NDA (II) 2024 General Ability Test · Question 52 of 141

Correct — C, Mitochondria and plastids. These are the only two eukaryotic organelles that possess their OWN genetic material — a small circular DNA molecule plus their own ribosomes — allowing them to make some of their own proteins and divide independently of the nucleus. This semi-autonomy is the cornerstone of the endosymbiotic theory (both are thought to descend from once free-living bacteria).

• (a)Endoplasmic reticulum and plastids — Plastids do carry DNA, but the endoplasmic reticulum does NOT — the ER is a membrane network for synthesis and transport with no genome of its own. So the pair is wrong.
• (b)Endoplasmic reticulum and mitochondria — Mitochondria carry DNA, but the endoplasmic reticulum has none. One correct + one incorrect member means the pair fails.
• (d)Lysosomes and Golgi apparatus — Neither the lysosome nor the Golgi apparatus contains any DNA — both are single-membrane organelles derived from the endomembrane system, with no genome.

Most of a eukaryotic cell's DNA sits in the nucleus, but mitochondria and plastids (chloroplasts in plants) additionally hold their own small, circular DNA and their own ribosomes. Because of this they are called 'semi-autonomous' organelles — they can synthesise some proteins and self-replicate.

Reason by elimination: only mitochondria and plastids have DNA, so any option pairing them with the ER, Golgi or lysosome must be wrong. Every option except (c) contains at least one DNA-less organelle. This links to the endosymbiotic theory — a favourite follow-up.

• Mitochondria and chloroplasts (plastids) contain their own circular DNA and 70S ribosomes.
• This semi-autonomy underpins the endosymbiotic theory (Lynn Margulis) — both evolved from engulfed prokaryotes.
• The endoplasmic reticulum, Golgi apparatus and lysosomes have NO DNA of their own.
• Mitochondrial DNA is maternally inherited in humans.

• Assuming the nucleus is the 'only' place with DNA — mitochondria and plastids also carry DNA.
• Pairing a DNA-bearing organelle with the ER/Golgi/lysosome and marking it correct.

Asked directly ('which organelle other than the nucleus contains DNA') or as an endosymbiotic-theory reasoning question.

• practice — not a real PYQ

  The presence of their own DNA in mitochondria and chloroplasts is the main evidence for which theory?

  • (a)Cell theory
  • (b)Endosymbiotic theory
  • (c)Germ theory
  • (d)Fluid-mosaic model

  Answer(b) Endosymbiotic theory — both organelles are thought to descend from once free-living bacteria.

• practice — not a real PYQ

  In humans, mitochondrial DNA is inherited

  • (a)only from the father
  • (b)only from the mother
  • (c)equally from both parents
  • (d)from neither parent

  Answer(b) only from the mother — mitochondria are inherited maternally through the egg.