Biology MCQs

Question #661

The genetic condition resulting from a point mutation in the hemoglobin gene leading to sickle-shaped red blood cells is:

A. Hemophilia

B. Cystic fibrosis

C. Thalassemia

D. Sickle cell anemia

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Correct Answer: Option D

Explanation:
Sickle cell anemia is an autosomal recessive disorder caused by a single nucleotide substitution (GAG → GTG) in the β-globin gene, resulting in glutamic acid replaced by valine, producing abnormal hemoglobin S. Under low oxygen, HbS polymerizes, distorting RBCs into sickle shape, causing pain and organ damage.

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Question #662

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The process of water evaporation from the leaves that creates a pulling force for water ascent is:

A. Root pressure

B. Transpiration

C. Capillary action

D. Guttation

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Correct Answer: Option B

Explanation:
Transpiration from stomata creates negative water potential in leaves, generating a tension (transpiration pull) that draws water upward through the xylem from roots. This cohesion-tension mechanism is the primary driver of water transport in tall trees. Root pressure and capillary action are minor forces.

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Question #663

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The junction between two neurons where neurotransmitters are released is the:

A. Synapse

B. Node of Ranvier

C. Dendrite

D. Axon hillock

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Correct Answer: Option A

Explanation:
A synapse is a specialized junction where the axon terminal of one neuron communicates with the dendrite or cell body of another neuron via neurotransmitters. The axon hillock is where action potential initiates, nodes of Ranvier are gaps in myelin sheath, dendrites receive signals.

This question belongs to: Science Biology

Question #664

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The mineral that is essential for the action of insulin and is a component of many enzymes is:

A. Sodium

B. Magnesium

C. Calcium

D. Zinc

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Correct Answer: Option D

Explanation:
Zinc is required for the synthesis, storage (as hexamers), and secretion of insulin in pancreatic beta cells. It also acts as a cofactor for numerous enzymes like carbonic anhydrase and DNA polymerases. Calcium is for bones/signaling, magnesium for ATP and chlorophyll, sodium for nerve impulses.

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Question #665

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The polysaccharide that forms the major structural component of plant cell walls is:

A. Glycogen

B. Cellulose

C. Starch

D. Chitin

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Correct Answer: Option B

Explanation:
Cellulose, a linear polymer of β-D-glucose units linked by β-1,4-glycosidic bonds, forms microfibrils that provide tensile strength to plant cell walls. Glycogen is animal storage, starch plant storage, chitin in fungi and arthropods. Cellulose is the most abundant organic polymer on Earth.

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Question #666

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The scientist who developed the concept of 'natural selection' independently of Darwin was:

A. Charles Lyell

B. Jean-Baptiste Lamarck

C. Thomas Malthus

D. Alfred Russel Wallace

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Correct Answer: Option D

Explanation:
Alfred Russel Wallace, a British naturalist, independently arrived at the theory of evolution by natural selection. His 1858 essay, sent to Darwin, prompted the joint presentation of their ideas. Darwin then published 'On the Origin of Species' in 1859. Malthus influenced population thinking, Lyell geology, Lamarck earlier evolutionary ideas.

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Question #667

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The component of the bacterial cell wall that is targeted by lysozyme is:

A. Lipopolysaccharide

B. Chitin

C. Cellulose

D. Peptidoglycan

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Correct Answer: Option D

Explanation:
Lysozyme, an enzyme found in tears, saliva, and egg white, hydrolyzes the β-1,4-glycosidic bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan, weakening the bacterial cell wall and causing lysis. It is part of innate immunity. Penicillin inhibits peptidoglycan synthesis.

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Question #668

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The form of energy that directly powers the synthesis of ATP in chloroplasts is:

A. Chemical energy of glucose

B. Electric current

C. Light energy

D. Proton gradient (chemiosmosis)

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Correct Answer: Option D

Explanation:
In both mitochondria and chloroplasts, ATP synthase uses the energy stored in a proton gradient across a membrane (thylakoid membrane in chloroplasts, inner mitochondrial membrane) to drive the synthesis of ATP from ADP and Pi. This process is chemiosmosis, proposed by Peter Mitchell.

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Question #669

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The type of inflorescence where the main axis terminates in a flower and younger flowers arise below it is:

A. Cymose

B. Racemose

C. Spike

D. Umbel

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Correct Answer: Option A

Explanation:
In cymose (definite) inflorescence, the main axis ends in a flower, limiting further growth, and lateral branches develop below it, which also end in flowers. Racemose is indeterminate with apical growth continuing. Spike and umbel are types of racemose. Cymose includes cymes.

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Question #670

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The vitamin that functions as a coenzyme in transamination and decarboxylation of amino acids is:

A. Vitamin B₆

B. Vitamin B₁

C. Vitamin B₂

D. Vitamin B₁₂

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Correct Answer: Option A

Explanation:
Vitamin B₆ (pyridoxine, pyridoxal, pyridoxamine) is a coenzyme (pyridoxal phosphate, PLP) for many enzymes involved in amino acid metabolism, including transaminases and decarboxylases. B₁ acts in carbohydrate metabolism, B₂ in redox reactions, B₁₂ in methylation and DNA synthesis.

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Question #671

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The fluid that lubricates joints and reduces friction is:

A. Aqueous humor

B. Cerebrospinal fluid

C. Pleural fluid

D. Synovial fluid

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Correct Answer: Option D

Explanation:
Synovial fluid is a viscous, egg-white-like fluid secreted by the synovial membrane in synovial joints (e.g., knee, hip). It lubricates articular cartilage, reducing friction and wear, and also nourishes cartilage. CSF cushions CNS, pleural fluid reduces lung friction, aqueous humor is in the eye.

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Question #672

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The process by which a bacterium acquires genes from a bacteriophage is:

A. Transformation

B. Conjugation

C. Transduction

D. Mutation

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Correct Answer: Option C

Explanation:
Transduction is the transfer of bacterial DNA from one bacterium to another by a bacteriophage. Generalized transduction occurs when phage accidentally packages host DNA; specialized transduction involves specific genes near the prophage integration site. Conjugation needs direct contact, transformation free DNA.

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Question #673

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The type of epithelial tissue that lines the urinary bladder and allows stretching is:

A. Transitional epithelium

B. Columnar epithelium

C. Stratified squamous

D. Simple squamous

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Correct Answer: Option A

Explanation:
Transitional epithelium (urothelium) is stratified, with cells that can change shape from cuboidal to squamous when the bladder distends. It lines the renal pelvis, ureters, bladder, and part of the urethra. Squamous is flat, cuboidal cube-shaped, columnar tall.

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Question #674

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The structure in the female reproductive system where the fetus develops is the:

A. Fallopian tube

B. Vagina

C. Uterus

D. Ovary

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Correct Answer: Option C

Explanation:
The uterus is a hollow, muscular organ where the fertilized egg implants into the endometrium and develops into an embryo and fetus. The ovaries produce eggs and hormones, the fallopian tubes are the fertilization site, and the vagina is the birth canal and copulatory organ.

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Question #675

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The technique of creating a gene library by inserting DNA fragments into plasmid vectors and introducing into bacteria is:

A. DNA sequencing

B. Microarray

C. Cloning

D. PCR

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Correct Answer: Option C

Explanation:
Molecular cloning involves inserting a DNA fragment into a vector (e.g., plasmid), which is then taken up by host cells (e.g., E. coli). As the bacteria replicate, they produce many copies of the inserted DNA, creating a gene library. PCR amplifies without vectors, sequencing reads bases, microarrays analyze expression.

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Question #676

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The pigment that gives the brown color to algae such as kelp is:

A. Phycocyanin

B. Phycoerythrin

C. Fucoxanthin

D. Chlorophyll

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Correct Answer: Option C

Explanation:
Fucoxanthin is a carotenoid pigment found in brown algae (Phaeophyceae) that gives them their characteristic brown or olive-green color, masking the green chlorophyll. Phycoerythrin is red (red algae), phycocyanin blue (cyanobacteria, some red algae). Brown algae include kelps and Fucus.

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Question #677

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The condition characterized by increased intraocular pressure damaging the optic nerve is:

A. Conjunctivitis

B. Glaucoma

C. Cataract

D. Retinal detachment

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Correct Answer: Option B

Explanation:
Glaucoma is a group of eye diseases that result in damage to the optic nerve, often associated with elevated intraocular pressure. It can lead to permanent vision loss if untreated. Cataract is lens clouding, conjunctivitis inflammation of the conjunctiva, retinal detachment is separation of the retina.

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Question #678

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The symbiotic relationship where one organism benefits and the other is harmed is:

A. Mutualism

B. Amensalism

C. Commensalism

D. Parasitism

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Correct Answer: Option D

Explanation:
Parasitism (+/-) is a symbiotic interaction where the parasite benefits at the expense of the host. Examples: tapeworms, Plasmodium. Mutualism is +/+, commensalism +/0, amensalism -/0. Parasites may live on (ectoparasites) or inside (endoparasites) the host.

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Question #679

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The structure that protects the tip of the growing shoot is the:

A. Terminal bud

B. Root cap

C. Leaf primordia

D. Apical meristem

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Correct Answer: Option A

Explanation:
The terminal (apical) bud, containing the shoot apical meristem, is covered by young leaf primordia, which protect the delicate meristematic tissue. The root cap protects the root apical meristem. Leaf primordia develop into leaves. Terminal buds are often dormant in winter.

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Question #680

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The enzyme that synthesizes a DNA copy from an RNA template in retroviruses is:

A. Helicase

B. Reverse transcriptase

C. RNA polymerase

D. DNA polymerase

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Correct Answer: Option B

Explanation:
Reverse transcriptase is an enzyme unique to retroviruses that transcribes single-stranded RNA into double-stranded DNA (cDNA). This DNA integrates into the host genome. DNA polymerase synthesizes DNA from DNA, RNA polymerase from DNA. Reverse transcriptase is used in RT-PCR and cDNA synthesis.

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