CBSE 12th Biology Question Paper 2026 (Set 1)

The placenta acts as an endocrine tissue and produces hormones such as estrogens, progesterone, human chorionic gonadotropin (hCG), human placental lactogen (hPL), and relaxin. Among these, hCG is produced by the placenta during pregnancy, so option (b) is the one that would not be correct only if it were a different hormone. Since the visible option text is truncated, the intended correct answer in NCERT-based questions is usually progesterone is not considered a placental hormone in the same sense early on; however, placenta does produce progesterone later. As the question/options are incomplete, the standard board-level answer for 'not produced by placenta' is prolactin.

Pistil-pollen interaction is mediated by chemical components present on the pollen and stigma. These chemical signals help in recognition and compatibility between pollen and pistil. Water availability, light exposure, and humidity are not the main factors governing this specific interaction.

Histones are rich in basic amino acids because they bind tightly to negatively charged DNA. The two main amino acids present in histones are lysine and arginine. Therefore, option (d) is correct.

Homo habilis lived in East African grasslands, used stone tools/weapons, and was likely partly frugivorous, including fruits in its diet. Dryopithecus was an ape-like ancestor, Australopithecines were more primitive bipedal hominins, and Homo erectus came later and is known for more advanced tools and fire use.

Sickle cell anemia is caused by a point mutation in the beta-globin gene, where a single base substitution changes glutamic acid to valine. This is not a frameshift mutation, not due to dust particles, and not caused by a change in chromosome number.