General Science MCQs – Page 58 (Q571-580)

Tuberculosis, a serious and historically often deadly infectious lung disease, is primarily caused by the bacterium Mycobacterium tuberculosis, which typically spreads through airborne respiratory droplets released when an infected person coughs or sneezes, primarily infecting and damaging lung tissue, though it can also spread to affect other organs in more severe cases. Tuberculosis remains a significant global public health concern, particularly in developing regions including parts of Pakistan, and it is typically treated with a lengthy, multi-drug antibiotic regimen lasting several months, since the bacterium is notably slow-growing and can develop resistance if treatment is incomplete or inconsistent.

Typhoid fever is primarily caused by infection with the bacterium Salmonella typhi, typically transmitted through consumption of food or water contaminated with fecal matter from an infected person, causing symptoms including sustained high fever, abdominal pain, and weakness. Typhoid remains a significant public health concern in regions with inadequate sanitation infrastructure and unreliable access to clean drinking water, including parts of Pakistan, making improved water treatment, proper sewage management, and food handling hygiene practices essential preventive measures, alongside available vaccination options for individuals at particularly high risk of exposure.

Antibiotics are generally effective medicines for treating infections caused by bacteria, working through various mechanisms such as disrupting bacterial cell wall formation or interfering with essential bacterial protein synthesis processes, targeting cellular structures and functions specific to bacteria that human cells simply do not possess. Antibiotics have no effect whatsoever on viral infections like the common cold or influenza, since viruses lack these bacterial-specific target structures entirely, and the inappropriate, unnecessary use of antibiotics for viral illnesses has significantly contributed to the serious and growing global public health problem of antibiotic-resistant bacteria.

White blood cells, also known as leukocytes, primarily play the role of defending the body against infection, actively detecting, targeting, and eliminating invading pathogens like bacteria, viruses, and fungi, as well as identifying and destroying abnormal or cancerous cells, as a core functional component of the body's overall immune system. Unlike the far more numerous red blood cells, white blood cells exist as several distinct specialized types, including neutrophils, lymphocytes, and macrophages, each contributing a different, specialized function within the coordinated, multi-layered immune defense system that continuously protects the body against disease.

Down syndrome is a genetic condition generally caused by the presence of an extra copy of chromosome 21, resulting in three total copies instead of the normal two, a condition medically termed trisomy 21, which occurs due to a chromosomal error during the formation of egg or sperm cells or in very early embryonic development. This additional genetic material affects physical development and can cause characteristic facial features, developmental delays, and an increased risk for certain health conditions. Down syndrome is one of the most common chromosomal conditions, and its likelihood increases notably with advancing maternal age at conception.

Sickle cell anemia is best classified as an inherited genetic blood disorder, caused by a specific mutation in the gene responsible for producing hemoglobin, resulting in abnormally shaped, rigid, crescent or sickle-shaped red blood cells that can block small blood vessels, cause severe pain episodes, and reduce the blood's overall oxygen-carrying efficiency. Since it is inherited genetically, sickle cell disease requires two copies of the mutated gene, one from each parent, for the full disease to manifest, while carrying just a single copy generally results in the milder sickle cell trait, which interestingly also provides some natural resistance against severe malaria infection.

Type 1 diabetes is generally characterized by the body's inability to produce sufficient insulin, resulting from an autoimmune process in which the body's own immune system mistakenly attacks and destroys the insulin-producing beta cells within the pancreas, typically developing in childhood or adolescence and requiring lifelong insulin therapy for effective management. Unlike type 2 diabetes, which is more strongly linked to lifestyle and insulin resistance developing gradually over time, type 1 diabetes cannot currently be prevented through diet or lifestyle changes, since it stems fundamentally from this specific underlying autoimmune destruction of the body's own insulin-producing cellular machinery.

Type 2 diabetes is generally characterized primarily by the body's cells becoming resistant to insulin, meaning that even though the pancreas may still produce adequate or even elevated insulin levels, particularly in earlier disease stages, the body's cells fail to respond effectively to it, resulting in persistently elevated blood glucose levels. Type 2 diabetes is strongly associated with risk factors including obesity, physical inactivity, and genetic predisposition, and unlike type 1 diabetes, it can often be effectively managed, and in some cases even partially reversed, through significant lifestyle modifications including improved diet, regular exercise, and, when necessary, appropriate oral medications.

Kwashiorkor, a serious form of childhood malnutrition, is primarily caused by a severe deficiency of dietary protein, despite often occurring alongside adequate or even relatively sufficient overall caloric intake from carbohydrates, distinguishing it from marasmus, a related malnutrition condition caused by an overall severe deficiency of both calories and protein together. Kwashiorkor is characterized by symptoms including a notably swollen, distended abdomen caused by fluid retention, stunted growth, and skin and hair changes, and it remains a significant public health concern in regions experiencing food insecurity, poverty, or limited access to diverse, protein-rich diets.

Dietary fiber, or roughage, largely indigestible plant material found in foods like whole grains, fruits, vegetables, and legumes, is primarily beneficial to the body mainly by aiding digestion and preventing constipation, since it adds bulk to stool and helps stimulate the muscular contractions of the intestines, called peristalsis, that move waste material efficiently through the digestive tract. Beyond its digestive benefits, adequate dietary fiber intake is also associated with numerous other health benefits, including helping regulate blood sugar levels, lowering cholesterol, and supporting a healthy population of beneficial gut bacteria within the digestive system.