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 #1481
The 'Hormone Antidiuretic Hormone' (ADH), also known as vasopressin, is synthesized in the hypothalamus and stored in the posterior pituitary. Its primary action in the kidney is to:
A. Decrease potassium reabsorption
B. Decrease water reabsorption in the collecting ducts
C. Increase water reabsorption in the collecting ducts by inserting aquaporin-2 channels
D. Increase sodium excretion
Discuss
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Correct Answer: Option C

Explanation:
Antidiuretic Hormone (ADH), or vasopressin, is released from the posterior pituitary in response to high blood osmolarity (dehydration) or low blood volume. Its primary action is on the kidneys, specifically the late distal convoluted tubules and the collecting ducts. ADH binds to V2 receptors on the basolateral membrane of the principal cells, triggering the insertion of aquaporin-2 water channels into the apical membrane. This makes the tubule highly permeable to water, increasing water reabsorption from the filtrate back into the blood, producing concentrated urine and conserving body water.
This question belongs to: Science Biology
Question #1482
In plant physiology, the 'Senescence' refers to the process of:
A. Rapid cell division
B. Flower opening
C. Seed germination
D. Aging and programmed death of plant organs or the whole plant
Discuss
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Correct Answer: Option D

Explanation:
Senescence in plants is the biological process of aging, culminating in the structured, programmed death of plant organs (like leaves, flowers, or fruits) or the entire plant. It involves the coordinated breakdown of macromolecules (proteins, nucleic acids, chlorophyll) and the mobilization of nutrients (like nitrogen and phosphorus) from the senescing organ to other growing parts of the plant (like developing seeds). It is a highly regulated process influenced by hormones like ethylene and abscisic acid, and delayed by cytokinins.
This question belongs to: Science Biology
Question #1483
The 'Hormone Oxytocin' is synthesized in the hypothalamus and released by the posterior pituitary. Its two primary physiological roles in females are:
A. Stimulating uterine contractions during childbirth and milk ejection (let-down reflex) during lactation
B. Stimulating milk production and inhibiting uterine contractions
C. Stimulating follicle growth and ovulation
D. Maintaining the uterine lining and preventing menstruation
Discuss
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Correct Answer: Option A

Explanation:
Oxytocin is a peptide hormone produced by the paraventricular nucleus of the hypothalamus and released by the posterior pituitary. In females, it has two major roles: 1) During childbirth, it stimulates powerful contractions of the uterine smooth muscle, facilitating labor and delivery (this is a positive feedback loop). 2) During lactation, it stimulates the contraction of myoepithelial cells surrounding the alveoli in the mammary glands, causing the ejection (let-down) of milk into the ducts in response to suckling. It does not produce milk; prolactin does that.
This question belongs to: Science Biology
Question #1484
In the human body, the 'Basal ganglia' are a group of subcortical nuclei located deep within the cerebral hemispheres. They are primarily involved in:
A. Regulating voluntary motor movements, procedural learning, and habit formation
B. Controlling the endocrine system
C. Regulating the sleep-wake cycle
D. Processing visual information
Discuss
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Correct Answer: Option A

Explanation:
The basal ganglia are a group of interconnected subcortical nuclei (including the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus) located deep within the white matter of the cerebral hemispheres. They are crucial components of the extrapyramidal motor system. Their primary functions are to regulate voluntary motor movements (by facilitating desired movements and inhibiting unwanted ones), procedural learning (learning by repetition), routine behaviors, and habit formation. Dysfunction of the basal ganglia leads to movement disorders like Parkinson's disease and Huntington's disease.
This question belongs to: Science Biology
Question #1485
The 'Hormone Prolactin' is secreted by the anterior pituitary gland. Its primary physiological role is to:
A. Trigger ovulation
B. Maintain the corpus luteum
C. Stimulate the development of mammary glands and the production of milk (lactogenesis)
D. Stimulate uterine contractions
Discuss
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Correct Answer: Option C

Explanation:
Prolactin (PRL) is a peptide hormone secreted by the lactotroph cells of the anterior pituitary gland. Its primary and namesake function is to stimulate the development of the mammary glands during pregnancy and to initiate and maintain the production of milk (lactogenesis) after childbirth. While prolactin levels rise significantly during pregnancy, the high levels of estrogen and progesterone inhibit actual milk secretion until after delivery. Suckling by the infant is the primary stimulus for continued prolactin release.
This question belongs to: Science Biology
Question #1486
In genetics, the '5' cap' is a modified guanine nucleotide added to the 5' end of eukaryotic mRNA. Its primary functions include:
A. Protecting the mRNA from degradation and facilitating ribosome binding for translation initiation
B. Terminating transcription
C. Adding the poly-A tail
D. Splicing out introns
Discuss
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Correct Answer: Option A

Explanation:
The 5' cap is a specially altered nucleotide (7-methylguanosine) attached via a 5'-5' triphosphate linkage to the 5' end of a eukaryotic mRNA molecule shortly after transcription begins. Its primary functions are to protect the nascent mRNA from degradation by 5' exonucleases, to facilitate the export of the mature mRNA from the nucleus to the cytoplasm, and, crucially, to be recognized by the eukaryotic initiation factor 4E (eIF4E), which is essential for recruiting the ribosome to the mRNA to initiate translation.
This question belongs to: Science Biology
Question #1487
The 'Hormone Growth Hormone' (GH), also known as somatotropin, is secreted by the anterior pituitary. Its primary effects include:
A. Decreasing fat breakdown
B. Lowering blood glucose levels
C. Inhibiting protein synthesis
D. Stimulating growth, cell reproduction, and cell regeneration, particularly in bones and muscles
Discuss
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Correct Answer: Option D

Explanation:
Growth Hormone (GH), or somatotropin, is a peptide hormone secreted by the somatotroph cells of the anterior pituitary gland. Its primary effects are to stimulate growth, cell reproduction, and cell regeneration, particularly in bones (stimulating the epiphyseal plates) and skeletal muscle. It also has significant metabolic effects: it increases protein synthesis (anabolic), promotes the breakdown of fats (lipolysis) to use as energy, and raises blood glucose levels (diabetogenic effect) by reducing glucose uptake by cells. Its effects are largely mediated by Insulin-like Growth Factors (IGFs), primarily produced by the liver.
This question belongs to: Science Biology
Question #1488
In plant physiology, the 'Guttation' is the process by which water is exuded from the plant in liquid form. This typically occurs from specialized structures at the leaf margins called:
A. Hydathodes
B. Lenticels
C. Nectaries
D. Stomata
Discuss
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Correct Answer: Option A

Explanation:
Guttation is the exudation of water in liquid form from the intact, uninjured surfaces of plants, typically from the margins or tips of leaves. This occurs when root pressure is high (usually at night or early morning when transpiration is low and soil moisture is high) and the rate of water absorption exceeds the rate of transpiration. The water is forced out through specialized structures called hydathodes (or water stomata), which are located at the leaf margins and lack the mechanism to close like regular stomata.
This question belongs to: Science Biology
Question #1489
In the human body, the 'Limbic system' is a complex set of structures in the brain. The 'Amygdala', a key component of the limbic system, is primarily associated with:
A. Forming new declarative memories
B. Controlling voluntary motor movements
C. Regulating body temperature
D. Processing emotions, particularly fear and aggression
Discuss
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Correct Answer: Option D

Explanation:
The limbic system is a group of brain structures located on both sides of the thalamus, supporting emotion, behavior, motivation, long-term memory, and olfaction. The amygdala is an almond-shaped collection of nuclei located deep within the medial temporal lobes. It is a crucial component of the limbic system primarily associated with processing emotions, particularly fear, anxiety, and aggression. It plays a key role in the 'fight or flight' response and in attaching emotional significance to memories. The hippocampus is primarily for forming new declarative memories.
This question belongs to: Science Biology
Question #1490
The 'Hormone Luteinizing Hormone' (LH) is secreted by the anterior pituitary. In females, the mid-cycle surge of LH directly triggers:
A. Menstruation
B. Ovulation and the formation of the corpus luteum
C. The growth of ovarian follicles
D. The thickening of the uterine lining
Discuss
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Correct Answer: Option B

Explanation:
Luteinizing Hormone (LH) is a gonadotropin secreted by the gonadotroph cells of the anterior pituitary. In females, during the late follicular phase, rising estrogen levels exert positive feedback on the pituitary, causing a massive, sudden surge of LH (the LH surge). This surge directly triggers ovulation (the rupture of the mature Graafian follicle and release of the secondary oocyte) and subsequently stimulates the remaining follicular cells to transform into the corpus luteum, which secretes progesterone.
This question belongs to: Science Biology
Question #1491
In genetics, the 'Spliceosome' is a large, complex molecular machine found within the nucleus of eukaryotic cells. Its primary function is to:
A. Synthesize mRNA from a DNA template
B. Add the 5' cap and poly-A tail to mRNA
C. Translate mRNA into protein
D. Remove introns from pre-mRNA and join the exons together to form mature mRNA
Discuss
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Correct Answer: Option D

Explanation:
The spliceosome is a large, dynamic complex composed of five small nuclear ribonucleoproteins (snRNPs, pronounced 'snurps') and numerous other protein factors. It assembles on the pre-mRNA transcript in the nucleus. Its primary function is to catalyze the splicing of pre-mRNA: it precisely recognizes the splice sites at the boundaries of introns and exons, removes the non-coding intron sequences, and ligates (joins) the coding exons together to form a continuous, mature mRNA molecule that can be exported to the cytoplasm for translation.
This question belongs to: Science Biology
Question #1492
The 'Hormone Thyroid Stimulating Hormone' (TSH) is secreted by the anterior pituitary. Its primary target organ and function are:
A. The ovaries; stimulating ovulation
B. The thyroid gland; stimulating the production and release of thyroid hormones (T3 and T4)
C. The adrenal cortex; stimulating cortisol release
D. The kidneys; stimulating water reabsorption
Discuss
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Correct Answer: Option B

Explanation:
Thyroid Stimulating Hormone (TSH), also known as thyrotropin, is a glycoprotein hormone secreted by the thyrotroph cells of the anterior pituitary gland. Its primary and specific target is the thyroid gland. TSH binds to receptors on the thyroid follicular cells, stimulating all aspects of their function: the uptake of iodine, the synthesis of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), and the release of these hormones into the bloodstream. TSH secretion is regulated by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus and by negative feedback from T3 and T4.
This question belongs to: Science Biology
Question #1493
In plant anatomy, the 'Periderm' is a secondary protective tissue that replaces the epidermis in stems and roots undergoing secondary growth. It consists of three main layers: the phellem, phellogen, and phelloderm. The 'phellem' is also known as:
A. Vascular cambium
B. Secondary cortex
C. Cork
D. Cork cambium
Discuss
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Correct Answer: Option C

Explanation:
The periderm is the outer protective covering of stems and roots that have undergone secondary growth (thickening), replacing the primary epidermis. It is composed of three distinct layers: 1) Phellem (cork): The outermost layer, consisting of dead, compactly arranged cells with suberized (waterproof) walls that provide protection and prevent water loss. 2) Phellogen (cork cambium): The middle, meristematic layer that produces phellem outwards and phelloderm inwards. 3) Phelloderm (secondary cortex): The innermost layer, consisting of living, parenchymatous cells.
This question belongs to: Science Biology
Question #1494
The 'Hormone Adrenocorticotropic Hormone' (ACTH) is secreted by the anterior pituitary. Its primary target and function are:
A. The gonads; stimulating sex hormone production
B. The adrenal cortex; stimulating the production and release of glucocorticoids (primarily cortisol)
C. The adrenal medulla; stimulating adrenaline release
D. The thyroid gland; stimulating thyroid hormone release
Discuss
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Correct Answer: Option B

Explanation:
Adrenocorticotropic Hormone (ACTH) is a peptide hormone secreted by the corticotroph cells of the anterior pituitary gland. Its primary target is the adrenal cortex (the outer layer of the adrenal glands). ACTH stimulates the growth of the adrenal cortex and the synthesis and secretion of its steroid hormones, primarily the glucocorticoids (like cortisol), and to a lesser extent, androgens and mineralocorticoids. ACTH secretion is controlled by Corticotropin-Releasing Hormone (CRH) from the hypothalamus and by the negative feedback of cortisol.
This question belongs to: Science Biology
Question #1495
In the human body, the 'Reticular Activating System' (RAS) is a network of neurons located in the brainstem. Its primary function is to:
A. Process visual and auditory information
B. Regulate heart rate and breathing
C. Regulate arousal, wakefulness, and the sleep-wake transition
D. Control voluntary motor movements
Discuss
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Correct Answer: Option C

Explanation:
The Reticular Activating System (RAS), or Ascending Reticular Activating System (ARAS), is a complex network of neurons located in the core of the brainstem (spanning the medulla, pons, and midbrain). It projects diffusely to the thalamus and cerebral cortex. Its primary function is to regulate the overall level of arousal, consciousness, and wakefulness of the brain. It filters incoming sensory information, allowing important stimuli to reach conscious awareness, and plays a crucial role in the sleep-wake cycle and transitions between sleep stages.
This question belongs to: Science Biology
Question #1496
The 'Hormone Melanocyte-Stimulating Hormone' (MSH) in humans is primarily derived from the cleavage of a larger precursor protein called:
A. Prothrombin
B. Prorenin
C. Pro-opiomelanocortin (POMC)
D. Proinsulin
Discuss
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Correct Answer: Option C

Explanation:
In humans, the intermediate lobe of the pituitary is rudimentary, and most Melanocyte-Stimulating Hormone (MSH) is produced in the anterior lobe (pars distalis). It is not synthesized as a separate hormone but is derived from the proteolytic cleavage of a large precursor polypeptide called pro-opiomelanocortin (POMC). POMC is cleaved to produce several biologically active peptides, including Adrenocorticotropic Hormone (ACTH), beta-lipotropin, beta-endorphin, and various forms of MSH (alpha, beta, gamma).
This question belongs to: Science Biology
Question #1497
In plant physiology, the 'Transpiration pull' theory, also known as the cohesion-tension theory, was proposed to explain the ascent of sap in tall trees. The key forces involved are:
A. Cohesion between water molecules, adhesion to xylem walls, and tension created by transpiration
B. Active transport by xylem parenchyma
C. Osmotic pressure in the leaves
D. Root pressure and capillarity
Discuss
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Correct Answer: Option A

Explanation:
The cohesion-tension theory, primarily proposed by Dixon and Joly (and later supported by Denison), is the most widely accepted mechanism for the ascent of sap in tall trees. It relies on the physical properties of water. Transpiration from the leaves creates a negative pressure (tension) in the xylem. This tension pulls the water column upwards. The water column remains unbroken due to the high cohesive force between water molecules (hydrogen bonding) and the adhesive force of water to the hydrophilic walls of the xylem vessels and tracheids. This creates a continuous, passive pull from the top.
This question belongs to: Science Biology
Question #1498
The 'Hormone Insulin-like Growth Factor 1' (IGF-1) is primarily produced by the liver in response to Growth Hormone (GH). Its primary function is to:
A. Inhibit the release of GH
B. Lower blood glucose levels
C. Mediate the growth-promoting effects of GH on bones and tissues
D. Stimulate the production of thyroid hormones
Discuss
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Correct Answer: Option C

Explanation:
Insulin-like Growth Factor 1 (IGF-1), also known as somatomedin C, is a peptide hormone structurally similar to insulin. It is primarily synthesized and secreted by the liver (and to a lesser extent by other tissues) in response to stimulation by Growth Hormone (GH). IGF-1 mediates most of the growth-promoting (anabolic) effects of GH. It stimulates the proliferation and differentiation of chondrocytes (cartilage cells) in the epiphyseal plates of bones, promotes protein synthesis in muscles, and supports the growth of various other tissues.
This question belongs to: Science Biology
Question #1499
In the human body, the 'Hypothalamus' contains several nuclei that regulate various functions. The 'Supraoptic nucleus' primarily synthesizes:
A. Dopamine
B. Releasing hormones
C. Somatostatin
D. Antidiuretic Hormone (ADH) and Oxytocin
Discuss
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Correct Answer: Option D

Explanation:
The hypothalamus contains numerous nuclei, each with specific functions. The supraoptic nucleus (SON) and the paraventricular nucleus (PVN) are large neurosecretory nuclei located in the anterior hypothalamus. The supraoptic nucleus primarily synthesizes Antidiuretic Hormone (ADH, or vasopressin), while the paraventricular nucleus primarily synthesizes Oxytocin (though both nuclei produce both hormones in smaller amounts). These hormones are transported down the axons of these neurons and stored in the posterior pituitary for release into the bloodstream.
This question belongs to: Science Biology
Question #1500
The 'Hormone Gastric Inhibitory Peptide' (GIP), also known as Glucose-dependent Insulinotropic Peptide, is secreted by the K cells of the duodenum and jejunum. Its primary function in the presence of elevated blood glucose is to:
A. Inhibit insulin release
B. Stimulate glucagon release
C. Inhibit gastric acid secretion and stimulate insulin release from the pancreas
D. Stimulate gastric acid secretion
Discuss
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Correct Answer: Option C

Explanation:
Gastric Inhibitory Peptide (GIP), now more commonly called Glucose-dependent Insulinotropic Peptide, is an incretin hormone secreted by the K cells of the small intestine in response to the ingestion of food, particularly glucose and fats. Its name reflects its two main actions: 1) It inhibits gastric acid secretion and slows gastric emptying (the 'gastric inhibitory' effect). 2) In the presence of elevated blood glucose, it potently stimulates the beta cells of the pancreas to secrete insulin (the 'insulinotropic' effect), preparing the body to handle the incoming nutrients.
This question belongs to: Science Biology

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