Everyday Science

Explanation: Vitamin D is synthesized in the skin when it is exposed to ultraviolet B (UVB) rays from sunlight.

Explanation: The elbow joint is a classic example of a hinge joint, which allows movement in only one plane (flexion and extension), similar to the hinge of a door.

Explanation: Type 2 diabetes is primarily caused by insulin resistance, where the body's cells fail to respond effectively to insulin, leading to elevated blood glucose levels over time.

Explanation: A cloudburst is an extreme and sudden rainfall event, typically defined as precipitation exceeding 100 mm per hour over a localized area, often causing flash floods.

Explanation: Natural gas is predominantly composed of methane (CH4), typically comprising 70–90% of its volume, making it the primary hydrocarbon in natural gas used for fuel.

Explanation: SiO2, or silicon dioxide, is the primary component of sand and quartz. It is one of the most abundant compounds in the Earth's crust.

Explanation: Quartz has the chemical formula SiO2 (silicon dioxide). It is one of the most abundant minerals in Earth's crust and is a key component of sand, granite, and many other rocks.

Explanation: Anthracite is the purest and highest quality form of coal, containing 86–98% carbon and having the highest energy density. Lignite (brown coal) is the lowest quality with the least carbon content.

Explanation: Water molecules are bonded to each other through hydrogen bonds — a relatively weak electrostatic attraction between the positively charged hydrogen of one molecule and the negatively charged oxygen of another.

Explanation: The decibel (dB) is the internationally standard unit used to measure sound intensity level. It is a logarithmic unit that expresses the ratio of a sound's intensity relative to a reference level.

Explanation: Glass is primarily used in greenhouses because it allows sunlight (short-wave radiation) to enter but traps the infrared radiation (heat) emitted by the interior, creating a warm environment for plants.

Explanation: According to international environmental standards and Pakistan's own environmental policy, a minimum of 33% forest cover is required for a country to maintain ecological balance and environmental stability.

Explanation: Carbon fixation occurs in the stroma of the chloroplast during the Calvin Cycle (light-independent reactions), where CO2 is converted into glucose using ATP and NADPH produced in the light reactions.

Explanation: Photochemical smog primarily consists of ozone, aldehydes, peroxyacetyl nitrates (PANs), and nitrogen oxides formed by sunlight-driven reactions. Particulate matter is characteristic of industrial smog, not photochemical smog.

Explanation: Sedimentation is a primary physical water treatment process in which solid particles suspended in water settle to the bottom of a tank under gravity, clarifying the water before further treatment.

Explanation: Droughts contribute to wildfires through multiple mechanisms: they create arid, moisture-deficient conditions, dry out vegetation eliminating its natural fire resistance, and turn trees and shrubs into highly combustible fuel.

Explanation: Carbon dioxide (CO2) is the most significant greenhouse gas responsible for maintaining Earth's temperature by absorbing and re-emitting infrared radiation, preventing heat from escaping into space.

Explanation: Restriction enzymes (also called restriction endonucleases) are molecular scissors that recognize and cut DNA at specific sequences called restriction sites. They are fundamental tools in genetic engineering.

Explanation: AUG is the universal start codon in mRNA that signals the ribosome to begin translation of a protein. It codes for the amino acid methionine and marks the beginning of every polypeptide chain.

Explanation: At dairy reception facilities, fresh milk is stored in large refrigerated silo tanks (silos) that maintain optimal temperature and hygiene conditions until it is processed for pasteurization and packaging.

Explanation: Food cans are made from steel coated with a thin layer of tin to prevent corrosion and rust. This is why food cans are commonly called "tin cans," even though the primary structural material is steel.

Explanation: Enzymes are biological catalysts made up of polypeptide chains (proteins). Their three-dimensional protein structure, especially the active site, determines their specificity and catalytic function.

Explanation: Fruit ripening is primarily driven by enzymatic activity. Enzymes like cellulases, amylases, and pectinases break down cell walls and starches, softening the fruit and developing its flavor and color.

Explanation: Sucrose (common table sugar) is a disaccharide formed by a glycosidic bond between one molecule of glucose and one molecule of fructose. It is produced naturally in plants through photosynthesis.

Explanation: In ecology, a community refers to two or more populations of different species that coexist and interact in the same habitat or geographic area, forming a biotic unit.

Explanation: The nucleolus is a dense region inside the cell nucleus where ribosomal RNA (rRNA) is synthesized and ribosomal subunits are assembled, earning it the name "ribosome factory."

Explanation: Earth is the densest planet in the Solar System with an average density of approximately 5.51 g/cm³. Its dense iron-nickel core and rocky mantle contribute to this high density.

Explanation: S-waves (shear waves) can only travel through solid materials because they require a medium that can resist shear stress. They cannot pass through liquids or gases, which is why the Earth's outer core (liquid) blocks S-waves.