Miscellaneous: UPSC Previous Year Questions (Science and Technology)

Explanation

A pressure cooker is a sealed chamber that traps the steam generated as its contents are heated. As steam builds, pressure increases, driving the boiling point of water past 212°F (100°C). In general, this higher temperature shortens cooking times and, due to a lack of evaporation, extracts flavor more efficiently from foods.

Statement 1 is correct: The area of the hole directly influences the pressure and temperature inside the cooker. The hole in the lid is where steam escapes through the pressure regulator (weight valve). A smaller hole allows less steam to escape, which increases the pressure inside, raising the boiling point of water and increasing the cooking temperature. If the hole is larger, more steam escapes, reducing the pressure and lowering the cooking temperature.

Statement 2 is incorrect: A higher flame heats the pressure cooker faster but it does not increase the maximum cooking temperature once the cooker reaches its operating pressure. The pressure and temperature inside the cooker are controlled by the pressure regulator (weight valve), not the external flame. Once the required pressure is reached, excess heat only results in more steam escaping through the valve rather than increasing the cooking temperature.

Statement 3 is correct: The weight of the lid (specifically, the weight valve) is a key factor in determining the cooking temperature. The weight of the pressure regulator (weight valve) on the lid determines the maximum pressure inside the cooker. A heavier weight means the steam must build up more pressure before it can escape, increasing the boiling point of water and the cooking temperature. If the weight is lighter, steam escapes more easily, resulting in lower pressure and temperature inside the cooker.

Explanation

The artificial culture media, also referred to as the growth medium, is a setting for the development of many kinds of microorganisms. The agarose and nutrients needed for the microorganism’s growth are present in the culture medium. This medium is first sterilised to prevent contamination, which prevents the growth of undesirable microorganisms and ensures that it only contains the microbes of interest.

Option 1 is correct: Bacteria can be easily grown on artificial or synthetic media as these provide the necessary nutrients for their growth. These media typically include essential components like carbon, nitrogen, vitamins, and minerals. For instance, nutrient agar and broth are commonly used for culturing bacteria, and Escherichia coli can be grown on Luria-Bertani (LB) agar.

Option 2 is correct: Fungi, including yeasts and molds, can thrive on artificial media specifically formulated for their growth. Media such as Sabouraud dextrose agar and potato dextrose agar are designed to support fungal growth by providing nutrients and maintaining an acidic pH, which inhibits bacterial contamination.

Option 3 is incorrect: Viruses differ significantly from bacteria and fungi because they cannot replicate independently. Being obligate intracellular parasites they require living host cells to reproduce. Thus, they are cultured by infecting host systems such as bacterial cells (for bacteriophages) or eukaryotic cells (for animal viruses) and cannot grow on synthetic media alone.

Explanation

Statement 1 is correct: Sodium Lamps emit light omnidirectionally (360 degrees), necessitating the use of reflectors to direct light toward the desired area. LED Lamps emit light directionally (typically around 180 degrees), allowing for more efficient illumination with minimal light loss.

Statement 2 is incorrect: Sodium Lamps have a shorter operational lifespan compared to LEDs. LED Lamps offer a longer lifespan, often exceeding that of sodium lamps, leading to reduced maintenance and replacement costs.

Statement 3 is correct: Sodium Lamps produce a nearly monochromatic light, resulting in poor color rendering and making it difficult to distinguish colors under their illumination. LED Lamps provide a broad spectrum of visible light, offering superior color rendering and enhancing visibility and safety in street lighting applications.

Explanation

Bisphenol A (BPA) is an industrial chemical primarily used in the production of polycarbonate plastics and epoxy resins. Polycarbonate plastics are known for their durability and clarity and are commonly utilized in items such as water bottles, food storage containers, and eyewear. It has been identified as an endocrine disruptor, meaning it can interfere with the body’s hormonal systems. Research has linked BPA exposure to various health issues, including reproductive disorders, metabolic disease, and developmental problems in children. Due to these concerns, many regulatory agencies have evaluated the safety of BPA in consumer products.

Explanation

Triclosan is an ingredient added to many consumer products intended to reduce or prevent bacterial contamination. It is added to some antibacterial soaps and body washes, toiletries, toothpastes, and some cosmetics. Some short-term animal studies have shown that exposure to high doses of triclosan is associated with a decrease in the levels of some thyroid hormones. Other studies have raised the possibility that exposure to triclosan contributes to making bacteria resistant to antibiotics.

Explanation

Water is often referred to as the "universal solvent" because it can dissolve more substances than any other liquid. This exceptional ability is primarily due to its dipolar nature. A water molecule has a bent shape, with the oxygen atom carrying a partial negative charge and the hydrogen atoms carrying partial positive charges. This polarity allows water molecules to surround and interact with various solutes, effectively breaking them apart and dissolving them. Water can develop a strong attraction to another substance, such as salt (NaCl) to the point where it can interfere with the attractive forces holding the sodium and chloride in the salt complex together and dissolve it. In organic chemistry, a dipolar compound or simply dipole is an electrically neutral molecule carrying a positive and a negative charge in at least one canonical description.