General Science GK Questions with Answers – Page 32

In an apple, the fleshy part we eat develops from the thalamus, the swollen tip of the flower stalk, and not from the ovary, which is why it is called a false fruit.

A ring of muscle at the lower end of the stomach, the pyloric sphincter, opens and closes to let food pass into the small intestine a little at a time.

. A light-year works as a unit of distance only because light in a vacuum always travels at the same speed, so the distance it covers in a year is fixed.

Triclosan is an antibacterial and antifungal agent added mainly to personal-care products. It has been used in antibacterial soaps, hand washes, toothpastes, deodorants, shaving creams, mouthwashes and cosmetics, and sometimes in kitchen items and textiles to stop the growth of germs.

Bisphenol A is the main building block from which polycarbonate plastic is made. Polycarbonate is a hard, clear and shatter-resistant plastic once widely used for reusable water bottles, baby feeding bottles, food containers, CDs and spectacle lenses.

A Carnot engine is an ideal reversible engine, not an irreversible one, and its efficiency is 1 − T2/T1 with temperatures in kelvin.

Clay is a plastic material: it deforms permanently under even a small force, so its stress is not proportional to its strain.

When only conservative forces do work on a system, the sum of its kinetic and potential energy stays the same; this is the principle of conservation of mechanical energy.

In uniform circular motion the speed stays the same but the direction keeps turning, and that change needs an acceleration pointing to the centre.

Inside a long, narrow solenoid the field lines run straight and parallel and are evenly spaced, which is the picture of a uniform field.

If gametes carried the full chromosome number, fertilisation would double it in every generation. Meiosis halves the number when gametes are formed, so that the union of two gametes restores the original diploid number and keeps it constant from one generation to the next.

His detailed drawings of the stages are the basis of the account still given in textbooks.

Interphase occupies more than ninety-five per cent of the duration of the cell cycle, because in it the cell must grow to a sufficient size, synthesise proteins and RNA, duplicate its entire DNA and prepare the structures needed for division.

This single difference is the reason meiosis I is called the reduction division. In anaphase I the two homologous chromosomes of each bivalent are pulled to opposite poles, but each of them still consists of two sister chromatids joined at an undivided centromere.

In the zygotene sub-stage of prophase I the two members of each pair of homologous chromosomes come to lie side by side along their whole length, matching point for point, and the structure that forms between them and holds them together is called the synaptonemal complex.

By this sub-stage the homologous chromosomes have already paired in zygotene and are held together as bivalents or tetrads, each made of four chromatids.

Meiosis begins with a single round of DNA replication and is then followed by two successive nuclear divisions. Meiosis I is the reduction division, in which homologous chromosomes separate and the two cells formed already carry half the parental chromosome number.

An animal cell divides its cytoplasm by a cleavage furrow, in which the plasma membrane is pulled inward around the middle until the cell is pinched into two.

Once the chromosomes are aligned on the metaphase plate and every kinetochore is attached to a spindle fibre, the centromere holding the two sister chromatids together splits.

In this stage the condensed chromosomes, each consisting of two sister chromatids, are moved by the spindle fibres until their centromeres lie in one plane across the middle of the cell, known as the metaphase plate or equatorial plate.