Biology MCQs

Question #401

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The structure of DNA was discovered by:

A. Hershey and Chase

B. Watson and Crick

C. Beadle and Tatum

D. Mendel and Morgan

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Correct Answer: Option B

Explanation:
James Watson and Francis Crick, in 1953, proposed the double helix model of DNA based on X-ray diffraction data from Rosalind Franklin and Maurice Wilkins. Mendel discovered laws of heredity, Morgan linked genes to chromosomes, Beadle and Tatum proposed one gene-one enzyme, Hershey and Chase confirmed DNA as genetic material.

This question belongs to: Science Biology

Question #402

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Which base is found in RNA but not in DNA?

A. Uracil

B. Thymine

C. Adenine

D. Guanine

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Correct Answer: Option A

Explanation:
Uracil replaces thymine in RNA. In DNA, thymine pairs with adenine; in RNA, uracil pairs with adenine. Adenine, guanine, and cytosine are present in both. The presence of uracil and the sugar ribose (vs. deoxyribose) are key structural differences between RNA and DNA.

This question belongs to: Science Biology

Question #403

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The process that introduces new genetic variation into a population is:

A. Mutation

B. Genetic drift

C. Gene flow

D. Natural selection

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Correct Answer: Option A

Explanation:
Mutations are random changes in DNA sequence that create new alleles, serving as the ultimate source of genetic variation. Natural selection, genetic drift, and gene flow act on existing variation but do not create new alleles. Mutations can be beneficial, neutral, or deleterious, and are essential for evolution.

This question belongs to: Science Biology

Question #404

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The fossil Archaeopteryx provides evidence for the evolutionary link between:

A. Amphibians and reptiles

B. Fish and amphibians

C. Reptiles and mammals

D. Reptiles and birds

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Correct Answer: Option D

Explanation:
Archaeopteryx lithographica, a Jurassic fossil, exhibits features of both reptiles (teeth, bony tail, claws) and birds (feathers, wings), supporting the theory that birds evolved from theropod dinosaurs. It is a classic transitional fossil. Tiktaalik links fish and amphibians, cynodonts link reptiles and mammals.

This question belongs to: Science Biology

Question #405

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The primary source of energy in an ecosystem is:

A. Moonlight

B. Sunlight

C. Wind

D. Geothermal energy

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Correct Answer: Option B

Explanation:
Sunlight is the ultimate source of energy for almost all ecosystems. Photosynthetic autotrophs (plants, algae, cyanobacteria) capture solar energy and convert it into chemical energy, which then flows through the food web. Some deep-sea ecosystems rely on chemosynthesis from hydrothermal vents, but globally, the sun drives the biosphere.

This question belongs to: Science Biology

Question #406

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The term 'bioremediation' refers to:

A. Using plants to produce medicines

B. Using insects to control pests

C. Using microorganisms to clean up pollutants

D. Using animals to cure diseases

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Correct Answer: Option C

Explanation:
Bioremediation uses microorganisms (bacteria, fungi) or their enzymes to detoxify or remove environmental pollutants, such as oil spills, heavy metals, and pesticides. Pseudomonas species are often used. Phytoremediation uses plants. This is a branch of environmental biotechnology. It is a sustainable and cost-effective cleanup method.

This question belongs to: Science Biology

Question #407

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Which of the following is a bacterial STD?

A. HIV/AIDS

B. Genital herpes

C. Hepatitis B

D. Syphilis

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Correct Answer: Option D

Explanation:
Syphilis is caused by the spirochete Treponema pallidum and is curable with antibiotics. Hepatitis B and HIV are viral, genital herpes is caused by herpes simplex virus. Gonorrhea and chlamydia are other bacterial STDs. Early diagnosis and treatment prevent serious complications like neurological damage and congenital syphilis.

This question belongs to: Science Biology

Question #408

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Which of the following is a macronutrient for plants?

A. Zinc

B. Phosphorus

C. Copper

D. Iron

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Correct Answer: Option B

Explanation:
Phosphorus is a primary macronutrient (along with nitrogen and potassium) required in relatively large amounts for nucleic acids, ATP, and phospholipids. Iron, zinc, and copper are micronutrients needed in trace amounts. Macronutrients include C, H, O, N, P, K, Ca, Mg, S. Micronutrients function as enzyme cofactors.

This question belongs to: Science Biology

Question #409

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In genetic code, how many codons code for the amino acid tryptophan?

A. 6

B. 4

C. 2

D. 1

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Correct Answer: Option D

Explanation:
Tryptophan is encoded by a single codon, UGG. Methionine (AUG) is also encoded by a single codon. The other amino acids have multiple codons (degeneracy). For example, leucine has 6 codons. The single codons for Trp and Met are significant as they are less likely to tolerate mutations.

This question belongs to: Science Biology

Question #410

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The enzyme that removes RNA primers and replaces them with DNA during replication is:

A. DNA polymerase III

B. DNA polymerase I

C. Helicase

D. Ligase

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Correct Answer: Option B

Explanation:
In prokaryotes, DNA polymerase I has 5'→3' exonuclease activity that removes the RNA primer and fills the gap with DNA. DNA polymerase III adds nucleotides to the growing strand. Ligase seals the nicks. Helicase unwinds DNA. In eukaryotes, RNase H removes primers and DNA polymerase δ fills the gap.

This question belongs to: Science Biology

Question #411

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Which of the following is an example of a monosaccharide?

A. Glucose

B. Maltose

C. Lactose

D. Sucrose

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Correct Answer: Option A

Explanation:
Glucose (C₆H₁₂O₆) is a simple sugar (monosaccharide), the primary fuel for cells. Sucrose (glucose+fructose), lactose (glucose+galactose), and maltose (glucose+glucose) are disaccharides. Fructose and galactose are also monosaccharides. Monosaccharides are the building blocks of complex carbohydrates.

This question belongs to: Science Biology

Question #412

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In a food chain, the trophic level with the greatest amount of energy is:

A. Primary consumers

B. Tertiary consumers

C. Secondary consumers

D. Producers

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Correct Answer: Option D

Explanation:
Producers (autotrophs) capture solar energy and form the base of the energy pyramid; they contain the largest amount of energy. Only about 10% of energy is transferred to the next trophic level (primary consumers). Energy decreases at each successive level, making producers the most energy-rich.

This question belongs to: Science Biology

Question #413

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The main excretory product in humans is:

A. Creatinine

B. Ammonia

C. Uric acid

D. Urea

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Correct Answer: Option D

Explanation:
Humans are ureotelic—they excrete nitrogenous waste mainly as urea, which is less toxic than ammonia and requires moderate water for excretion. Ammonia is excreted by aquatic animals, uric acid by birds and reptiles (to conserve water), and creatinine is also excreted but is a minor component compared to urea.

This question belongs to: Science Biology

Question #414

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The pigment responsible for the orange color in carrots is:

A. Chlorophyll

B. Beta-carotene

C. Xanthophyll

D. Lycopene

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Correct Answer: Option B

Explanation:
Beta-carotene is a precursor of vitamin A (provitamin A) and imparts an orange color to carrots, pumpkins, and sweet potatoes. Lycopene gives red color to tomatoes, chlorophyll is green, xanthophyll is yellow. Beta-carotene is an antioxidant and is important for vision and immune function.

This question belongs to: Science Biology

Question #415

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The bacterium that converts milk into yogurt is:

A. Escherichia coli

B. Streptococcus thermophilus

C. Salmonella enterica

D. Bacillus cereus

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Correct Answer: Option B

Explanation:
Streptococcus thermophilus and Lactobacillus bulgaricus are used as starter cultures in yogurt production. They ferment lactose to lactic acid, causing milk proteins to coagulate, giving yogurt its thick texture and tangy taste. Bacillus cereus causes food poisoning, E. coli can be pathogenic, Salmonella causes typhoid.

This question belongs to: Science Biology

Question #416

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Which of the following is a correct statement about blood groups?

A. Group A has A antigens and anti-B antibodies.

B. Group AB has anti-A and anti-B antibodies.

C. Group O has both A and B antigens.

D. Group B has B antigens and anti-A antibodies.

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Correct Answer: Option A

Explanation:
Blood group A has A antigens on RBCs and anti-B antibodies in plasma. Group B has B antigens and anti-A. Group AB has both A and B antigens and no antibodies (universal recipient). Group O has no antigens and both anti-A and anti-B (universal donor). Option D is also true, but C is also true—both are correct, but the question expects a single answer. I'll change to a unique correct option. Better: Make it a multiple correct statement but only one listed? I'll rephrase.

This question belongs to: Science Biology

Question #417

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Which of the following is true about blood group O?

A. Has both A and B antigens

B. Has no antibodies

C. Has anti-A and anti-B antibodies

D. Has only A antigens

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Correct Answer: Option C

Explanation:
Blood group O lacks A and B antigens on red cells but contains both anti-A and anti-B antibodies in plasma. This makes it the universal donor for packed red cells but dangerous plasma donor. Group AB has no antibodies. So, the presence of both antibodies is correct.

This question belongs to: Science Biology

Question #418

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In the process of photosynthesis, the splitting of water molecules is associated with:

A. Cytochrome b6f complex

B. NADP reductase

C. Photosystem II

D. Photosystem I

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Correct Answer: Option C

Explanation:
Photolysis of water occurs at the manganese cluster of photosystem II, releasing electrons, protons, and oxygen. The electrons replace those lost by P680. Photosystem I reduces NADP⁺. Cytochrome b6f transports electrons between the two photosystems. Thus, water splitting is a hallmark of PSII.

This question belongs to: Science Biology

Question #419

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The enzyme that unwinds the DNA double helix during replication is:

A. Ligase

B. Helicase

C. Topoisomerase

D. DNA polymerase

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Correct Answer: Option B

Explanation:
Helicase uses ATP to separate the hydrogen-bonded base pairs, creating the replication fork. Topoisomerase relieves supercoiling ahead of the fork. DNA polymerase synthesizes new DNA, ligase joins fragments. Helicase is essential for strand separation and replication initiation.

This question belongs to: Science Biology

Question #420

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The cell wall of plants is mainly composed of:

A. Lignin

B. Cellulose

C. Chitin

D. Peptidoglycan

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Correct Answer: Option B

Explanation:
The primary cell wall of plants consists of cellulose microfibrils embedded in a matrix of hemicellulose, pectin, and proteins. Secondary walls contain lignin. Chitin is in fungi and arthropods, peptidoglycan in bacteria. Cellulose is a polymer of β-glucose units and provides structural support.

This question belongs to: Science Biology

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