allows only certain organisms to grow, and a **differential** medium makes different organisms look different.

**Luria-Bertani broth:** contains tryptone and yeast extract, so it is complex, not synthetic. ✗
**Nutrient broth:** contains beef extract and peptone, so it is complex, not defined. ✗
**Sabouraud dextrose agar:** has a low pH and is used to select for fungi. It is selective, not differential. ✗
**Trypticase soy agar:** made from digests of casein and soybean, so it is **complex**. ✓

Answer **D**.