NEET 2025 Botany Question 128 Solution

In prokaryotes, membrane-bound organelles (like mitochondria, Golgi apparatus, ER) are absent. Instead, extensions of the plasma membrane invaginate into the cytoplasm to form specialised membranous structures called mesosomes:

• • These extensions can be in the form of vesicles, tubules, and lamellae.
• • They are characteristic features of prokaryotes (predominantly Gram-positive bacteria).

According to NCERT, mesosomes perform vital coordinated cellular roles:

• • 1. Cell wall synthesis: Assist in synthesizing and assembling peptidoglycan layers.
• • 2. DNA replication and segregation: Help in anchoring the bacterial chromosome during binary fission and distributing replicated DNA to daughter cells.
• • 3. Respiration: Carry respiratory electron transport chains and dehydrogenases (functioning analogous to mitochondrial cristae).
• • 4. Secretion processes and surface area enhancement for enzymatic activities.

Evaluating the other options:

• • Chromatophores: Pigment-containing membrane extensions in photosynthetic prokaryotes (e.g. cyanobacteria).
• • Cristae: Infoldings of the inner membrane of mitochondria in eukaryotic cells.
• • Endoplasmic Reticulum: A eukaryotic endomembrane network, completely absent in prokaryotes.

The prokaryotic membranous structure responsible for cell wall synthesis, DNA replication, and respiration is the Mesosome.