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101. A student observes concentric rings of bone matrix around a central canal containing blood vessels and nerves. Which structure is being described?
ⓐ. Trabecula
ⓑ. Osteon (Haversian system)
ⓒ. Epiphysis
ⓓ. Perichondrium
Correct Answer: Osteon (Haversian system)
Explanation: An osteon is the basic structural and functional unit of compact bone, organized as concentric lamellae arranged around a central (Haversian) canal. The central canal carries blood vessels and nerves, ensuring nutrient supply and waste removal for bone cells embedded in the matrix. This cylindrical arrangement provides high strength and resistance to bending and torsion along the long axis of bones. Osteons are aligned in the direction of mechanical stress, which is why compact bone is especially strong in weight-bearing regions. The presence of concentric rings with a central canal is the classic microscopic hallmark of an osteon. Therefore, the described structure is an osteon.
102. In compact bone, the Haversian canal is primarily important because it:
ⓐ. Stores fat as an energy reserve inside bone tissue
ⓑ. Houses osteocytes that directly secrete bone matrix
ⓒ. Provides a hollow space to reduce bone weight without weakening it
ⓓ. Contains blood vessels and nerves that nourish the osteon
Correct Answer: Contains blood vessels and nerves that nourish the osteon
Explanation: The Haversian canal is the central channel of an osteon and serves as the main route for blood vessels and nerve fibers within compact bone. Because osteocytes are embedded in a hard, mineralized matrix, they rely on diffusion for nutrients and waste exchange rather than direct contact with the bloodstream. The central canal brings vessels close enough to allow this exchange through microchannels in the bone. This vascular supply supports bone maintenance, repair, and remodeling by ensuring cells remain viable. The nerve supply also contributes to sensing and signaling within bone. Hence, the Haversian canal’s key importance is carrying vessels and nerves to nourish the osteon.
103. Osteocytes are best described as:
ⓐ. Mature bone cells located in lacunae that help maintain bone matrix
ⓑ. Bone-resorbing cells that dissolve mineralized matrix at active sites
ⓒ. Cartilage-forming cells embedded in a gel-like matrix
ⓓ. Blood-forming cells that give rise to platelets and leukocytes
Correct Answer: Mature bone cells located in lacunae that help maintain bone matrix
Explanation: Osteocytes are the mature, long-lived cells of bone formed when osteoblasts become trapped in the matrix they secrete. They reside in small spaces called lacunae and extend fine cytoplasmic processes through canaliculi to communicate and exchange materials. Their role is to maintain the surrounding bone matrix and participate in sensing mechanical stress, helping guide remodeling where needed. Because bone is mineralized, osteocytes depend on this canalicular network for nutrient diffusion and waste removal. This positioning and maintenance role is fundamental to keeping bone tissue functional and responsive. Therefore, osteocytes are mature bone cells in lacunae that maintain the matrix.
104. Canaliculi in bone are best understood as:
ⓐ. Thick collagen bundles that attach muscle to bone
ⓑ. Central channels that directly contain arteries and veins
ⓒ. Tiny channels that connect lacunae and allow nutrient/waste exchange for osteocytes
ⓓ. Layers of calcified matrix deposited only during early development
Correct Answer: Tiny channels that connect lacunae and allow nutrient/waste exchange for osteocytes
Explanation: Canaliculi are microscopic channels radiating from lacunae, forming a communication and transport network within compact bone. Osteocyte processes extend through these channels, allowing exchange of nutrients, ions, and metabolic wastes between osteocytes and toward the vascular supply in central canals. This is essential because the mineralized matrix does not permit free diffusion over long distances. The canalicular system also supports cell-to-cell signaling, helping bone respond to mechanical loading and maintain structural integrity. Without canaliculi, osteocytes would be isolated and unable to survive effectively within hard bone. Thus, canaliculi are tiny connecting channels enabling exchange and communication.
105. The periosteum of a bone is best described as:
ⓐ. An outer fibrous covering with an inner osteogenic layer important for growth and repair
ⓑ. A hollow central cavity that stores synovial fluid
ⓒ. A soft epithelial lining that prevents abrasion at joints
ⓓ. A cartilage layer that remains permanent in adult long bones
Correct Answer: An outer fibrous covering with an inner osteogenic layer important for growth and repair
Explanation: The periosteum is a tough connective tissue membrane covering the external surface of bones (except at articular regions). Its outer fibrous layer provides protection and serves as an attachment site for tendons and ligaments, supporting force transmission. The inner osteogenic layer contains cells capable of forming new bone, which is critical for appositional growth and fracture healing. It also contains blood vessels that supply the outer bone and contribute to repair processes. Because it is biologically active, damage to periosteum can slow healing and remodeling. Therefore, the periosteum is an outer fibrous covering with an osteogenic layer important for growth and repair.
106. Which cell type is primarily responsible for bone resorption during remodeling?
ⓐ. Osteocyte
ⓑ. Osteoblast
ⓒ. Osteoclast
ⓓ. Fibroblast
Correct Answer: Osteoclast
Explanation: Osteoclasts are large, specialized cells that break down bone matrix during normal growth, calcium balance, and repair. They attach to the bone surface and create a sealed microenvironment where acids and enzymes dissolve mineral components and degrade the organic matrix. This resorption is essential for shaping bones, removing micro-damage, and making space for new bone deposition. Bone remodeling depends on the coordinated activity of osteoclasts and bone-forming cells to maintain strength and mineral homeostasis. The hallmark function tested in exams is that osteoclasts are the primary resorptive cells of bone. Hence, osteoclasts are responsible for bone resorption.
107. In spongy (cancellous) bone, the main structural units that form a lattice-like network are:
ⓐ. Osteons
ⓑ. Trabeculae
ⓒ. Haversian canals
ⓓ. Volkmann canals
Correct Answer: Trabeculae
Explanation: Spongy bone is organized into a network of thin bony plates or rods called trabeculae, which create a lightweight but strong internal scaffold. This architecture distributes forces efficiently and reduces overall bone weight while maintaining mechanical support. Trabeculae are arranged along lines of stress, allowing the structure to resist compression and bending in functional directions. The spaces between trabeculae commonly house bone marrow and blood vessels, supporting hematopoiesis and metabolic activity. Unlike compact bone, spongy bone does not rely on tightly packed osteons as its main pattern. Therefore, the lattice-like units of spongy bone are trabeculae.
108. Volkmann canals are best described as:
ⓐ. Channels that run perpendicular to osteons and connect blood supply between central canals
ⓑ. Cavities that store fat inside cartilage to increase flexibility
ⓒ. Spaces that hold osteocytes and form the main unit of compact bone
ⓓ. Fibers that attach periosteum directly to bone marrow
Correct Answer: Channels that run perpendicular to osteons and connect blood supply between central canals
Explanation: Volkmann canals, also known as perforating canals, run perpendicular to the long axis of the bone and the central (Haversian) canals of the osteons.
They contain blood vessels and nerves and serve to interconnect the vascular supply of adjacent central canals, as well as connecting them to the blood supply of the periosteum (outer bone membrane) and endosteum (inner bone membrane). This network is crucial for providing nutrients and removing waste products from the bone tissue.
109. The hardness of bone is mainly due to deposition of inorganic salts, largely in the form of:
ⓐ. Calcium phosphate crystals such as $Ca_{10}(PO_4)_6(OH)*2$
ⓑ. Sodium chloride crystals embedded between collagen fibers
ⓒ. Calcium carbonate only, with negligible phosphate content
ⓓ. Potassium phosphate stored in bone marrow cells
Correct Answer: Calcium phosphate crystals such as $Ca*{10}(PO_4)_6(OH)*2$
Explanation: Bone matrix becomes hard primarily because inorganic mineral salts are deposited within the collagenous framework of the extracellular matrix. The dominant mineral component is calcium phosphate in a crystalline form commonly represented as hydroxyapatite, which provides compressional strength and rigidity. This mineralization allows bones to support body weight, protect organs, and act as levers for movement. Collagen contributes tensile strength, but without mineral deposition the tissue would be flexible rather than rigid. The combination of a protein framework and calcium phosphate crystals gives bone its characteristic strength. Hence, calcium phosphate crystals such as $Ca*{10}(PO_4)_6(OH)_2$ are the main cause of bone hardness.
110. A long bone needs maximum strength against bending with minimal weight. Which arrangement best explains why compact bone is more suitable for the shaft?
ⓐ. Randomly arranged fibers in multiple directions to resist all stresses equally
ⓑ. A thick cartilage sleeve that remains flexible under load
ⓒ. Repeating osteons aligned with the long axis to resist tension and compression efficiently
ⓓ. Wide fluid-filled cavities that absorb shocks like cushions
Correct Answer: Repeating osteons aligned with the long axis to resist tension and compression efficiently
Explanation: The shaft of a long bone experiences significant bending and weight-bearing forces during movement and standing. Compact bone is organized into osteons that are typically aligned parallel to the long axis, matching the direction of major stresses. This alignment helps resist compression on one side of a bending bone and tension on the other, improving mechanical efficiency. The dense packing of osteons and lamellae creates a strong, rigid structure with high load-bearing capacity. At the same time, the hollow medullary cavity limits weight without sacrificing the outer strength needed at the shaft. Therefore, aligned osteons in compact bone explain the shaft’s strength with minimal weight.
111. A tissue shows chondrocytes in lacunae within a smooth, glassy matrix; it supports tracheal rings and forms articular surfaces. Which cartilage is this?
ⓐ. Fibrocartilage
ⓑ. Hyaline cartilage
ⓒ. Elastic cartilage
ⓓ. Dense regular connective tissue
Correct Answer: Hyaline cartilage
Explanation: Hyaline cartilage is characterized by chondrocytes housed in lacunae and a homogeneous, glassy extracellular matrix. It provides firm support with flexibility, which is ideal for structures like tracheal rings that must stay open without being rigid. At joints, hyaline cartilage forms articular cartilage that reduces friction and absorbs shock during movement. The matrix is rich in ground substance that resists compression while maintaining shape. This cartilage is a classic skeletal connective tissue used where smooth, resilient support is needed. Therefore, the correct identification is hyaline cartilage.
112. Which cartilage type is best suited to provide flexible support to the external ear pinna and epiglottis?
ⓐ. Hyaline cartilage
ⓑ. Fibrocartilage
ⓒ. Articular cartilage
ⓓ. Elastic cartilage
Correct Answer: Elastic cartilage
Explanation: Elastic cartilage contains chondrocytes in lacunae like other cartilages but has abundant elastic fibers in its matrix. These elastic fibers allow the tissue to bend and recoil, maintaining shape even after repeated deformation. This property is essential in structures such as the external ear pinna and epiglottis, where flexibility and shape retention are critical. The matrix is more resilient than hyaline cartilage for repeated flexing, yet still provides supportive strength. This structure-function match makes elastic cartilage the standard answer for flexible, shape-preserving support. Hence, elastic cartilage is correct.
113. A student notes that cartilage heals slowly after injury. The most direct biological reason is that cartilage is generally:
ⓐ. Avascular, so nutrients and repair factors reach it mainly by diffusion
ⓑ. Richly vascular, so inflammation is excessive and delays healing
ⓒ. Made of keratin, so it cannot remodel after damage
ⓓ. Filled with osteons, which block all cell movement during repair
Correct Answer: Avascular, so nutrients and repair factors reach it mainly by diffusion
Explanation: Cartilage typically lacks blood vessels, so it does not receive direct, rapid delivery of oxygen, nutrients, and repair cells through circulation. Instead, chondrocytes depend on diffusion from surrounding tissues, which is slower—especially through a dense matrix. During injury, the limited vascular access reduces the speed and intensity of the repair response compared with well-vascularized tissues. This also limits the supply of building materials and signaling molecules needed for remodeling. As a result, cartilage repair tends to be slow and often incomplete. Therefore, avascularity with diffusion-based nourishment best explains slow healing.
114. Intervertebral discs and the pubic symphysis contain cartilage that resists compression and tensile stress due to abundant collagen bundles. Which cartilage is this?
ⓐ. Elastic cartilage
ⓑ. Hyaline cartilage
ⓒ. Fibrocartilage
ⓓ. Areolar connective tissue
Correct Answer: Fibrocartilage
Explanation: Fibrocartilage is designed for high mechanical stress because its matrix contains dense collagen fibers along with cartilage cells in lacunae. This makes it stronger in tension than hyaline cartilage while still resisting compression, a combination required in intervertebral discs. The pubic symphysis also experiences repeated stress and must absorb shock while holding bones firmly together. The collagen-rich structure provides durability and reduces risk of deformation under load. This is why fibrocartilage is classically associated with discs, symphyses, and similar shock-absorbing sites. Hence, fibrocartilage is the correct answer.
115. A key functional role of articular cartilage at movable joints is to:
ⓐ. Produce synovial fluid by active secretion
ⓑ. Anchor tendons directly to bone with parallel collagen bundles
ⓒ. Generate nerve impulses for joint reflexes
ⓓ. Reduce friction and absorb shock on bone ends during movement
Correct Answer: Reduce friction and absorb shock on bone ends during movement
Explanation: Articular cartilage covers the ends of bones at synovial joints and provides a smooth, low-friction surface for movement. Its resilient matrix distributes compressive forces, reducing stress on underlying bone during walking, running, or lifting. This shock-absorbing property protects joint surfaces from wear and helps maintain efficient motion over time. The cartilage also helps keep movements smooth by minimizing mechanical resistance between articulating surfaces. These roles are mechanical and protective rather than fluid production or force transmission like tendons. Therefore, reducing friction and absorbing shock is the correct function.
116. Which statement best describes the cells of cartilage tissue?
ⓐ. Osteocytes arranged in concentric lamellae around a central canal
ⓑ. Chondrocytes located in lacunae within a firm extracellular matrix
ⓒ. Fibroblasts arranged in rows between parallel collagen bundles
ⓓ. Epithelial cells resting on a basement membrane in layers
Correct Answer: Chondrocytes located in lacunae within a firm extracellular matrix
Explanation: The characteristic cells of cartilage are chondrocytes, which occupy small spaces called lacunae in the matrix. These cells synthesize and maintain the cartilaginous extracellular matrix that provides firmness and flexibility. The matrix is rich in ground substance that binds water, allowing resistance to compression. Chondrocytes can occur singly or in small groups as they divide and expand within the matrix. This lacuna-based cell housing is a defining histological clue separating cartilage from bone and dense connective tissue. Hence, chondrocytes in lacunae correctly describe cartilage cells.
117. Which feature most directly explains why cartilage is firm yet flexible compared with bone?
ⓐ. It contains osteons and abundant mineral salts throughout the matrix
ⓑ. It is made only of parallel collagen bundles with almost no ground substance
ⓒ. Its matrix is rich in ground substance that holds water and resists compression without heavy mineralization
ⓓ. It is formed from epithelial layers that continuously regenerate to stay strong
Correct Answer: Its matrix is rich in ground substance that holds water and resists compression without heavy mineralization
Explanation: Cartilage owes its resilience to a matrix rich in ground substance that binds water, creating turgidity and resistance to compression. Because it is not heavily mineralized like bone, the tissue can bend and recover shape under stress rather than remaining rigid. This water-rich matrix acts like a shock absorber, distributing forces across the tissue. Collagen and, in some types, elastic fibers provide additional strength and flexibility, but the hydrated ground substance is central to the “firm-yet-flexible” property. This structural composition supports smooth joint function and flexible support structures. Therefore, water-binding ground substance without heavy mineralization best explains cartilage flexibility.
118. Perichondrium is most accurately described as:
ⓐ. A fibrous connective tissue covering that supports cartilage growth and repair in many cartilages
ⓑ. A central canal containing blood vessels inside each cartilage unit
ⓒ. A lining epithelium that secretes mucus to protect cartilage
ⓓ. A mineralized layer that converts cartilage into compact bone permanently
Correct Answer: A fibrous connective tissue covering that supports cartilage growth and repair in many cartilages
Explanation: Perichondrium is a dense connective tissue sheath that surrounds many cartilages and provides support as well as a source of cells for growth. It contains fibroblast-like cells that can differentiate toward cartilage-forming cells, enabling appositional growth and contributing to repair potential. It also helps provide a pathway for nutrient diffusion toward the avascular cartilage. The presence of perichondrium is a common identification point in basic histology for many cartilaginous regions. While not present in every cartilage location, its role as a supportive covering is conceptually central. Therefore, perichondrium is a fibrous covering aiding growth and repair.
119. Which cartilage type is most specifically associated with providing tensile strength and acting as a strong shock absorber where load is high?
ⓐ. Elastic cartilage
ⓑ. Hyaline cartilage
ⓒ. Articular cartilage
ⓓ. Fibrocartilage
Correct Answer: Fibrocartilage
Explanation: Fibrocartilage is specialized for high load-bearing regions because it combines cartilage cells with a matrix rich in collagen fibers. This composition provides strong tensile strength along with resistance to compression, making it highly effective as a shock absorber. Such mechanical demands are prominent in structures like intervertebral discs and certain joint pads where forces are intense and repetitive. The collagen-rich architecture prevents excessive deformation and supports stability under stress. This makes fibrocartilage distinct from hyaline cartilage, which is smoother and more uniformly flexible, and from elastic cartilage, which emphasizes bending and recoil. Hence, fibrocartilage is the correct choice.
120. During growth, lengthening of long bones is linked to cartilage present at the epiphyseal region. This cartilage is important because it:
ⓐ. Is replaced by tendon tissue to transmit muscle pull
ⓑ. Forms a rigid mineralized tube that prevents any growth
ⓒ. Acts as a permanent joint cushion that never changes
ⓓ. Provides a growth zone where cartilage is added and later replaced by bone
Correct Answer: Provides a growth zone where cartilage is added and later replaced by bone
Explanation: The cartilage at the epiphyseal region, known as the epiphyseal plate or growth plate, is a layer of hyaline cartilage vital for the longitudinal growth of long bones. Chondrocytes (cartilage cells) in this region constantly divide, adding new cartilage. This new cartilage is then systematically calcified, broken down, and replaced by bone tissue, causing the bone to lengthen from the diaphyseal side of the plate. This process is called endochondral ossification.
121. Which formed element is primarily responsible for oxygen transport in blood?
ⓐ. Erythrocytes
ⓑ. Platelet fragments
ⓒ. Neutrophil granulocytes
ⓓ. Plasma proteins complex
Correct Answer: Erythrocytes
Explanation: Erythrocytes are the major cellular component of blood specialized for gas transport. They contain hemoglobin, which binds oxygen reversibly in the lungs and releases it in tissues based on local conditions. Their biconcave shape increases surface area and improves flexibility to pass through narrow capillaries. The absence of a nucleus in mature mammalian erythrocytes provides more space for hemoglobin, enhancing oxygen-carrying capacity. This design makes erythrocytes the most efficient carriers of oxygen among blood components. Therefore, erythrocytes are primarily responsible for oxygen transport.
122. Which plasma protein is most directly essential for blood clot formation?
ⓐ. Albumin fraction
ⓑ. Globulin fraction
ⓒ. Fibrinogen
ⓓ. Hormone carriers
Correct Answer: Fibrinogen
Explanation: Fibrinogen is a soluble plasma protein that serves as the key precursor for fibrin formation during coagulation. When the clotting pathway is activated, fibrinogen is converted into insoluble fibrin strands that form a stabilizing mesh. This fibrin network traps blood cells and reinforces the initial platelet plug at the site of injury. Without sufficient fibrinogen, clots remain weak and bleeding control becomes inefficient. The role of fibrinogen is therefore central and direct in forming a stable clot. Hence, fibrinogen is essential for clot formation.
123. Which blood component initiates the platelet plug during the early phase of hemostasis?
ⓐ. Lymphocyte cells
ⓑ. Erythrocyte cells
ⓒ. Plasma water
ⓓ. Platelets
Correct Answer: Platelets
Explanation: Platelets rapidly adhere to damaged vessel walls and become activated, forming the first physical barrier to blood loss. Activation causes platelets to change shape, aggregate with each other, and release chemical mediators that amplify the response. This platelet plug provides a temporary seal until the coagulation cascade deposits fibrin for long-term stability. Platelets also provide a surface that supports assembly of clotting factor complexes, making clotting efficient and localized. Their quick response is critical for preventing excessive bleeding from small vessel injuries. Therefore, platelets initiate the platelet plug in early hemostasis.
124. Which cell type is most abundant among circulating white blood cells in typical adult blood?
ⓐ. Eosinophil granulocytes
ⓑ. Neutrophils
ⓒ. Basophil granulocytes
ⓓ. Monocyte phagocytes
Correct Answer: Neutrophils
Explanation: Neutrophils are the most numerous leukocytes in peripheral blood and form the first major cellular line of defense in many infections. They rapidly migrate to sites of tissue injury or microbial entry and perform phagocytosis. Their cytoplasmic granules contain enzymes and antimicrobial substances that help kill engulfed organisms. Because they respond quickly and are produced in large numbers, neutrophils dominate the leukocyte count under normal conditions. This high baseline presence supports immediate innate immune protection. Hence, neutrophils are typically the most abundant white blood cells.
125. Which term refers to the liquid part of blood that contains clotting factors?
ⓐ. Plasma
ⓑ. Serum portion
ⓒ. Tissue fluid
ⓓ. Lymph stream
Correct Answer: Plasma
Explanation: Plasma is the straw-colored fluid matrix of blood in which blood cells and platelets are suspended. It contains water, electrolytes, nutrients, hormones, wastes, and crucially the clotting proteins such as fibrinogen. Because clotting factors remain present, plasma can participate in coagulation when a vessel is injured. In contrast, removing clotting factors yields a different fluid used in certain tests. Plasma also helps maintain osmotic balance and transports many substances throughout the body. Therefore, the liquid part containing clotting factors is plasma.
126. In human blood, oxygen is mainly carried in which form?
ⓐ. Dissolved oxygen only
ⓑ. Bicarbonate ions
ⓒ. Oxyhemoglobin
ⓓ. Plasma oxygenates
Correct Answer: Oxyhemoglobin
Explanation: Most oxygen in blood is transported bound to hemoglobin inside erythrocytes, forming oxyhemoglobin. Hemoglobin’s structure allows reversible binding, enabling oxygen pickup in the lungs and release in tissues where oxygen is needed. Only a small fraction of oxygen remains dissolved directly in plasma, which is not sufficient for body demands. The hemoglobin-bound form greatly increases the oxygen-carrying capacity of blood without raising osmotic pressure excessively. This mechanism is central to efficient aerobic metabolism in tissues. Therefore, oxygen is mainly carried as oxyhemoglobin.
127. Which statement best describes the main role of albumin in plasma?
ⓐ. Antibody defense function
ⓑ. Clot mesh formation
ⓒ. Oxygen binding role
ⓓ. Osmotic balance
Correct Answer: Osmotic balance
Explanation: Albumin is the most abundant plasma protein and is a major contributor to plasma oncotic pressure. By maintaining osmotic balance, it helps keep water within the blood vessels and limits excessive fluid leakage into tissues. This stabilizes blood volume and supports normal circulation and tissue perfusion. Albumin also serves as a carrier for several small molecules, but its defining systemic role is maintaining fluid balance. When albumin levels fall, edema can occur due to reduced oncotic pressure. Hence, albumin’s main role is osmotic balance.
128. Which formed element is directly involved in adaptive immunity by producing antibodies (via differentiated forms)?
ⓐ. Lymphocytes
ⓑ. Neutrophil cells
ⓒ. Platelet fragments
ⓓ. Erythrocyte cells
Correct Answer: Lymphocytes
Explanation: Lymphocytes are central to adaptive immunity, which provides specific and memory-based defense against pathogens. B-lymphocytes can differentiate into plasma cells that secrete antibodies targeting particular antigens. T-lymphocytes coordinate immune responses and can directly kill infected cells or regulate other immune cells. This specificity and memory distinguish lymphocyte-mediated responses from rapid, non-specific innate defenses. Their actions help ensure long-term protection after infection or vaccination. Therefore, lymphocytes are directly involved in antibody-based adaptive immunity.
129. In a typical blood sample, which component forms the largest proportion by volume?
ⓐ. Buffy coat layer
ⓑ. Platelet layer
ⓒ. Plasma
ⓓ. WBC fraction
Correct Answer: Plasma
Explanation: Plasma constitutes the largest volume fraction of blood, typically accounting for over half of total blood volume. It serves as the transport medium for nutrients, hormones, gases in dissolved form, and metabolic wastes. Plasma also contains proteins that maintain osmotic pressure, support immunity, and enable clotting. The formed elements (RBCs, WBCs, and platelets) occupy the remaining fraction, with WBCs and platelets forming only a thin buffy coat. Because plasma is the continuous fluid phase, it dominates blood volume. Hence, plasma forms the largest proportion by volume.
130. Which blood group antigen is present on RBCs of a person with blood group A?
ⓐ. Rh antigen
ⓑ. A antigen
ⓒ. Both A and B
ⓓ. No surface antigens
Correct Answer: A antigen
Explanation: Blood group A is defined by the presence of A antigen on the surface of red blood cells. This surface antigen determines compatibility reactions because the immune system can recognize non-self antigens during transfusion. As a result, individuals with group A typically have antibodies against the B antigen in their plasma. The antigen-based classification is crucial for safe transfusions and preventing agglutination reactions. The identifying feature remains the RBC surface antigen pattern rather than plasma composition alone. Therefore, the RBCs of blood group A carry A antigen.
131. Lymph is best defined as:
ⓐ. Tissue fluid
ⓑ. Venous blood
ⓒ. Bone marrow fluid
ⓓ. Digestive secretion
Correct Answer: Tissue fluid
Explanation: Lymph is essentially the tissue (interstitial) fluid that enters lymphatic capillaries and is carried through lymphatic vessels. It forms from plasma that filters out of blood capillaries into spaces between cells and then returns to circulation via the lymphatic system. Because it drains tissues, it helps maintain fluid balance and prevents accumulation of excess interstitial fluid. Lymph also acts as a transport medium, carrying absorbed fats from the intestine and moving immune cells between tissues and lymphoid organs. Its composition resembles tissue fluid more than blood, especially due to the absence of red blood cells under normal conditions. Therefore, defining lymph as tissue fluid is correct.
132. Compared with blood, normal lymph typically has:
ⓐ. Many erythrocytes present
ⓑ. High platelet concentration
ⓒ. No erythrocytes
ⓓ. Thick fibrin clots
Correct Answer: No erythrocytes
Explanation: Under normal conditions, lymph does not contain red blood cells because it originates mainly from interstitial fluid rather than directly from blood within vessels. The lymphatic capillaries collect excess tissue fluid, proteins, and cells like lymphocytes, but RBCs generally remain inside blood vessels. The absence of erythrocytes is a key conceptual point used to distinguish lymph from blood in basic biology questions. While some proteins may be present and clotting can occur under certain conditions, the typical defining feature is the lack of RBCs. This also explains why lymph is usually pale rather than red. Hence, “no erythrocytes” is the correct statement for normal lymph.
133. The lymph from most of the body ultimately drains into:
ⓐ. Pulmonary artery branches
ⓑ. Hepatic portal vein
ⓒ. Renal veins network
ⓓ. Thoracic duct
Correct Answer: Thoracic duct
Explanation: The thoracic duct is the major lymphatic channel that collects lymph from a large portion of the body, including both lower limbs, the abdomen, and the left side of the thorax, head, and upper limb. It transports this lymph toward the venous circulation, returning fluids and proteins back to the bloodstream. This drainage pathway is vital for maintaining blood volume and preventing tissue fluid accumulation. The thoracic duct also carries lipid-rich lymph from intestinal lacteals after fat absorption. Because it is the principal lymph-collecting duct, it is the standard answer for “most of the body.” Therefore, thoracic duct is correct.
134. Lymph nodes primarily function to:
ⓐ. Produce bile salts
ⓑ. Filter lymph
ⓒ. Store glycogen granules
ⓓ. Secrete digestive enzymes
Correct Answer: Filter lymph
Explanation: Lymph nodes act as biological filters placed along lymph vessels, trapping foreign particles, microbes, and debris present in lymph. As lymph flows through nodes, immune cells within them can recognize antigens and mount a defensive response. This filtering reduces the spread of infections and helps keep tissue fluid cleaner before it returns to the bloodstream. Lymph nodes also support activation and proliferation of lymphocytes, strengthening adaptive immune reactions. Their strategic placement ensures surveillance of lymph from specific body regions. Hence, filtering lymph is the primary function of lymph nodes.
135. In intestinal villi, lymphatic capillaries specialized for fat absorption are called:
ⓐ. Lacteals
ⓑ. Portal venules
ⓒ. Bile canaliculi
ⓓ. Bronchioles
Correct Answer: Lacteals
Explanation: Lacteals are specialized lymphatic capillaries present within intestinal villi that absorb dietary lipids. After digestion, fats are packaged into chylomicrons, which enter lacteals rather than blood capillaries because of their larger size. The resulting lipid-rich lymph is called chyle and is transported through lymphatic vessels to reach the venous circulation. This pathway is essential for efficient absorption of fats and fat-soluble substances from the small intestine. The structural match—villi with a central lymph capillary—is a common exam-tested association. Therefore, lacteals is the correct term.
136. A key reason lymph flow is one-way in larger lymph vessels is the presence of:
ⓐ. Thick elastic walls only
ⓑ. High arterial pressure
ⓒ. Valves
ⓓ. RBC packing
Correct Answer: Valves
Explanation: Lymphatic vessels operate under low pressure, so they require structural mechanisms to prevent backflow and maintain forward movement. Valves inside larger lymph vessels ensure lymph moves in a single direction toward the venous circulation. This one-way design works together with skeletal muscle contractions, breathing movements, and smooth muscle activity in vessel walls to propel lymph forward. Without valves, lymph could pool or flow backward, reducing drainage efficiency and increasing tissue fluid accumulation. The valve system is therefore a core anatomical adaptation supporting lymph transport. Hence, valves are the correct feature enabling one-way flow.
137. In lymph, the most common white blood cells are typically:
ⓐ. Neutrophils only
ⓑ. Lymphocytes
ⓒ. Basophils mainly
ⓓ. Eosinophils mostly
Correct Answer: Lymphocytes
Explanation: Lymph is closely linked to immune function and commonly contains a high proportion of lymphocytes, which circulate between blood, tissues, lymph vessels, and lymphoid organs. As lymph passes through lymph nodes, lymphocytes can be added, activated, and recirculated, increasing their presence in the lymph stream. This makes lymph an important transport route for immune surveillance and antigen-driven responses. While other leukocytes may appear, lymphocytes are the most characteristic and dominant group in typical lymph. This aligns with the role of lymph in adaptive immunity and immune communication. Therefore, lymphocytes are the most common white blood cells in lymph.
138. Lymph helps prevent edema mainly by:
ⓐ. Making urine rapidly
ⓑ. Raising arterial pressure
ⓒ. Blocking capillary filtration
ⓓ. Draining excess fluid
Correct Answer: Draining excess fluid
Explanation: Fluid continuously filters out of blood capillaries into tissue spaces, and if it were not returned, tissues would swell due to fluid accumulation. The lymphatic system collects this excess interstitial fluid and returns it to the venous circulation, maintaining normal tissue volume. This drainage also returns plasma proteins that leak into tissues, helping preserve osmotic balance and blood volume. When lymphatic drainage is impaired, fluid builds up and edema becomes prominent. Thus, lymph’s role is not to stop filtration entirely, but to remove what remains in the tissue spaces. Therefore, draining excess fluid is the main mechanism by which lymph prevents edema.
139. The fluid that enters lymphatic capillaries originates mainly from:
ⓐ. Interstitial fluid
ⓑ. Cerebrospinal fluid
ⓒ. Gastric juice
ⓓ. Bile secretion
Correct Answer: Interstitial fluid
Explanation: Lymph begins as interstitial fluid formed when plasma filters out of blood capillaries into the spaces between tissue cells. Most of this fluid is reabsorbed into capillaries, but the remaining portion enters blind-ended lymphatic capillaries to become lymph. This process is essential for fluid balance, because it prevents progressive fluid buildup in tissues. The lymphatic pathway also returns proteins and transports immune cells, linking tissue spaces to immune surveillance. The origin from interstitial fluid explains why lymph composition resembles tissue fluid rather than digestive or neural fluids. Hence, interstitial fluid is the main source of lymph.
140. Lymph enters the bloodstream most directly by emptying into:
ⓐ. Arterioles
ⓑ. Veins
ⓒ. Capillary beds
ⓓ. Cardiac chambers
Correct Answer: Veins
Explanation: The lymphatic system ultimately returns lymph to the blood circulation by draining into large veins near the heart. This return restores fluid volume, returns plasma proteins to the bloodstream, and completes the cycle of capillary filtration and tissue drainage. Major lymphatic ducts deliver lymph at venous junctions, ensuring lymph mixes back into circulating blood efficiently. Because venous pressure is relatively low compared with arterial pressure, it favors entry of lymph into the bloodstream. This connection is fundamental for maintaining stable blood volume and preventing edema. Therefore, lymph most directly empties into veins.
141. Skeletal muscle fibers are described as “syncytial” mainly because they are:
ⓐ. Multinucleated
ⓑ. Single-nucleated
ⓒ. Enucleated
ⓓ. Binucleated
Correct Answer: Multinucleated
Explanation: Skeletal muscle fibers form by fusion of many myoblasts during development, producing one long cell with multiple nuclei. Because the cytoplasm is continuous and contains many nuclei, the fiber behaves like a syncytium in structure and function. The nuclei are typically positioned toward the periphery, leaving the central region packed with contractile myofibrils. This multinucleation supports high protein synthesis demands needed to maintain large amounts of actin, myosin, and associated proteins. It also helps the fiber repair and adapt to training by distributing gene expression across a long cell. Therefore, the defining basis for the syncytial description is that skeletal fibers are multinucleated.
142. In a sarcomere, the structure that forms the boundary and gives rise to the light band pattern is the:
ⓐ. M line
ⓑ. H zone
ⓒ. A band
ⓓ. Z line
Correct Answer: Z line
Explanation: The Z line (Z disc) marks the end of one sarcomere and the beginning of the next, serving as the anchoring point for thin filaments. Because sarcomeres repeat in a highly ordered way along myofibrils, these boundaries help create the regular striated appearance seen under the microscope. Thin filaments extend from the Z line toward the center, and their arrangement contributes to the light I band region. During contraction, Z lines move closer as the sarcomere shortens, reflecting the key mechanical change in skeletal muscle. The Z line therefore defines sarcomere limits and organizes filament alignment. Hence, the boundary of a sarcomere is the Z line.
143. The dark A band of a skeletal muscle fiber is mainly due to the presence of:
ⓐ. Only thin filaments
ⓑ. Thick filaments
ⓒ. Only elastic fibers
ⓓ. Only collagen fibers
Correct Answer: Thick filaments
Explanation: The A band corresponds to the region containing thick filaments, primarily myosin, which gives it a darker appearance in striated muscle. This band also includes areas where thick and thin filaments overlap, but the defining feature is the length of the thick filaments themselves. Because thick filaments remain constant in length during contraction, the A band does not change appreciably as the muscle shortens. The contrast between A and I bands arises from orderly filament arrangement rather than connective tissue fibers. This structural basis is central to identifying sarcomere regions in diagrams and micrographs. Therefore, the A band is mainly due to thick filaments.
144. The immediate trigger for skeletal muscle contraction after a nerve impulse is the:
ⓐ. Release of hemoglobin into sarcoplasm
ⓑ. Breakdown of glycogen into glucose
ⓒ. Rise of Ca2+ in sarcoplasm
ⓓ. Entry of NaCl into mitochondria
Correct Answer: Rise of Ca2+ in sarcoplasm
Explanation: When a motor impulse reaches the muscle fiber, electrical changes spread along the membrane and into the fiber through internal membrane systems, leading to release of Ca2+ into the sarcoplasm. The increased Ca2+ binds to regulatory proteins on the thin filament, shifting them so that myosin-binding sites become accessible. This allows cross-bridge formation between myosin heads and actin, initiating the sliding process. Without the Ca2+ rise, the regulatory block remains and contraction cannot start even if ATP is present. The Ca2+ signal is therefore the key switch that converts excitation into mechanical interaction of filaments. Hence, the immediate trigger is a rise of Ca2+ in the sarcoplasm.
145. During skeletal muscle contraction, the I band:
ⓐ. Shortens
ⓑ. Lengthens
ⓒ. Remains unchanged
ⓓ. Disappears permanently
Correct Answer: Shortens
Explanation: The I band contains regions where only thin filaments are present without overlap by thick filaments. As contraction occurs, thin filaments slide deeper toward the center of the sarcomere, increasing the overlap with thick filaments. This reduces the width of the non-overlap region, so the I band becomes narrower. The A band stays largely constant because thick filament length does not change, but the overlap zones change, altering I band and H zone widths. This predictable band behavior is a classic test point for the sliding filament model. Therefore, the I band shortens during contraction.
146. The functional unit of contraction in a skeletal muscle myofibril is the:
ⓐ. Myosin filament
ⓑ. Actin filament
ⓒ. Myofibril
ⓓ. Sarcomere
Correct Answer: Sarcomere
Explanation: A sarcomere is the repeating segment between two Z lines and represents the smallest unit that can shorten during contraction. It contains the organized arrangement of thin and thick filaments that interact through cross-bridge cycling. When sarcomeres shorten in series along a myofibril, the entire fiber shortens, producing visible contraction. This unit-based organization explains striations and the consistent pattern of band changes during contraction. Understanding sarcomeres is essential for linking microscopic filament movement to macroscopic muscle action. Hence, the sarcomere is the functional unit of contraction.
147. A motor unit is best described as:
ⓐ. A tendon and the muscle it attaches to
ⓑ. One motor neuron and all muscle fibers it innervates
ⓒ. One muscle fiber and the nerve ending near it
ⓓ. A group of sarcomeres in a single myofibril
Correct Answer: One motor neuron and all muscle fibers it innervates
Explanation: A motor unit consists of a single motor neuron along with every skeletal muscle fiber that receives its branches. When that neuron fires, all fibers in the motor unit contract together, producing a coordinated mechanical response. The size of a motor unit influences precision of movement: smaller units allow fine control, while larger units generate stronger, less precise force. This concept explains graded muscle strength through recruitment of additional motor units rather than “partial contraction” of a single fiber. It also underlies many clinical observations about nerve injury and muscle weakness patterns. Therefore, a motor unit is one motor neuron and all muscle fibers it innervates.
148. The structure that carries the action potential deep into a skeletal muscle fiber to coordinate contraction is the:
ⓐ. Golgi tendon organ
ⓑ. Intercalated disc
ⓒ. T-tubule
ⓓ. Node of Ranvier
Correct Answer: T-tubule
Explanation: T-tubules are inward extensions of the muscle cell membrane that transmit electrical excitation from the surface into the interior of the fiber. This ensures that Ca2+ release and contraction begin almost simultaneously throughout the thickness of a large skeletal muscle cell. Without T-tubules, only the surface would be activated quickly, leading to inefficient and poorly coordinated contraction. Their close functional association with internal calcium stores supports rapid excitation–contraction coupling. This arrangement is a key adaptation for strong, synchronized contractions in voluntary muscles. Hence, T-tubules carry the action potential deep into the muscle fiber.
149. Which feature is most characteristic of skeletal muscle compared with smooth muscle?
ⓐ. No striations and spindle-shaped cells
ⓑ. Involuntary control with single nucleus
ⓒ. Branching fibers joined by special junctions
ⓓ. Striations with voluntary control
Correct Answer: Striations with voluntary control
Explanation: Skeletal muscle shows clear striations because its myofibrils are organized into repeating sarcomeres with precise alignment. This striated architecture supports rapid, forceful, and highly controlled contractions needed for posture and voluntary movement. Control is typically under the somatic nervous system, enabling deliberate activation of specific muscles. In contrast, smooth muscle lacks visible striations due to different filament arrangement and is generally involuntary. The combination of striations and voluntary control is therefore the most reliable distinguishing feature for skeletal muscle in basic tissue questions. Hence, skeletal muscle is characterized by striations with voluntary control.
150. The primary energy source that directly powers cross-bridge cycling in skeletal muscle is:
ⓐ. ATP
ⓑ. DNA
ⓒ. Urea
ⓓ. Bile
Correct Answer: ATP
Explanation: ATP provides the immediate energy required for myosin heads to detach from actin and reset for the next cross-bridge cycle. Its hydrolysis energizes the myosin head, allowing repeated binding, power stroke, and release steps that produce sliding of filaments. ATP is also essential for pumping Ca2+ back into internal stores, enabling relaxation and readiness for the next contraction. When ATP is severely depleted, cross-bridges cannot detach efficiently, leading to sustained stiffness. This direct role makes ATP the central chemical currency for muscle contraction mechanics. Therefore, ATP is the primary energy source for cross-bridge cycling.
151. Cardiac muscle fibers are best identified by which microscopic feature?
ⓐ. Long unbranched fibers with peripheral nuclei
ⓑ. Spindle-shaped cells without branching
ⓒ. Flat cells arranged in many layers
ⓓ. Branched fibers with intercalated discs
Correct Answer: Branched fibers with intercalated discs
Explanation: Cardiac muscle is distinguished by branching muscle fibers that connect end-to-end through intercalated discs. These discs contain strong attachment sites that hold cells together during powerful contractions and specialized junctions that allow rapid electrical spread. This structural design helps the myocardium behave as a coordinated functional unit for rhythmic pumping. The fibers are striated like skeletal muscle, but the branching pattern and disc connections are characteristic of the heart. This combination supports synchronized contraction without voluntary control. Therefore, branched fibers with intercalated discs best identifies cardiac muscle.
152. Smooth muscle is typically described as:
ⓐ. Spindle-shaped cells with one nucleus
ⓑ. Branched cells with two nuclei
ⓒ. Large multinucleated striated fibers
ⓓ. Flat cells forming a surface lining
Correct Answer: Spindle-shaped cells with one nucleus
Explanation: Smooth muscle cells are elongated and taper at both ends, giving a spindle-like shape, and each cell usually contains a single centrally placed nucleus. Their contractile filaments are not arranged into sarcomeres, so striations are not visible under a light microscope. This architecture supports slow, sustained contractions suitable for hollow organs and blood vessels. Smooth muscle is generally involuntary and is regulated by autonomic signals and local factors. The single-cell design allows graded, coordinated contractions in tissues like gut walls. Hence, spindle-shaped cells with one nucleus is the correct description.
153. The non-striated appearance of smooth muscle is mainly because:
ⓐ. Filaments are not arranged into sarcomeres
ⓑ. Fibers are filled with collagen bundles
ⓒ. Cells contain no contractile proteins
ⓓ. Myelin covers the muscle surface
Correct Answer: Filaments are not arranged into sarcomeres
Explanation: Smooth muscle contains actin and myosin, but they are arranged in a less ordered pattern compared with striated muscles. Because sarcomeres are not formed in a repeating aligned manner, alternating dark and light bands do not appear. This structural arrangement supports flexible contraction in multiple directions, useful in organs that change shape. The absence of striations is therefore an organizational feature, not a lack of contractile proteins. Smooth muscle can still generate force efficiently for sustained activity. Therefore, the correct reason is that filaments are not arranged into sarcomeres.
154. Which structure most directly enables rapid electrical coupling between cardiac muscle cells?
ⓐ. Collagen fibers around bundles
ⓑ. Thick keratinized covering
ⓒ. Gap junctions in intercalated discs
ⓓ. Cartilage-like matrix between cells
Correct Answer: Gap junctions in intercalated discs
Explanation: Gap junctions allow ions and small signaling molecules to pass directly from one cardiac muscle cell to the next. This creates low-resistance pathways so an action potential can spread quickly across the myocardium. The result is coordinated contraction of large regions of heart muscle in a synchronized manner. These junctions are concentrated within intercalated discs, along with anchoring junctions that maintain mechanical integrity. Without effective gap junction coupling, the heart would pump inefficiently due to poor coordination. Hence, gap junctions in intercalated discs are key for rapid electrical coupling.
155. Most smooth muscles of the gut wall contract under:
ⓐ. Voluntary control by motor cortex
ⓑ. Involuntary control by autonomic inputs
ⓒ. Direct control by sensory neurons
ⓓ. Command by skeletal tendon reflex
Correct Answer: Involuntary control by autonomic inputs
Explanation: Smooth muscle in the digestive tract is regulated primarily by the autonomic nervous system along with local chemical signals and intrinsic enteric circuits. This control supports automatic processes such as peristalsis and mixing movements without conscious effort. The contractions are often rhythmic and can be modulated by stretch, hormones, and neurotransmitters. Because the function is continuous and essential for digestion, involuntary regulation is more suitable than voluntary command. This pattern is a core concept distinguishing smooth from skeletal muscle. Therefore, involuntary control by autonomic inputs best describes gut smooth muscle regulation.
156. A key functional advantage of cardiac muscle is that it:
ⓐ. Produces voluntary movements of limbs
ⓑ. Maintains posture for long periods
ⓒ. Stores large fat droplets for insulation
ⓓ. Contracts rhythmically without fatigue
Correct Answer: Contracts rhythmically without fatigue
Explanation: Cardiac muscle is specialized for continuous, rhythmic contraction throughout life to maintain blood circulation. It has abundant mitochondria and a high oxidative capacity, supporting sustained ATP production for ongoing activity. The coordinated electrical properties and intercalated disc connections allow efficient, synchronized pumping. Unlike skeletal muscle, the heart is not designed for intermittent voluntary bursts but for constant endurance work. Its physiology supports reliable contraction with minimal fatigue under normal conditions. Therefore, the correct advantage is rhythmic contraction without fatigue.
157. Compared with skeletal muscle, cardiac muscle typically has:
ⓐ. Peripheral nuclei in each fiber
ⓑ. A single central nucleus in most cells
ⓒ. No mitochondria in cytoplasm
ⓓ. No membrane systems for excitation
Correct Answer: A single central nucleus in most cells
Explanation: Cardiac muscle cells are usually single-nucleated with the nucleus located centrally, unlike skeletal muscle fibers that commonly have multiple peripheral nuclei. This reflects the fact that cardiac muscle cells are individual branched cells rather than fused multinucleated fibers. The central nucleus is a practical microscopic clue used to distinguish cardiac muscle in tissue sections. This feature aligns with the cellular organization required for intercalated disc connections and coordinated conduction. Cardiac tissue remains metabolically active and rich in organelles despite having one nucleus. Hence, a single central nucleus in most cells is the correct comparison point.
158. Which feature best supports the ability of smooth muscle to maintain prolonged contraction with low energy use?
ⓐ. Latch-like sustained cross-bridge state
ⓑ. Intercalated discs with desmosomes
ⓒ. Sarcomeres aligned in myofibrils
ⓓ. Peripheral multinuclei in long fibers
Correct Answer: Latch-like sustained cross-bridge state
Explanation: Smooth muscle can maintain tone for long durations using a mechanism often described as a latch-like state, where tension is sustained with reduced ATP consumption. This is especially important in blood vessels and sphincters that must remain partially contracted for extended periods. The result is efficient maintenance of pressure or closure without rapid fatigue. This energy-saving property complements the slow, graded contraction pattern typical of smooth muscle. It is a functional adaptation rather than a structural feature like intercalated discs or sarcomeres. Therefore, a latch-like sustained cross-bridge state best explains prolonged low-energy contraction.
159. A tissue shows striations and branching fibers, but contraction is not under voluntary control. Which tissue is this?
ⓐ. Skeletal muscle
ⓑ. Smooth muscle
ⓒ. Cardiac muscle
ⓓ. Dense regular connective tissue
Correct Answer: Cardiac muscle
Explanation: Cardiac muscle is striated because its contractile proteins are arranged in an organized pattern, yet it is involuntary in control and functions automatically. The fibers are branched and connected by intercalated discs, supporting mechanical strength and synchronized electrical activity. This combination of striations with involuntary, rhythmic contraction distinguishes it from skeletal muscle, which is striated but voluntary and typically unbranched. Smooth muscle is involuntary but lacks striations and has spindle-shaped cells. Therefore, striations plus branching with involuntary action identifies cardiac muscle.
160. Smooth muscle is commonly found in:
ⓐ. Biceps brachii
ⓑ. Wall of intestine
ⓒ. Tendon of Achilles
ⓓ. Cortex of kidney
Correct Answer: Wall of intestine
Explanation: The intestinal wall contains layers of smooth muscle that generate peristalsis and segmentation movements to propel and mix food. Smooth muscle is well suited for this role because it contracts slowly, can sustain activity, and functions under involuntary control. Its cells work in coordinated patterns to produce wave-like contractions along the gut. This supports digestion and absorption without conscious effort. The presence of smooth muscle in the gastrointestinal tract is a standard location-based identification point in tissue questions. Hence, the wall of the intestine is a common site for smooth muscle.
161. The presence of intercalated discs is a defining feature of:
ⓐ. Cardiac muscle
ⓑ. Skeletal muscle
ⓒ. Smooth muscle
ⓓ. Areolar tissue
Correct Answer: Cardiac muscle
Explanation: Intercalated discs are specialized junctional complexes unique to cardiac muscle that connect adjacent cardiac cells end-to-end. They provide strong mechanical attachment so cells do not separate during repeated forceful contractions. They also contain junctions that allow rapid electrical signal spread, enabling the heart to contract as a coordinated unit. This feature is not seen in skeletal muscle, which relies on individual fibers activated by motor neurons, nor in smooth muscle, which lacks such disc structures. Because intercalated discs are both a structural and functional hallmark, they are central in tissue identification. Therefore, intercalated discs define cardiac muscle.
162. Which pairing correctly matches muscle type with control?
ⓐ. Skeletal—voluntary
ⓑ. Smooth—voluntary
ⓒ. Cardiac—voluntary
ⓓ. Skeletal—involuntary
Correct Answer: Skeletal—voluntary
Explanation: Skeletal muscle is under voluntary control through the somatic nervous system, enabling conscious movements such as walking, writing, and posture adjustments. Its fibers are activated via motor neurons, and the brain can recruit motor units to vary force. Smooth muscle is generally involuntary and responds to autonomic signals and local factors, while cardiac muscle is also involuntary and has intrinsic rhythmicity. Control type is a frequent exam trap because both skeletal and cardiac are striated but differ in control. The correct match therefore emphasizes that skeletal muscle is the voluntary type. Hence, the correct pairing is skeletal—voluntary.
163. Striations are visible in which muscle types?
ⓐ. Skeletal and smooth
ⓑ. Smooth and cardiac
ⓒ. Skeletal and cardiac
ⓓ. Smooth only
Correct Answer: Skeletal and cardiac
Explanation: Striations appear when actin and myosin are organized into repeating sarcomeres that align across the fiber, producing alternating light and dark bands. Both skeletal and cardiac muscles have this highly ordered sarcomeric arrangement, so striations are visible under the microscope. Smooth muscle contains the same basic contractile proteins but lacks sarcomere-based alignment, so it appears non-striated. This structural difference is directly linked to the appearance of the tissue and is a reliable identification cue. It also explains why skeletal and cardiac muscles share band-related contraction concepts. Therefore, striations are seen in skeletal and cardiac muscle.
164. The presence of intercalated discs in cardiac muscle most directly supports:
ⓐ. Greater insulation by storing lipids
ⓑ. Coordinated contraction by linking cells mechanically and electrically
ⓒ. Rapid voluntary control by motor neurons
ⓓ. Formation of bone-like rigid support
Correct Answer: Coordinated contraction by linking cells mechanically and electrically
Explanation: Intercalated discs contain attachment junctions that hold cardiac cells together during powerful contractions and junctions that permit electrical continuity between cells. Mechanical linkage prevents tearing under stress, while electrical coupling allows impulses to spread rapidly from cell to cell. Together, these properties ensure the myocardium contracts in a synchronized manner, producing an effective pumping action. This coordination is essential because the heart must function as an integrated unit rather than isolated cells contracting independently. The discs therefore combine structural stability with signal transmission capacity. Hence, intercalated discs support coordinated contraction by linking cells mechanically and electrically.
165. A tissue shows spindle-shaped cells with a single central nucleus and no striations. What is the most accurate control type for this tissue?
ⓐ. Voluntary
ⓑ. Voluntary during sleep only
ⓒ. Mixed voluntary-involuntary
ⓓ. Involuntary
Correct Answer: Involuntary
Explanation: Spindle-shaped, non-striated cells with a single central nucleus are characteristic of smooth muscle. Smooth muscle contractions are typically regulated by the autonomic nervous system, hormones, and local chemical signals rather than conscious control. This involuntary control suits functions such as regulating vessel diameter, moving contents through the gut, and controlling airway caliber. The absence of striations reflects a non-sarcomeric arrangement, which supports slower, sustained contractions. Because these actions are essential and continuous, they are not dependent on voluntary command. Therefore, the correct control type is involuntary.
166. A student sees striations but notes that the fibers branch and form cell-to-cell junction lines. Which combination is correct?
ⓐ. Skeletal muscle—voluntary—unbranched
ⓑ. Cardiac muscle—involuntary—branched
ⓒ. Smooth muscle—involuntary—striated
ⓓ. Skeletal muscle—involuntary—branched
Correct Answer: Cardiac muscle—involuntary—branched
Explanation: Cardiac muscle is striated because it has sarcomeres, but it differs from skeletal muscle by having branched cells and distinct junction lines formed by intercalated discs. Its contraction is involuntary and rhythmic, coordinated by intrinsic pacemaker activity and conduction pathways. These features together create a tissue that can contract in a synchronized way to pump blood continuously. Skeletal muscle is also striated but is typically unbranched and under voluntary control. Smooth muscle is involuntary but lacks striations and branching patterns typical of cardiac cells. Therefore, the correct combination is cardiac muscle—involuntary—branched.
167. Which feature is most useful for distinguishing cardiac muscle from skeletal muscle in a microscope slide?
ⓐ. Presence of striations
ⓑ. Presence of sarcolemma
ⓒ. Presence of actin and myosin
ⓓ. Presence of branching and intercalated discs
Correct Answer: Presence of branching and intercalated discs
Explanation: Both skeletal and cardiac muscles show striations due to sarcomere organization, so striations alone cannot reliably separate them. Cardiac muscle cells are branched and connected by intercalated discs, which appear as dark transverse lines at cell junctions. These discs also reflect the specialized coupling needed for coordinated heart contraction. Skeletal muscle fibers are typically long, cylindrical, unbranched, and multinucleated with nuclei near the periphery. Therefore, branching plus intercalated discs is the most discriminating slide feature between cardiac and skeletal muscle. Hence, the presence of branching and intercalated discs is the best distinguishing feature.
168. Which statement correctly links sarcomeres to muscle appearance and control?
ⓐ. Sarcomeres occur only in smooth muscle and explain involuntary contractions
ⓑ. Sarcomeres occur in skeletal and cardiac muscle and produce striations; control differs between them
ⓒ. Sarcomeres occur in all muscles and always produce voluntary movement
ⓓ. Sarcomeres occur only in cardiac muscle and explain intercalated discs
Correct Answer: Sarcomeres occur in skeletal and cardiac muscle and produce striations; control differs between them
Explanation: Sarcomeres are repeating contractile units that align in myofibrils, creating the striated appearance of skeletal and cardiac muscle. This shared structural feature explains why both tissues show banding patterns and follow similar sliding filament principles. However, their control systems differ: skeletal muscle is generally voluntary via somatic motor neurons, while cardiac muscle is involuntary and driven by intrinsic rhythmicity with autonomic modulation. Intercalated discs are unique to cardiac tissue and are not a direct product of sarcomere formation. Smooth muscle lacks sarcomeric alignment and therefore lacks visible striations. Thus, the correct link is sarcomeres in skeletal and cardiac producing striations, with different control types.
169. If intercalated disc function is disrupted, the most immediate functional problem would be:
ⓐ. Reduced ability of cardiac cells to contract together as a unit
ⓑ. Loss of oxygen transport due to fewer erythrocytes
ⓒ. Failure of tendon force transmission to bone
ⓓ. Inability of smooth muscle to maintain tone in vessels
Correct Answer: Reduced ability of cardiac cells to contract together as a unit
Explanation: Intercalated discs provide both mechanical linkage and electrical coupling between cardiac muscle cells. If their function is impaired, electrical signals do not spread efficiently and mechanical integrity between cells weakens, causing loss of synchronization. This leads to uncoordinated contraction patterns, reducing the efficiency of pumping and potentially producing rhythm disturbances. Because the heart relies on coordinated, wave-like activation to eject blood effectively, any break in cell-to-cell coupling has a direct functional consequence. This issue is specific to cardiac tissue’s junction-dependent syncytial behavior rather than blood, tendons, or smooth muscle tone. Therefore, the immediate problem is reduced coordinated contraction of cardiac cells.
170. Which triad correctly matches muscle type with striation visibility and control?
ⓐ. Smooth—striated—voluntary
ⓑ. Skeletal—striated—involuntary
ⓒ. Cardiac—striated—involuntary
ⓓ. Cardiac—non-striated—voluntary
Correct Answer: Cardiac—striated—involuntary
Explanation: Cardiac muscle contains sarcomeres, so it appears striated under the microscope, similar to skeletal muscle. However, its activity is involuntary, driven by intrinsic pacemaker mechanisms and modulated by autonomic inputs, ensuring continuous rhythmic pumping. Smooth muscle is involuntary but lacks striations, while skeletal muscle is striated and typically voluntary. This triad is a common exam classification point because students often confuse cardiac control with skeletal due to shared striations. The correct combination therefore highlights striations with involuntary control for cardiac tissue. Hence, cardiac—striated—involuntary is the correct match.
171. Which neuronal part most directly receives signals from other neurons and carries them toward the cell body?
ⓐ. Axon
ⓑ. Axon terminal
ⓒ. Dendrite
ⓓ. Myelin sheath
Correct Answer: Dendrite
Explanation: Dendrites are the main receptive processes of a neuron and are structurally adapted to receive incoming signals from many other neurons. They conduct these signals toward the cell body, where integration of multiple inputs occurs. Their branching pattern increases surface area, allowing a neuron to form numerous synaptic contacts. Functionally, this supports complex processing, because excitatory and inhibitory inputs can be summed before the neuron decides to generate an impulse. While axons mainly conduct impulses away from the cell body, dendrites are specialized for input reception and inward conduction. Therefore, dendrites most directly receive and carry signals toward the soma.
172. The region of a neuron that contains the nucleus and most cell organelles is the:
ⓐ. Cell body (soma)
ⓑ. Node of Ranvier
ⓒ. Axon hillock
ⓓ. Synaptic cleft
Correct Answer: Cell body (soma)
Explanation: The cell body (soma) is the metabolic and integrative center of the neuron, containing the nucleus and most organelles required for protein synthesis and maintenance. It supports the high energy and biosynthetic demands of neurons, including production of membrane proteins, neurotransmitter-related enzymes, and structural components. Signals arriving via dendrites are processed within the soma, and the overall health of the neuron depends on the soma’s metabolic activity. Damage to the cell body can disrupt neuronal survival because essential cellular functions are concentrated there. The node and synaptic cleft are specialized conduction/communication regions, not the main organelle hub. Hence, the soma is the region containing nucleus and organelles.
173. Which statement best describes the functional significance of the axon in a typical neuron?
ⓐ. It mainly increases surface area for receiving synapses
ⓑ. It stores neurotransmitters in large granules permanently
ⓒ. It houses the nucleus and controls metabolism
ⓓ. It conducts impulses away from the cell body to targets
Correct Answer: It conducts impulses away from the cell body to targets
Explanation: The axon is specialized for transmitting nerve impulses from the neuron’s cell body toward other neurons, muscles, or glands. Once an impulse is initiated near the initial segment, it propagates along the axon membrane as a traveling electrical signal. This allows rapid long-distance communication within the body, linking sensory input, processing centers, and effectors. The axon typically ends in terminals that form synapses and deliver signals to the next cell using neurotransmitters. Dendrites are primarily for receiving inputs, whereas the axon is the main output pathway. Therefore, the axon conducts impulses away from the cell body to targets.
174. The gap between two communicating neurons at a chemical synapse is called the:
ⓐ. Myelin gap
ⓑ. Synaptic cleft
ⓒ. Schwann space
ⓓ. Dendritic groove
Correct Answer: Synaptic cleft
Explanation: The synaptic cleft is the microscopic gap between the presynaptic terminal of one neuron and the postsynaptic membrane of another cell. In a chemical synapse, neurotransmitters are released from presynaptic vesicles into this cleft and then diffuse across to bind receptors on the postsynaptic side. This arrangement allows one neuron to influence another while keeping their cytoplasms separate. The cleft also ensures signaling is directional and finely regulated by neurotransmitter release and receptor availability. Because diffusion across the cleft is essential for chemical transmission, the term specifically refers to that intervening space. Hence, the gap is the synaptic cleft.
175. In a myelinated axon, the primary role of the myelin sheath is to:
ⓐ. Increase conduction speed
ⓑ. Form synaptic vesicles
ⓒ. Produce neurotransmitters
ⓓ. Store glycogen for neurons
Correct Answer: Increase conduction speed
Explanation: Myelin sheath acts as an insulating covering around axons, reducing current leakage across the membrane and improving the efficiency of impulse propagation. By limiting ion exchange to specific gaps, the impulse effectively “jumps” between nodes, which greatly increases conduction speed compared with continuous conduction. This faster signaling is especially important for quick reflexes and coordinated movement. Myelin also supports energy efficiency because fewer membrane regions require active ion pumping after impulses. Although myelin supports conduction, it is not responsible for neurotransmitter production or vesicle formation. Therefore, increasing conduction speed is the primary role of myelin.
176. Nodes of Ranvier are functionally important because they:
ⓐ. Contain the nucleus of the neuron
ⓑ. Produce myelin around the axon
ⓒ. Allow saltatory conduction by concentrating ion exchange
ⓓ. Serve as the site of neurotransmitter storage
Correct Answer: Allow saltatory conduction by concentrating ion exchange
Explanation: Nodes of Ranvier are periodic gaps in the myelin sheath where the axonal membrane is exposed to the extracellular fluid. These nodes contain high densities of voltage-gated ion channels, allowing rapid depolarization and repolarization to occur at discrete points. As a result, the impulse appears to leap from node to node, a mechanism known as saltatory conduction. This greatly increases conduction velocity and reduces energy cost because fewer membrane segments undergo full ionic cycling. The nodes do not house the nucleus or store neurotransmitters; their key role is enabling efficient impulse propagation. Hence, nodes are essential for saltatory conduction through concentrated ion exchange.
177. The glial cells that form myelin sheaths in the central nervous system are:
ⓐ. Schwann cells
ⓑ. Oligodendrocytes
ⓒ. Microglia
ⓓ. Astrocytes
Correct Answer: Oligodendrocytes
Explanation: Oligodendrocytes are neuroglial cells in the central nervous system that produce myelin and wrap it around axons to insulate them. This insulation supports rapid signal transmission by enabling saltatory conduction across nodes. A single oligodendrocyte can extend processes to myelinate segments of multiple axons, reflecting efficient organization within the CNS. This role contrasts with Schwann cells, which myelinate axons in the peripheral nervous system. Microglia mainly serve immune defense functions, and astrocytes support neurons metabolically and structurally. Therefore, oligodendrocytes form CNS myelin sheaths.
178. Which neuroglial cell type acts as the primary immune defense and phagocytic cell within the central nervous system?
ⓐ. Ependymal cell
ⓑ. Astrocyte
ⓒ. Oligodendrocyte
ⓓ. Microglia
Correct Answer: Microglia
Explanation: Microglia are specialized glial cells that function as the resident immune and phagocytic system of the central nervous system. They monitor the neural environment and respond to infection, injury, or degeneration by removing debris and damaged cellular components. This protective role helps maintain tissue homeostasis and limits secondary damage after neural injury. Microglia can become activated and change shape and behavior to enhance defense and cleanup functions. Their immune-like activity distinguishes them from astrocytes, which provide metabolic and structural support, and oligodendrocytes, which form myelin. Hence, microglia are the primary CNS immune defense glia.
179. Neuroglia are best described as cells that:
ⓐ. Support and protect neurons
ⓑ. Conduct impulses as fast as axons
ⓒ. Form contractile fibers for movement
ⓓ. Secrete digestive enzymes into blood
Correct Answer: Support and protect neurons
Explanation: Neuroglia are non-neuronal cells that provide essential support functions required for neuronal survival and efficient signaling. They help maintain the extracellular environment, provide structural scaffolding, assist in nutrient and waste handling, and contribute to repair and defense mechanisms. Certain glial cells form myelin sheaths to increase conduction speed, while others participate in immune surveillance or cerebrospinal fluid-related roles. Unlike neurons, neuroglia are not primarily responsible for conducting nerve impulses over long distances. Their collective function is to create and maintain conditions that allow neurons to function reliably. Therefore, neuroglia are best described as supporting and protecting neurons.
180. The specialized region of the axon terminal that releases neurotransmitter to communicate with the next cell is best called the:
ⓐ. Axon hillock
ⓑ. Synaptic knob
ⓒ. Dendritic spine
ⓓ. Node of Ranvier
Correct Answer: Synaptic knob
Explanation: The synaptic knob is the bulb-like ending of an axon terminal that contains synaptic vesicles filled with neurotransmitter. When an action potential arrives, it triggers events that cause vesicles to fuse with the terminal membrane and release neurotransmitter into the synaptic cleft. This chemical messenger then binds receptors on the postsynaptic membrane to transmit the signal. The synaptic knob is therefore the key presynaptic specialization for communication, distinct from the axon hillock where impulses are initiated and nodes where conduction is boosted. Its vesicle-rich structure directly supports neurotransmitter release and synaptic transmission. Hence, the neurotransmitter-releasing terminal region is the synaptic knob.
181. Which neuronal region is most directly responsible for initiating the action potential in a typical neuron?
ⓐ. Dendritic tip
ⓑ. Axon hillock
ⓒ. Nissl body
ⓓ. Schwann sheath
Correct Answer: Axon hillock
Explanation: The axon hillock is the transition zone between the cell body and the axon where incoming signals are integrated and the decision to fire is made. It has a high density of voltage-gated ion channels, making it the most excitable part of the neuron. When the summed excitatory inputs exceed threshold at this region, an action potential is initiated and then propagates down the axon. This functional role makes the axon hillock the trigger point for neuronal output. Dendrites mainly receive signals, and Nissl bodies are involved in protein synthesis rather than impulse initiation. Therefore, the axon hillock is the region responsible for starting the action potential.
182. Nissl bodies in a neuron indicate a high capacity for:
ⓐ. Protein synthesis
ⓑ. Lipid storage
ⓒ. Hemoglobin production
ⓓ. Calcium mineralization
Correct Answer: Protein synthesis
Explanation: Nissl bodies are dense regions of rough endoplasmic reticulum with ribosomes in the neuronal cell body and dendrites. They reflect the neuron’s strong need to synthesize proteins, including receptors, ion channels, neurotransmitter-related enzymes, and structural components. Because neurons maintain complex membranes and long processes, continuous protein production is essential for function and maintenance. The presence of Nissl bodies is therefore a classic marker of high biosynthetic activity in neurons. They are not associated with lipid storage, hemoglobin production, or mineral deposition. Hence, Nissl bodies indicate high protein synthesis capacity.
183. Which structure is absent in the axon of most neurons but present in the cell body and dendrites?
ⓐ. Nucleus
ⓑ. Neurofibrils
ⓒ. Nissl substance
ⓓ. Mitochondria
Correct Answer: Nissl substance
Explanation: Nissl substance represents rough endoplasmic reticulum with ribosomes, which is prominent in the cell body and extends into dendrites. Axons generally lack Nissl substance, reflecting differences in local protein synthesis capacity. This is an important identification point because the axon is specialized for impulse conduction and relies more on proteins synthesized in the soma and transported along the axon. Mitochondria and cytoskeletal elements can be present in axons to support energy needs and transport. The nucleus is restricted to the soma, but the question contrasts typical distribution of Nissl substance specifically. Therefore, Nissl substance is absent in the axon.
184. The main direction of impulse conduction in a typical neuron is:
ⓐ. Dendrite → cell body → axon
ⓑ. Axon → dendrite → cell body
ⓒ. Cell body → dendrite → axon
ⓓ. Axon terminal → cell body → dendrite
Correct Answer: Dendrite → cell body → axon
Explanation: In a typical neuron, dendrites receive signals from other neurons and carry them toward the cell body. The cell body integrates these inputs, and if threshold is reached near the trigger zone, an impulse is generated and conducted along the axon. The axon then transmits the signal toward its terminals to communicate with the next cell. This input-to-integration-to-output sequence represents the standard functional polarity of neurons. While some specialized neurons may differ, this direction is the core concept tested in foundational questions. Hence, the main direction is dendrite to cell body to axon.
185. Which neuronal part forms the major output region that communicates with other cells?
ⓐ. Axon terminal
ⓑ. Dendritic branch
ⓒ. Cell body nucleus
ⓓ. Nissl granules
Correct Answer: Axon terminal
Explanation: The axon terminal is specialized to transmit the neuron’s signal to another neuron, muscle cell, or gland cell. It contains synaptic vesicles and molecular machinery that enables neurotransmitter release when an impulse arrives. This chemical release across a synapse produces a response in the target cell, making the axon terminal the primary output interface. Dendrites are mainly input structures, and the nucleus supports cellular control rather than direct communication. Nissl granules indicate protein synthesis capacity, not output signaling. Therefore, the axon terminal is the main output region.
186. The myelin sheath increases conduction speed mainly by:
ⓐ. Increasing synaptic vesicle number
ⓑ. Enlarging the nucleus
ⓒ. Increasing dendritic branching
ⓓ. Concentrating conduction at nodes
Correct Answer: Concentrating conduction at nodes
Explanation: Myelin acts as an insulator around the axon, reducing ion leakage and preventing continuous depolarization along the entire membrane. As a result, significant ion exchange occurs mainly at the nodes of Ranvier, where the axonal membrane is exposed and rich in voltage-gated channels. This produces saltatory conduction, in which the impulse effectively jumps from node to node, greatly increasing speed. The mechanism also reduces energy cost because fewer membrane areas require active restoration of ion gradients. Myelin does not primarily increase vesicle number, dendritic branching, or nucleus size. Therefore, it increases conduction speed by concentrating conduction at nodes.
187. Which term best describes the junction where neurotransmitter is released from a neuron to influence another cell?
ⓐ. Lacuna
ⓑ. Synapse
ⓒ. Osteon
ⓓ. Sarcomere
Correct Answer: Synapse
Explanation: A synapse is the specialized functional junction between a neuron and another neuron or effector cell where information is transmitted. In chemical synapses, the presynaptic neuron releases neurotransmitter from vesicles into a small gap, and the transmitter binds to receptors on the postsynaptic membrane. This allows precise, directional communication and enables complex processing through excitation or inhibition. Synapses can occur between neurons or between neurons and muscles or glands. The term is specific to neural communication, unlike lacuna (bone/cartilage space), osteon (bone unit), or sarcomere (muscle unit). Hence, the correct term is synapse.
188. A sensory neuron carrying impulses from skin to spinal cord is best described functionally as:
ⓐ. Efferent neuron
ⓑ. Intercalated disc neuron
ⓒ. Motor end plate neuron
ⓓ. Afferent neuron
Correct Answer: Afferent neuron
Explanation: Afferent neurons carry sensory information from receptors in the body toward the central nervous system. Signals such as touch, pain, temperature, and pressure detected in the skin are transmitted by these neurons to the spinal cord and brain for processing. This direction—toward the CNS—defines afferent pathways, distinguishing them from efferent neurons that carry commands outward to muscles and glands. The term is functional and based on signal flow rather than shape alone. Understanding afferent versus efferent is central to reflex and pathway questions. Therefore, a sensory neuron from skin to spinal cord is an afferent neuron.
189. The insulating covering formed by Schwann cells is typically associated with:
ⓐ. Central nervous system axons
ⓑ. Peripheral nervous system axons
ⓒ. Cardiac muscle fibers
ⓓ. Smooth muscle bundles
Correct Answer: Peripheral nervous system axons
Explanation: Schwann cells are the glial cells responsible for forming myelin around axons in the peripheral nervous system. Their myelin wrapping insulates peripheral axons and enhances conduction speed through saltatory conduction. This is distinct from the central nervous system, where oligodendrocytes provide myelination. Schwann cells also play a supportive role in peripheral nerve repair and maintenance. Because the question focuses on the insulating covering formed by Schwann cells, the correct association is with peripheral axons. Hence, Schwann cell myelin is linked to peripheral nervous system axons.
190. The primary function of dendritic spines is to:
ⓐ. Store ATP for long-term neuron survival
ⓑ. Generate myelin to speed conduction
ⓒ. Provide sites for synaptic contact and signal reception
ⓓ. Form blood cells within nervous tissue
Correct Answer: Provide sites for synaptic contact and signal reception
Explanation: Dendritic spines are small protrusions on dendrites that increase the surface area available for synaptic connections. They serve as key postsynaptic sites where neurotransmitter receptors and signaling machinery are concentrated. This allows neurons to receive and process a large number of inputs, supporting learning-related changes in synaptic strength. Because spine structure can change with activity, they also contribute to synaptic plasticity and network adaptation. Their role is therefore linked directly to receiving and modulating synaptic signals, not myelin formation or blood cell production. Hence, dendritic spines provide sites for synaptic contact and signal reception.
191. Earthworm shows “true metamerism” mainly because:
ⓐ. Body is divided only externally into rings without internal partitions
ⓑ. Body is divided into repeated segments with internal septa and organ repetition
ⓒ. Body has a single unsegmented coelom with no compartmentalization
ⓓ. Body segmentation is restricted only to the head region
Correct Answer: Body is divided into repeated segments with internal septa and organ repetition
Explanation: In earthworm, metamerism is not just a surface appearance; the body is organized into a series of repeated units (metameres) along the antero-posterior axis. Externally, grooves mark segment boundaries, and internally, transverse septa partition the coelom into segmental chambers. Many structures show segmental repetition, which supports coordinated movement and physiological organization across the body. This combination of external segmentation with internal compartmentalization is why it is termed true metamerism. The repeated segment plan is therefore a core diagnostic feature of annelids like earthworm.
192. The prostomium of an earthworm is best described as:
ⓐ. The last body segment bearing the anus
ⓑ. A reproductive band formed in the middle region
ⓒ. A segment bearing the male genital pores
ⓓ. A pre-oral lobe above the mouth, not a true segment
Correct Answer: A pre-oral lobe above the mouth, not a true segment
Explanation: Prostomium is a small lobe that lies just in front of the mouth and overhangs it. It is considered a pre-oral structure rather than a true body segment, so it is not counted as one of the metameres. Functionally, it helps the worm in probing and burrowing through soil by acting like a sensory and assisting structure at the anterior end. The mouth itself is associated with the first segment (peristomium), while prostomium remains an anterior lobe. This positional and structural distinction is frequently tested with segment-identification traps.
193. In a typical adult earthworm (Pheretima), the trunk generally consists of about:
ⓐ. 100–120 segments
ⓑ. 30–40 segments
ⓒ. 10–20 segments
ⓓ. 200–250 segments
Correct Answer: 100–120 segments
Explanation: Adult Pheretima commonly shows a long, cylindrical body divided into a large number of small ring-like segments. Standard descriptions place this segment count roughly in the range of about 100–120, reflecting the extensive metameric organization. This high segment number is consistent with its burrowing lifestyle, where repeated segmental units work together with musculature and coelomic compartments for locomotion. Such a range is commonly used in exam questions to differentiate earthworm from animals with fewer, fixed segments. The value also reinforces that most trunk segments are similar in appearance except specialized regions.
194. The clitellum in Pheretima is a thick glandular band present on:
ⓐ. Segments 5–7
ⓑ. Segments 9–11
ⓒ. Segments 14–16
ⓓ. Segments 18–20
Correct Answer: Segments 14–16
Explanation: Clitellum is a prominent, girdle-like thickening formed by glandular tissue on a specific mid-body region in mature earthworms. In Pheretima, it is located on segments 14–16 and is used as a key external landmark to recognize maturity and body regions relative to it. Its secretions support reproductive processes such as providing mucus and materials associated with cocoon formation. Because the segment numbers are fixed and frequently asked, clitellum location is an important segmentation-based identification point. Hence, segments 14–16 correctly represent the clitellar region.
195. Internal segmentation in earthworm is mainly due to:
ⓐ. Intersegmental septa dividing the coelom into compartments
ⓑ. A single continuous body cavity without partitions
ⓒ. A rigid exoskeleton forming separate rings
ⓓ. Cartilage plates separating body regions
Correct Answer: Intersegmental septa dividing the coelom into compartments
Explanation: Inside an earthworm, the coelomic cavity is partitioned by transverse intersegmental septa, creating a series of segmental compartments. This internal division matches the external segment pattern and is one of the reasons earthworm is considered truly segmented. Compartmentalization helps organize organs segment-wise and supports efficient locomotion because each segment can change shape with muscular action against coelomic fluid. It also improves functional independence of segments while maintaining overall coordination. This internal architecture is therefore a defining feature of annelids’ body plan.
196. In Pheretima, setae are generally present in:
ⓐ. Only the anterior 10 segments
ⓑ. Only the clitellar region
ⓒ. Only the last 10 segments
ⓓ. Almost all segments except first, last, and clitellum
Correct Answer: Almost all segments except first, last, and clitellum
Explanation: Setae are small bristle-like structures embedded in the body wall that assist in anchorage and locomotion during burrowing. In Pheretima, they are distributed segmentally across most of the trunk, providing repeated points of grip against the soil. However, they are characteristically absent in the first segment, the last segment, and the clitellar region. This distribution pattern is frequently used in objective questions because it connects segmentation with locomotory adaptation. Therefore, the correct statement is that setae occur in almost all segments except first, last, and clitellum.
197. “True segmentation” in earthworm implies that:
ⓐ. Only the digestive tract is segmented, not the body wall
ⓑ. Both external grooves and internal septa correspond to repeated segments
ⓒ. Segmentation occurs only during embryonic stage and disappears in adults
ⓓ. Only the nervous system is segmentally arranged, not the coelom
Correct Answer: Both external grooves and internal septa correspond to repeated segments
Explanation: In earthworm, the segmentation seen as ring-like divisions on the surface is backed by internal partitioning of the body cavity. External grooves mark the boundaries of metameres, while internal septa divide the coelom into serial compartments that align with those boundaries. This dual level of segmentation is the reason it is categorized as true segmentation rather than a superficial ring pattern. It also supports the segment-wise repetition of structures and coordinated movement. The concept is central to annelid organization and helps distinguish them from animals that show only external ring-like markings.
198. A major locomotory advantage of segmental coelomic compartments in earthworm is that they:
ⓐ. Prevent any change in segment shape during movement
ⓑ. Make the body rigid by replacing muscles with bone
ⓒ. Allow effective peristaltic movement by acting as fluid-filled units
ⓓ. Stop diffusion across the skin by forming thick cuticle plates
Correct Answer: Allow effective peristaltic movement by acting as fluid-filled units
Explanation: Earthworm locomotion depends on alternating contraction of circular and longitudinal muscles along the body. Segmental coelomic compartments act like fluid-filled units against which muscles can work, enabling each segment to elongate or shorten efficiently. This compartmental design supports wave-like peristaltic movements that pass along the body, producing forward progression in soil. By limiting fluid displacement between segments, the partitions improve control and effectiveness of local shape changes. This relationship between segmentation, coelomic fluid, and muscular action explains why annelids are highly effective burrowers.
199. The first true segment of earthworm that contains the mouth is the:
ⓐ. Pygidium
ⓑ. Clitellum
ⓒ. Prostomium
ⓓ. Peristomium
Correct Answer: Peristomium
Explanation: The mouth opening of an earthworm is located on the first true segment, called the peristomium. This is distinct from the prostomium, which is a small pre-oral lobe lying above and in front of the mouth but not counted as a true segment. Recognizing peristomium as the first segment is important for interpreting segment-based landmarks and understanding anterior morphology. Many identification questions test this distinction because both structures are near the anterior end and easily confused. Therefore, the correct first segment bearing the mouth is the peristomium.
200. Earthworm segmentation is termed “homonomous” mainly because:
ⓐ. Most segments are similar in structure along the trunk
ⓑ. Every segment forms a different specialized organ system
ⓒ. Only the head region is segmented, not the trunk
ⓓ. Segments are present only externally without internal repetition
Correct Answer: Most segments are similar in structure along the trunk
Explanation: Homonomous metamerism refers to a segmented body plan in which most segments are broadly similar in structure and basic organization. In earthworm, the trunk is made of many repeated metameres that follow the same overall pattern, supporting uniform locomotory and physiological function along much of the body length. While certain regions are specialized (such as clitellar and terminal areas), the general segment similarity remains the defining idea behind homonomous segmentation. This contrasts with heteronomous segmentation where segments are highly specialized into distinct regions. Hence, earthworm segmentation is termed homonomous because most segments are similar.