Biology MCQs

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Biology MCQs

Practice complete Biology MCQs covering Introduction to Biology, Cell Biology, Cell Structure, Cell Division, Biomolecules, Plant Physiology, Human Physiology, Genetics, Evolution, Biotechnology, Ecology, Classification of Living Organisms, Plant Kingdom, Animal Kingdom, Microbiology, Human Diseases, Nutrition, Reproduction, Environmental Biology, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Question #1461
The 'Hormone Progesterone' is primarily responsible for maintaining pregnancy. During the menstrual cycle, its levels are highest during the:
A. Menstrual phase
B. Ovulation phase
C. Follicular (proliferative) phase
D. Luteal (secretory) phase
Discuss
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Correct Answer: Option D

Explanation:
Progesterone is the primary hormone of the luteal phase (also called the secretory phase) of the menstrual cycle. After ovulation, the ruptured Graafian follicle transforms into the corpus luteum, which secretes large amounts of progesterone. Progesterone prepares and maintains the uterine endometrium (thickening it, increasing blood supply, and stimulating glandular secretion) for the potential implantation of a fertilized egg. If pregnancy does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation begins.
This question belongs to: Science Biology
Question #1462
In genetics, the 'Lac operon' is an example of a(n):
A. Constitutive operon
B. Repressible operon
C. Attenuated operon
D. Inducible operon
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Correct Answer: Option D

Explanation:
The lac operon in E. coli is a classic example of an inducible operon. It is normally 'off' (repressed) because the lac repressor protein, produced by the 'i' gene, binds to the operator, preventing transcription of the structural genes (z, y, a) needed for lactose metabolism. However, when lactose is present in the environment, it is converted to allolactose, which acts as an inducer. Allolactose binds to the repressor, changing its shape and preventing it from binding to the operator, thus 'inducing' or allowing transcription to occur.
This question belongs to: Science Biology
Question #1463
The 'Hormone Somatostatin' is a peptide hormone that acts as a universal inhibitor in the body. It is secreted by the hypothalamus, pancreas, and gastrointestinal tract, and its primary function is to:
A. Stimulate the release of growth hormone
B. Inhibit the release of growth hormone, insulin, glucagon, and various gastrointestinal hormones
C. Increase blood glucose levels
D. Stimulate gastric acid secretion
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Correct Answer: Option B

Explanation:
Somatostatin, also known as growth hormone-inhibiting hormone (GHIH), is a peptide hormone produced by the delta cells of the pancreatic islets, the hypothalamus, and various cells in the gastrointestinal tract. It acts as a powerful, universal inhibitor. It inhibits the release of growth hormone (GH) and thyroid-stimulating hormone (TSH) from the anterior pituitary. In the pancreas, it inhibits the secretion of both insulin and glucagon. In the gut, it inhibits the release of gastrin, secretin, and other GI hormones, slowing down digestion and absorption.
This question belongs to: Science Biology
Question #1464
In the human body, the 'Medulla oblongata' is a vital part of the brainstem that controls involuntary functions such as:
A. Memory and learning
B. Heartbeat, breathing, and blood pressure
C. Balance and coordination
D. Vision and hearing
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Correct Answer: Option B

Explanation:
The medulla oblongata is the lowest part of the brainstem, connecting the pons to the spinal cord. It contains vital autonomic centers that control essential, involuntary life-sustaining functions. These include the cardiovascular center (regulating heart rate and blood vessel diameter), the respiratory center (regulating the rate and depth of breathing), and reflex centers for vomiting, coughing, sneezing, and swallowing. Damage to the medulla is often fatal due to the cessation of these vital functions.
This question belongs to: Science Biology
Question #1465
The 'Hormone Melanocyte-Stimulating Hormone' (MSH) is secreted by the intermediate lobe of the pituitary gland (in some species) and primarily acts to:
A. Stimulate the growth of hair
B. Inhibit the production of melanin
C. Stimulate the production of melanin in melanocytes
D. Regulate blood pressure
Discuss
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Correct Answer: Option C

Explanation:
Melanocyte-Stimulating Hormone (MSH) is a peptide hormone produced primarily by the intermediate lobe of the pituitary gland (pars intermedia), though in humans, this lobe is rudimentary and MSH is mainly derived from the cleavage of pro-opiomelanocortin (POMC) in the anterior lobe. Its primary function, especially in lower vertebrates like amphibians and reptiles, is to stimulate the melanocytes in the skin to produce and disperse melanin, the pigment responsible for skin, hair, and eye color, leading to darkening of the skin. In humans, its role in pigmentation is less significant.
This question belongs to: Science Biology
Question #1466
In the context of human diseases, 'Kala-azar' is a severe parasitic disease. The vector for this disease is the:
A. Female Aedes mosquito
B. Female Phlebotomus sandfly
C. Female Culex mosquito
D. Female Anopheles mosquito
Discuss
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Correct Answer: Option B

Explanation:
Kala-azar, also known as visceral leishmaniasis, is a severe systemic disease caused by the protozoan parasite Leishmania donovani. The disease is transmitted to humans through the bite of an infected female Phlebotomus sandfly (in the Old World) or Lutzomyia sandfly (in the New World). The sandfly injects the infective promastigote stage of the parasite into the skin during a blood meal. Anopheles transmits malaria, Aedes transmits dengue and yellow fever, and Culex transmits filariasis.
This question belongs to: Science Biology
Question #1467
The 'Hormone Thymosin' is secreted by the thymus gland and plays a crucial role in the immune system by:
A. Producing antibodies
B. Killing pathogens directly
C. Promoting the differentiation and maturation of T-lymphocytes
D. Suppressing the immune response
Discuss
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Correct Answer: Option C

Explanation:
Thymosin is a group of peptide hormones secreted by the epithelial cells of the thymus gland. The thymus is the primary site for the maturation of T-lymphocytes (T cells), which are essential for cell-mediated immunity. Thymosin plays a critical role in this process by promoting the differentiation, development, and maturation of immature T cells (thymocytes) into functional, immunocompetent T cells. As the thymus involutes (shrinks) after puberty, thymosin levels decline.
This question belongs to: Science Biology
Question #1468
In the human body, the 'Pons' is a structure in the brainstem that contains the:
A. Visual and auditory reflex centers
B. Thermoregulatory center
C. Pneumotaxic and apneustic centers for respiratory regulation
D. Cardiovascular center
Discuss
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Correct Answer: Option C

Explanation:
The pons is a prominent bulge in the brainstem, located between the midbrain and the medulla oblongata. It serves as a relay station between different parts of the brain. Crucially, the pons contains the pneumotaxic center and the apneustic center, which are part of the respiratory control network. These centers modulate the activity of the primary respiratory center in the medulla, regulating the rate and depth of breathing. The cardiovascular center is in the medulla, and visual/auditory reflexes are in the midbrain.
This question belongs to: Science Biology
Question #1469
The 'Hormone Angiotensin II' is a potent vasoconstrictor. It also stimulates the adrenal cortex to secrete:
A. Aldosterone
B. Adrenaline
C. Noradrenaline
D. Cortisol
Discuss
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Correct Answer: Option A

Explanation:
Angiotensin II is a powerful octapeptide hormone formed in the blood by the action of angiotensin-converting enzyme (ACE). It has multiple effects to increase blood pressure and volume. It is a potent vasoconstrictor, increasing systemic vascular resistance. Crucially, it also acts on the zona glomerulosa of the adrenal cortex to stimulate the secretion of the mineralocorticoid hormone aldosterone. Aldosterone then acts on the kidneys to increase sodium and water reabsorption, further increasing blood volume and pressure.
This question belongs to: Science Biology
Question #1470
In genetics, the 'TATA box' is a conserved DNA sequence found in the promoter region of many eukaryotic genes. It is recognized and bound by:
A. DNA ligase
B. RNA polymerase I
C. The ribosome
D. TATA-binding protein (TBP), a subunit of TFIID
Discuss
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Correct Answer: Option D

Explanation:
The TATA box (consensus sequence TATAAA) is a highly conserved DNA sequence located about 25-30 base pairs upstream of the transcription start site in the promoter region of many eukaryotic genes transcribed by RNA polymerase II. It is specifically recognized and bound by the TATA-binding protein (TBP), which is a crucial subunit of the general transcription factor TFIID. The binding of TBP initiates the assembly of the pre-initiation complex, including RNA polymerase II, allowing transcription to begin.
This question belongs to: Science Biology
Question #1471
The 'Hormone Cholecystokinin' (CCK) is secreted by the I cells of the duodenal mucosa in response to the presence of fats and proteins. Its primary actions include:
A. Inhibiting the release of bile
B. Increasing blood glucose levels
C. Stimulating gastric acid secretion
D. Inhibiting gastric emptying and stimulating the gall bladder to contract and the pancreas to secrete digestive enzymes
Discuss
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Correct Answer: Option D

Explanation:
Cholecystokinin (CCK) is a peptide hormone released by the I cells of the duodenum when acidic chyme containing fats (lipids) and partially digested proteins enters from the stomach. CCK has two major digestive actions: 1) It stimulates the gall bladder to contract, releasing stored bile into the duodenum to emulsify fats. 2) It stimulates the pancreatic acinar cells to secrete a juice rich in digestive enzymes (lipases, proteases, amylase). It also slows down gastric emptying, allowing more time for digestion in the small intestine.
This question belongs to: Science Biology
Question #1472
In the human body, the 'Midbrain' contains the superior and inferior colliculi, which are collectively known as the:
A. Corpora quadrigemina
B. Corpora lutea
C. Corpora allata
D. Corpora cavernosa
Discuss
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Correct Answer: Option A

Explanation:
The midbrain (mesencephalon) is the uppermost part of the brainstem. Its dorsal surface features four rounded elevations called the corpora quadrigemina (meaning 'four bodies'). These consist of two upper, larger swellings called the superior colliculi, which are reflex centers for visual movements (like tracking moving objects), and two lower, smaller swellings called the inferior colliculi, which are part of the auditory pathway and relay sound information to the thalamus.
This question belongs to: Science Biology
Question #1473
The 'Hormone Secretin' was the first hormone to be discovered. It was discovered by:
A. Andrew Schally and Roger Guillemin
B. Edward Kendall
C. William Bayliss and Ernest Starling
D. Otto Loewi
Discuss
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Correct Answer: Option C

Explanation:
Secretin was the first hormone ever to be identified, marking the birth of endocrinology as a distinct field. It was discovered in 1902 by British physiologists William Bayliss and Ernest Starling. They observed that when acidic chyme entered the duodenum, it stimulated the pancreas to secrete bicarbonate-rich juice, even if all nerves to the pancreas were cut. They concluded that a chemical messenger (which Starling coined the term 'hormone' for in 1905) was released from the intestinal mucosa into the blood to stimulate the pancreas. They named this messenger secretin.
This question belongs to: Science Biology
Question #1474
In plant physiology, the 'Vernalization' refers to the induction of flowering by:
A. Exposure to continuous light
B. Exposure to a prolonged period of low temperature
C. Exposure to continuous darkness
D. Exposure to high temperatures
Discuss
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Correct Answer: Option B

Explanation:
Vernalization is the process by which many plants, particularly biennials and winter annuals (like winter wheat, cabbage, and carrots), require exposure to a prolonged period of low temperature (cold treatment) before they can initiate flowering. This prevents the plant from flowering in the autumn, ensuring it survives the winter and flowers in the spring or summer. The cold stimulus is perceived by the apical meristem or the germinating seed.
This question belongs to: Science Biology
Question #1475
The 'Hormone Insulin' is a peptide hormone composed of two polypeptide chains, A and B, linked by:
A. Peptide bonds
B. Hydrogen bonds
C. Disulfide bridges
D. Ionic bonds
Discuss
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Correct Answer: Option C

Explanation:
Insulin is a peptide hormone produced by the beta cells of the Islets of Langerhans in the pancreas. It is initially synthesized as a single, inactive polypeptide precursor called proinsulin. During processing, a connecting peptide (C-peptide) is removed, leaving two polypeptide chains: the A chain (21 amino acids) and the B chain (30 amino acids). These two chains are held together by two interchain disulfide bridges (covalent bonds between sulfur atoms of cysteine residues), and there is also one intrachain disulfide bridge within the A chain.
This question belongs to: Science Biology
Question #1476
In the human body, the 'Cerebellum' is a large structure located at the base of the brain. Its primary functions include:
A. Coordinating voluntary movements, maintaining posture, and balance
B. Regulating heart rate and breathing
C. Controlling emotions and memory
D. Processing visual and auditory information
Discuss
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Correct Answer: Option A

Explanation:
The cerebellum, meaning 'little brain', is a highly folded structure located at the posterior base of the skull, beneath the occipital lobes of the cerebrum and behind the brainstem. While it does not initiate movement, its primary functions are to coordinate voluntary motor movements, ensure muscle synergy, maintain posture, and regulate balance and equilibrium. It receives sensory input from the spinal cord, vestibular system, and cerebral cortex, and fine-tunes motor output to ensure smooth, accurate movements. Damage to the cerebellum results in ataxia (clumsy, uncoordinated movements).
This question belongs to: Science Biology
Question #1477
The 'Hormone Glucagon' is secreted by the alpha cells of the pancreas. Its primary effect on the liver is to:
A. Promote the conversion of glucose to glycogen (glycogenesis)
B. Increase the uptake of glucose by liver cells
C. Inhibit the release of glucose into the blood
D. Promote the breakdown of glycogen to glucose (glycogenolysis) and the synthesis of glucose from non-carbohydrates (gluconeogenesis)
Discuss
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Correct Answer: Option D

Explanation:
Glucagon is a peptide hormone secreted by the alpha cells of the pancreatic islets in response to low blood glucose levels (hypoglycemia). Its primary target is the liver, where it acts to raise blood glucose levels. It stimulates glycogenolysis (the breakdown of stored glycogen into glucose) and gluconeogenesis (the synthesis of new glucose from non-carbohydrate sources like amino acids and glycerol). It also promotes the breakdown of fats (lipolysis) in adipose tissue. It has the opposite effect of insulin.
This question belongs to: Science Biology
Question #1478
In genetics, the 'Poly-A tail' is a sequence of adenine nucleotides added to the 3' end of eukaryotic mRNA. Its primary functions include:
A. Binding to the DNA template
B. Protecting the mRNA from degradation by exonucleases and facilitating its export from the nucleus and translation
C. Initiating translation
D. Splicing out introns
Discuss
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Correct Answer: Option B

Explanation:
The poly-A tail is a long chain of adenine nucleotides (typically 100-250) added to the 3' end of a pre-mRNA molecule during post-transcriptional processing in the nucleus. Its primary functions are to protect the mRNA molecule from enzymatic degradation in the cytoplasm (by exonucleases), to facilitate the export of the mature mRNA from the nucleus to the cytoplasm, and to promote translation by helping to recruit ribosomes. It also plays a role in determining the lifespan of the mRNA in the cytoplasm.
This question belongs to: Science Biology
Question #1479
The 'Hormone Parathyroid Hormone' (PTH) is secreted by the parathyroid glands. Its primary effect on blood calcium levels is to:
A. Fluctuate them
B. Increase them
C. Have no effect on them
D. Decrease them
Discuss
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Correct Answer: Option B

Explanation:
Parathyroid Hormone (PTH) is a peptide hormone secreted by the chief cells of the four parathyroid glands in response to low blood calcium levels (hypocalcemia). Its primary function is to increase blood calcium levels (hypercalcemic effect). It achieves this by: 1) Stimulating osteoclasts to break down bone, releasing calcium. 2) Increasing calcium reabsorption and stimulating the activation of Vitamin D in the kidneys. 3) Indirectly increasing calcium absorption in the gut via active Vitamin D. It has the opposite effect of calcitonin.
This question belongs to: Science Biology
Question #1480
In the human body, the 'Thalamus' is a large, dual-lobed mass of grey matter located in the diencephalon. Its primary function is to act as a:
A. Major relay station for sensory and motor signals to the cerebral cortex
B. Master gland for the endocrine system
C. Center for regulating body temperature
D. Control center for involuntary functions like breathing
Discuss
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Correct Answer: Option A

Explanation:
The thalamus is a paired structure forming the main part of the diencephalon, situated above the brainstem. It is often described as the 'gateway to the cerebral cortex'. Its primary function is to act as a major relay station, receiving almost all incoming sensory information (except olfaction) and motor signals from various parts of the body and the brain, processing them, and then projecting them to the appropriate specific areas of the cerebral cortex. It also plays a role in regulating consciousness, sleep, and alertness.
This question belongs to: Science Biology

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