General Science GK Questions with Answers – Page 71

A restriction endonuclease recognises a short palindromic sequence in DNA and cuts both strands there, leaving sticky ends that can pair with another piece cut by the same enzyme; Hind II was the first such enzyme to be discovered and EcoRI from Escherichia coli is the most widely used.

These are the organs in which lymphocytes are produced and in which they mature into cells able to tell self from non-self; the B cells complete this training in the bone marrow and the T cells in the thymus, a gland behind the breastbone that shrinks with age.

The correct answer is B, the oral polio vaccine, which contains live poliovirus weakened so that it can multiply in the gut and raise immunity without causing the disease; it is the vaccine given as two drops in the pulse polio rounds.

The antibodies, mainly of the IgA class, come ready-made in the first milk, the colostrum, and the child's own immune system does no work, which is why the protection begins at once and lasts only a few months; antibodies of the IgG class reach the foetus through the placenta in…

On meeting an antigen a B lymphocyte multiplies and turns into a plasma cell, which pours out antibodies, that is immunoglobulins, into the blood; this arm of the defence is called humoral immunity, while T lymphocytes kill infected cells and regulate the response in cell-mediated immunity.

BCG stands for Bacillus Calmette-Guerin, a live but weakened strain of the bovine tuberculosis bacterium, and in India it is given soon after birth under the Universal Immunisation Programme, mainly to prevent the severe forms of childhood tuberculosis.

In 1796 Edward Jenner used matter from a cowpox sore to protect a boy against smallpox, the first vaccination in the modern sense, and the word vaccine comes from vacca, the Latin for cow.

The liver needs vitamin K to make prothrombin and several other clotting factors, so a deficiency of it lengthens the clotting time and causes bleeding; this is why a newborn is given vitamin K and why the vitamin is sometimes called the anti-haemorrhagic vitamin.

Landsteiner and Wiener found the antigen in 1940 while working with the blood of the rhesus monkey, and the first two letters of rhesus gave the factor its name; a person with the D antigen on the red cells is Rh positive and one without it is Rh negative.

A person of group AB carries both the A and the B antigen on the red cells, and because the body does not make antibodies against its own antigens, the plasma carries neither anti-A nor anti-B; blood of any group can therefore be transfused into such a person, who is…

The red cells of group O carry neither the A antigen nor the B antigen, so when they are transfused the antibodies in the recipient's plasma find nothing to bind to and the cells are not destroyed, which is why group O, and strictly O negative, can be given to…

The correct answer is A, Karl Landsteiner, the Austrian physician who found in 1900 that human blood falls into groups according to the antigens on the red cells, which made safe transfusion possible, and who received the Nobel Prize in Physiology or Medicine for it in 1930; with Wiener he…

Of the four, ultraviolet lies furthest towards the short-wavelength, high-energy end of the electromagnetic spectrum. All electromagnetic waves travel at the speed of light in vacuum, but they differ in wavelength and frequency.

The pulmonary veins carry oxygen-rich blood from the lungs into the left atrium. In double circulation, blood passes through the heart twice in each full round.

Metals produce a ringing sound when struck, a property called sonority, which is why bells are made of metal. Sonorous means 'producing a deep, ringing sound'.

Power is the reciprocal of focal length in metres, and 10 cm is 0.1 m, so P = 1 ÷ 0.1 = 10 D. The power of a lens measures how strongly it converges or diverges light.

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.

X-rays are electromagnetic waves made of uncharged photons, so electric and magnetic fields cannot bend them. Electric and magnetic fields exert force only on charged particles: a charge q feels a force qE in an electric field and qvB in a magnetic field.

The great majority of plant viruses carry their genes as single-stranded RNA. Viruses contain either DNA or RNA, never both, wrapped in a protein coat.

Cyclohexane, C 6 H 12, has 6 C–C single bonds and 12 C–H single bonds, 18 single bonds in all and no double or triple bond.