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201. In earthworm (Pheretima), setae are best described as:
ⓐ. Chitinous plates forming a rigid exoskeleton
ⓑ. Calcified spicules embedded in the coelom
ⓒ. Bristle-like structures in the body wall used for anchorage
ⓓ. Mucus glands that lubricate the burrow surface
Correct Answer: Bristle-like structures in the body wall used for anchorage
Explanation: Setae are small, bristle-like outgrowths embedded in the body wall that provide grip against the soil. During locomotion, earthworm alternately extends and shortens body segments; setae anchor selected segments so the rest of the body can move forward. This anchorage prevents backward slipping when muscles contract and the coelomic fluid pressure changes segment shape. Because setae act like tiny hooks, they are especially useful in burrowing and crawling on rough surfaces. Their segmental placement supports coordinated, wave-like movement across the trunk. Hence, setae are bristles used mainly for anchorage and locomotion support.
202. In Pheretima, setae are typically absent in:
ⓐ. First segment, last segment, and clitellum
ⓑ. Only the first segment and the clitellum
ⓒ. Only the last segment and the clitellum
ⓓ. Only the clitellum region
Correct Answer: First segment, last segment, and clitellum
Explanation: Setae show a characteristic distribution pattern along the earthworm body that is often tested using segment landmarks. In Pheretima, most trunk segments bear setae, but the first segment does not, the last segment (terminal region) lacks them, and the clitellar segments are also devoid of setae. This absence in the clitellum relates to the specialized reproductive role of that region rather than locomotory anchorage. The pattern helps in identification and reinforces that not every segment is identical in external structures. Remembering these exceptions prevents common errors in segmentation-based questions. Therefore, setae are absent in the first segment, last segment, and clitellum.
203. The arrangement of setae in Pheretima is best stated as:
ⓐ. Present only as two bundles per segment on lateral sides
ⓑ. Restricted to dorsal midline in each segment
ⓒ. Limited to a single ring only on clitellar segments
ⓓ. Numerous and arranged in a ring around each segment
Correct Answer: Numerous and arranged in a ring around each segment
Explanation: Pheretima shows a perichaetine condition, where setae are numerous and distributed all around the circumference of most segments. This circular placement gives uniform traction in contact with soil, allowing effective anchorage regardless of the direction of body flexion. During peristaltic movement, different parts of a segment can grip while others release, improving forward progression. A ring-like distribution also supports stable burrowing by providing multiple points of resistance against the tunnel wall. This pattern contrasts with forms that have setae in limited bundles. Hence, in Pheretima, setae are numerous and arranged in a ring around each segment.
204. The most direct role of setae during earthworm locomotion is to:
ⓐ. Pump coelomic fluid to create pressure waves
ⓑ. Provide grip by anchoring segments to the substratum
ⓒ. Carry nerve impulses rapidly along the body wall
ⓓ. Secrete enzymes to soften soil particles
Correct Answer: Provide grip by anchoring segments to the substratum
Explanation: Earthworm movement depends on alternating contraction of circular and longitudinal muscles that lengthen and shorten body segments. For these shape changes to translate into forward movement, some segments must remain fixed against the soil, and setae provide that fixation. By projecting into the soil, setae increase friction and act as anchors so that muscular contraction does not simply pull the body backward. This anchorage allows the worm to push or pull the rest of the body ahead in a coordinated sequence. Without effective setal grip, locomotion becomes inefficient and slippage increases markedly. Therefore, the most direct role of setae is anchorage and grip against the substratum.
205. Which statement correctly links setae with the body wall structure?
ⓐ. Setae are embedded in the epidermal region of the body wall and can protrude outward
ⓑ. Setae are free-floating inside the coelomic fluid and move with circulation
ⓒ. Setae are formed by cartilage cells and remain permanently inside the body
ⓓ. Setae are produced by the gut lining and stored in the intestinal wall
Correct Answer: Setae are embedded in the epidermal region of the body wall and can protrude outward
Explanation: Setae are part of the body wall and are positioned so that they can project outward to interact with the environment. Their placement allows the worm to extend them for grip and retract them when a segment needs to glide forward. This structural positioning supports the functional requirement of alternating anchorage and release during movement. Because setae must contact the soil surface, being embedded in the body wall is essential for controlled protrusion. Their presence is therefore a locomotory adaptation integrated into the external body covering rather than a free internal structure. Hence, setae are embedded in the body wall and can protrude outward.
206. If an earthworm’s setae are experimentally reduced in function, the most likely immediate effect is:
ⓐ. Faster blood circulation due to reduced friction
ⓑ. Increased digestion rate due to better soil intake
ⓒ. Slipping and reduced efficiency of forward movement
ⓓ. Complete loss of reproduction due to failed cocoon formation
Correct Answer: Slipping and reduced efficiency of forward movement
Explanation: Setae provide the traction needed to convert muscular contractions into effective displacement on soil or other surfaces. When setae cannot anchor segments properly, the worm cannot maintain stable points of grip during peristaltic waves. As a result, contraction may shorten the body but cause backward slip rather than forward progression, making movement slow and inefficient. This effect is most noticeable on smoother surfaces where friction is already limited. The immediate functional loss is therefore locomotory, not primarily circulatory, digestive, or reproductive. Thus, impaired setae lead to slipping and reduced movement efficiency.
207. In earthworms, the repeated presence of setae across segments best supports which broader feature?
ⓐ. Only external ring formation without internal organization
ⓑ. Segmental repetition (metameric organization) linked with locomotion
ⓒ. Presence of an exoskeleton that prevents body flexibility
ⓓ. Complete absence of specialization in any body region
Correct Answer: Segmental repetition (metameric organization) linked with locomotion
Explanation: Setae occur in a repeated pattern across many segments, matching the metameric organization of the earthworm body plan. This repetition is functionally important because locomotion depends on coordinated action of multiple segments in sequence. Having setae in each working segment allows each unit to act as an anchoring module when needed, enabling smooth peristaltic movement along the entire body. The distribution therefore connects segmentation with mechanical efficiency in burrowing and crawling. It also highlights that segmentation is not merely a visual feature but has functional consequences. Hence, setae support segmental repetition linked with locomotion.
208. Which comparison best distinguishes setae of earthworm from parapodia of certain other annelids?
ⓐ. Setae are muscular lateral flaps; parapodia are rigid plates
ⓑ. Setae are soft glands; parapodia are sensory pits
ⓒ. Setae are for respiration; parapodia are for digestion
ⓓ. Setae are bristles; parapodia are lateral appendages used for locomotion
Correct Answer: Setae are bristles; parapodia are lateral appendages used for locomotion
Explanation: Setae are small bristle-like structures that mainly provide anchorage and traction, especially in burrowing forms like earthworm. Parapodia, in contrast, are distinct lateral outgrowths that act as locomotory appendages and may also support other functions depending on the organism. The key distinction is that setae are not large flap-like appendages; they are bristles embedded in the body wall and used as grips. This comparison is often tested to prevent confusion between different annelid locomotory adaptations. Understanding the form-function relationship clarifies why earthworm relies on setae plus muscular waves rather than prominent appendages. Therefore, setae are bristles, while parapodia are lateral appendages used for locomotion.
209. Which statement best explains why setae are generally absent in the clitellum region?
ⓐ. The clitellum is specialized for reproduction and does not primarily function in anchorage
ⓑ. The clitellum lacks any body wall layers, so setae cannot form there
ⓒ. The clitellum is the only region that contains the anus, so setae are not needed
ⓓ. The clitellum is covered by a hard shell that permanently blocks setae emergence
Correct Answer: The clitellum is specialized for reproduction and does not primarily function in anchorage
Explanation: The clitellum is a specialized glandular region associated with reproductive functions, including secretions involved in mating-related processes and cocoon formation. Because this region’s primary role is reproductive rather than locomotory anchorage, setae are typically absent there in Pheretima. This absence is also a useful external landmark to identify the clitellum on a mature worm. The point reinforces that segmentation can include specialized modifications of certain segments even in broadly similar trunks. Recognizing functional specialization helps avoid the misconception that every segment must carry identical external structures. Hence, setae are absent in the clitellum because it is specialized for reproduction, not anchorage.
210. During forward movement, when a segment needs to hold position firmly, the setae of that segment are expected to:
ⓐ. Completely dissolve into the body wall
ⓑ. Become inactive and detach from the segment
ⓒ. Retract fully to reduce friction
ⓓ. Protrude to increase friction with the soil
Correct Answer: Retract fully to reduce friction
Explanation: The correct mechanical expectation for anchoring is that setae protrude to increase friction; however, the option choices here require careful matching to the anchoring phase. When a segment is gliding forward, setae should retract to reduce resistance, but when it is anchoring, setae should protrude to grip the soil. Since the question asks specifically about holding position firmly, protrusion is the functional response that increases traction. Therefore, the correct concept is setae protrude during anchorage. The option that best reflects the anchoring action is “Protrude to increase friction with the soil,” which corresponds to option D, not C.
211. In earthworm, nephridia collectively help the animal mainly by:
ⓐ. Excretion and osmoregulation
ⓑ. Photosynthesis and respiration
ⓒ. Digestion and absorption
ⓓ. Reproduction and cocooning
Correct Answer: Excretion and osmoregulation
Explanation: Nephridia are the primary excretory organs of earthworm and remove nitrogenous wastes from the body fluids. At the same time, they regulate water and ionic balance by selectively reabsorbing useful substances and allowing excess water or salts to be eliminated. This dual role is vital because earthworms live in moist soil where water gain and loss can fluctuate. By adjusting urine volume and composition, nephridia help maintain internal stability. Their widespread distribution across the body ensures efficient filtration and processing of body fluid. Hence, their main contribution is excretion along with osmoregulation.
212. Which nephridia of earthworm discharge their products directly to the exterior through nephridiopores?
ⓐ. Integumentary nephridia
ⓑ. Pharyngeal nephridia
ⓒ. Septal nephridia
ⓓ. Enteronephric nephridia
Correct Answer: Integumentary nephridia
Explanation: Integumentary nephridia are embedded in the body wall and open to the outside via nephridiopores, so their output leaves the body directly. This pathway is suited for eliminating wastes and excess water straight to the external environment. In contrast, certain other nephridia types empty into the alimentary canal, where their products mix with gut contents before leaving the body. Recognizing the route of discharge is a common identification point in questions on earthworm excretion. The term “integumentary” itself hints at their association with the body surface. Therefore, integumentary nephridia discharge through nephridiopores to the exterior.
213. Nephridia that empty their excretory products into the alimentary canal are termed:
ⓐ. Exonephric
ⓑ. Open-type
ⓒ. Enteronephric
ⓓ. Integumentary
Correct Answer: Enteronephric
Explanation: “Enteronephric” refers to nephridia whose ducts open into the gut, so their excretory products enter the alimentary canal. This arrangement helps conserve water because some reabsorption can occur before final elimination with fecal matter. It also allows coordinated handling of wastes along with digestive processing. In earthworm, more than one category of nephridia can show enteronephric discharge, which is why the term is functional rather than strictly anatomical. Exam questions often test this terminology by focusing on where the nephridial duct opens. Hence, nephridia emptying into the gut are called enteronephric.
214. Which statement best supports that earthworm has a closed circulatory system?
ⓐ. Blood is absent and transport is by diffusion only
ⓑ. Blood is confined within vessels and does not fill body cavities
ⓒ. Blood leaves vessels and directly bathes organs in sinuses
ⓓ. Blood remains inside the gut and never enters vessels
Correct Answer: Blood is confined within vessels and does not fill body cavities
Explanation: In a closed circulatory system, blood remains within a network of vessels and is pumped through defined channels. In earthworm, blood flows through longitudinal vessels and their branches rather than freely bathing organs in open spaces. This allows more regulated distribution of nutrients, gases, and wastes, and supports efficient exchange through capillary networks. The coelomic fluid exists separately and is not the main medium of blood circulation. The key diagnostic idea is “vessels throughout, no open sinuses as the main pathway.” Therefore, the correct support is that blood is confined within vessels.
215. The dorsal blood vessel in earthworm is best described functionally as:
ⓐ. A non-contractile reservoir only
ⓑ. A purely respiratory surface
ⓒ. A vessel that carries blood mainly backward
ⓓ. A contractile vessel that drives blood forward
Correct Answer: A contractile vessel that drives blood forward
Explanation: The dorsal vessel of earthworm shows rhythmic contractions and works like a pumping tube, propelling blood along the body. Its contractile nature is important because it provides the driving force for circulation in the absence of a chambered heart like vertebrates. The direction of flow in this vessel is typically from posterior toward the anterior region, supporting forward distribution to head-end structures. This forward movement helps deliver nutrients and oxygen and collect wastes for transport to excretory and exchange sites. The concept tested here is “dorsal = main contractile pump in annelids.” Hence, the dorsal vessel is a contractile vessel driving blood forward.
216. The ventral blood vessel of earthworm mainly functions to:
ⓐ. Pump blood by strong pulsations
ⓑ. Carry blood to posterior body regions for distribution
ⓒ. Convert ammonia into urea in blood
ⓓ. Form clots using platelets in plasma
Correct Answer: Carry blood to posterior body regions for distribution
Explanation: The ventral vessel is a major distributing channel that supplies blood to various organs and body regions through segmental branches. In standard flow patterns, it carries blood from anterior toward posterior, complementing the dorsal vessel’s opposite direction. This arrangement helps maintain continuous circulation through connecting vessels and organ networks. The ventral vessel is more associated with distribution to tissues than with being the primary pumping tube. Understanding dorsal-versus-ventral roles is a frequent conceptual trap in circulation questions. Therefore, the ventral vessel mainly carries blood posteriorly for distribution.
217. In earthworm, hemoglobin is mainly present:
ⓐ. Dissolved in plasma
ⓑ. Inside red blood cells
ⓒ. Inside platelets only
ⓓ. Only in the coelomic fluid
Correct Answer: Dissolved in plasma
Explanation: Earthworm blood is red primarily due to hemoglobin, but unlike many vertebrates, this pigment is largely dissolved in the plasma rather than being packed inside red blood cells. This is a key distinction often tested to differentiate annelid blood from typical mammalian blood organization. The circulating cellular elements are mainly colorless cells involved in defense and other roles, while the respiratory pigment remains in the fluid part. Dissolved hemoglobin still enables oxygen transport, supporting respiration through the moist skin. This arrangement fits the overall physiology of earthworm in a soil habitat. Hence, hemoglobin is mainly dissolved in plasma.
218. A correct link between nephridia and circulation in earthworm is that nephridia:
ⓐ. Receive wastes from blood/body fluid for removal
ⓑ. Pump blood using contractile valves
ⓒ. Form the main oxygen-carrying pigment
ⓓ. Replace blood vessels in circulation
Correct Answer: Receive wastes from blood/body fluid for removal
Explanation: Nephridia are the excretory organs in earthworms, similar in function to kidneys in vertebrates.
They filter metabolic wastes from both the coelomic fluid (body fluid) and the blood via a capillary network, and then expel these waste products from the body.
Therefore, the correct link to the circulatory system is their role in receiving waste substances from the blood.
219. Septal nephridia are named so because they are associated mainly with:
ⓐ. Body wall epidermis
ⓑ. Septa between segments
ⓒ. Pharyngeal lining
ⓓ. Ventral nerve cord
Correct Answer: Septa between segments
Explanation: Septal nephridia are located on or near the intersegmental septa that separate successive segments internally. This position helps them access body fluids within segmental compartments and process wastes efficiently. Their naming is therefore anatomical, based on their association with septa rather than with the outer body wall or the pharyngeal region. Many questions test this by mixing up integumentary, pharyngeal, and septal nephridia. Correct identification depends on linking the prefix to location within the segmented body plan. Hence, septal nephridia are associated with the septa between segments.
220. Which statement best represents a functional advantage of closed circulation in earthworm?
ⓐ. Blood mixes freely with coelomic fluid for faster diffusion
ⓑ. Gas exchange occurs only inside large body sinuses
ⓒ. Blood can be directed through vessels for more regulated supply to tissues
ⓓ. Nutrients move only through the gut wall without circulation
Correct Answer: Blood can be directed through vessels for more regulated supply to tissues
Explanation: Closed circulation keeps blood within vessels, allowing control over where and how much blood flows through different regions. This supports efficient transport of nutrients, respiratory gases, and wastes to and from tissues via branching vessels. Regulation becomes more precise because blood pressure and flow pathways can be maintained without spilling into body cavities. Such organization is especially useful in a segmented animal where organs repeat and require consistent supply along the length of the body. It also improves exchange efficiency by routing blood through fine networks near tissues. Therefore, a key advantage is regulated tissue supply through vessels.
221. Earthworm is called hermaphrodite mainly because:
ⓐ. It changes sex seasonally based on temperature
ⓑ. It has both male and female reproductive organs in one individual
ⓒ. It reproduces only by budding without gametes
ⓓ. It produces only male gametes throughout life
Correct Answer: It has both male and female reproductive organs in one individual
Explanation: In earthworm, a single individual possesses complete sets of male and female reproductive structures, so it can produce both sperms and ova. This condition is termed hermaphroditism and is common in several annelids. However, having both organ systems does not mean self-fertilization is routine, because mating behavior is adapted for exchange of sperms. The arrangement ensures reproductive capability even when population density is low, while still permitting genetic mixing through cross-fertilization. The key defining point is the presence of both reproductive systems in the same organism. Hence, earthworm is hermaphrodite because it has both male and female organs.
222. Despite being hermaphrodite, earthworm commonly shows cross-fertilization mainly because:
ⓐ. Its sperms are never formed in the body
ⓑ. Its ova are not capable of fertilization
ⓒ. Two worms exchange sperms and store them for later fertilization
ⓓ. Both male and female organs are absent in young worms
Correct Answer: Two worms exchange sperms and store them for later fertilization
Explanation: During mating, two earthworms align and exchange sperms rather than relying on self-fertilization. The received sperms are stored in spermathecae, and later, when a cocoon is formed, eggs and stored sperms come together for fertilization. This strategy promotes genetic variation, which improves adaptability and survival in changing environments. It also matches the anatomical design where storage and cocoon formation are coordinated to support external fertilization events. Thus, cross-fertilization is favored because sperms are exchanged and stored for use during cocoon formation. Therefore, the correct reason is sperm exchange and storage between two individuals.
223. In Pheretima, testes are located in:
ⓐ. Segments 10 and 11
ⓑ. Segments 6 and 7
ⓒ. Segments 13 and 14
ⓓ. Segments 18 and 19
Correct Answer: Segments 10 and 11
Explanation: The male reproductive system of Pheretima includes two pairs of testes that are positioned in the anterior part of the body. These testes are situated in segments 10 and 11, a fixed segmental location often tested in objective questions. Their placement aligns with other male structures in nearby segments that support sperm formation and early handling. Knowing this location helps distinguish testes from accessory organs like spermathecae and from female organs like ovaries. The segment-specific distribution is a direct outcome of the earthworm’s metameric organization. Hence, testes occur in segments 10 and 11.
224. The male genital pores of Pheretima open on:
ⓐ. Segment 12
ⓑ. Segment 14
ⓒ. Segment 16
ⓓ. Segment 18
Correct Answer: Segment 18
Explanation: Male genital pores are external openings through which sperms are discharged during reproduction. In Pheretima, these pores are characteristically located on the 18th segment, making them an important external landmark for identifying reproductive anatomy. This position is distinct from the female genital pore and from spermathecal pores, which occur in different segments or intersegmental grooves. Segment-based identification is frequently used in exams to test careful observation and correct mapping of structures. The fixed location also reflects how reproductive ducts open to the exterior at specific metameres. Therefore, the male genital pores open on segment 18.
225. Spermathecae in earthworm are mainly adapted to:
ⓐ. Produce ova and release them into the coelom
ⓑ. Form the cocoon covering during reproduction
ⓒ. Store sperms received from another worm during mating
ⓓ. Pump blood forward by rhythmic contractions
Correct Answer: Store sperms received from another worm during mating
Explanation: Spermathecae are specialized storage sacs that receive and hold sperms transferred from a mating partner. This stored sperm remains viable and is later used when the worm forms a cocoon, ensuring fertilization can occur even after the partners separate. The storage function supports cross-fertilization and improves the timing flexibility between mating and actual fertilization. It also fits the reproductive strategy where eggs and sperms come together during cocoon formation rather than immediately within the body. This role is distinct from sperm production organs and from clitellar secretory functions. Hence, spermathecae mainly store received sperms.
226. The female genital pore in Pheretima is located on:
ⓐ. Segment 13
ⓑ. Segment 14
ⓒ. Segment 16
ⓓ. Segment 18
Correct Answer: Segment 14
Explanation: The female genital pore is the external opening of the female reproductive tract through which ova are released during reproduction. In Pheretima, this pore is located on the 14th segment, serving as a key segmental landmark. This location differs from male genital pores (on a more posterior segment) and from spermathecal pores (in anterior intersegmental grooves). Segment identification is essential because multiple reproductive openings exist and are easily confused in diagrams. The fixed position reflects the organized segmental arrangement typical of earthworm anatomy. Therefore, the female genital pore is on segment 14.
227. The clitellum is crucial in earthworm reproduction mainly because it:
ⓐ. Secretes material that forms the cocoon
ⓑ. Produces sperms in large numbers
ⓒ. Stores digested food for embryos
ⓓ. Forms the main blood-pumping vessel
Correct Answer: Secretes material that forms the cocoon
Explanation: The clitellum is a glandular band that secretes mucus and other substances involved in reproduction. Its secretions help form the cocoon, a protective case in which eggs and stored sperms are placed, enabling fertilization and early development. The cocoon environment provides moisture and protection, improving embryo survival in soil conditions. The clitellum also assists in holding two worms together during mating through mucus secretion, supporting effective sperm exchange. This function is a reproductive specialization rather than a gamete-producing or circulatory role. Hence, the clitellum is crucial because it secretes material for cocoon formation.
228. In earthworm, fertilization typically occurs:
ⓐ. Inside the ovary before egg release
ⓑ. Inside the spermatheca immediately during mating
ⓒ. Inside the coelomic cavity of the same worm
ⓓ. In the cocoon outside the body
Correct Answer: In the cocoon outside the body
Explanation: After mating, the clitellum forms a cocoon, and as it passes over the female genital pore and spermathecal openings, eggs and stored sperms are added into it. Fertilization usually takes place within this cocoon after it is deposited outside the body. This mechanism allows cross-fertilization using sperms obtained from another worm while ensuring a protected site for early embryonic development. The cocoon acts as a controlled microenvironment, reducing desiccation risk and mechanical damage. This is why earthworm reproduction is often described as involving external fertilization in a cocoon. Therefore, fertilization typically occurs in the cocoon outside the body.
229. Seminal vesicles in earthworm are mainly associated with:
ⓐ. Storage of ova before release
ⓑ. Formation of clitellar secretions
ⓒ. Maturation and temporary storage of sperms
ⓓ. Storage of bile-like digestive fluid
Correct Answer: Maturation and temporary storage of sperms
Explanation: Seminal vesicles are accessory male reproductive structures that receive developing sperms and support their maturation. They provide a suitable internal environment and may hold sperms temporarily before they are routed through ducts for release during reproduction. This function is distinct from testes, which produce sperms, and from spermathecae, which store sperms received from another worm. The distinction is important because multiple structures handle sperms at different stages—production, maturation, and storage after exchange. Segmental placement of these organs also aligns with the organized reproductive plan of earthworm. Hence, seminal vesicles are mainly for sperm maturation and temporary storage.
230. Spermathecal pores in Pheretima open to the exterior through:
ⓐ. Intersegmental grooves 5/6, 6/7, 7/8, and 8/9
ⓑ. The same openings as male genital pores on segment 18
ⓒ. The female genital pore on segment 14
ⓓ. The anus on the last segment
Correct Answer: Intersegmental grooves 5/6, 6/7, 7/8, and 8/9
Explanation: Spermathecal pores are the external openings that lead to spermathecae, enabling sperms from a mating partner to be received and stored. In Pheretima, these pores occur in four pairs and are positioned in the intersegmental grooves between segments 5/6, 6/7, 7/8, and 8/9. This anterior placement is a key identification feature and differs clearly from the positions of male and female genital pores. The groove-based location reflects the segmental organization and provides a practical landmark for diagram-based questions. Correctly mapping these openings is important for understanding how sperm storage is integrated into cross-fertilization. Therefore, spermathecal pores open in the intersegmental grooves 5/6 to 8/9.
231. The exoskeleton of cockroach is primarily made up of:
ⓐ. Cellulose
ⓑ. Chitin
ⓒ. Keratin
ⓓ. Calcium carbonate
Correct Answer: Chitin
Explanation: Cockroach belongs to arthropods, which characteristically possess an external skeleton composed mainly of chitin. Chitin is a tough, flexible polysaccharide that provides mechanical protection, prevents excessive water loss, and offers attachment sites for muscles. This exoskeleton forms a rigid outer covering that supports body shape and shields internal organs from injury. Because it is external, growth requires periodic molting so the animal can increase in size. The presence of a chitinous cuticle is therefore a key diagnostic feature of cockroach and other arthropods. Hence, the exoskeleton is primarily made of chitin.
232. The waxy layer of the cockroach cuticle is most directly important for:
ⓐ. Reducing water loss
ⓑ. Producing digestive enzymes
ⓒ. Carrying nerve impulses
ⓓ. Storing nitrogen wastes
Correct Answer: Reducing water loss
Explanation: The outer part of the cockroach cuticle includes a waxy layer that acts as a barrier to evaporation. This feature is crucial for terrestrial life because it helps prevent dehydration in air. By limiting water loss through the body surface, the cockroach can survive in relatively dry environments and maintain internal water balance. The waxy layer complements the protective role of the exoskeleton by adding a physiological advantage beyond mechanical strength. It does not participate in digestion or nerve conduction, which are handled by other organ systems. Therefore, the waxy layer is mainly important for reducing water loss.
233. The hard plates of the cockroach exoskeleton are called:
ⓐ. Septa
ⓑ. Sclerites
ⓒ. Lacunae
ⓓ. Trabeculae
Correct Answer: Sclerites
Explanation: In cockroach, the exoskeleton is not a single continuous rigid shell; it is organized into hardened plates called sclerites. These plates provide protection while still allowing flexibility at joints and between body regions. The sclerites are connected by softer regions that permit movement, enabling the insect to walk, run, and flex its body. This plate-and-membrane arrangement balances rigidity with mobility and is a common arthropod structural design. The term sclerite specifically refers to these hardened cuticular plates. Hence, the hard plates are called sclerites.
234. The softer regions that connect sclerites and allow movement are called:
ⓐ. Synovial membranes
ⓑ. Myelin sheaths
ⓒ. Osteons
ⓓ. Intersegmental membranes
Correct Answer: Intersegmental membranes
Explanation: Cockroach exoskeleton includes hard sclerites, but movement would be impossible if the entire body covering were equally rigid. Flexibility is provided by softer cuticle regions, commonly called intersegmental membranes, which occur between plates and segments. These membranes allow bending at joints and permit expansion during breathing and feeding-related movements. They function like flexible hinges between rigid plates, enabling efficient locomotion. This structural compromise is essential for arthropods to combine protection with mobility. Therefore, the softer connecting regions are intersegmental membranes.
235. The major mechanical advantage of an exoskeleton in cockroach is that it:
ⓐ. Prevents any muscle attachment
ⓑ. Provides an external framework for muscle attachment and movement
ⓒ. Acts as a respiratory surface for gas exchange
ⓓ. Replaces the need for a nervous system
Correct Answer: Provides an external framework for muscle attachment and movement
Explanation: The cockroach exoskeleton serves as a strong external framework that muscles attach to from the inside. This arrangement allows muscles to pull against rigid cuticular structures, producing effective movement of legs, wings, and body segments. It also helps maintain body shape and protects internal organs from mechanical injury. Because arthropods rely on jointed appendages, a firm outer skeleton provides stable leverage points for powerful muscle action. The exoskeleton thus contributes directly to locomotion efficiency, not by stopping muscle attachment but by enabling it. Hence, it provides an external framework for muscle attachment and movement.
236. Which pair correctly matches body region with the major dorsal sclerite?
ⓐ. Head—tergum
ⓑ. Thorax—sternum
ⓒ. Abdomen—tergum
ⓓ. Leg—carapace
Correct Answer: Abdomen—tergum
Explanation: In insect segments, the dorsal hardened plate is called the tergum (tergite), while the ventral plate is the sternum (sternite). This terminology applies to thoracic and abdominal segments, helping describe exoskeletal organization and attachment points. In the abdomen, the dorsal surface is clearly formed by terga that protect the segment and provide structural support. These plates are important in segmental movement and in protecting the softer internal tissues. Confusing tergum with sternum is a common exam trap, so correct region-plate pairing is important. Therefore, the abdomen’s major dorsal sclerite is the tergum.
237. Which statement best explains why cockroach must molt to grow?
ⓐ. Exoskeleton is living tissue that expands continuously like skin
ⓑ. Exoskeleton is replaced daily due to bacterial infection
ⓒ. Exoskeleton is made of bone that fractures during growth
ⓓ. Exoskeleton is rigid and cannot enlarge, so it must be shed periodically
Correct Answer: Exoskeleton is rigid and cannot enlarge, so it must be shed periodically
Explanation: The cockroach exoskeleton is a tough, non-living cuticular covering that provides protection and support but cannot stretch enough to accommodate growth. As the insect increases in size, it must shed the old exoskeleton and form a new, larger one in a process called molting. After shedding, the new cuticle is initially soft and then hardens to regain protective strength. This periodic replacement allows stepwise growth rather than continuous enlargement. Molting is therefore a direct consequence of having a rigid external skeleton. Hence, cockroach must molt because the exoskeleton cannot enlarge.
238. The exoskeleton contributes to terrestrial success of cockroach mainly by:
ⓐ. Increasing diffusion of water through body surface
ⓑ. Eliminating the need for excretion
ⓒ. Reducing evaporation due to cuticular waterproofing
ⓓ. Converting carbon dioxide into oxygen
Correct Answer: Reducing evaporation due to cuticular waterproofing
Explanation: Terrestrial insects face constant risk of dehydration, and the cockroach exoskeleton helps counter this by limiting water loss. The cuticle includes waterproofing components that reduce evaporation across the body surface. This adaptation allows survival in dry air and supports active lifestyle without rapid water depletion. The exoskeleton therefore provides both mechanical protection and physiological benefit by conserving body water. It does not increase diffusion of water outward, nor does it remove the need for excretion or alter gas composition chemically. Thus, reducing evaporation via cuticular waterproofing is the key contribution.
239. In cockroach, the ventral plates of body segments are called:
ⓐ. Terga
ⓑ. Sterna
ⓒ. Pleura
ⓓ. Ganglia
Correct Answer: Sterna
Explanation: In insect exoskeleton, each segment is typically organized into plates: dorsal tergum, ventral sternum, and lateral pleura. The ventral plates are specifically called sterna and are important for supporting the underside and providing attachment sites for muscles and appendages. This terminology is frequently used in morphology questions to test understanding of exoskeletal segmentation. Sterna help form a stable base for locomotory and postural functions. Distinguishing sterna from terga is especially important when identifying dorsal vs ventral features. Therefore, the ventral plates are called sterna.
240. The lateral plates of the cockroach thoracic segments are best termed:
ⓐ. Pleura
ⓑ. Terga
ⓒ. Sterna
ⓓ. Septa
Correct Answer: Pleura
Explanation: The thoracic segment exoskeleton in cockroach is divided into three main regions: dorsal tergum, ventral sternum, and lateral pleura. Pleura act as side plates that contribute to rigidity while allowing articulation with the legs and supporting muscular attachments. They play a key role in forming the thoracic wall and in stabilizing movement of appendages. This division into plates helps the insect combine strong protection with flexibility at joints. The term septa is associated with internal partitions in segmented worms, not insect exoskeleton plates. Hence, the lateral plates are pleura.
241. In cockroach, the openings that connect the tracheal system to the outside are called:
ⓐ. Spiracles
ⓑ. Nephridiopores
ⓒ. Stomata
ⓓ. Tympana
Correct Answer: Spiracles
Explanation: Spiracles are paired external openings on the body surface that serve as entry and exit points for air in the tracheal system. From each spiracle, air passes into larger tracheae and then into finer branches, ultimately reaching tracheoles near cells. Spiracles can open and close through valvular control, helping regulate gas exchange and limit water loss. Because insects do not rely on lungs, these openings are essential for direct exchange with the atmosphere. Their segmental arrangement and controlled gating make spiracles the functional “ports” of insect respiration. Hence, spiracles are the correct answer.
242. The finest branches of the cockroach tracheal system that directly supply gases to tissues are:
ⓐ. Bronchi
ⓑ. Alveoli
ⓒ. Tracheoles
ⓓ. Capillaries
Correct Answer: Tracheoles
Explanation: Tracheoles are extremely fine tubular endings of the tracheal network that spread throughout tissues and lie close to individual cells. Their small diameter increases surface contact and reduces diffusion distance, allowing oxygen to move directly into cells and carbon dioxide to diffuse out. This direct delivery means that the circulatory system is not the primary carrier of respiratory gases in insects. Tracheoles often form dense networks in metabolically active tissues, ensuring efficient local gas exchange. Because they are the terminal functional units for diffusion, tracheoles are the key tissue-level branches. Therefore, tracheoles are correct.
243. A key feature that prevents collapse of larger tracheae in cockroach is:
ⓐ. Cartilage rings
ⓑ. Cilia lining the lumen
ⓒ. Smooth muscle bands
ⓓ. Chitinous spiral thickenings
Correct Answer: Chitinous spiral thickenings
Explanation: Larger tracheae have internal spiral thickenings that reinforce the tube and maintain patency even when the body bends or pressure changes occur. These spiral supports are part of the cuticular lining, giving strength without making the tubes rigid and immobile. This ensures continuous airflow through the tracheal trunks toward smaller branches. Without such reinforcement, the air passages could collapse during movement, reducing oxygen delivery to tissues. The design balances flexibility with structural support, which is crucial in an active insect. Hence, chitinous spiral thickenings are the correct feature.
244. In cockroach, oxygen is transported to tissues mainly by:
ⓐ. Hemoglobin inside red blood cells
ⓑ. Direct diffusion through tracheoles
ⓒ. Oxygen-binding proteins in lymph
ⓓ. Filtration through Malpighian tubules
Correct Answer: Direct diffusion through tracheoles
Explanation: In cockroach, air travels through tracheae and tracheoles, and oxygen reaches body cells largely by diffusion over very short distances. Because this tracheal network delivers oxygen directly, the blood (hemolymph) does not play the primary role in oxygen transport as in vertebrates. The extensive branching ensures that most cells lie close to a tracheole, enabling efficient exchange. Ventilatory movements can enhance air flow in larger tubes, but final transfer to cells is by diffusion. This arrangement supports rapid tissue oxygenation during activity. Therefore, direct diffusion through tracheoles is the correct mechanism.
245. The main function of air sacs in cockroach respiration is to:
ⓐ. Aid ventilation
ⓑ. Secrete enzymes
ⓒ. Filter wastes
ⓓ. Store nutrients
Correct Answer: Aid ventilation
Explanation: Air sacs are expandable portions of the tracheal system that act as reservoirs to facilitate movement of air through tracheae during body movements. By changing volume with abdominal contractions and relaxations, they help push fresh air deeper into the tracheal network and assist in removing carbon dioxide-rich air. This improves ventilation especially during active states when oxygen demand is high. Air sacs also reduce overall body weight while maintaining an efficient internal air distribution system. Their role is mechanical and respiratory, not digestive or excretory. Hence, air sacs primarily aid ventilation.
246. Spiracles in cockroach are adapted to reduce water loss mainly by:
ⓐ. Remaining permanently open for continuous airflow
ⓑ. Lining with mucus that traps oxygen
ⓒ. Opening and closing through valves
ⓓ. Converting water vapor into liquid water
Correct Answer: Opening and closing through valves
Explanation: Spiracles are equipped with valvular mechanisms that allow them to open when gas exchange is needed and close to limit dehydration. Since insects have a large surface-area-to-volume ratio and live in air, water conservation is essential for survival. By controlling spiracle opening, the cockroach reduces the escape of water vapor while still meeting oxygen requirements. This control works alongside the protective cuticle to maintain internal water balance. The system therefore balances respiration with conservation, especially under dry conditions. Hence, valvular opening and closing is the key adaptation.
247. The most common mechanism that actively helps move air through tracheae in cockroach is:
ⓐ. Beating of cilia inside tracheae
ⓑ. Rhythmic abdominal movements
ⓒ. Contraction of cardiac muscle discs
ⓓ. Peristalsis of the gut wall
Correct Answer: Rhythmic abdominal movements
Explanation: Cockroach enhances ventilation mainly by rhythmic movements of the abdomen that change internal body volume and pressure. These movements promote air flow through larger tracheae and air sacs, helping renew oxygen supply and remove carbon dioxide. While diffusion is sufficient at the tracheole level, bulk flow in larger tubes becomes important during activity. Abdominal pumping acts as a ventilatory mechanism without requiring cilia or lung-like structures. This is especially effective because the tracheal system is distributed throughout the body. Therefore, rhythmic abdominal movements are the main active aid for airflow.
248. If spiracles remain closed for a prolonged period, the most immediate effect is:
ⓐ. Faster blood circulation
ⓑ. Increased urine formation
ⓒ. Higher digestion rate
ⓓ. Reduced gas exchange
Correct Answer: Reduced gas exchange
Explanation: Spiracles are the gateways for air to enter and leave the tracheal system, so prolonged closure restricts oxygen entry and carbon dioxide removal. Even though tissues can temporarily rely on stored air in tracheae and air sacs, continued closure reduces the gradient needed for effective diffusion at tracheoles. This can quickly impair cellular respiration, especially in active tissues with high oxygen demand. The limitation is respiratory rather than circulatory or digestive in the immediate sense. Thus, the earliest functional consequence is reduced exchange of respiratory gases. Hence, reduced gas exchange is the correct effect.
249. Which sequence correctly represents the airflow pathway from outside to tissues in cockroach?
ⓐ. Spiracle → trachea → tracheole
ⓑ. Tracheole → trachea → spiracle
ⓒ. Alveolus → bronchiole → trachea
ⓓ. Gill filament → trachea → spiracle
Correct Answer: Spiracle → trachea → tracheole
Explanation: Air enters the insect body through spiracles, which open into larger tracheal trunks that branch repeatedly into finer tubes. These branches ultimately form tracheoles, which penetrate tissues and bring air close to cells for diffusion. This direct pathway is a defining feature of insect respiration and explains why oxygen transport is not primarily dependent on blood. The sequence also reflects increasing surface area and decreasing diameter to optimize diffusion at the tissue level. Recognizing this order prevents common confusion between entry points and terminal branches. Therefore, the correct pathway is spiracle to trachea to tracheole.
250. In cockroach, the site where oxygen actually diffuses into cells and carbon dioxide diffuses out is mainly the:
ⓐ. Spiracle opening
ⓑ. Larger tracheal trunk
ⓒ. Tracheole end network
ⓓ. Dorsal blood vessel
Correct Answer: Tracheole end network
Explanation: The tracheole network forms the terminal respiratory surface of the tracheal system and lies extremely close to body cells. Because the diffusion distance is minimal at tracheole ends, oxygen can enter cells efficiently and carbon dioxide can leave cells effectively. Larger tracheae primarily serve as conducting passages, while spiracles regulate entry and exit of air. This division of roles ensures that conduction and exchange are optimized separately within the system. The tracheole ends therefore function as the true exchange interface for tissue respiration. Hence, the tracheole end network is the main diffusion site.
251. The main excretory organs of cockroach are:
ⓐ. Malpighian tubules
ⓑ. Nephridia
ⓒ. Flame cells
ⓓ. Green glands
Correct Answer: Malpighian tubules
Explanation: Cockroach primarily excretes nitrogenous wastes through Malpighian tubules, which are slender tubules associated with the alimentary canal. They remove wastes from the body fluid and discharge them into the gut for elimination along with feces. This system also supports water and salt balance by selective handling of ions and water. It is a characteristic excretory mechanism of many terrestrial insects, helping conserve water efficiently. Because these tubules are the principal structures involved, they are recognized as the main excretory organs. Hence, Malpighian tubules are correct.
252. Malpighian tubules open into the alimentary canal at the junction of:
ⓐ. Foregut and midgut
ⓑ. Ileum and rectum
ⓒ. Pharynx and esophagus
ⓓ. Midgut and hindgut
Correct Answer: Midgut and hindgut
Explanation: Malpighian tubules are attached near the posterior region of the digestive tract and empty their contents into the gut rather than directly outside. In cockroach, they open into the alimentary canal at the junction of the midgut and hindgut. This location ensures that wastes entering the gut can be processed and eventually eliminated with fecal matter. It also supports water conservation because the hindgut can reabsorb water and salts before excretion. The junction-based placement is a standard anatomical point used in exam questions. Therefore, the correct junction is midgut and hindgut.
253. The chief nitrogenous waste excreted by cockroach is:
ⓐ. Urea
ⓑ. Uric acid
ⓒ. Ammonia
ⓓ. Creatinine
Correct Answer: Uric acid
Explanation: Cockroach is primarily uricotelic, meaning it excretes nitrogen mainly as uric acid. Uric acid is relatively insoluble and can be eliminated with minimal water loss, which is highly advantageous for terrestrial insects. This adaptation supports survival in environments where water availability may be limited. The excretory material is delivered into the gut and removed along with feces as semi-solid waste. By using uric acid, the cockroach reduces dehydration risk while still eliminating nitrogenous wastes. Hence, uric acid is the chief nitrogenous waste.
254. Malpighian tubules remove wastes mainly from:
ⓐ. Hemolymph
ⓑ. Tracheal air
ⓒ. Salivary secretion
ⓓ. Gastric juice
Correct Answer: Hemolymph
Explanation: Malpighian tubules function by extracting nitrogenous wastes and excess ions from the insect’s body fluid, known as hemolymph. Their epithelial cells actively transport waste materials into the tubule lumen, creating an excretory fluid that enters the gut. This mechanism is not dependent on filtration by a closed circulatory system, but rather on secretion and transport from hemolymph. Because hemolymph bathes organs in an open circulatory setup, it serves as the main source reservoir from which wastes are removed. This directly links Malpighian tubules to systemic waste clearance. Therefore, wastes are removed mainly from hemolymph.
255. A key advantage of Malpighian tubules in terrestrial insects is that they:
ⓐ. Require large water loss to flush wastes
ⓑ. Replace the need for a digestive system
ⓒ. Convert oxygen into carbon dioxide
ⓓ. Conserve water while eliminating nitrogenous wastes
Correct Answer: Conserve water while eliminating nitrogenous wastes
Explanation: Malpighian tubules help insects eliminate nitrogenous wastes while minimizing water loss, a major requirement for terrestrial life. Waste products enter the gut, and then water and useful ions can be reabsorbed in the hindgut, leaving concentrated or semi-solid waste for elimination. This design supports uric acid excretion, which further reduces water requirement because uric acid is poorly soluble. Together, these features allow efficient waste removal without dehydration. The system therefore acts as an important physiological adaptation for living on land. Hence, conserving water during excretion is the key advantage.
256. The fluid produced by Malpighian tubules ultimately leaves the body mainly through:
ⓐ. Nephridiopores
ⓑ. Spiracles
ⓒ. Anus
ⓓ. Sweat glands
Correct Answer: Anus
Explanation: Malpighian tubules discharge their excretory contents into the alimentary canal, so the wastes move along with intestinal contents. After water and salts are reabsorbed in the hindgut, the remaining waste is expelled as part of fecal matter. Therefore, elimination occurs through the terminal opening of the digestive tract. This pathway is consistent with the insect strategy of combining excretion with defecation to conserve water. It also explains why insects lack separate urinary openings like many vertebrates. Hence, the excretory output leaves mainly through the anus.
257. The primary process by which Malpighian tubules add wastes into their lumen is best described as:
ⓐ. Active secretion
ⓑ. Photosynthetic fixation
ⓒ. Passive diffusion only
ⓓ. Bone remodeling
Correct Answer: Active secretion
Explanation: Malpighian tubules mainly form excretory fluid by actively transporting ions and nitrogenous waste products from hemolymph into the tubule lumen. This active secretion creates an osmotic gradient that draws water into the tubules, forming a primary urine-like fluid. Later, selective reabsorption in the hindgut reduces water loss and concentrates wastes. The process is therefore driven by transport mechanisms rather than simple filtration like in many vertebrate kidneys. This principle is commonly tested to contrast insect excretion with nephron-based filtration models. Therefore, active secretion best describes the primary mechanism.
258. If the rectum reabsorbs more water than usual, the expected outcome is:
ⓐ. More dilute feces and waste
ⓑ. More concentrated waste with less water loss
ⓒ. Complete stoppage of digestion
ⓓ. Increased oxygen delivery by blood
Correct Answer: More concentrated waste with less water loss
Explanation: In cockroach, after Malpighian tubules deliver excretory material into the gut, the hindgut—especially the rectal region—reabsorbs water and useful salts. Increased reabsorption means more water is returned to the body and less is lost in feces. As a result, the eliminated waste becomes more concentrated and drier, which supports water conservation. This adjustment is particularly important under dry conditions where dehydration risk is high. The effect is primarily on excretion and water balance, not digestion stoppage or oxygen delivery. Hence, more concentrated waste with less water loss is the expected outcome.
259. Malpighian tubules in cockroach are structurally best described as:
ⓐ. Flat sacs embedded in the liver
ⓑ. Cartilage-lined air tubes in the thorax
ⓒ. Bony channels inside the legs
ⓓ. Fine blind-ended tubules projecting into the body cavity
Correct Answer: Fine blind-ended tubules projecting into the body cavity
Explanation: Malpighian tubules are numerous, thin, thread-like tubules that arise near the gut and extend into the body cavity as blind-ended structures. Their blind ends lie in the hemolymph, allowing efficient exchange and transport of wastes into the tubule lumen. This structural design increases surface area for secretion and supports effective waste removal from body fluids. Their association with the alimentary canal enables wastes to be delivered directly into the gut for elimination. They are therefore not air tubes, bones, or liver sacs, but fine blind-ended excretory tubules. Hence, the correct description is fine blind-ended tubules projecting into the body cavity.
260. The best reason cockroach can excrete uric acid efficiently is that:
ⓐ. Uric acid is highly soluble and needs lots of water to remove
ⓑ. Uric acid forms solid/semi-solid waste, reducing water requirement
ⓒ. Uric acid is converted into glucose before elimination
ⓓ. Uric acid diffuses out through the skin surface
Correct Answer: Uric acid forms solid/semi-solid waste, reducing water requirement
Explanation: Uric acid is poorly soluble and can be eliminated as a concentrated paste or semi-solid form, which requires very little water. This is a major advantage for terrestrial insects because it prevents excessive dehydration during excretion. The Malpighian tubule–hindgut system further enhances this by reabsorbing water and salts before waste is expelled. Together, these adaptations allow nitrogen removal with minimal water loss, supporting survival in dry habitats. The efficiency is not because uric acid is highly soluble or converted to glucose, and it is not mainly lost through skin diffusion. Therefore, uric acid’s semi-solid elimination is the key reason for efficient excretion.
261. Cockroach has an open circulatory system because:
ⓐ. Blood enters sinuses
ⓑ. Blood stays in capillaries
ⓒ. Blood remains in arteries only
ⓓ. Blood flows in veins only
Correct Answer: Blood enters sinuses
Explanation: In an open circulatory system, the circulating fluid does not remain confined within a continuous network of capillaries. In cockroach, the fluid (hemolymph) is pumped through vessels for part of its path but then leaves the vessels to flow into body spaces called sinuses. Organs are bathed directly by hemolymph within the hemocoel, and the fluid later returns toward the heart rather than staying within closed capillary loops. This arrangement creates relatively low pressure and slower, more diffuse distribution compared with closed systems. The defining idea is vessel-to-sinus flow, not continuous vessel confinement. Therefore, “blood enters sinuses” correctly captures open circulation.
262. The circulating fluid in cockroach is called:
ⓐ. Plasma
ⓑ. Hemolymph
ⓒ. Lymph
ⓓ. Interstitial fluid
Correct Answer: Hemolymph
Explanation: The circulatory fluid of insects is termed hemolymph because it combines roles that, in vertebrates, are separated into blood and tissue fluid. Hemolymph circulates through the hemocoel and transports nutrients, hormones, and metabolic wastes between tissues. It also contains cells involved in defense and wound responses, supporting internal protection. Unlike vertebrate blood, it generally does not serve as the primary carrier of oxygen because gas exchange is mainly handled by the tracheal system. Its movement is driven by the dorsal tubular heart and aided by body movements. Hence, the correct term for cockroach circulatory fluid is hemolymph.
263. The main body cavity through which hemolymph circulates in cockroach is the:
ⓐ. Coelom
ⓑ. Hemocoel
ⓒ. Nephrocoel
ⓓ. Peritoneal cavity
Correct Answer: Hemocoel
Explanation: Cockroach has a body cavity called hemocoel, which functions as the principal space filled with circulating hemolymph. In open circulation, hemolymph leaves vessels and spreads through this cavity to bathe organs directly. This is different from a true coelom, which in many animals is a separate body cavity lined fully by mesoderm and not the main blood-filled space. The hemocoel is organized into regions (sinuses) by diaphragms, helping guide hemolymph flow. Because most internal transport occurs through this cavity, hemocoel is the correct anatomical term. Therefore, hemolymph circulates mainly within the hemocoel.
264. The cockroach heart is best described as a:
ⓐ. Solid muscular block
ⓑ. Pair of lateral pumps
ⓒ. Chambered lung-like sac
ⓓ. Dorsal tubular vessel
Correct Answer: Dorsal tubular vessel
Explanation: The cockroach heart is a long dorsal tube that runs along the back side of the body and functions as the main pumping organ. It is segmented into chambers and helps maintain hemolymph movement through rhythmic contractions. Unlike vertebrate hearts, it does not pump blood through a closed capillary network; instead, it drives hemolymph into vessels that open into sinuses. Its dorsal position and tubular structure are key identification points in insect anatomy. The heart receives hemolymph through openings and propels it forward into the aorta. Thus, it is correctly described as a dorsal tubular vessel.
265. Openings that allow hemolymph to enter the heart chambers in cockroach are called:
ⓐ. Valves
ⓑ. Alveoli
ⓒ. Nephridia
ⓓ. Ostia
Correct Answer: Ostia
Explanation: Ostia are paired openings in the walls of the cockroach heart that permit hemolymph to enter the heart from surrounding spaces. They ensure inflow during relaxation of the heart and help maintain directional movement during pumping. This inflow mechanism is important because hemolymph is not returning via a closed venous system; instead, it is collected from the hemocoel. The presence of ostia is a characteristic feature of arthropod hearts and is frequently tested as a structural marker of open circulation. Their role is specifically related to heart filling rather than gas exchange or excretion. Therefore, the openings are correctly called ostia.
266. Cockroach hemolymph is not the main carrier of oxygen mainly because:
ⓐ. Tracheae supply O2
ⓑ. Hemolymph is absent
ⓒ. Heart does not pump
ⓓ. Ostia remain closed
Correct Answer: Tracheae supply O2
Explanation: In cockroach, respiration is primarily handled by the tracheal system, which delivers oxygen directly to tissues through branching tracheae and tracheoles. Because oxygen reaches cells without needing transport by the circulatory fluid, hemolymph is not specialized for carrying large amounts of oxygen. This is why respiratory pigments typical of many vertebrates are generally not central to insect oxygen delivery. Hemolymph focuses more on transporting nutrients, hormones, and wastes and supporting defense reactions. The division of labor between tracheal respiration and open circulation is a major insect adaptation. Hence, tracheae supplying oxygen is the main reason hemolymph is not the primary oxygen carrier.
267. The hemocoel of cockroach is commonly divided into sinuses mainly by:
ⓐ. Septa
ⓑ. Tracheal rings
ⓒ. Diaphragms
ⓓ. Cartilage plates
Correct Answer: Diaphragms
Explanation: In cockroach, the hemocoel is organized into distinct sinuses separated by membranous partitions called diaphragms. These diaphragms help guide the flow of hemolymph and contribute to functional compartmentalization within the body cavity. The arrangement supports more directed circulation around major organ systems rather than completely random movement throughout the cavity. This structural feature is often tested as it links open circulation with internal body organization. The partitions are not rigid cartilage or tracheal supports; they are internal membranes associated with the body wall and musculature. Therefore, hemocoel sinuses are divided mainly by diaphragms.
268. The sinus that surrounds the heart in cockroach is the:
ⓐ. Perineural sinus
ⓑ. Perivisceral sinus
ⓒ. Pericardial sinus
ⓓ. Pleural sinus
Correct Answer: Pericardial sinus
Explanation: The heart of cockroach lies dorsally and is enclosed within the pericardial sinus, which is the dorsal compartment of the hemocoel. This sinus is closely associated with heart filling because hemolymph from nearby spaces can enter the heart through ostia. The naming aligns with its relationship to the heart region, helping students map sinuses to their locations and functions. In contrast, the perivisceral sinus is associated with the gut region, and the perineural sinus lies near the ventral nerve cord. Knowing which sinus contains the heart is a standard anatomy check in insect circulation. Thus, the heart is surrounded by the pericardial sinus.
269. The main function of hemolymph in cockroach is best represented by:
ⓐ. Transport of nutrients
ⓑ. Gas exchange in alveoli
ⓒ. Formation of bile
ⓓ. Bone mineral storage
Correct Answer: Transport of nutrients
Explanation: Hemolymph primarily serves as a transport medium for nutrients absorbed from the gut to tissues and for distributing hormones and other chemical signals. It also helps carry metabolic wastes to excretory structures and supports immune-like functions through circulating cells. Because oxygen delivery is mainly via the tracheal system, hemolymph’s most emphasized role is not respiratory transport but internal distribution of materials needed for metabolism and coordination. In an open system, hemolymph directly bathes organs, making exchange of nutrients and metabolites effective at the tissue level. This functional emphasis is a common exam point to avoid confusing insect circulation with vertebrate blood roles. Therefore, transport of nutrients is the best representation of hemolymph function.
270. In an open circulatory system like cockroach, blood pressure is generally:
ⓐ. Very high
ⓑ. Relatively low
ⓒ. Identical to mammals
ⓓ. Pulsatile only in capillaries
Correct Answer: Relatively low
Explanation: Open circulation operates without a closed capillary network, so hemolymph is not maintained under high pressure throughout a sealed vessel system. When hemolymph enters sinuses and bathes organs, the pressure drops and circulation becomes slower and less forceful compared with closed systems. The heart provides rhythmic pumping, but the return pathway is through open spaces rather than pressurized veins and capillaries. This lower pressure is sufficient because oxygen delivery is not dependent on rapid blood flow to tissues in insects. The system is efficient for nutrient and waste transport while minimizing the energetic cost of maintaining high vascular pressure. Hence, blood pressure in cockroach open circulation is relatively low.
271. In frog, a key feature supporting life on land is:
ⓐ. Scales with keratin layers
ⓑ. A rigid bony carapace
ⓒ. Moist glandular skin
ⓓ. A shell-covered egg
Correct Answer: Moist glandular skin
Explanation: Frog skin is thin, moist, and richly supplied with blood vessels, which supports important amphibian functions on land. The mucus keeps the surface wet, preventing excessive drying and enabling cutaneous gas exchange. Many frogs also have skin glands that produce secretions aiding in protection and moisture retention. Because amphibians lack a thick waterproof body covering, maintaining a moist skin surface is essential for survival, especially during activity outside water. This trait directly links to their dependence on humid habitats and their ability to respire through the skin. Therefore, moist glandular skin is a key land-life adaptation.
272. The characteristic “amphibian” nature of frog is best reflected by:
ⓐ. Life in water and on land
ⓑ. Life only in desert sand
ⓒ. Life only in deep oceans
ⓓ. Life only in tree canopies
Correct Answer: Life in water and on land
Explanation: Frogs are termed amphibians because their life history and adaptations connect both aquatic and terrestrial environments. Their eggs and early larval stage are typically aquatic, while adults can live and move on land, returning to water for breeding. They show structural and physiological features that support both habitats, such as limbs for jumping and skin respiration requiring moisture. This dual association is not merely habitat preference; it is built into their reproduction, development, and respiration patterns. The idea is central to amphibian classification and frequently tested as a definition-based concept. Hence, frog’s amphibian nature is best reflected by life in water and on land.
273. The main respiratory surface in an adult frog during prolonged submergence in water is:
ⓐ. Lungs
ⓑ. Gills
ⓒ. Skin
ⓓ. Tracheae
Correct Answer: Skin
Explanation: When an adult frog remains underwater, lung breathing is limited because it cannot continuously gulp air. In such conditions, gas exchange mainly occurs through the moist, vascular skin by diffusion, a process called cutaneous respiration. The thin epidermis and rich capillary network allow oxygen to enter the blood and carbon dioxide to leave effectively, provided the skin stays wet. This mechanism is especially important during rest, hibernation, or extended periods in water. Adult frogs do not have functional gills like the larval stage, making skin the key underwater surface. Therefore, skin is the main respiratory surface during prolonged submergence.
274. In frog, the external tympanum is most directly related to:
ⓐ. Hearing
ⓑ. Smell
ⓒ. Taste
ⓓ. Touch
Correct Answer: Touch
Explanation: The tympanum in frog is a circular membrane behind the eye that functions as an eardrum for receiving sound vibrations. These vibrations are transmitted to the internal ear structures, allowing the frog to detect calls, predators, and environmental sounds. The tympanum’s position and membrane nature make it suited to respond to air-borne vibrations, which is important for communication, especially during breeding. While frogs also have sensory abilities for smell and vision, the tympanum is specifically an auditory adaptation. Hence, its direct functional role is hearing, not touch. Therefore, the correct option should be “Hearing,” and the correct answer is not D.
275. The frog heart is best described as:
ⓐ. Two-chambered
ⓑ. Four-chambered
ⓒ. Three-chambered
ⓓ. Single-chambered
Correct Answer: Three-chambered
Explanation: Frog has a three-chambered heart consisting of two atria and one ventricle. The right atrium receives deoxygenated blood returning from the body, while the left atrium receives oxygenated blood coming from the lungs and skin. Both streams enter the single ventricle, where mixing is limited by structural features and the pattern of blood flow into major arteries. This arrangement supports amphibians that rely on both pulmonary and cutaneous respiration. The three-chamber plan is a standard comparative point distinguishing amphibians from fishes (two chambers) and birds/mammals (four chambers). Therefore, frog heart is three-chambered.
276. A frog’s eggs generally require water mainly because they:
ⓐ. Have a hard calcareous shell
ⓑ. Lack a protective shell and can desiccate
ⓒ. Contain air sacs for buoyancy
ⓓ. Develop without any cell division
Correct Answer: Lack a protective shell and can desiccate
Explanation: Frog eggs are typically jelly-coated but do not possess a hard, waterproof shell. Because of this, they can lose water rapidly and dry out if laid in dry conditions. The gelatinous coverings help protect and support the embryo in water, but they do not replace the protective function of a rigid shell seen in many terrestrial eggs. This is why frogs usually return to aquatic or very moist sites for breeding and egg-laying. The dependence of eggs on water is a key amphibian trait linked to reproductive strategy and habitat choice. Hence, frog eggs require water mainly because they lack a protective shell and can desiccate.
277. The larval stage (tadpole) is adapted for aquatic life mainly due to:
ⓐ. Presence of fins and gill-based respiration
ⓑ. Presence of hair and sweat glands
ⓒ. Presence of claws and feathers
ⓓ. Presence of thick keratin scales
Correct Answer: Presence of fins and gill-based respiration
Explanation: Tadpoles are primarily aquatic and show features that support swimming and underwater respiration. They typically possess a tail fin for locomotion and respire using gills during early development, matching their water-based habitat. This contrasts with adult frogs that rely on lungs and skin and have limbs adapted for land movement. The tadpole stage also aligns with the amphibian life cycle where a major transformation occurs during metamorphosis. These adaptations allow efficient feeding and survival in water before the shift to adult form. Therefore, the presence of fins and gill-based respiration best explains tadpole aquatic adaptation.
278. A direct evidence of metamorphosis in frog development is:
ⓐ. Appearance of a crop and gizzard
ⓑ. Formation of a carapace and plastron
ⓒ. Change of warm-blooded to cold-blooded state
ⓓ. Replacement of tail and gills by limbs and lungs
Correct Answer: Replacement of tail and gills by limbs and lungs
Explanation: Metamorphosis in frogs involves major structural and functional changes from tadpole to adult. The tadpole’s tail is gradually reduced, and gill-based respiration is replaced by lung breathing, while limbs develop to support land movement. These changes reflect a shift from an aquatic larva to a semi-terrestrial adult with different feeding and locomotion patterns. Metamorphosis is not a minor growth change; it is a reorganization of body plan that aligns with habitat transition. This transformation is one of the most characteristic life-history traits of amphibians. Hence, replacement of tail and gills by limbs and lungs is direct evidence of metamorphosis.
279. In adult frog, the chamber that receives oxygenated blood from lungs/skin is:
ⓐ. Right atrium
ⓑ. Ventricle
ⓒ. Left atrium
ⓓ. Sinus venosus
Correct Answer: Left atrium
Explanation: In frogs, oxygenated blood returning from respiratory surfaces enters the heart through the left atrium. This blood comes from lungs and also from skin pathways, reflecting the frog’s dual respiratory modes. The right atrium, in contrast, primarily receives deoxygenated blood returning from body tissues. Both atria then pass blood into the single ventricle, where mixing is limited by flow patterns rather than complete separation. Identifying which atrium receives oxygenated blood is a common conceptual check in amphibian circulation. Therefore, the left atrium receives oxygenated blood from lungs/skin.
280. A typical amphibian trait shown by frogs is:
ⓐ. Endothermy
ⓑ. Ectothermy
ⓒ. Constant body temperature
ⓓ. Heat production by shivering
Correct Answer: Ectothermy
Explanation: Frogs are ectothermic, meaning their body temperature depends largely on environmental temperature rather than internal heat production. This is why frogs show behavioral adaptations like basking to warm up and seeking shade or water to cool down. Their metabolic rate generally varies with external conditions, influencing activity patterns and seasonal behavior. This trait is common in amphibians and contrasts with endothermic animals that maintain a relatively constant internal temperature. Ectothermy also relates to energy efficiency, as less energy is spent on heat production, but it creates dependence on suitable environmental conditions. Hence, ectothermy is a typical amphibian trait in frogs.
281. In an adult frog resting quietly in water, the dominant mode of respiration is:
ⓐ. Pulmonary respiration
ⓑ. Buccopharyngeal respiration
ⓒ. Cutaneous respiration
ⓓ. Branchial respiration
Correct Answer: Cutaneous respiration
Explanation: Adult frogs can exchange gases through their thin, moist, highly vascular skin, and this becomes especially important when they are submerged or resting in water. Oxygen dissolved in water diffuses across the skin into blood capillaries, while carbon dioxide diffuses outward. Because the lungs cannot be ventilated continuously underwater, skin respiration provides a reliable pathway for gas exchange. The mucus coating keeps the skin surface wet, which is essential for diffusion to occur efficiently. This mode supports the amphibian lifestyle by enabling respiration without frequent surfacing. Therefore, cutaneous respiration is the dominant mode in a resting frog in water.
282. Buccopharyngeal respiration in frog mainly involves gas exchange through the:
ⓐ. Skin of the body
ⓑ. Lining of the stomach
ⓒ. Tracheal tubes
ⓓ. Moist lining of buccal cavity
Correct Answer: Moist lining of buccal cavity
Explanation: Buccopharyngeal respiration occurs when a frog exchanges gases across the moist, richly supplied lining of the buccal and pharyngeal region. Even with the mouth closed, rhythmic movements of the floor of the buccal cavity keep air in contact with this lining, allowing diffusion of oxygen into blood and carbon dioxide out. This mode is particularly useful during rest on land when the frog’s activity level is low. It complements skin and lung respiration, providing flexibility in different environmental conditions. The key requirement is a moist surface and close capillary network for diffusion. Hence, the moist lining of the buccal cavity is the main site in buccopharyngeal respiration.
283. The respiratory mode that becomes most important for an adult frog during active movement on land is:
ⓐ. Pulmonary respiration
ⓑ. Cutaneous respiration
ⓒ. Branchial respiration
ⓓ. Tracheal respiration
Correct Answer: Pulmonary respiration
Explanation: During active movement on land, the oxygen demand of muscles increases and carbon dioxide production rises. Under these conditions, lung ventilation becomes the most effective way to rapidly exchange larger volumes of gases compared with diffusion-limited surfaces. The frog uses buccal pumping to move air into and out of the lungs, improving oxygen uptake. While skin still contributes, it cannot alone meet the higher metabolic requirements during vigorous activity. Lung respiration thus provides a faster and more controlled exchange mechanism. Therefore, pulmonary respiration becomes most important during active terrestrial movement.
284. The larval stage (tadpole) primarily respires through:
ⓐ. Lungs only
ⓑ. Gills
ⓒ. Skin only
ⓓ. Spiracles
Correct Answer: Gills
Explanation: Tadpoles are adapted to aquatic life and primarily rely on gills for respiration during early development. Gills provide a large surface area in contact with water, enabling efficient uptake of dissolved oxygen and removal of carbon dioxide. This matches the tadpole’s habitat and swimming lifestyle before metamorphosis. As development proceeds, gill-based respiration reduces and lung-based respiration increases, reflecting the transition toward adult form. The key larval respiratory feature is therefore gill respiration. Hence, tadpoles primarily respire through gills.
285. The moist condition of frog skin is essential mainly because it:
ⓐ. Enables diffusion of gases across skin
ⓑ. Prevents blood from clotting
ⓒ. Produces digestive enzymes
ⓓ. Forms hard protective scales
Correct Answer: Enables diffusion of gases across skin
Explanation: Gas exchange through the skin requires that respiratory gases dissolve in a thin water layer before diffusing across living tissues. Frog skin is kept moist by mucus secretions, which maintain this water film and allow oxygen and carbon dioxide to move efficiently by diffusion. Without moisture, diffusion across the skin becomes severely limited, reducing the effectiveness of cutaneous respiration. This is why frogs depend on humid habitats and often stay near water sources. The skin’s rich capillary network supports rapid exchange when moisture is present. Therefore, the moist condition is essential because it enables diffusion of gases across the skin.
286. In frogs, air is forced into lungs mainly by:
ⓐ. Expansion of rib cage
ⓑ. Diaphragm contraction
ⓒ. Continuous cilia beating
ⓓ. Buccal pumping
Correct Answer: Buccal pumping
Explanation: Frogs lack a well-developed rib cage mechanism and do not use a diaphragm like mammals for inhalation. Instead, they use buccal pumping, where the floor of the buccal cavity moves to push air into the lungs. Air first enters the buccal cavity through the nostrils, and then pressure changes created by buccal movements drive it into the lungs. This method is effective for amphibians and supports pulmonary respiration, especially on land. It also allows controlled ventilation without chest expansion. Hence, buccal pumping is the main way air is forced into frog lungs.
287. During hibernation in moist conditions, the frog mainly relies on:
ⓐ. Pulmonary respiration
ⓑ. Cutaneous respiration
ⓒ. Buccopharyngeal respiration
ⓓ. Gill respiration
Correct Answer: Cutaneous respiration
Explanation: In hibernation, a frog’s metabolic rate drops, and it often remains in a moist environment such as mud or the bottom of a pond. Under these conditions, lung ventilation becomes minimal, and gas exchange must occur without active breathing. The moist, vascular skin provides a steady diffusion pathway for oxygen uptake and carbon dioxide removal at low metabolic demands. This makes cutaneous respiration especially important during prolonged inactivity. The dependence on moisture ensures the skin remains an effective respiratory surface. Therefore, during hibernation, frogs mainly rely on cutaneous respiration.
288. Buccopharyngeal respiration is most significant when the frog is:
ⓐ. Swimming rapidly underwater
ⓑ. Chasing prey actively on land
ⓒ. Resting on land with mouth closed
ⓓ. In the tadpole stage before metamorphosis
Correct Answer: Resting on land with mouth closed
Explanation: When a frog is resting on land, its oxygen requirement is moderate and it can exchange gases through multiple surfaces. Buccopharyngeal respiration becomes significant because the moist lining of the buccal cavity remains in contact with air even when the mouth is closed. Gentle movements of the buccal floor refresh the air over this lining and maintain diffusion gradients. This provides a quiet, energy-efficient mode of respiration during rest, complementing skin and occasional lung breathing. It is especially useful when the frog is not ventilating lungs forcefully. Hence, buccopharyngeal respiration is most significant during rest on land with the mouth closed.
289. A frog that stays submerged for a longer time can still obtain oxygen mainly due to:
ⓐ. Air stored in stomach
ⓑ. Gas exchange by kidneys
ⓒ. Oxygen storage in bones
ⓓ. Diffusion through vascular skin
Correct Answer: Diffusion through vascular skin
Explanation: When a frog remains underwater, it cannot depend continuously on lung ventilation, so it uses cutaneous respiration to meet oxygen needs. The skin is richly supplied with capillaries, and oxygen dissolved in water can diffuse into the blood across the moist skin surface. Carbon dioxide simultaneously diffuses out, maintaining gas balance. This mechanism is effective during rest or low activity underwater and supports the amphibian ability to remain submerged for extended periods. The critical factor is the vascular, moist skin acting as a respiratory surface. Therefore, diffusion through vascular skin enables longer underwater stay.
290. The pair of respiratory modes used by adult frog both in water and on land is best stated as:
ⓐ. Cutaneous and pulmonary
ⓑ. Branchial and pulmonary
ⓒ. Branchial and buccopharyngeal
ⓓ. Tracheal and cutaneous
Correct Answer: Cutaneous and pulmonary
Explanation: Adult frogs can respire through both skin and lungs, allowing flexibility across aquatic and terrestrial settings. In water, cutaneous respiration becomes highly useful because the moist skin can exchange gases with dissolved oxygen. On land, pulmonary respiration becomes more prominent, especially during activity, while skin still contributes when the surface remains moist. This dual system is central to amphibian adaptation and explains their dependence on moisture and their ability to function in both habitats. The two modes together cover a wide range of environmental and activity conditions. Hence, the best pair for adult frog in water and on land is cutaneous and pulmonary.
291. In an adult frog, the heart is three-chambered because it has:
ⓐ. One atrium and two ventricles
ⓑ. Two atria and one ventricle
ⓒ. Two atria and two ventricles
ⓓ. One atrium and one ventricle
Correct Answer: Two atria and one ventricle
Explanation: The frog heart consists of two atria (right and left) and a single ventricle, making it three-chambered. The right atrium mainly receives deoxygenated blood from the body, while the left atrium mainly receives oxygenated blood from lungs and skin. Both atria open into the same ventricle, so complete separation like birds and mammals does not occur. However, blood flow patterns and internal features help reduce complete mixing, supporting effective circulation. This heart design suits amphibians that use both pulmonary and cutaneous respiration. Therefore, the correct description is two atria and one ventricle.
292. The chamber of frog heart that primarily receives oxygenated blood from lungs/skin is the:
ⓐ. Left atrium
ⓑ. Right atrium
ⓒ. Ventricle
ⓓ. Sinus venosus
Correct Answer: Left atrium
Explanation: Oxygenated blood returning from respiratory surfaces enters the left atrium of the frog. This reflects the separation of incoming streams at the atrial level, where the right atrium is mainly associated with systemic venous return. From the left atrium, oxygenated blood passes into the ventricle along with blood from the right atrium. Although a single ventricle exists, this atrial separation is important for directing relatively oxygen-rich blood into appropriate arterial pathways. It is a standard identification point in amphibian circulation questions. Hence, the left atrium primarily receives oxygenated blood.
293. In a frog, the structure that collects deoxygenated blood from the body and opens into the right atrium is the:
ⓐ. Pulmonary vein
ⓑ. Left atrium
ⓒ. Dorsal aorta
ⓓ. Sinus venosus
Correct Answer: Sinus venosus
Explanation: The sinus venosus is a thin-walled collecting chamber that receives venous blood returning from the body through major veins. It then passes this deoxygenated blood into the right atrium, supporting the systemic-to-cardiac return pathway. This structure is prominent in amphibians and helps regulate the inflow of venous blood into the heart. It is distinct from pulmonary veins, which carry oxygenated blood to the left atrium. Understanding sinus venosus prevents confusion between collecting chambers and atrial chambers. Therefore, sinus venosus is the correct structure.
294. The arterial trunk that leaves the frog ventricle and gives rise to major arterial arches is the:
ⓐ. Vena cava
ⓑ. Dorsal aorta
ⓒ. Truncus arteriosus
ⓓ. Pulmonary vein
Correct Answer: Truncus arteriosus
Explanation: Blood leaves the single ventricle of a frog through a major outflow tract commonly termed the truncus arteriosus, which then distributes blood into arterial arches. This outflow pathway is essential because the ventricle is the only pumping chamber, so all blood must pass through this route before being directed to different circulations. Structural features within the outflow tract help channel blood toward pulmonary and systemic circuits. This arrangement supports amphibian physiology by coordinating flow from a partially separated ventricle into multiple arterial pathways. Correct identification is important in questions on incomplete double circulation. Hence, truncus arteriosus is the correct answer.
295. The best reason mixing of oxygenated and deoxygenated blood in frog is limited (though not fully prevented) is:
ⓐ. Complete interventricular septum
ⓑ. Two separate ventricles
ⓒ. Absence of pulmonary circulation
ⓓ. Spiral valve and flow streaming in the outflow tract
Correct Answer: Spiral valve and flow streaming in the outflow tract
Explanation: Frogs have a single ventricle, so some mixing is possible, but internal flow patterns and the spiral valve in the outflow region help reduce complete mixing. The spiral valve guides blood streams so that relatively oxygen-rich blood is preferentially directed into systemic pathways, while relatively oxygen-poor blood is directed toward pulmonary circuits. This “streaming” effect improves efficiency without a fully divided ventricle. It aligns with the amphibian need to manage blood returning from both body and respiratory surfaces. The mechanism is not as perfect as a septum, but it is functionally important. Therefore, spiral valve and flow streaming best explain limited mixing.
296. A correct statement about circulation in adult frog is that it shows:
ⓐ. Single circulation only
ⓑ. Double circulation that is not fully separated
ⓒ. Double circulation with complete separation
ⓓ. No pulmonary pathway at all
Correct Answer: Double circulation that is not fully separated
Explanation: Adult frogs have both pulmonary (to lungs/skin) and systemic (to body tissues) circuits, so circulation is double. However, because the ventricle is single, the separation of oxygenated and deoxygenated blood is incomplete compared with four-chambered hearts. Atrial separation and the outflow tract features help direct blood, but they do not create total separation. This pattern is therefore described as incomplete double circulation. It suits amphibians because skin and lungs both contribute to oxygenation, and activity levels vary widely. Hence, the correct statement is double circulation that is not fully separated.
297. Metamorphosis in frog is best defined as:
ⓐ. Simple growth with no change in body plan
ⓑ. Formation of eggs without fertilization
ⓒ. A major transformation from larva to adult with structural reorganization
ⓓ. Conversion of warm-blooded to cold-blooded state
Correct Answer: A major transformation from larva to adult with structural reorganization
Explanation: Frog metamorphosis is a developmental process where the aquatic larva (tadpole) transforms into a semi-terrestrial adult. It includes major anatomical and physiological changes, not just an increase in size. Features like the tail are reduced, limbs develop, and the mode of respiration shifts from gill-based to lung and skin-based. Feeding habits and digestive tract structure also change to match the adult lifestyle. These coordinated changes represent a reorganization of the body plan to support a new habitat and function. Therefore, metamorphosis is a major larva-to-adult transformation with structural reorganization.
298. A classic visible sign of frog metamorphosis is:
ⓐ. Development of scales on the skin
ⓑ. Gradual loss of tail with development of limbs
ⓒ. Formation of feathers and wings
ⓓ. Appearance of milk glands
Correct Answer: Gradual loss of tail with development of limbs
Explanation: During metamorphosis, the tadpole’s tail is progressively resorbed while limbs develop, shifting locomotion from swimming to jumping and walking. This change reflects the transition from a purely aquatic larva to a semi-terrestrial adult frog. Tail resorption is not simply “cut off”; it is a controlled developmental process with tissue breakdown and reuse of materials. Limb formation supports movement on land and aligns with changes in posture and muscle organization. Because these changes are external and obvious, they are commonly used as key indicators of metamorphosis. Hence, gradual tail loss with limb development is the classic visible sign.
299. The hormone most directly responsible for regulating frog metamorphosis is:
ⓐ. Thyroxine
ⓑ. Adrenaline
ⓒ. Insulin
ⓓ. Estrogen
Correct Answer: Thyroxine
Explanation: Thyroxine, a thyroid hormone, plays a central role in initiating and coordinating the metamorphic changes in frogs. It influences multiple tissues, ensuring that changes like limb development, tail resorption, and respiratory transition occur in a regulated sequence. Because metamorphosis involves synchronized remodeling across organs, a systemic hormonal control is necessary. Thyroxine provides this endocrine signal, aligning development with physiological readiness and environmental timing. Deficiency or disruption of thyroid function can delay or impair metamorphic progression. Therefore, thyroxine is the hormone most directly responsible for frog metamorphosis.
300. A functional change commonly associated with frog metamorphosis is:
ⓐ. Tadpole becomes filter-feeding with a longer intestine
ⓑ. Adult develops gills as the main respiratory organ
ⓒ. Adult shifts toward carnivory with a shorter intestine than tadpole
ⓓ. Adult becomes completely sedentary with no locomotion
Correct Answer: Adult shifts toward carnivory with a shorter intestine than tadpole
Explanation: Tadpoles commonly feed on plant matter or organic debris, which typically requires a longer intestine for digestion and absorption. As metamorphosis proceeds, the frog transitions toward a carnivorous diet, and the digestive system reorganizes accordingly. The intestine becomes comparatively shorter in the adult, reflecting the higher digestibility of animal food and the changed feeding strategy. This dietary shift is part of the broader transformation that includes changes in mouth structure, musculature, and behavior. It demonstrates that metamorphosis is not only external but also deeply physiological. Hence, adult carnivory with a shorter intestine than tadpole is a correct functional change.