General Science Questions (MCQs) for Competitive Examinations

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In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. The chromosome holds not only the genetic code, but many of the proteins responsible for helping express it.

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The Passenger Pigeon or Wild Pigeon is an extinct North American bird. The species lived in enormous migratory flocks until the early 20th century, when continued hunting and habitat destruction led to its demise.

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An organism having more than two sets of homologous chromosomes is known as polyploid and the phenomenon of having them is called polyploidy. Polyploidy refers to a numerical change in a whole set of chromosomes. Polyploidy may occur due to abnormal cell division, either during mitosis, or commonly during metaphase-I in meiosis.

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Carbohydrates are the main and quick energy source for human beings. Simple carbohydrates (like sugar-sweetened beverages) are digested quickly and send immediate bursts of glucose (energy) into the blood stream. Complex carbohydrates are digested more slowly and supply a lower steadier release of glucose into the blood stream.

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Anatomy, a field in the biological sciences concerned with the identification and description of the body structures of living things. Gross anatomy involves the study of major body structures by dissection and observation and in its narrowest sense is concerned only with the human body.

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The activity of enzymes, which are generally globular proteins, is determined by their three-dimensional structure. This structure allows them to bind to a substrate and catalyze their involvement in a reaction. Enzymes vary in size, ranging from 62 amino acid residues for the monomer of 4-oxalocrotonate tautomerase, to over 2,500 residues in animal fatty acid synthase. Their specific ability to bind to substrates enables reactions to occur in the body, playing a crucial role in metabolism.

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Frogs that spend the coldest times of the year inside of the mud or within rotten heaps of leaves during hibernation receive their necessary oxygen through their skin. This is referred to as cutaneous gas exchange. They use their skin to soak in the oxygen their bodies require. Outside of hibernation period, frogs usually respire using their lungs.

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Buccal cavity (oral cavity) refers to the mouth cavity: the beginning of the alimentary canal, which leads to the pharynx and (in vertebrates) to the oesophagus. It is part of the digestive system. In mammals it contains the tongue and teeth, which assist in the mechanical breakdown of food, and the openings of the salivary glands.

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The organs which have different basic structure and origin abut are similar in their appearance and functioning, are called analogous organs. An example of analogous organs are the wings of insects, bats and birds that evolved independently in each lineage separately after diverging from an ancestor without wings.

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Fermentation is the process by which complex organic compounds, such as glucose, are broken down by the action of enzymes into simpler compounds in the absence of oxygen (anaerobic). Yeasts can convert sugars to alcohol and carbon dioxide by fermentation. Fermentation is used to produce wine, beer, yogurt and other products.