Biology MCQs

Question #161

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The phenomenon of bending of plant shoot towards a unilateral light source is due to:

A. Photolysis of chlorophyll

B. Differential distribution of auxin, with higher concentration on shaded side

C. Inhibition of growth by light

D. Uniform distribution of auxin

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Correct Answer: Option B

Explanation:
Phototropism (positive in shoots) is caused by the migration of auxin to the shaded side of the shoot, promoting cell elongation more on that side, causing the shoot to bend towards light. This asymmetric auxin distribution was demonstrated by Went's experiments. Auxin is sensitive to light and moves laterally. This is a growth response to directional light.

This question belongs to: Science Biology

Question #162

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Which of the following is a characteristic of fungi?

A. Heterotrophic nutrition with chitinous cell wall

B. Autotrophic nutrition

C. Cell wall of cellulose

D. Presence of chloroplasts

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Correct Answer: Option A

Explanation:
Fungi are eukaryotic, heterotrophic (saprophytic or parasitic), with cell walls containing chitin and glucans, not cellulose. They lack chloroplasts and are non-photosynthetic. Examples: yeasts, molds, mushrooms. They store food as glycogen. Reproduction can be asexual or sexual. Fungi play a key role as decomposers in ecosystems and are used in antibiotics production.

This question belongs to: Science Biology

Question #163

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The biological name of the housefly is:

A. Drosophila melanogaster

B. Musca domestica

C. Periplaneta americana

D. Apis indica

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Correct Answer: Option B

Explanation:
Musca domestica is the common housefly, a dipteran insect. Periplaneta americana is the American cockroach, Drosophila melanogaster is the fruit fly used in genetics, Apis indica is the Indian honeybee. Housefly can act as a mechanical vector for diseases like typhoid, cholera. Scientific names help precise identification.

This question belongs to: Science Biology

Question #164

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The enzyme that converts glucose to ethanol in yeast fermentation is:

A. Zymase

B. Invertase

C. Pepsin

D. Urease

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Correct Answer: Option A

Explanation:
Zymase is the enzyme complex in yeast (Saccharomyces cerevisiae) that catalyzes the anaerobic breakdown of glucose to ethanol and CO₂ (alcoholic fermentation). Invertase hydrolyzes sucrose to glucose and fructose. Urease acts on urea. Pepsin is a protease. Fermentation is used in baking and brewing industries. The overall equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂.

This question belongs to: Science Biology

Question #165

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Which of the following is a correct match of scientist and contribution?

A. Edward Jenner - Smallpox vaccine

B. Alexander Fleming - Pasteurization

C. Louis Pasteur - Discovery of penicillin

D. Robert Hooke - Discovery of bacteria

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Correct Answer: Option A

Explanation:
Edward Jenner developed the first successful smallpox vaccine (1796). Pasteur invented pasteurization and rabies vaccine, not penicillin. Fleming discovered penicillin. Hooke coined the term 'cell' but did not discover bacteria; Leeuwenhoek observed bacteria. Thus, the correct match is Jenner - smallpox vaccine.

This question belongs to: Science Biology

Question #166

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Which of the following organisms is commonly used as a model organism in genetics?

A. Periplaneta americana

B. Bombyx mori

C. Drosophila melanogaster

D. Musca domestica

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Correct Answer: Option C

Explanation:
Drosophila melanogaster (fruit fly) is a widely used model organism in genetics due to its short life cycle, large polytene chromosomes, easy culture, and high fecundity. Thomas Hunt Morgan established its use, discovering linkage and chromosomal theory. Musca domestica is housefly, Periplaneta cockroach, Bombyx silkworm. Many Nobel-winning genetic discoveries were made using Drosophila.

This question belongs to: Science Biology

Question #167

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The condition in which the blood pH falls below 7.35 is known as:

A. Alkalosis

B. Homeostasis

C. Acidosis

D. Apoptosis

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Correct Answer: Option C

Explanation:
Acidosis is a condition of decreased blood pH (7.45). Homeostasis is maintenance of stable internal environment. Apoptosis is programmed cell death. Acidosis can be respiratory (due to CO₂ retention) or metabolic (due to accumulation of acids like lactic acid or ketone bodies).

This question belongs to: Science Biology

Question #168

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The endoskeleton of the human body is composed mainly of:

A. Keratin

B. Chitin

C. Cartilage only

D. Bone and cartilage

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Correct Answer: Option D

Explanation:
The human endoskeleton consists of 206 bones and cartilage at joints and in structures like the nose, ears, and intervertebral discs. Bone is mineralized connective tissue, cartilage is a specialized connective tissue. Chitin is found in arthropod exoskeleton and fungal walls, keratin is a protein in skin, hair, nails. The skeleton provides support, protection, and movement.

This question belongs to: Science Biology

Question #169

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Which of the following is the causative agent of peptic ulcers?

A. Bacillus subtilis

B. Escherichia coli

C. Helicobacter pylori

D. Streptococcus pneumoniae

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Correct Answer: Option C

Explanation:
Helicobacter pylori is a spiral-shaped bacterium that colonizes the stomach lining, disrupting the mucous layer and causing inflammation, leading to gastric and duodenal ulcers. It was discovered by Barry Marshall and Robin Warren (Nobel 2005). S. pneumoniae causes pneumonia, E. coli is gut microbiota but some strains cause diarrhea, B. subtilis is a harmless soil bacterium.

This question belongs to: Science Biology

Question #170

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The term 'ecology' was coined by:

A. Charles Darwin

B. Robert Hooke

C. Gregor Mendel

D. Ernst Haeckel

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Correct Answer: Option D

Explanation:
Ernst Haeckel, a German zoologist, coined the term 'ecology' (Ökologie) in 1866, derived from Greek 'oikos' (house) and 'logos' (study), meaning the study of organisms in relation to their environment. Darwin contributed evolution, Mendel genetics, Hooke cell theory. Ecology encompasses interactions between organisms and their abiotic and biotic environment.

This question belongs to: Science Biology

Question #171

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Which of the following pollutants is responsible for Minamata disease?

A. Lead

B. Arsenic

C. Cadmium

D. Mercury

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Correct Answer: Option D

Explanation:
Minamata disease is a neurological syndrome caused by severe mercury poisoning, first discovered in Minamata, Japan, due to industrial wastewater containing methylmercury that bioaccumulated in fish. Lead causes plumbism, cadmium causes Itai-itai disease, arsenic causes arsenicosis. Mercury affects the central nervous system, causing numbness, muscle weakness, and vision problems.

This question belongs to: Science Biology

Question #172

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The primary energy carrier molecule in cells is:

A. Glucose

B. ATP

C. NADH

D. FADH₂

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Correct Answer: Option B

Explanation:
Adenosine triphosphate (ATP) is the universal energy currency of the cell, storing energy in its high-energy phosphate bonds. Hydrolysis to ADP releases energy for cellular work. NADH and FADH₂ are electron carriers in respiration, ultimately used to produce ATP. Glucose is a fuel molecule, broken down to produce ATP. ATP is directly used in processes like muscle contraction and active transport.

This question belongs to: Science Biology

Question #173

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Which of the following is a correct statement about mitochondria?

A. They are single-membrane organelles.

B. They are found in both prokaryotes and eukaryotes.

C. They contain 80S ribosomes.

D. They have their own circular DNA.

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Correct Answer: Option D

Explanation:
Mitochondria are double-membrane organelles with circular DNA (like prokaryotes) and 70S ribosomes, supporting the endosymbiotic origin. They are absent in prokaryotes. They are the site of aerobic respiration. The matrix contains enzymes for Krebs cycle. The inner membrane forms cristae, housing electron transport chain and ATP synthase.

This question belongs to: Science Biology

Question #174

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In a typical angiosperm embryo sac, the number of haploid nuclei is:

A. 7

B. 4

C. 6

D. 8

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Correct Answer: Option D

Explanation:
A mature embryo sac (female gametophyte) in angiosperms is 7-celled but 8-nucleate: 3 antipodal cells (3 nuclei), 2 synergids (2 nuclei), 1 egg cell (1 nucleus), and 1 central cell with 2 polar nuclei. Thus total 8 haploid nuclei. The central cell is homodiploid (2 polar nuclei). Double fertilization involves these nuclei. This is typical of Polygonum type of development.

This question belongs to: Science Biology

Question #175

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Which of the following tissues in plants is responsible for transportation of water and minerals?

A. Epidermis

B. Xylem

C. Phloem

D. Cortex

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Correct Answer: Option B

Explanation:
Xylem is a complex permanent tissue composed of tracheids, vessels, xylem parenchyma, and xylem fibers. It conducts water and dissolved minerals from roots to aerial parts unidirectionally. Phloem transports organic nutrients bidirectionally. Cortex is ground tissue for storage, epidermis provides protection. Xylem vessels are dead at maturity, with lignified walls.

This question belongs to: Science Biology

Question #176

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The basic structural and functional unit of the nervous system is:

A. Neuron

B. Nephron

C. Axon

D. Dendrite

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Correct Answer: Option A

Explanation:
The neuron is the nerve cell, the fundamental unit of the nervous system, responsible for receiving, processing, and transmitting electrochemical signals. It consists of a cell body (soma), dendrites, and axon. Axon and dendrite are parts of a neuron. Nephron is the unit of kidney. Neurons communicate via synapses using neurotransmitters.

This question belongs to: Science Biology

Question #177

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Which of the following vitamins is required for the synthesis of collagen?

A. Vitamin K

B. Vitamin C

C. Vitamin D

D. Vitamin A

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Correct Answer: Option B

Explanation:
Vitamin C (ascorbic acid) is a cofactor for prolyl and lysyl hydroxylase enzymes that hydroxylate proline and lysine in collagen synthesis, necessary for stabilizing collagen triple helix. Deficiency leads to impaired collagen formation, causing scurvy—fragile blood vessels, bleeding gums, poor wound healing. Vitamin A is for vision, D for bone, K for clotting.

This question belongs to: Science Biology

Question #178

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The phase of the cardiac cycle when the ventricles relax and fill with blood is called:

A. Systole

B. Atrial contraction

C. Ejection phase

D. Diastole

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Correct Answer: Option D

Explanation:
Diastole is the relaxation phase of the cardiac cycle, during which the ventricles fill with blood from the atria. Systole is the contraction phase, pumping blood out. Atrial contraction (atrial systole) contributes to ventricular filling. Ejection phase is part of ventricular systole when blood is ejected. Normal diastolic and systolic pressures are 80 and 120 mmHg respectively.

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Question #179

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Which part of the human kidney filters blood under high pressure?

A. Glomerulus

B. Renal pelvis

C. Loop of Henle

D. Collecting duct

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Correct Answer: Option A

Explanation:
The glomerulus is a tuft of capillaries enclosed by the Bowman's capsule, where ultrafiltration occurs due to high hydrostatic pressure in the afferent arteriole. It filters water, ions, glucose, amino acids, urea into Bowman's space. Proteins and cells are retained. Filtration is passive. The filtrate then passes through the tubules for processing. GFR is regulated by JGA.

This question belongs to: Science Biology

Question #180

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Which of the following is a characteristic feature of all living organisms?

A. Movement

B. Photosynthesis

C. Nervous system

D. Cellular respiration

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Correct Answer: Option D

Explanation:
Cellular respiration is a universal characteristic of living organisms, occurring in every cell to release energy from organic molecules. Movement is not universal (e.g., plants are stationary). Photosynthesis is restricted to autotrophs. A nervous system is absent in plants and simple animals. Thus, cellular respiration is fundamental to all life forms, from bacteria to humans.

This question belongs to: Science Biology

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