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

Explanation:
Bacteria exhibit diverse roles; many are beneficial (e.g., gut flora, nitrogen fixers, decomposers), while some are pathogenic and cause diseases. Fungi are extensively used in food production, such as yeast (Saccharomyces) in baking and brewing, and molds (Penicillium) in cheese making (e.g., Roquefort, Camembert). Viruses are considered non-living outside a host cell because they lack metabolic machinery and cannot replicate independently; they only exhibit living characteristics when inside a host. Thus, statements 1 and 2 are correct.

Explanation:
Osteomalacia is the softening of bones in adults due to vitamin D deficiency, leading to inadequate mineralization of bone matrix. In children, the equivalent is rickets. Vitamin D aids calcium absorption. Deficiency may result from poor dietary intake, lack of sunlight, or malabsorption. Bones become weak and prone to fractures.

Explanation:
Smooth endoplasmic reticulum (SER) lacks ribosomes and is involved in synthesis of lipids, steroid hormones, and detoxification of drugs and toxins via cytochrome P450 enzymes. Rough ER is for protein synthesis, Golgi for packaging, lysosomes for digestion. SER is abundant in liver and gonadal cells.