Biology MCQs

Question #281

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Which of the following is an example of an X-linked recessive disorder?

A. Hemophilia

B. Sickle cell anemia

C. Down syndrome

D. Cystic fibrosis

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Correct Answer: Option A

Explanation:
Hemophilia A and B are X-linked recessive disorders caused by mutations in genes for clotting factor VIII or IX on the X chromosome. It predominantly affects males, while females are usually carriers. Down syndrome is an autosomal aneuploidy, cystic fibrosis and sickle cell anemia are autosomal recessive. X-linked disorders follow a characteristic pattern of inheritance.

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Question #282

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Which of the following is a primary lymphoid organ?

A. Bone marrow

B. Tonsils

C. Lymph node

D. Spleen

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Correct Answer: Option A

Explanation:
Primary lymphoid organs are where lymphocytes are produced and mature. Bone marrow (where B cells mature) and thymus (where T cells mature) are primary. Secondary lymphoid organs, like spleen, lymph nodes, and tonsils, are where mature lymphocytes encounter antigens and initiate immune responses. The bone marrow also is the site of hematopoiesis.

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Question #283

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Which of the following vitamins is essential for blood clotting?

A. Vitamin K

B. Vitamin A

C. Vitamin C

D. Vitamin E

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Correct Answer: Option A

Explanation:
Vitamin K is a fat-soluble vitamin required for the synthesis of clotting factors II (prothrombin), VII, IX, and X in the liver. Deficiency leads to prolonged clotting time and bleeding disorders. Vitamin A is for vision, C for collagen synthesis and antioxidant, E for antioxidant. Vitamin K is found in green leafy vegetables and synthesized by gut bacteria.

This question belongs to: Science Biology

Question #284

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The organelle that is the site of the Krebs cycle in the cell is the:

A. Mitochondrial matrix

B. Inner mitochondrial membrane

C. Chloroplast stroma

D. Cytoplasm

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Correct Answer: Option A

Explanation:
The Krebs cycle (citric acid cycle) occurs in the mitochondrial matrix in eukaryotes. The enzymes for the cycle are soluble in the matrix. The inner membrane houses the electron transport chain and ATP synthase. Cytoplasm is the site of glycolysis, chloroplast stroma is the site of the Calvin cycle. Thus, the matrix is the correct location.

This question belongs to: Science Biology

Question #285

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The fungus from which the antibiotic penicillin was originally extracted is:

A. Rhizopus stolonifer

B. Aspergillus niger

C. Penicillium notatum

D. Saccharomyces cerevisiae

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Correct Answer: Option C

Explanation:
Alexander Fleming discovered penicillin in 1928 from the mold Penicillium notatum (later renamed P. chrysogenum). Aspergillus niger is used for citric acid production, Saccharomyces is yeast, Rhizopus is a bread mold. Penicillin was the first true antibiotic and its mass production during WWII saved countless lives. It inhibits bacterial cell wall synthesis.

This question belongs to: Science Biology

Question #286

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Which of the following is the correct sequence of taxonomic hierarchy from lowest to highest?

A. Species → Genus → Family → Order → Class → Phylum → Kingdom

B. Species → Family → Genus → Order → Class → Phylum → Kingdom

C. Genus → Species → Family → Order → Class → Phylum → Kingdom

D. Species → Genus → Order → Family → Class → Phylum → Kingdom

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Correct Answer: Option A

Explanation:
The correct taxonomic hierarchy in ascending order is: Species (lowest) → Genus → Family → Order → Class → Phylum (or Division in plants) → Kingdom (highest). Some classifications add Domain above Kingdom. This system groups organisms based on shared characteristics. Binomial nomenclature uses Genus and Species. Option A correctly places Family before Order.

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Question #287

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In the female reproductive cycle, ovulation is triggered by a surge in:

A. Progesterone

B. Luteinizing hormone (LH)

C. Estrogen

D. Follicle-stimulating hormone (FSH)

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Correct Answer: Option B

Explanation:
A mid-cycle surge in LH (luteinizing hormone) from the anterior pituitary triggers ovulation—the release of the secondary oocyte from the mature Graafian follicle. FSH stimulates follicle development. Estrogen levels rise before ovulation and provide positive feedback for the LH surge. Progesterone is secreted after ovulation by the corpus luteum.

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Question #288

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The type of cell division that reduces chromosome number by half is:

A. Amitosis

B. Fission

C. Mitosis

D. Meiosis

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Correct Answer: Option D

Explanation:
Meiosis is reductional division occurring in germ cells to produce haploid gametes (n) from a diploid cell (2n). It involves two successive divisions (Meiosis I and II) and introduces genetic variation through crossing over and independent assortment. Mitosis maintains chromosome number, amitosis is direct division, and fission is asexual reproduction in prokaryotes.

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Question #289

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Which of the following is a unique feature of plant cells compared to animal cells?

A. Presence of Golgi apparatus

B. Presence of mitochondria

C. Presence of ribosomes

D. Presence of plastids

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Correct Answer: Option D

Explanation:
Plastids (chloroplasts, chromoplasts, leucoplasts) are unique to plant cells and some protists. They are involved in photosynthesis, storage, and imparting color. Mitochondria, Golgi apparatus, and ribosomes are present in both plant and animal cells. The cell wall and large central vacuole are also distinguishing features of plant cells.

This question belongs to: Science Biology

Question #290

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The cell wall of fungi is composed of:

A. Cellulose

B. Chitin

C. Peptidoglycan

D. Hemicellulose

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Correct Answer: Option B

Explanation:
Fungal cell walls contain chitin, a polymer of N-acetylglucosamine, which also forms the exoskeleton of arthropods. Plant cell walls are primarily cellulose, bacterial cell walls contain peptidoglycan (except Mycoplasma). Hemicellulose is a component of plant cell walls along with cellulose. Chitin provides structural strength and rigidity to fungi.

This question belongs to: Science Biology

Question #291

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The process of removal of metabolic wastes from the body is called:

A. Digestion

B. Circulation

C. Excretion

D. Respiration

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Correct Answer: Option C

Explanation:
Excretion is the elimination of nitrogenous waste products (urea, uric acid, ammonia) and other metabolic wastes from the body, primarily by the kidneys. Digestion is breakdown of food, circulation is transport, respiration is gas exchange and energy release. Excretion maintains homeostasis of body fluids and prevents toxic accumulation.

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Question #292

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The neurotransmitter that is deficient in Parkinson's disease is:

A. Norepinephrine

B. Serotonin

C. Acetylcholine

D. Dopamine

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Correct Answer: Option D

Explanation:
Parkinson's disease is a neurodegenerative disorder characterized by the loss of dopamine-producing neurons in the substantia nigra region of the brain. This leads to motor symptoms like tremors, rigidity, and bradykinesia. L-DOPA (levodopa), a precursor of dopamine, is used in treatment. Acetylcholine is related to Alzheimer's, serotonin to depression.

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Question #293

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The gland that secretes melatonin, regulating the sleep-wake cycle, is the:

A. Thyroid gland

B. Pituitary gland

C. Adrenal gland

D. Pineal gland

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Correct Answer: Option D

Explanation:
The pineal gland is a small endocrine gland in the brain that secretes melatonin, a hormone that regulates circadian rhythms and sleep-wake cycles. Melatonin production is influenced by light exposure: it increases in darkness and decreases in light. The pituitary is the master gland, thyroid regulates metabolism, adrenal secretes adrenaline.

This question belongs to: Science Biology

Question #294

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The largest artery in the human body is the:

A. Aorta

B. Pulmonary artery

C. Carotid artery

D. Coronary artery

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Correct Answer: Option A

Explanation:
The aorta is the main and largest artery originating from the left ventricle, distributing oxygenated blood to all parts of the body through its branches. The pulmonary artery carries deoxygenated blood to lungs. Coronary arteries supply the heart muscle, carotid arteries supply the brain. The aorta has a diameter of about 2-3 cm in adults.

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Question #295

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The type of muscle tissue that is voluntary and striated is:

A. Smooth muscle

B. Cardiac muscle

C. Skeletal muscle

D. Visceral muscle

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Correct Answer: Option C

Explanation:
Skeletal muscle is attached to bones, is under voluntary control, and has a striated appearance due to the arrangement of actin and myosin filaments. Smooth muscle (visceral) is non-striated and involuntary, found in internal organs. Cardiac muscle is striated but involuntary, found only in the heart. Skeletal muscles are multinucleated.

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Question #296

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The membrane that surrounds and protects the lungs is called:

A. Pleura

B. Peritoneum

C. Meninges

D. Pericardium

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Correct Answer: Option A

Explanation:
The pleura is a double-layered serous membrane surrounding each lung; the visceral pleura adheres to the lung surface, and the parietal pleura lines the chest wall. The space between them contains pleural fluid, reducing friction during breathing. Pericardium surrounds the heart, peritoneum lines the abdominal cavity, meninges cover the brain and spinal cord.

This question belongs to: Science Biology

Question #297

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Which of the following is NOT a characteristic of the Kingdom Fungi?

A. Cell wall of chitin

B. Heterotrophic nutrition

C. Autotrophic nutrition

D. Multicellular (except yeast) and filamentous

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Correct Answer: Option C

Explanation:
Fungi are heterotrophic organisms; they cannot perform photosynthesis because they lack chlorophyll and chloroplasts. They obtain nutrients through absorption after extracellular digestion (saprophytic or parasitic). The cell wall contains chitin, and most are multicellular with a filamentous body (mycelium), though yeasts are unicellular. Thus, autotrophy is not a fungal characteristic.

This question belongs to: Science Biology

Question #298

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Which of the following structures prevents the entry of food into the trachea during swallowing?

A. Tongue

B. Glottis

C. Epiglottis

D. Uvula

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Correct Answer: Option C

Explanation:
The epiglottis is a cartilaginous flap that covers the glottis (the opening into the larynx and trachea) during swallowing, directing food and liquid into the esophagus. The tongue moves food, the glottis is the opening itself, and the uvula is a soft tissue hanging at the back of the palate that assists in speech and prevents nasal regurgitation.

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Question #299

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The organ that produces urea as the main nitrogenous waste in humans is the:

A. Spleen

B. Kidney

C. Pancreas

D. Liver

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Correct Answer: Option D

Explanation:
The liver synthesizes urea from ammonia (which is toxic) via the urea cycle (ornithine cycle). Ammonia is produced from the deamination of amino acids. Urea is less toxic and is transported via blood to the kidneys for excretion in urine. The kidneys only filter and excrete urea; they do not produce it.

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Question #300

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The hormone that opposes the action of insulin and increases blood glucose levels is:

A. Thyroxine

B. Glucagon

C. Growth hormone

D. Cortisol

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Correct Answer: Option B

Explanation:
Glucagon, from the pancreatic alpha cells, raises blood glucose by stimulating glycogenolysis and gluconeogenesis in the liver. Cortisol and growth hormone also raise blood glucose but glucagon is the primary direct antagonist of insulin. Thyroxine increases metabolic rate. The balance between insulin (hypoglycemic) and glucagon (hyperglycemic) maintains glucose homeostasis.

This question belongs to: Science Biology

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