General Science GK Questions with Answers – Page 72

Silver and copper are the two best conductors of heat among metals. Metals conduct heat because their free electrons carry energy quickly through the solid.

Velocity multiplied by time is displacement, so the area between a velocity-time graph and the time axis gives the displacement.

A bacterium is a prokaryote, so its DNA lies in an irregular region called the nucleoid, with no nuclear membrane around it.

Photo 51 is the X-ray diffraction photograph of DNA that revealed its helical shape. The picture was taken in May 1952 at King's College London by Rosalind Franklin and her student Raymond Gosling.

Twenty crests and twenty troughs make twenty complete waves in 0.1 second, so the frequency is 200 Hz and the wavelength is 330 ÷ 200 = 1.65 m. One complete wave, or one cycle, contains one crest and one trough (for sound, one compression and one rarefaction).

Reducing manganese dioxide with aluminium, 3MnO₂ + 4Al → 3Mn + 2Al₂O₃, gives out a large amount of heat. This method of reducing a metal oxide with aluminium powder is called aluminothermy, or the Goldschmidt thermite process.

A freely falling object moves with a uniform acceleration, the acceleration due to gravity, g, about 9.8 m/s² near the Earth's surface.

In aerobic tissues, where oxygen is available, glucose is broken down completely into carbon dioxide, water and energy. Aerobic respiration begins with glycolysis in the cytoplasm, which gives pyruvate.

Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas: 2Na + 2H₂O → 2NaOH + H₂.

The order is plasmid (1952), DNA double helix (1953), DNA fingerprinting (1984) and the cloning of Dolly (1996). Joshua Lederberg coined the word "plasmid" in 1952 for genetic material that lives outside the chromosome; plasmids later became the main vectors of genetic engineering.

Insulin is a protein (peptide) hormone made in the human body by the beta cells of the islets of Langerhans in the pancreas.

After fertilisation, each ovule grows into a seed, and the ovary that holds the ovules grows into the fruit. In flowering plants, a pollen tube carries two male gametes to the ovule.

Gold is a noble metal at the bottom of the reactivity series, so it does not react with oxygen, water or ordinary acids.

Biogas is mostly methane, usually about 50 to 75 percent, and it is the methane that burns with a clean blue flame and no smoke.

In photosynthesis, green plants take carbon dioxide from the air and combine it with water, using sunlight, to make carbohydrates such as glucose.

The breakdown of glucose into pyruvate, called glycolysis, takes place in the cytoplasm (cytosol) of the cell. Glycolysis is the first step of respiration in almost every living cell.

Holothuria, the sea cucumber, is an echinoderm, a non-chordate group, so it never has a notochord at any stage of life.

When blood glucose is more than the body needs, the hormone insulin helps convert it into glycogen, which is stored mainly in the liver and the muscles.

Cicadas, froghoppers and pond skaters all have three body parts, six legs and a pair of antennae, the marks of the class Insecta.

Furnace oil is a heavy refinery product, it is burnt by industry for heat and power, and its high sulphur content makes it a polluting fuel.