Biology MCQs

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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Page 42 of 103
Question #821
Amino acids are linked together in proteins by which type of bond?
A. Phosphodiester bond
B. Hydrogen bond
C. Glycosidic bond
D. Peptide bond
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Correct Answer: Option D

Explanation:
Proteins are polymers of amino acids. The amino acids are linked together by peptide bonds, which are covalent bonds formed between the carboxyl group (-COOH) of one amino acid and the amino group (-NH2) of the next, with the release of a water molecule (dehydration synthesis). Glycosidic bonds link sugars, and phosphodiester bonds link nucleotides.
This question belongs to: Science Biology
Question #822
Which of the following is a saturated fatty acid?
A. Linoleic acid
B. Oleic acid
C. Palmitic acid
D. Linolenic acid
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Correct Answer: Option C

Explanation:
Saturated fatty acids have no double bonds between the carbon atoms in their hydrocarbon chain, making them 'saturated' with hydrogen atoms. They are typically solid at room temperature. Palmitic acid and stearic acid are common saturated fats. Oleic, linoleic, and linolenic acids are unsaturated fatty acids, containing one or more double bonds.
This question belongs to: Science Biology
Question #823
Which mineral is an essential component of hemoglobin?
A. Iodine
B. Iron
C. Calcium
D. Magnesium
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Correct Answer: Option B

Explanation:
Iron (Fe) is a crucial mineral that forms the core of the heme group in hemoglobin, the protein in red blood cells responsible for oxygen transport. Without adequate iron, the body cannot produce enough healthy red blood cells, leading to iron-deficiency anemia. Calcium is for bones, iodine is for thyroid hormones, and magnesium is for enzyme function.
This question belongs to: Science Biology
Question #824
Night blindness is caused by the deficiency of which vitamin?
A. Vitamin D
B. Vitamin C
C. Vitamin A
D. Vitamin B1
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Correct Answer: Option C

Explanation:
Vitamin A (Retinol) is essential for the formation of rhodopsin (visual purple), a pigment in the rod cells of the retina necessary for vision in low light conditions. Deficiency of Vitamin A leads to night blindness (nyctalopia), where a person has difficulty seeing in dim light. Severe deficiency can also cause xerophthalmia and complete blindness.
This question belongs to: Science Biology
Question #825
Beriberi is a disease caused by the deficiency of:
A. Vitamin B1 (Thiamine)
B. Vitamin B6 (Pyridoxine)
C. Vitamin B3 (Niacin)
D. Vitamin B2 (Riboflavin)
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Correct Answer: Option A

Explanation:
Beriberi is caused by a severe deficiency of Vitamin B1 (Thiamine). It affects the cardiovascular system (wet beriberi, causing edema and heart failure) and the nervous system (dry beriberi, causing muscle wasting and nerve damage). It is common in populations whose staple diet is polished rice, as the thiamine-rich husk is removed during polishing.
This question belongs to: Science Biology
Question #826
Scurvy is characterized by bleeding gums and is caused by the deficiency of:
A. Vitamin A
B. Vitamin D
C. Vitamin B12
D. Vitamin C
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Correct Answer: Option D

Explanation:
Scurvy is caused by a deficiency of Vitamin C (Ascorbic acid). Vitamin C is essential for the synthesis of collagen, a structural protein in connective tissues. Its deficiency leads to weakened blood vessels, causing symptoms like bleeding gums, loose teeth, joint pain, and poor wound healing. It was historically common among sailors lacking fresh fruits and vegetables.
This question belongs to: Science Biology
Question #827
Rickets in children is caused by the deficiency of:
A. Vitamin D
B. Vitamin B1
C. Vitamin A
D. Vitamin C
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Correct Answer: Option A

Explanation:
Rickets is a childhood bone disorder caused by a severe deficiency of Vitamin D (Calciferol), or sometimes calcium or phosphate. Vitamin D is essential for the absorption of calcium and phosphorus from the gut. Its deficiency leads to soft, weak bones, resulting in skeletal deformities like bowed legs, delayed growth, and bone pain. Osteomalacia is the adult equivalent.
This question belongs to: Science Biology
Question #828
Kwashiorkor is a severe form of malnutrition primarily caused by:
A. Protein deficiency
B. Iron deficiency
C. Calorie deficiency
D. Vitamin A deficiency
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Correct Answer: Option A

Explanation:
Kwashiorkor is a severe form of malnutrition in children caused by a significant deficiency of protein in the diet, despite potentially adequate calorie intake. It is characterized by edema (swelling, especially in the belly due to low albumin), an enlarged liver, thinning hair, and a 'flaky paint' skin rash. Marasmus is caused by overall protein-calorie deficiency.
This question belongs to: Science Biology
Question #829
Marasmus is a disease of severe malnutrition characterized by:
A. Edema and fatty liver
B. Bone deformities
C. Bleeding gums
D. Overall wasting of body tissues and severe calorie-protein deficiency
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Correct Answer: Option D

Explanation:
Marasmus is a form of severe malnutrition caused by a deficiency of both calories and protein. It results in extreme wasting of muscle and subcutaneous fat, making the child look emaciated or 'wasted'. Unlike kwashiorkor, marasmus typically does not present with edema. The child is extremely weak, has a 'old man' face, and is highly susceptible to infections.
This question belongs to: Science Biology
Question #830
Which of the following is an essential amino acid that must be obtained from the diet?
A. Serine
B. Glycine
C. Alanine
D. Lysine
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Correct Answer: Option D

Explanation:
Essential amino acids are those that the human body cannot synthesize in sufficient quantities and must be obtained through the diet. There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Glycine, alanine, and serine are non-essential amino acids that the body can produce.
This question belongs to: Science Biology
Question #831
Pernicious anemia is caused by the deficiency of:
A. Vitamin B12
B. Vitamin C
C. Folic acid
D. Iron
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Correct Answer: Option A

Explanation:
Pernicious anemia is a specific type of megaloblastic anemia caused by the inability to absorb Vitamin B12 (Cobalamin) due to a lack of intrinsic factor, a protein secreted by the stomach. Vitamin B12 is essential for red blood cell formation and neurological function. Its deficiency leads to the production of large, immature, and dysfunctional red blood cells.
This question belongs to: Science Biology
Question #832
Body Mass Index (BMI) is calculated using which parameters?
A. Weight and height
B. Weight and age
C. Height and waist circumference
D. Fat percentage and muscle mass
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Correct Answer: Option A

Explanation:
Body Mass Index (BMI) is a simple index used to classify underweight, overweight, and obesity. It is calculated as a person's weight in kilograms divided by the square of their height in meters (kg/m2). While it is a useful population-level screening tool, it does not directly measure body fat and may not be accurate for athletes or the elderly.
This question belongs to: Science Biology
Question #833
Vitamin E is primarily known for its role as a:
A. Hormone precursor
B. Blood clotting factor
C. Antioxidant protecting cell membranes
D. Coenzyme in energy metabolism
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Correct Answer: Option C

Explanation:
Vitamin E (Tocopherol) is a fat-soluble vitamin that acts primarily as a powerful antioxidant. It protects cell membranes from oxidative damage by neutralizing free radicals, which are unstable molecules that can damage cells. It also supports immune function and has anti-inflammatory properties. Deficiency is rare but can cause neurological problems and hemolytic anemia.
This question belongs to: Science Biology
Question #834
The structure of DNA was described as a double helix by:
A. Schrödinger and Heisenberg
B. Darwin and Wallace
C. Mendel and Morgan
D. Watson and Crick
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Correct Answer: Option D

Explanation:
The double helix structure of DNA was proposed by James Watson and Francis Crick in 1953, based on X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins. They proposed that DNA consists of two antiparallel polynucleotide chains coiled around a common axis, with specific base pairing (A-T, G-C) holding the strands together.
This question belongs to: Science Biology
Question #835
DNA replication is said to be semi-conservative because:
A. DNA is replicated only during the S phase
B. Each new DNA molecule consists of one old (parental) strand and one newly synthesized strand
C. Replication occurs in both directions from the origin
D. Both strands of the new DNA molecule are newly synthesized
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Correct Answer: Option B

Explanation:
Semi-conservative replication means that when a new DNA double helix is formed, it consists of one original (parental) strand and one newly synthesized strand. This was proven by the Meselson-Stahl experiment in 1958 using isotopes of nitrogen (15N and 14N) in E. coli. This mechanism ensures genetic continuity.
This question belongs to: Science Biology
Question #836
The process of synthesizing mRNA from a DNA template is called:
A. Translation
B. Replication
C. Transcription
D. Transduction
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Correct Answer: Option C

Explanation:
Transcription is the first step of gene expression, where a specific segment of DNA is copied into RNA (specifically mRNA) by the enzyme RNA polymerase. This occurs in the nucleus of eukaryotes. The mRNA then carries the genetic code from the DNA to the ribosomes in the cytoplasm for translation (protein synthesis).
This question belongs to: Science Biology
Question #837
The genetic code is read in triplets of nucleotides called:
A. Anticodons
B. Introns
C. Codons
D. Exons
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Correct Answer: Option C

Explanation:
The genetic code is a sequence of nucleotide triplets in mRNA called codons. Each codon consists of three consecutive nitrogenous bases and specifies a particular amino acid or a stop signal during protein synthesis. For example, AUG is the start codon (methionine). Anticodons are the complementary triplets found on tRNA molecules.
This question belongs to: Science Biology
Question #838
Translation, the process of protein synthesis, occurs at the:
A. Mitochondria
B. Golgi apparatus
C. Ribosome
D. Nucleus
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Correct Answer: Option C

Explanation:
Translation is the process where the genetic code carried by mRNA is decoded to synthesize a specific sequence of amino acids, forming a protein. This process occurs at the ribosomes in the cytoplasm. Ribosomes read the mRNA codons and match them with the anticodons of tRNA molecules carrying the corresponding amino acids.
This question belongs to: Science Biology
Question #839
The Lac operon in E. coli is an example of an:
A. Attenuated operon
B. Repressible operon
C. Constitutive operon
D. Inducible operon
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Correct Answer: Option D

Explanation:
The Lac operon in E. coli is a classic example of an inducible operon. It is normally 'off' (repressed) because a repressor protein binds to the operator, preventing transcription. However, when the inducer (allolactose, derived from lactose) is present, it binds to the repressor, inactivating it and allowing RNA polymerase to transcribe the genes needed for lactose metabolism.
This question belongs to: Science Biology
Question #840
Mendel's Law of Segregation states that:
A. Alleles of different genes assort independently
B. Traits are blended in the offspring
C. During gamete formation, the two alleles for each gene separate from each other
D. Dominant traits are more common in the population
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Correct Answer: Option C

Explanation:
The Law of Segregation (Mendel's First Law) states that an organism possesses two alleles for each trait, and these alleles separate (segregate) during the formation of gametes (meiosis). Each gamete receives only one allele. This explains why a recessive trait can disappear in the F1 generation but reappear in the F2 generation.
This question belongs to: Science Biology

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