General Science Previous Year Questions (PYQ) with Answers – Page 20

RTGs power spacecraft using heat from the natural decay of plutonium-238; they are not reactors and involve no fission. In an RTG, a radioactive isotope gives off heat as it decays on its own.

Of the three, only red sanders is native to India; cashew and papaya were brought from the Americas. Red sanders (Pterocarpus santalinus) is endemic to the southern Eastern Ghats, mainly the Seshachalam and nearby hills of Andhra Pradesh.

Each of the three groups includes species that carry toxins in their bodies to deter predators. Butterflies: the Monarch butterfly feeds as a caterpillar on milkweed and stores its bitter cardiac glycosides, so birds that eat it fall sick; its bright orange colour is a warning.

Only this split of boron-10 and boron-11 gives an average atomic mass of 10.81. The relative atomic mass of an element is the average of its isotopes' masses, each weighted by how common it is.

An atomic clock keeps time by locking onto the fixed frequency of radiation that makes atoms such as cesium-133 or rubidium jump between two energy levels.

Lithium is so light that it floats on kerosene or paraffin oil, so it is kept coated in petroleum jelly or paraffin wax, or under an inert gas, instead of under oil.

Prokaryotes have no true nucleus, so there is no membrane around their genetic material. Prokaryotes are the simplest cells: bacteria and cyanobacteria (blue-green algae).

One mole of N₂ weighs 28 g, so half a mole weighs 14 g. A nitrogen molecule is made of two nitrogen atoms, each with an atomic mass of 14 u, so its molecular mass is 28 u and its molar mass is 28 g per mole.

The nitride ion, N³⁻, carries a charge of minus three, so its valency is -3. Nitrogen has five electrons in its outer shell.

The Higgs boson found at CERN in 2012 has a mass of about 125 GeV, which among the given options is closest to 100 GeV.

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.

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.

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.

Groundnut, horse-gram and soybean are all legumes of the family Fabaceae (Leguminosae), the pea family. Members of the pea family bear their seeds in pods and carry root nodules in which Rhizobium bacteria fix atmospheric nitrogen.

Diagnostic laboratories spin blood samples in a centrifuge to separate the plasma or serum from the blood cells. In centrifugation a sample is rotated at high speed, so the denser particles are pushed to the bottom of the tube and the lighter liquid stays on top.

Chlorophyll is held in the chloroplasts, the green plastids of leaf cells where photosynthesis takes place. A chloroplast is a double-membrane organelle.

Any particle smaller than an atom is a subatomic particle, and the muon qualifies just as the electron, proton and neutron do.

Lysosomes are membrane-bound sacs of digestive enzymes that break down foreign material such as bacteria and worn-out cell parts. Lysosomes are formed by the Golgi apparatus and contain hydrolytic enzymes that work in an acidic interior.

A healthy young human ear can hear sounds with frequencies from about 20 hertz to about 20,000 hertz. Frequency is the number of vibrations per second, measured in hertz, and our ears sense it as pitch.