General Science MCQs – Page 60 (Q591-600)

The overall set of chemical processes by which the body converts food into usable energy and builds or breaks down necessary molecules is generally called metabolism, encompassing both catabolic reactions, which break down larger molecules to release energy, and anabolic reactions, which use energy to build up larger, more complex molecules needed for growth, repair, and normal cellular function. Metabolic rate, the speed at which the body performs these chemical processes, varies between individuals based on factors including age, muscle mass, and hormonal activity, particularly thyroid hormone levels, which significantly influence how quickly or slowly a person's overall metabolism operates.

Antibodies passed naturally from a mother to her baby, providing temporary protection against certain infections during early infancy, is a classic example of passive immunity, since the baby receives ready-made, pre-formed antibodies directly, rather than actively producing its own immune response against a specific pathogen. This natural passive immunity occurs both across the placenta during pregnancy and later through breastfeeding, but it provides only temporary protection, gradually declining over the first several months of an infant's life as the maternal antibodies are naturally broken down, which is part of why timely childhood vaccination schedules are so medically important.

Blood plasma is the blood component primarily responsible for transporting nutrients, hormones, and waste products in dissolved form throughout the circulatory system, serving as the liquid medium in which red blood cells, white blood cells, and platelets are suspended, while also carrying dissolved proteins, electrolytes, glucose, and countless other essential substances between different tissues and organs of the body. Making up roughly 55 percent of total blood volume and composed mostly of water, plasma is also the source material from which various valuable medical blood products are derived, including clotting factors and immunoglobulins used in specialized medical treatments.

Chickenpox, a common, highly contagious childhood illness characterized by an itchy, blister-like skin rash, is caused by the varicella-zoster virus, a member of the herpesvirus family that, following initial infection and recovery, can remain dormant within the body's nerve tissue for decades before potentially reactivating later in life to cause a different, related condition called shingles. Widespread childhood vaccination against chickenpox, introduced in many countries beginning in the 1990s, has significantly reduced both the overall incidence of the disease and its occasional but serious potential complications in vaccinated populations.

Dietary fiber describes a substance in food that the body cannot digest but that still helps move waste through the intestines, primarily composed of complex plant carbohydrates, including cellulose, that resist breakdown by the human digestive system's enzymes due to a lack of the specific enzymes needed to break certain plant cell wall bonds. Despite not being directly absorbed or providing significant caloric energy itself, dietary fiber plays several important beneficial roles in digestive health, cholesterol regulation, and blood sugar management, and it is generally categorized into two main types, soluble and insoluble fiber, each offering somewhat different specific health benefits.

A balanced human diet is generally recommended to include a proper combination of five basic major food groups, typically comprising grains, vegetables, fruits, protein-rich foods, and dairy or equivalent calcium sources, each contributing different essential nutrients needed for overall health, growth, and proper bodily function. Nutritional guidelines from health authorities worldwide generally recommend consuming appropriate proportions from each of these food groups to ensure adequate intake of carbohydrates, proteins, fats, vitamins, minerals, and fiber, since relying too heavily on any single food group while neglecting others can lead to various nutritional deficiencies or imbalances over time.

Vitamins and minerals are the basic nutrient group primarily needed by the body in only very small trace amounts, called micronutrients, yet they remain absolutely essential for maintaining proper health, supporting countless biochemical processes ranging from immune function and bone formation to nerve signaling and energy metabolism. This contrasts with macronutrients, carbohydrates, proteins, and fats, which the body requires in much larger quantities to meet its primary energy and structural needs. Despite being needed only in small amounts, deficiencies in specific vitamins or minerals can still cause serious, well-documented health conditions, as demonstrated by diseases like scurvy, rickets, and anemia.

A deficiency of vitamin B12 in the diet is commonly associated with pernicious anemia, a condition characterized by the production of abnormally large, immature, and poorly functioning red blood cells, since vitamin B12 is essential for proper DNA synthesis during normal red blood cell formation within the bone marrow. Vitamin B12 deficiency can result either from inadequate dietary intake, particularly relevant for strict vegetarians and vegans since B12 is found almost exclusively in animal-derived foods, or from an inability to properly absorb the vitamin due to a lack of a specific stomach protein called intrinsic factor, which is required for its proper intestinal absorption.

Excess dietary fat that is not immediately needed for energy is generally stored by the body mainly as adipose tissue, specialized connective tissue composed of fat-storing cells called adipocytes, which serves as the body's primary long-term energy reserve, providing insulation against heat loss, and cushioning and protecting internal organs from physical impact. While excessive accumulation of adipose tissue is strongly associated with various health risks, including cardiovascular disease and type 2 diabetes, a moderate, healthy amount of adipose tissue is actually essential for normal bodily function, hormone regulation, and overall metabolic health.

Genetic material carrying hereditary traits is passed from parents to offspring primarily through chromosomes found within the nucleus of reproductive cells, since chromosomes are the structures that organize and package an organism's DNA, ensuring it is accurately and completely copied and distributed during both ordinary cell division and, critically, during the specialized process of meiosis that produces the sperm and egg cells involved in sexual reproduction. Each parent contributes exactly half of the offspring's total chromosome complement, ensuring the resulting offspring receives a complete, correctly balanced set of hereditary genetic instructions inherited from both parents.