General Science Questions (MCQs) for Competitive Examinations

Notes:
Chloroxylenol, also known as para-chloro-meta-xylenol, is an antiseptic and disinfectant which is used for skin disinfection and cleaning surgical instruments. It is also used within a number of household disinfectants and wound cleaners.

Notes:
Chameleons have specialized cells, chromatophores, which contain pigments in their cytoplasm, in three layers below their transparent outer skin. Dispersion of the pigment granules in the chromatophores sets the intensity of each color. Chromatophores contain pigments and reflect light, which are responsible for creating coloration. In chameleons, there are four types of chromatophores: xanthophores, erythrophores, iridiophores, and melanophores (Cooper and Greenberg, 1992).

Notes:
Cotton is the most popular of the BT crops. In BT cotton, BT gene was isolated and transferred from a bacterium Bacillus thurigiensis to American cotton. The American cotton was subsequently crossed with Indian cotton to introduce the gene into native varieties. The BT cotton variety contains a foreign gene obtained from Bacillus thuringiensis. This bacterial gene, introduced genetically into the cotton seeds, protects the plants from bollworm (A. lepidoptora), a major pest of cotton.

Notes:
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest. Pesticides are a special kind of products for crop protection. A pesticide is generally a chemical or biological agent (such as a virus, bacterium, antimicrobial or disinfectant) that through its effect deters, incapacitates, kills or otherwise discourages pests. Target pests can include insects, plant pathogens, weeds, molluscs, birds, mammals, fish, nematodes (roundworms), and microbes that destroy property, cause nuisance, spread disease or are vectors for disease.

Notes:
Black soil is most suitable for the cultivation of cotton. The deep and medium black lava soil of the Deccan and Malwa plateaus is considered ideal, though it can be grown on alluvial and red soil as well. The black cotton soil is also known as regur.

Notes:
In plants, secondary growth is the result of the activity of the two lateral or secondary meristems, the cork cambium and vascular cambium. Secondary growth increases the girth of the plant root or stem, rather than its length. In contrast, primary meristems, found at the apex of the stem, is responsible for the primary growth (lengthening) of the plant.

Notes:
The phosphate groups on DNA are ionic and charged. Each phosphate group on the DNA backbone has one unit of negative charge (-1). Charged molecules attract water and are hydrophilic. DNA has two hydrophilic polar external backbones made of sugars and phosphate groups joined by ester bonds. Therefore, DNA as nucleic acid is characterized by presence of phosphodiester bond.

Notes:
When a DNA solution is heated enough, the double-stranded DNA unwinds, and the Hydrogen bonds that hold the two strands together weaken and finally break. The process of breaking a double-stranded DNA into single strands is known as DNA denaturation, or DNA melting. The hyper-chromicity of DNA occurs when the DNA duplex is denatured.

Notes:
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation. As per scientific evidence, by the age of 25 years nearly all bones are completely ossified in humans. Ossification test is a guess work based on the fusion of joints in the human body b/w birth and age 25. If all joints are fused the person must be of 25yrs of age or older.

Notes:
Credit for developing cell theory is usually given to three scientists: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. In 1839, Schwann and Schleiden suggested that cells were the basic unit of life. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.