Consider statements about human immunity: 1. Skin is a physical barrier. 2. Phagocytosis is a specific immune response. 3. Memory cells provide long-term immunity. Which are correct? MCQ with Answer and Explanation

Explanation:
Fossils are the preserved remains or traces of ancient organisms, providing direct, chronological evidence of evolutionary changes and past life forms over millions of years. Homologous organs (like the forelimbs of humans, whales, and bats) share a common structural plan and evolutionary origin, indicating divergent evolution from a common ancestor. Analogous organs (like the wings of birds and insects) perform similar functions but have different structural plans and evolutionary origins, indicating convergent evolution, not common ancestry. Thus, statements 1 and 2 are correct.

Explanation:
Platelets (thrombocytes) are small, anucleate cell fragments that adhere to the site of injury, release clotting factors, and aggregate to form a platelet plug, initiating the coagulation cascade. RBCs transport oxygen, WBCs defend against infection, and plasma proteins like albumin maintain osmotic balance. Clotting factors are also present in plasma, but platelets are the primary cellular component.

Explanation:
Insulin, secreted by the pancreas, promotes cellular glucose uptake, lowering blood sugar levels. Adrenaline (epinephrine) from the adrenal medulla triggers the fight-or-flight response, increasing heart rate and energy supply. Thyroxine, produced by the thyroid gland, requires iodine as an essential component for its synthesis; iodine deficiency causes goiter. All statements are correct.