Biology MCQs

Question #441

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The process by which bacteria reproduce asexually is:

A. Conjugation

B. Transformation

C. Binary fission

D. Budding

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Correct Answer: Option C

Explanation:
Binary fission is the primary asexual reproduction method in bacteria, where the cell divides into two identical daughter cells after DNA replication. Budding occurs in yeast and some bacteria. Conjugation and transformation are methods of genetic exchange, not reproduction. Binary fission allows rapid population growth.

This question belongs to: Science Biology

Question #442

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The type of immunity that a newborn acquires from breast milk is:

A. Natural passive

B. Artificial passive

C. Artificial active

D. Natural active

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Correct Answer: Option A

Explanation:
Natural passive immunity is transferred from mother to child via placental transfer of IgG antibodies (in utero) and IgA antibodies in breast milk (colostrum). It provides temporary protection without the infant's immune system being activated. Active immunity results from natural infection or vaccination.

This question belongs to: Science Biology

Question #443

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The mineral element essential for the synthesis of thyroid hormones is:

A. Zinc

B. Calcium

C. Iodine

D. Iron

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Correct Answer: Option C

Explanation:
Iodine is a key constituent of the thyroid hormones thyroxine (T₄) and triiodothyronine (T₃). Deficiency leads to goiter and hypothyroidism. Iron is for hemoglobin, calcium for bones, zinc for enzyme function. Iodized salt is a public health measure to ensure adequate iodine intake.

This question belongs to: Science Biology

Question #444

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The genus of the bacteria used in the production of vinegar from alcohol is:

A. Bacillus

B. Lactobacillus

C. Pseudomonas

D. Acetobacter

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Correct Answer: Option D

Explanation:
Acetobacter aceti and related species oxidize ethanol to acetic acid (vinegar) in the presence of oxygen. This is an aerobic fermentation process. Lactobacillus produces lactic acid, Pseudomonas can spoil food, Bacillus includes various industrial strains. Vinegar is used as a condiment and preservative.

This question belongs to: Science Biology

Question #445

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The cells that transmit nerve impulses in the nervous system are called:

A. Glial cells

B. Neurons

C. Epithelial cells

D. Fibroblasts

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Correct Answer: Option B

Explanation:
Neurons are the excitable cells that generate and transmit electrochemical impulses. Glial cells (neuroglia) provide support, insulation, and nutrients. Fibroblasts form connective tissue, epithelial cells line surfaces. The neuron is the functional unit of the nervous system, connected at synapses.

This question belongs to: Science Biology

Question #446

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In which cell organelle does the Krebs cycle take place?

A. Cytoplasm

B. Inner mitochondrial membrane

C. Mitochondrial matrix

D. Stroma of chloroplast

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Correct Answer: Option C

Explanation:
The Krebs cycle (citric acid cycle) occurs in the mitochondrial matrix in eukaryotes. It oxidizes acetyl-CoA to CO₂, producing NADH, FADH₂, and GTP. The inner membrane houses the electron transport chain. Glycolysis occurs in cytoplasm, the Calvin cycle in chloroplast stroma. The matrix contains the necessary soluble enzymes.

This question belongs to: Science Biology

Question #447

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The term 'genetically modified organism' (GMO) refers to:

A. An organism whose DNA has been altered using genetic engineering

B. A cloned organism

C. An organism produced by selective breeding

D. A hybrid organism produced by cross-pollination

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Correct Answer: Option A

Explanation:
GMOs are organisms whose genetic material has been modified through recombinant DNA technology, introducing or deleting specific genes. Selective breeding and cross-pollination are traditional methods that do not directly manipulate DNA. Cloning produces genetically identical copies without necessarily altering the genome. Examples: Bt cotton, Golden rice.

This question belongs to: Science Biology

Question #448

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The amount of air that can be forcefully exhaled after a normal tidal expiration is the:

A. Tidal volume

B. Expiratory reserve volume

C. Residual volume

D. Inspiratory reserve volume

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Correct Answer: Option B

Explanation:
Expiratory reserve volume (ERV) is the additional air exhaled forcibly after normal exhalation (~1,000–1,200 mL). Tidal volume is normal breath, inspiratory reserve is extra inhaled after normal inhalation, residual volume is air left after maximal exhalation. These are components of lung volumes and capacities.

This question belongs to: Science Biology

Question #449

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Which of the following is a protein deficiency disease characterized by edema and an enlarged liver?

A. Marasmus

B. Kwashiorkor

C. Scurvy

D. Beriberi

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Correct Answer: Option B

Explanation:
Kwashiorkor results from severe protein deficiency with adequate calorie intake, often seen in children after weaning. It presents with edema, pot belly, fatty liver, skin lesions, and apathy. Marasmus is due to overall calorie and protein deficiency causing wasting. Beriberi and scurvy are vitamin deficiencies.

This question belongs to: Science Biology

Question #450

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The layer of the Earth's atmosphere that contains the protective ozone layer is the:

A. Troposphere

B. Thermosphere

C. Mesosphere

D. Stratosphere

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Correct Answer: Option D

Explanation:
The ozone layer is located in the lower portion of the stratosphere, about 15–35 km above Earth. It absorbs most of the Sun's harmful ultraviolet radiation. Troposphere is the lowest layer, mesosphere and thermosphere above. Ozone depletion by CFCs led to the Antarctic ozone hole.

This question belongs to: Science Biology

Question #451

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

A. Predation

B. Parasitism

C. Mutualism

D. Commensalism

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Correct Answer: Option D

Explanation:
Commensalism (+/0) involves one species benefiting and the other neither harmed nor helped. Example: barnacles on a whale, or cattle egrets eating insects stirred by cattle. Mutualism benefits both (+/+), parasitism benefits one at expense of other (+/-), predation (+/-) involves killing. The distinction is based on the net effect.

This question belongs to: Science Biology

Question #452

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The structural and functional unit of heredity is the:

A. Gene

B. DNA

C. Chromosome

D. Nucleotide

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Correct Answer: Option A

Explanation:
A gene is a segment of DNA that codes for a functional product (protein or RNA) and is the basic unit of heredity. It determines traits. Chromosomes are structures containing many genes. DNA is the genetic material, and nucleotides are the building blocks. Genes are passed from parents to offspring.

This question belongs to: Science Biology

Question #453

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The element that is a central component of the chlorophyll molecule is:

A. Zinc

B. Iron

C. Calcium

D. Magnesium

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Correct Answer: Option D

Explanation:
Magnesium (Mg²⁺) is the central atom in the porphyrin ring of chlorophyll, essential for absorbing light energy during photosynthesis. Iron is central in heme (hemoglobin, cytochromes). Calcium is a secondary messenger and structural component, zinc is a cofactor. Magnesium deficiency causes chlorosis.

This question belongs to: Science Biology

Question #454

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The process that converts mRNA code into a sequence of amino acids is:

A. Translation

B. Translocation

C. Transcription

D. Replication

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Correct Answer: Option A

Explanation:
Translation occurs at ribosomes, where tRNA anticodons recognize mRNA codons and add the corresponding amino acids to a growing polypeptide chain. Replication duplicates DNA, transcription synthesizes mRNA from DNA, translocation is movement of chromosomes or protein transport.

This question belongs to: Science Biology

Question #455

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Which of the following nitrogenous wastes is the most toxic?

A. Uric acid

B. Creatinine

C. Ammonia

D. Urea

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Correct Answer: Option C

Explanation:
Ammonia (NH₃) is highly toxic and requires large volumes of water for its excretion; hence it is produced by aquatic animals. Urea is less toxic, uric acid least toxic and water-insoluble. Creatinine is a minor waste. Ammonia is converted to urea in the liver via the urea cycle in ureotelic organisms.

This question belongs to: Science Biology

Question #456

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The fluid that reduces friction during breathing in the pleural cavity is:

A. Lymph

B. Synovial fluid

C. Pleural fluid

D. Cerebrospinal fluid

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Correct Answer: Option C

Explanation:
The pleural cavity between the visceral and parietal pleura contains a thin layer of pleural fluid, lubricating the surfaces to reduce friction during lung expansion and contraction. Synovial fluid is in joints, cerebrospinal fluid surrounds the CNS, lymph is in the lymphatic system. Pleural effusion is excess accumulation.

This question belongs to: Science Biology

Question #457

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The number of ATP molecules produced from one glucose molecule during aerobic respiration is approximately:

A. 2

B. 4

C. 18

D. 36-38

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Correct Answer: Option D

Explanation:
In eukaryotes, complete oxidation of one glucose molecule via glycolysis, Krebs cycle, and electron transport chain yields a net of about 36-38 ATP molecules (depending on shuttle systems). Glycolysis yields 2 ATP, Krebs 2 ATP, and oxidative phosphorylation 32-34 ATP. This is much higher than anaerobic respiration (2 ATP).

This question belongs to: Science Biology

Question #458

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The part of the neuron that receives signals from other neurons is the:

A. Dendrite

B. Cell body

C. Axon terminal

D. Axon

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Correct Answer: Option A

Explanation:
Dendrites are branched extensions of the neuron cell body that receive synaptic inputs from other neurons and transmit graded potentials towards the soma. The axon conducts action potentials away from the soma to the terminals, which then synapse with other cells. Dendrites have receptor sites for neurotransmitters.

This question belongs to: Science Biology

Question #459

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The deficiency of vitamin B₁₂ often results from lack of which gastric factor?

A. Hydrochloric acid

B. Intrinsic factor

C. Pepsinogen

D. Mucus

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Correct Answer: Option B

Explanation:
Intrinsic factor, a glycoprotein secreted by gastric parietal cells, binds to vitamin B₁₂ and facilitates its absorption in the ileum. Absence or deficiency (pernicious anemia) leads to B₁₂ deficiency, causing megaloblastic anemia and neurological symptoms. HCl activates pepsin, pepsinogen is precursor, mucus protects.

This question belongs to: Science Biology

Question #460

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The organism that causes ringworm in humans belongs to which group?

A. Virus

B. Fungi

C. Protozoa

D. Bacteria

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Correct Answer: Option B

Explanation:
Ringworm (tinea) is a superficial fungal infection caused by dermatophytes (genera Trichophyton, Microsporum, Epidermophyton) that infect skin, hair, and nails. It is not a worm. Bacterial skin infections include impetigo, viral include warts, protozoan include leishmaniasis. Fungi are treated with antifungal agents.

This question belongs to: Science Biology

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