Which of the following statements about the circulatory system is correct? MCQ with Answer and Explanation

Explanation:
Adenine (A) pairs with thymine (T) via two hydrogen bonds. Guanine (G) pairs with cytosine (C) via three hydrogen bonds. This base pairing (complementarity) is key to the double helix structure and ensures accurate replication and transcription. The higher number of bonds between G-C contributes to DNA stability; GC-rich regions are harder to denature.

Explanation:
Mitochondria and chloroplasts contain circular DNA and 70S ribosomes, enabling them to transcribe and translate some proteins independently, though they rely on nuclear genes for most proteins. This partial autonomy supports the endosymbiotic origin hypothesis. The presence of their own genetic material and protein synthesis machinery qualifies them as semi-autonomous. Thus, both assertion and reason are correct, and the reason correctly explains the assertion.

Explanation:
Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, enabling the transport of water, ions, molecules, and even some viruses between them, thus ensuring cytoplasmic continuity. Gap junctions perform a similar function in animal cells, while tight junctions and desmosomes are for sealing and adhesion, respectively.