Biology MCQs

Notes:
Human immunodeficiency virus (HIV) attacks and kills crucial immune system cells, known as T-helper cells. A T cell, or T lymphocyte, is a type of lymphocyte (a subtype of white blood cell) that plays a central role in cell-mediated immunity. They are called T cells because they mature in the thymus from thymocytes.

Notes:
Tachycardia is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 80 beats per minute is accepted as tachycardia in adults. A healthy adult heart normally beats 60 to 100 times a minute when a person is at rest. Tachycardia occurs when an abnormality in the heart produces rapid electrical signals.

Notes:
Transport of soluble products of photosynthesis is called translocation. Translocation of soluble products of photosynthesis occurs in the part of the vascular tissue known as the phloem. The phloem is the principle food conducting tissue associated with xylem in the vascular system.

Notes:
The transport of water, nutrients and other substances from one part of a plant to another is called translocation. While, phloem transports synthesized food from the leaves to the rest of the plant body; water and minerals are transported from the roots upwards through the xylem tubes.

Notes:
A flower is the reproductive structure of many plants. The carpel is the female reproductive structure that produces eggs. The stamen is the male reproductive structure that produces sperm. Fertilization takes places in the ovary of the female flower. When a carrying agent like wind/
water/ animals carry pollen grains from male anthers to the female flower part i.e. stigma, a pollen tube forms and the pollen grain travels down the style and finally reaches the ovary where it fertilizes an ovule.

Notes:
Vitamins A, D, E, and K are the fat-soluble vitamins. Unlike water-soluble vitamins, these vitamins dissolve in fat and are stored in body tissues. Too much vitamin A, D, or K (Hypervitaminosis) can lead to increased levels that are unhealthy and can cause health consequences. For example, too much vitamin A can lead to birth defects.

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As exercise commences pulmonary ventilation (breathing) increases in direct proportion to the intensity and metabolic needs of the exercise. During heavy exercise, breathing rate in an average adult person can increase upto 25 per minute.

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All crustaceans have a body covered with a protective shell composed of a horny substance called chitin. The outer skeleton is not continuous but made up of divided sections called somites. It limits the growth of an organism therefore need to be shed from time to time.

Notes:
The Miller–Urey experiment of 1952 simulated the conditions present on the early Earth, and tested the chemical origin of life under those conditions in a laboratory. The experiment demonstrated how amino acids could be generated in a lab environment from simple compounds subjected to electrical discharges in the early Earth’s atmosphere. The spontaneous creation of amino acids was used in this experiment to explain life’s origin by chemosynthesis as proposed by oparin and later supported by Haldane.

Notes:
The plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. The cell membrane, therefore, is called a selectively permeable membrane.