General Science Questions (MCQs) for Competitive Examinations

Notes:
Light that enters the eye is focused onto the retina at the back of the eye. The retina contains light sensitive cells called rods and cones. The rod and cone cells contain special proteins which absorb light resulting in activation of the cell. The signals generated by the rods and cones of the retina are transmitted to the neurons which form the optic nerve. The signals are then sent to an area of the brain called the visual cortex where the information is processed.

Notes:
Sex determination in human beings depends on the particular pair of sex chromosomes an individual inherits. The homogametic sex, females, usually possess two identical sex chromosomes (XX). On the other hand, males, who are the heterogametic sex, typically present a pair of different sex chromosomes (XY). This distinct pair forms the blueprint that directs male physical and biological characteristics development.

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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.

Notes:
Methane (CH4) is a greenhouse gas and causes warming the same way that CO2 does. It absorbs radiation emitted from the surface and re-emits that radiation in all directions with some of the radiation returning to the surface where it is absorbed and converted to heat. In the first two decades after its release, methane is 84 times more potent than carbon dioxide.

Notes:
Pleiotropy describes the genetic effect of a single gene on multiple phenotypic traits. The underlying mechanism is that the gene codes for a product that is, for example, used by various cells, or has a signaling function on various targets. A classic example of pleiotropy is phenylketonuria, a human disease that affects multiple systems but is caused by one gene defect.

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DNA profiling (genetic finger printing) is a technique employed by forensic scientists to assist in the identification of individuals by their respective DNA profiles. DNA profiles are encrypted sets of numbers that reflect a person’s DNA makeup, which can also be used as the person’s identifier. Each individual has unique VNTR numbers and pattern except maternal twins.

Notes:
In the collateral type of vascular bundle, xylem and phloem are arranged side by side on the same radius. This may be either open or closed. Usually xylem is seen towards the inner side and phloem towards outer side. The collateral vascular bundle is also known as conjoint.

Notes:
Bulbil is a small bulblike organ of vegetative reproduction growing in leaf axils or on flower stalks of plants such as the onion and tiger lily. It is a reproductive organ that takes part in vegetative reproduction. The bulbils drop from the parent plant on to the ground, give out adventitious roots and develop into new plants. The other structures involved in vegetative propagation include rhizome, bulb, corm, cuttings, etc.

Notes:
Yeast is an important source of most B vitamins (except B12) and folate and contains potassium and magnesium. It is used in the preparation of vitamin B complex tablets. Therefore, seeds have been classified as endospermic with endosperm and nonendospermis without endosperm.