All Free Biology MCQs with Answers

2271. Genes are made up of ________ ?

• A. Histones
• B. Lipoproteins
• C. Polynucleotides
• D. Hydrocarbons

Explanation: Genes are made of polynucleotides because DNA is a polymer consisting of many nucleotide units joined in long chains, and genes are segments of that DNA. Histones are common distractors because they bind and organize DNA in chromosomes, but genes are not made of histone proteins.

2272. Wilkins X-ray diffraction showed the diameter of the DNA helix as ________?

• A. 10A
• B. 20A
• C. 30A
• D. 40A

Explanation: Wilkins's X-ray diffraction data supported a DNA helix diameter of about 20 Å, which is 2 nm because 10 Å = 1 nm and 20 Å ÷ 10 = 2 nm. Students may choose 10 Å by confusing the helix diameter with the approximate spacing between stacked base pairs, which is about 3.4 Å.

2273. The structure of DNA was proposed by_________?

• A. Louis Pasture
• B. William Harvey
• C. Charles Darwin
• D. Watson and Crick

Explanation: Watson and Crick proposed the double-helical model of DNA in 1953, using evidence including Chargaff's rules and X-ray diffraction data from Rosalind Franklin and Maurice Wilkins. Students may choose Darwin because he is famous for a major biological theory, but Darwin did not determine DNA structure.

2274. A genome is___________?

• A. Appearance of an individual
• B. Genetic basis of few characters
• C. Full set of genes of an individual
• D. All of these

Explanation: A genome is the complete genetic material of an organism, including its full set of genes and associated DNA sequences. The appearance of an individual is its phenotype, while the genetic basis of selected characters is not the entire genome. Students may choose all of these by treating phenotype and a few genes as equivalent to the complete genetic complement.

2275. Each turn of DNA contain ____________ nitrogenous base pairs?

• A. 5
• B. 10
• C. 20
• D. 25

Explanation: In the common B-form of DNA, one complete turn of the double helix contains about 10 base pairs. The bases are stacked inside the helix and one base pair is positioned approximately every 0.34 nm along its length. Students may choose c by confusing the number of nucleotides with the number of base pairs, since 10 base pairs contain 20 individual nucleotides.

2276. Purines and pyrimidines are in equal ration in DNA. It was indicated by_______________?

• A. F.Miescher
• B. Chargaff
• C. Watson & Crick
• D. Harshay & Chase

Explanation: Chargaff showed that DNA contains approximately equal amounts of purines and pyrimidines because adenine pairs with thymine and guanine pairs with cytosine. The likely alternative is Watson and Crick, who used such findings to propose the double-helix structure but did not make the original base-composition observation.

2277. Okazaki fragments are connected together through action of_________________?

• A. Primase
• B. Polymerase
• C. Helicase
• D. Ligase

Explanation: DNA ligase joins Okazaki fragments on the lagging strand by sealing breaks in the sugar-phosphate backbone and forming phosphodiester bonds. Primase makes RNA primers, polymerase adds nucleotides, and helicase separates the DNA strands. Students often choose polymerase because it synthesises DNA, but it does not join the completed fragments together.

2278. The evaporative cooling in the respiratory tract of dogs is called?

• A. Vasodilation
• B. Vasoconstriction
• C. Panting
• D. All of these

Explanation: Panting increases evaporation of water from the respiratory tract, and evaporation removes heat from a dog's body. Vasodilation and vasoconstriction change blood flow through vessels but do not describe the respiratory evaporative process, so option a is the likely distractor.

2279. The average internal temperature of human body is __________?

• A. 35 oC
• B. 36 oC
• C. 37 oC
• D. 38 oC

Explanation: The average internal temperature of a healthy human is approximately 37 °C, maintained by thermoregulatory mechanisms despite changes in the external environment. Students may choose 38 °C because fever can raise body temperature, but it is not the normal average.

2280. homeostasis discovered by __________?

• A. Walter Bradford Cannon
• B. Anselme Payen
• C. Jons jacob Berzeliis
• D. None of these

Explanation: Walter Bradford Cannon introduced the term homeostasis for the maintenance of a relatively stable internal environment. Anselme Payen is associated with early enzyme research, so students may select him when they confuse two historical scientific contributors.