In the five-kingdom classification, eukaryotic unicellular organisms with various modes of nutrition are placed in: MCQ with Answer and Explanation

Explanation:
The tracheal wall contains C-shaped hyaline cartilage rings that keep the airway open, preventing collapse due to negative pressure during inspiration. Smooth muscle and fibrous tissue connect the rings, ciliated epithelium sweeps mucus upward.

Explanation:
Innate immunity is the non-specific, inborn defense mechanism present from birth. It includes physical barriers (skin, mucous membranes), physiological barriers (stomach acid, tears), cellular barriers (neutrophils, macrophages), and cytokine barriers (interferons). Antibodies and memory cells are part of acquired (adaptive) immunity.

Explanation:
Genetic variation within a population provides the raw material upon which evolutionary forces act; without variation, evolution cannot occur. Natural selection acts directly on the phenotype (observable traits) of an organism, determining its survival and reproductive success. However, evolution is a population-level phenomenon; it involves changes in allele frequencies over generations, not changes occurring within a single individual's lifetime. Thus, statements 1 and 2 are correct.