All Free Biology MCQs with Answers

• A. Down's syndrome
• B. Turner's syndrome
• C. Jacob's syndrome
• D. Klinefelter's syndrome

Explanation: Klinefelter's syndrome is a genetic condition in which a boy is born with an extra X chromosome. Jacob's syndrome, XYY syndrome is a genetic condition in which a male has an extra Y chromosome. Down's syndrome is a trisomy 21. The additional chromosome in Down's Syndrome is NOT a sex chromosome. Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing.

• A. Isoleucine
• B. Tryptophan
• C. Valine
• D. Arginine

Explanation: Tryptophan is unique because it is the only amino acid specified by a single codon.

• A. Ribosomes
• B. Chloroplasts
• C. Deoxyribonucleic acids
• D. None of them

Explanation: Gene mutations can occur in deoxyribonucleic acids (DNA). DNA is the genetic material present in the nucleus of eukaryotic cells and in the nucleoid region of prokaryotic cells. It carries the instructions for the synthesis of proteins and other cellular components. Mutations can arise spontaneously or as a result of exposure to mutagenic agents such as radiation or certain chemicals. These mutations can involve changes in the DNA sequence, such as substitutions, insertions, or deletions of nucleotides. Gene mutations can affect the structure or function of proteins encoded by the mutated genes, potentially leading to various genetic disorders or abnormalities. Ribosomes are cellular structures responsible for protein synthesis. They are not directly involved in gene mutations. However, mutations in genes that encode ribosomal proteins can affect the functioning of ribosomes, leading to abnormalities in protein synthesis. Chloroplasts are organelles found in plant cells and some other eukaryotic organisms. They are involved in photosynthesis, the process by which plants convert sunlight into energy-rich molecules. Chloroplasts contain their own DNA, known as chloroplast DNA (cpDNA), which encodes some of the proteins required for photosynthesis. Mutations can occur in the cpDNA, leading to alterations in the photosynthetic process. Therefore, the correct option is "Deoxyribonucleic acids" since gene mutations primarily occur in the DNA molecules.

• A. 22 pairs of autosomes and 1 pair of sex chromosomes
• B. 22 pairs of autosomes and XY chromosomes
• C. 22 pairs of autosomes and XX chromosomes
• D. Haploid somatic cells and diploid germinal cells

Explanation: Diploid set of human chromosomes have 22 pairs of autosomes and 1 pair of sex chromosomes. That is why A is correct. B is wrong because this is only specific for male. C is wrong because it is specific for females.

• A. Is completely inert
• B. Carries few genes
• C. Carries many genes
• D. Contains genes for hemophilia and color blindness

Explanation: The (X / Y) chromosome carries the fewest number of genes. The Y chromosome is one-third the size of the X chromosome and contains about 55 genes while the X chromosome has about 900 genes.

• A. Both sperm and egg contain yolk
• B. All genetic information comes from sperm
• C. Sperm contains little cytoplasm
• D. Fertilization commonly occurs in the uterus

Explanation: The head of the sperm contains an extremely compact nucleus with very little cytoplasm.

• A. 100 nm
• B. 130 nm
• C. 170 nm
• D. 150 nm

Explanation: Assuming that each nucleotide is 0.34 nm in length, the length of a DNA strand with 500 nucleotides would be approximately: 500 nucleotides x 0.34 nm/nucleotide = 170 nm. Therefore, the answer is option (c) 170nm.

• A. Purine
• B. Pyrimidine
• C. H3PO4
• D. HNO3

Explanation: DNA and RNA consist of many nucleotides joined together by special ester linkages called phosphodiester bonds. Two nucleotides are linked by the phosphodiester bond which is formed by the linkage between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another. Two hydroxyls (OH) groups on the phosphate molecule bind to the 3' and 5' carbons on two independent pentose sugars to link the two nucleotides.

• A. 4 chromosomes
• B. 8 chromosomes
• C. 8 pair of chromosomes
• D. 3 chromosomes

Explanation: A sperm cell from the fruit fly Drosophila contains four chromosomes.

• A. 3.4 nm
• B. 0.3 nm
• C. 2 nm
• D. 0.2 nm

Explanation: The diameter of the DNA helix is 2 nm and the vertical rise per base pair is 0.34 nm.