All Free Biology MCQs with Answers
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19844 questions · page 736 of 1985
7351. Bacteria were grown in a medium containing heavy isotope of nitrogen (N15) for many generations and all their DNA contained heavy nitrogen only. A bacterium of this type was transferred to normal medium and allowed to duplicate. After two divisions of heavy DNA,
- A. Only one daughter cell will have heavy DNA
- B. Two daughter cells have normal DNA and other two have heavy DNA
- C. All daughter cells have heavy DNA
- D. Half daughter cells have heavy DNA and other half have normal DNA
Explanation: After two divisions, four bacterial cells are formed in which two daughter bacterial cells have normal DNA and other two have both normal and heavy DNA because DNA replicates by semiconservative method in bacteria.
Correct answer: Two daughter cells have normal DNA and other two have heavy DNA7352. The combination of XXY (47) chromosomes results in:
- A. Down's Syndrome
- B. Turner's Syndrome
- C. Klinefelter's Syndrome
- D. Sickle cell anemia
- E. Color blindness
Explanation: Klinefelter syndrome is a genetic condition in which a boy is born with an extra X chromosome. Instead of the typical XY chromosomes in men, they have XXY, so this condition is sometimes called XXY syndrome.
Correct answer: Klinefelter's Syndrome7353. The diagram shows a cell of an organism formed by reduction division. What is the diploid number for this organism?
- A. 10
- B. 20
- C. 30
- D. 40
- E. 44
Explanation: Haploid cells are formed by reduction division, which has half the number of chromosomes than diploid cells. To calculate the diploid number of cells just multiply the chromosome number in the haploid number by 2. So, 22x2=44.
Correct answer: 447354. The first cell to contain the diploid number of chromosomes is:
- A. 2
- B. 3
- C. 4
- D. 6
- E. 9
Explanation: Zygote(3) formed by the fusion of sperm(1) and ovum(2) is the first cell to have a diploid number of chromosomes.
Correct answer: 37355. Haploid and monoploid numbers of chromosomes of hexaploid wheat are:
- A. 21 and 42
- B. 7 and 21
- C. 21 and 7
- D. 42 and 21
Explanation: Wheat, Triticum, has basic chromosome number, n = 7; thus the hexaploid species (Triticum aestivum) have 6n = 42. Haploid chromosome number is the one present in gametes of that organism; gametes contain half the chromosomes of the somatic cells. Thus, haploid chromosome number of hexaploid wheat is 21. Monoploidy is presence of single basic chromosome set; thus monoploid of hexaploid wheat has x = 7 chromosomes. Correct answer is C.
Correct answer: 21 and 77356. An anticodon is the sequence of the nitrogenous bases on the:
- A. Complementary strand of DNA which codes for one amino acid
- B. Complementary strand of mRNA which codes for one amino acid
- C. tRNA molecule where the amino acid is attached
- D. tRNA molecule which recognizes the appropriate sequence of bases on the mRNA
- E. mRNA molecule which instructs the ribosomes to initiate
Explanation: Anticodons are present on the tRNA molecules which complement codons on the mRNA molecules, which is mentioned in statement D. All other options are factually wrong.
Correct answer: tRNA molecule which recognizes the appropriate sequence of bases on the mRNA7357. Which of the following is NOT the part of RNA?
- A. Nitrogenous bases
- B. Ribose Sugars
- C. Deoxyribose Sugars
- D. Phosphate groups
- E. Adenine
Explanation: Deoxyribose sugars are not part of RNA, rather ribose sugars are part of RNA. Deoxyribose sugars are found in DNA molecules.
Correct answer: Deoxyribose Sugars7358. The chromosomes with equal arms are called:
- A. Metacentric
- B. Submetacentric
- C. Acrocentric
- D. Telocentric
Explanation: Chromosomes with the centromere located near the middle and with two equal arms on either side are called metacentric chromosomes.
Correct answer: Metacentric7359. Cell X contains 24 chromosomes. It divides by mitosis to produce cells Y and Z. How many chromosomes does cell Z contain?
- A. 12
- B. 24
- C. 46
- D. 48
Explanation: Mitosis is a process of cell duplication, in which one cell divides into two genetically identical daughter cells. In the various stages of mitosis, the cell's chromosomes are copied and then distributed equally between the two new nuclei of the daughter cells. So cells Y and Z will have the same amount of chromosomes as the parent cell i.e. Cell X. So option B is correct and options A, C, and D are incorrect. Option A would be correct if cell X had undergone meiosis which divides the number of chromosomes into two. Option D would be after DNA replication but before mitosis, where the double amount of chromosomes is present temporarily.
Correct answer: 247360. Part of the amino acid sequences in normal and sickle cell hemoglobin are shown. Normal haemoglobin (Thr - pro - glu - glu) Sickle cell haemoglobin (thr - pro - val - glu) The mRNA codons for these amino acids are Glutamine (glu) GAA GAG, Threonine (thr) ACU ACC, Proline (pro) CCU CCC, Valine (val) GUA GUG. Which transfer RNA molecule is Involved in the formation of this part of the sickle cell haemoglobin?
- A. GUG
- B. CAU
- C. UGC
- D. GAG
Explanation: The transfer RNA has complementary base pairs to mRNA. The unique amino acid in sickle cell is valine, the mRNA codons of valine are GUG and GUA, the complementary bases are CAC and CAU (Guanine to Cytosine, Uracil to Adenine and vice versa). So option B is correct.
Correct answer: CAU