NEET Test 63

Parsec is the unit of distance used in astronomy. A star that is one parsec away from the Earth has a parallax (apparent shift), due to the Earth's movement around the Sun, of second of arc.

One parsec is approximately 3.08 x 10¹⁶ m.

Pauli's exclusion principle:

"No two electrons in an atom can have the same values of all the four quantum numbers."

e.g, 1s²

For 1^st electron, n = 1, l = 0, m = 0, s = + 1 / 2

For 2^nd electron, n = 1, l = 0, m = 0, s = - 1 / 2

For the two electrons in the same orbital, three quantum numbers are the same but the spin quantum numbers are different.

Virus is a nucleoprotein particle. It is made up of an outermost covering known as envelope, a protein coat, i.e, capsid and a core of nucleic acid. During virus reproduction, multiple copies of envelope, capsid and nucleic acids are formed inside the host cells.

Since ribosomes are absent in virus cells, so these are not reproduced during reproduction of viruses.

During transduction, a small double stranded piece of DNA is transferred from donor bacterium to recipient by a bacteriophage (virus).

Bentham and Hooker proposed the system of classification of seed plants and called it artificial system. It was published in their book called Genera Plantarum (1862-83).

Bentham and Hooker did not know the affinities of the families placed under 'Ordines Anomali' and the families were tentatively grouped together.

All species of pines are monoecious, in that male and female reproductive structures occur on the same plant. Once a pine tree reaches a certain stage of maturity, it forms male and female reproductive structures, termed strobili. In Pinus, the microspore nucleus divides by a periclinal wall and forms a very small prothallial cell and large central cell. The central cell cuts off a second prothallial cell and antheridial cell. The nucleus of the antheridial cell divides to form generative cell and tube cell. Thus, the pollen grain of Pinus is shed at four cell stage when it consists of two vegetative prothallial cells, a generative cell and a tube cell.