201. Assertion: Mitochondria are excluded from the endomembrane system despite being membrane-bound organelles.
Reason: Mitochondria possess cristae formed by folds of their inner membrane.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not explain the Assertion
ⓒ. Assertion is true, but Reason is false; the Reason cannot explain the Assertion
ⓓ. Assertion is false, but Reason is true; the Reason cannot explain the Assertion
Correct Answer: Both Assertion and Reason are true, but Reason does not explain the Assertion
Explanation: Endomembrane classification validates the Assertion: mitochondria are membrane-bound but lie outside that coordinated system. Mitochondria are not considered components of the endomembrane system, since their principal functions are not coordinated with the ER–Golgi–lysosome–vacuole pathway. The Reason states a valid relation: folds of the inner mitochondrial membrane form cristae. However, the presence of cristae does not explain the exclusion stated in the Assertion. It describes mitochondrial internal architecture rather than the functional criterion used to define endomembrane membership. The valid fact about cristae is separate from the criterion used for endomembrane classification. Membrane number or membrane folding is not sufficient for inclusion; coordinated participation in the endomembrane pathway is the decisive relation.
202. Match each structure in Column I with its relation in Column II. A Column II entry is used once.
| Column I | Column II |
|---|
| P. Endoplasmic reticulum | 1. Modification and packaging of cellular products |
| Q. Golgi apparatus | 2. Synthesis and intracellular membrane network |
| R. Lysosome | 3. Storage space enclosed by a tonoplast |
| S. Vacuole | 4. Intracellular digestion by hydrolytic enzymes |
ⓐ. P-2, Q-1, R-4, S-3
ⓑ. P-1, Q-2, R-3, S-4
ⓒ. P-4, Q-3, R-2, S-1
ⓓ. P-3, Q-4, R-1, S-2
Correct Answer: P-2, Q-1, R-4, S-3
Explanation: The endoplasmic reticulum forms an extensive intracellular membrane network and participates in the synthesis and handling of proteins or lipids, depending on its specialised region. The Golgi apparatus receives cellular products and modifies, sorts and packages them. Lysosomes contain hydrolytic enzymes used in intracellular digestion. A vacuole is a membrane-bound space enclosed by the tonoplast and may store water, sap, ions, excretory products or other materials. The mapping shows how distinct functions are distributed among components of one coordinated system. These organelles are not interchangeable; their inclusion in the same system reflects pathway cooperation rather than identical structure or activity. ER contributes synthesis and membrane continuity, Golgi modifies and packages, lysosomes digest, and vacuoles store or regulate materials.
203. A newly synthesised secretory protein is labelled inside a living cell. The label appears first in rough endoplasmic reticulum, later in Golgi cisternae and finally in vesicles near the plasma membrane. Little label enters mitochondria. The observation most strongly supports:
ⓐ. independent synthesis of the protein by every labelled organelle
ⓑ. movement from mitochondria to ER and then to the nucleus
ⓒ. coordinated transfer through the endomembrane pathway
ⓓ. direct conversion of Golgi cisternae into ribosomes
Correct Answer: coordinated transfer through the endomembrane pathway
Explanation: The labelled protein appears successively in structures that participate in synthesis, processing and export. Rough endoplasmic reticulum is associated with production of proteins destined for secretion. The Golgi apparatus receives such material, modifies and packages it, after which vesicles can carry the product toward the plasma membrane. The low mitochondrial labelling is consistent with mitochondria not belonging to this coordinated route. The time-dependent movement of one labelled product is stronger evidence for transfer than a static observation of organelle proximity. It does not imply that each compartment synthesised an unrelated copy. The recorded sequence demonstrates functional continuity across multiple endomembrane components. The decisive evidence concerns how the named components are arranged and coordinated within plasma-membrane transport and organisation. The progressive appearance of label records transport of the same protein through a directional secretory pathway rather than independent synthesis in each compartment.
204. An intracellular membrane network contains interconnected tubules and flattened cisternae. Space P lies inside these membrane elements, while region Q is the surrounding cytoplasm outside them. P and Q are respectively:
ⓐ. nucleoplasm and perinuclear space
ⓑ. Golgi lumen and extracellular fluid
ⓒ. vacuolar sap and mitochondrial matrix
ⓓ. ER lumen and the surrounding cytoplasm
Correct Answer: ER lumen and the surrounding cytoplasm
Explanation: The described network of tubules and cisternae is the endoplasmic reticulum. Its membrane separates two cellular regions. The enclosed internal space is the ER lumen, also called the luminal space, while the cytoplasm outside the ER membrane is the extraluminal region. Both regions occur inside the cell, so extraluminal does not mean extracellular. The terms describe position relative to the ER membrane. The nuclear and mitochondrial compartments have different surrounding structures, and vacuolar sap is enclosed by the tonoplast rather than by an interconnected ER network. The spatial description identifies P as ER lumen and Q as the surrounding cytoplasmic matrix.
205. Starting in the cytoplasm outside an ER cisterna, passing directly across the cisterna and returning to cytoplasm on the opposite side gives the sequence:
ⓐ. Cytoplasm → ER lumen → ER membrane → ER lumen → cytoplasm
ⓑ. Cytoplasm → ER membrane → ER lumen → ER membrane → cytoplasm
ⓒ. Cytoplasm → nuclear envelope → ER lumen → plasma membrane → cytoplasm
ⓓ. Cytoplasm → ER membrane → nucleoplasm → ER membrane → cytoplasm
Correct Answer: Cytoplasm → ER membrane → ER lumen → ER membrane → cytoplasm
Explanation: A cisterna is a flattened membrane-bound element of the endoplasmic reticulum. Beginning outside it, the path first crosses one ER membrane, enters the enclosed luminal space and then crosses the membrane on the opposite side to return to the extraluminal cytoplasm. The lumen is not itself a membrane, and it is not equivalent to nucleoplasm. The route contains two membrane crossings with one luminal interval between them. This spatial reasoning illustrates how ER membranes partition the intracellular environment into distinct regions while remaining embedded within the cytoplasm. The correct order is cytoplasm, membrane, lumen, membrane and cytoplasm. The first and second crossings involve opposite sides of the same cisternal boundary. A path that enters the lumen but does not cross again would end inside the ER rather than return to cytoplasm.
206. Evaluate the following statements about endoplasmic-reticulum organisation.
I. It forms a network of tubules and cisternae.
II. Its membranes enclose a luminal compartment.
III. It separates luminal space from surrounding cytoplasm.
IV. Its lumen is continuous with the extracellular environment through permanent open pores.
ⓐ. I, II and III only
ⓑ. I, III and IV only
ⓒ. I, II and IV only
ⓓ. II, III and IV only
Correct Answer: I, II and III only
Explanation: The endoplasmic reticulum is an internal network formed by membrane-bound tubules and flattened cisternae. Its membrane encloses a luminal space and separates that space from the surrounding extraluminal cytoplasm. This compartmentalisation allows particular cellular products and reactions to be handled within a controlled internal region. Statement IV is not part of ER organisation. The ER lumen is intracellular and is not maintained as a permanently open extension of the extracellular environment. Materials enter, leave or move through cellular pathways in regulated ways rather than through unrestricted external pores. Statements I, II and III together describe the form and compartment-forming role of the ER accurately. The condition stated for cellular organisation excludes a broader interpretation.
207. A chemical selectively ruptures ER membranes while initially leaving the plasma membrane and other organelles intact. The most immediate structural effect should be:
ⓐ. formation of new cristae inside the ER lumen
ⓑ. conversion of ER cisternae into non-membranous ribosomes
ⓒ. increased separation between luminal and extraluminal regions
ⓓ. loss of the boundary separating ER lumen from cytoplasm
Correct Answer: loss of the boundary separating ER lumen from cytoplasm
Explanation: The ER membrane creates the physical separation between its lumen and the surrounding cytoplasm. Rupturing that membrane removes the barrier that maintains the two regions as distinct compartments. Luminal contents may mix with the extraluminal cytoplasm, and reactions that depend on the controlled ER environment can be disturbed. The change does not generate mitochondrial cristae or transform membrane sheets into ribosomes. It also reduces rather than increases compartmental separation. The prediction follows directly from the relation between structure and function: an intact ER membrane establishes intracellular compartments, while membrane rupture eliminates the boundary needed to preserve them. Loss of these internal boundaries allows previously separated ER lumen and cytosol to mix even before other organelles are damaged. Rupture removes the membrane that separates the ER lumen from surrounding cytoplasm, so the immediate structural effect is loss of compartmental distinction.
208. An impermeable fluorescent marker is added to the cytoplasm of cells containing intact ER. The marker remains outside the ER lumen. After detergent disrupts ER membranes, it enters the former luminal region. This experiment supports the conclusion that:
ⓐ. the ER lumen and cytoplasm are freely continuous before detergent treatment
ⓑ. the marker enters the lumen through normal ER transport proteins after detergent treatment
ⓒ. intact ER membranes separate the lumen from the surrounding cytoplasm
ⓓ. the plasma membrane forms the direct boundary of every ER lumen
Correct Answer: intact ER membranes separate the lumen from the surrounding cytoplasm
Explanation: Before detergent treatment, the fluorescent marker remains in the cytoplasm and does not enter the ER lumen. This distribution shows that an intact ER membrane creates a boundary between the lumen and the surrounding cytoplasmic matrix. Detergent disrupts the membrane, after which the marker can occupy the former luminal region because the physical separation has been lost. The observation does not require active transport or chemical conversion of the marker. It is a compartmentalisation experiment in which membrane integrity is the manipulated variable and marker distribution is the readout. The result demonstrates that the ER lumen is an enclosed internal compartment rather than a freely continuous extension of the cytoplasm. The marker therefore reveals compartment continuity without crossing the ER membrane itself. Detergent removes the barrier and exposes the formerly enclosed lumen to the cytoplasmic marker.
209. A membrane network bears ribosomes on the surface facing the cytoplasm and is continuous with the outer membrane of the nuclear envelope. The network is:
ⓐ. rough ER with ribosomes engaged in protein synthesis
ⓑ. smooth endoplasmic reticulum specialised for lipid synthesis
ⓒ. Golgi apparatus receiving material at its trans face
ⓓ. a lysosomal system containing acidic hydrolases
Correct Answer: rough ER with ribosomes engaged in protein synthesis
Explanation: Ribosomes attached to the cytoplasmic surface create the rough appearance that identifies rough endoplasmic reticulum. This ER region is prominent in cells that synthesise and secrete large amounts of protein. Continuity with the outer nuclear membrane provides a second structural clue, linking the nuclear envelope with the ER network. Smooth ER lacks attached ribosomes and is associated mainly with lipid synthesis. Golgi cisternae form a separate polar stack, while lysosomes are digestive vesicles rather than ribosome-bearing networks. Surface ribosomes and continuity with the outer nuclear membrane converge on rough endoplasmic reticulum.
210. Four cellular records are shown below.
| Record | Major activity | Observed ER pattern |
|---|
| P | High secretion of protein | Extensive RER |
| Q | High synthesis of steroidal product | Extensive SER |
| R | Low secretory-protein output | Sparse RER |
| S | High secretion of protein | Sparse RER |
The record least consistent with the stated structure-function relation is:
ⓐ. P
ⓑ. S
ⓒ. Q
ⓓ. R
Correct Answer: S
Explanation: Cells that manufacture and secrete large amounts of protein usually possess extensive rough endoplasmic reticulum because attached ribosomes synthesise proteins entering the endomembrane pathway. Record P fits this relation. Smooth endoplasmic reticulum is associated with lipid synthesis, so extensive SER is compatible with the steroidal product in Q. Sparse RER is also consistent with the low secretory-protein output in R. Record S alone combines high protein secretion with sparse RER and is therefore the least consistent entry. The table must be read by comparing activity with the expected ER specialisation, not by choosing the row with the largest or smallest organelle description in isolation. The discrepancy in S indicates that the amount of rough ER would not normally support the stated high demand for synthesis and export of secretory proteins.
211. Assertion: Rough endoplasmic reticulum appears rough due to ribosomes attached to its cytoplasmic surface.
Reason: Rough endoplasmic reticulum lacks continuity with the outer nuclear membrane.
ⓐ. Both Assertion and Reason are true, and Reason correctly explains the Assertion
ⓑ. Both Assertion and Reason are true, but Reason does not explain the Assertion
ⓒ. Assertion is true, but Reason is false; the Reason cannot explain the Assertion
ⓓ. Assertion is false, but Reason is true; the Reason cannot explain the Assertion
Correct Answer: Assertion is true, but Reason is false; the Reason cannot explain the Assertion
Explanation: Ribosome attachment validates the Assertion by producing the studded appearance of rough ER. Ribosomes attached to the outer, cytoplasmic face of ER membranes create the studded appearance responsible for the term rough endoplasmic reticulum. The biological claim in the Reason is not valid, since RER is commonly continuous with the outer membrane of the nuclear envelope. This continuity helps place the ER within a wider internal membrane network but is not the immediate cause of roughness. Roughness depends on ribosome association. Ribosome attachment explains surface appearance, while nuclear-envelope continuity describes a separate spatial relation within the internal membrane system. Ribosome attachment explains roughness, whereas nuclear-envelope continuity is a separate spatial relation.
212. Ribosomes are experimentally detached from rough ER without immediately destroying the ER membrane or its lumen. The earliest expected result is:
ⓐ. formation of a rigid wall around every ER cisterna
ⓑ. immediate conversion of the ER lumen into nucleoplasm
ⓒ. increased roughness with enhanced secretory-protein synthesis
ⓓ. reduced roughness and impaired ER-targeted protein synthesis
Correct Answer: reduced roughness and impaired ER-targeted protein synthesis
Explanation: Attached ribosomes give RER its characteristic rough surface and synthesise many proteins entering the endomembrane pathway. Their selective detachment removes the visible particles responsible for roughness and reduces production of proteins normally made on RER-associated ribosomes. The ER membrane and lumen are stated to remain initially intact, so compartment formation need not disappear at once. Detachment does not create a cell wall or transform luminal space into nucleoplasm. The treatment isolates the contribution of ribosomes from the contribution of the ER membrane itself. Surface appearance and protein-synthetic capacity decline, while the basic membrane-bounded compartment may temporarily persist. Detachment removes the ribosome-studded character of rough ER and immediately reduces translation of proteins normally directed into its lumen. The earliest effect is therefore selective loss of rough-surface translation, not immediate disappearance of the ER lumen or membrane.
213. Match each structure in Column I with the most appropriate relation in Column II. A Column II entry is used once.
| Column I | Column II |
|---|
| P. RER | 1. Major site of lipid synthesis |
| Q. SER | 2. Ribosome-bearing region associated with protein secretion |
| R. Outer nuclear membrane | 3. May be continuous with rough ER |
| S. ER lumen | 4. Compartment enclosed by ER membrane |
ⓐ. P-1, Q-2, R-4, S-3
ⓑ. P-2, Q-1, R-3, S-4
ⓒ. P-3, Q-4, R-1, S-2
ⓓ. P-4, Q-3, R-2, S-1
Correct Answer: P-2, Q-1, R-3, S-4
Explanation: Rough ER carries ribosomes and is extensive in many cells involved in protein synthesis and secretion. Smooth ER lacks attached ribosomes and serves as a major site of lipid synthesis. The outer nuclear membrane may be continuous with rough ER, linking the nuclear envelope to the internal membrane network. The ER lumen is the enclosed compartment separated from the surrounding cytoplasm by the ER membrane. The mapping combines surface specialisation, synthetic role, membrane continuity and compartment identity. RER and SER belong to one connected organelle system, but differences in ribosome association give them distinct functional emphases. The mapping follows membrane continuity, ribosome attachment, lipid synthesis and nuclear-envelope relation. These four relations produce one coherent map without assigning a lipid-synthetic role to rough ER or a secretory role to smooth ER.
214. An animal endocrine cell produces a large quantity of a lipid-like steroidal hormone but secretes relatively little protein. Its cytoplasm is expected to contain:
ⓐ. abundant smooth ER and relatively little rough ER
ⓑ. abundant rough ER with no smooth membrane tubules
ⓒ. numerous lysosomes replacing the entire ER network
ⓓ. extensive Golgi stacks performing the initial lipid synthesis
Correct Answer: abundant smooth ER and relatively little rough ER
Explanation: Smooth endoplasmic reticulum is a major site of lipid synthesis and is especially developed in animal cells that produce lipid-like steroidal hormones. The low secretory-protein output reduces the expectation of an exceptionally extensive ribosome-bearing RER system. This does not mean RER or Golgi apparatus must be completely absent; cells retain multiple organelles for general maintenance. The dominant structural prediction follows from the specialised product described in the case. Initial lipid and steroid-related synthesis is associated with smooth ER rather than lysosomal digestion or Golgi cisternae. An abundance of smooth tubules matches the cell's principal synthetic demand.
215. Regions P and Q of one ER network produce the following records.
| Feature | Region P | Region Q |
|---|
| Surface ribosomes | Abundant | Absent |
| Secretory-protein synthesis | High | Low |
| Lipid synthesis | Lower | High |
The correct interpretation is:
ⓐ. P is Golgi apparatus, while Q is a lysosome
ⓑ. P is SER, while Q is RER
ⓒ. P and Q are two identical RER regions
ⓓ. P is RER, while Q is SER
Correct Answer: P is RER, while Q is SER
Explanation: Region P bears abundant ribosomes and shows high secretory-protein synthesis, identifying it as rough endoplasmic reticulum. Region Q lacks surface ribosomes and shows greater lipid synthesis, matching smooth endoplasmic reticulum. Both regions may remain continuous parts of one ER network even though their surface appearance and principal synthetic activities differ. The table does not support classification of either region as a separate Golgi or lysosomal compartment. Interpreting all three rows together is important: ribosome association explains roughness and protein production, while its absence accompanies the smooth appearance and lipid-synthetic role of SER. Ribosome-rich P supports protein synthesis, whereas ribosome-free Q supports lipid synthesis. The contrast follows directly from ribosome attachment: it shifts the same continuous ER network toward protein handling rather than lipid production. Ribosome-bearing cisternae with protein synthesis identify P as RER, whereas ribosome-free tubules associated with lipid synthesis identify Q as SER.
216. In a micrograph, a Golgi cisterna measuring \(4\,\text{mm}\) represents an actual diameter of \(0.5\,\mu\text{m}\). Under the same magnification, another cisterna measures \(8\,\text{mm}\). Its actual diameter and relation to the stated Golgi range are:
ⓐ. \(0.25\,\mu\text{m}\), below the stated range
ⓑ. \(0.50\,\mu\text{m}\), at the lower limit
ⓒ. \(1.00\,\mu\text{m}\), at the upper limit
ⓓ. \(1.50\,\mu\text{m}\), above the stated range
Correct Answer: \(1.00\,\mu\text{m}\), at the upper limit
Explanation: The second image measurement is twice the first: \[ \frac{8\,\text{mm}}{4\,\text{mm}}=2 \] The actual diameter must increase by the same factor: \[ 0.5\,\mu\text{m} \times 2=1.0\,\mu\text{m} \] Golgi cisternae are described as approximately \(0.5\text{–}1.0\,\mu\text{m}\) in diameter. The calculated value lies at the upper limit of that interval rather than outside it. The calculation preserves the common magnification and ends with a structural interpretation. It does not claim that every cisterna has the same diameter; it places the measured example within the representative range supplied for Golgi cisternae. Direct doubling is justified only because both cisternae were recorded at the same magnification. The doubled image diameter gives a doubled actual diameter. The scale relation remains proportional at the same magnification.
217. Arrange the following positions in the direction followed by material approaching and passing through a Golgi stack.
P. ER-derived transport vesicle
Q. Convex cis face
R. Central Golgi cisternae
S. Concave trans face
ⓐ. P → Q → R → S
ⓑ. Q → P → S → R
ⓒ. P → S → R → Q
ⓓ. R → Q → P → S
Correct Answer: P → Q → R → S
Explanation: Material leaving the endoplasmic reticulum is carried in vesicles that approach the receiving side of the Golgi apparatus. This side is the convex cis face, also called the forming face. Material then progresses through the interconnected cisternae toward the concave trans face, which functions as the maturing or releasing side. The sequence begins with the ER-derived vesicle and ends at the trans face. Reversing the cis and trans positions would reverse the normal polarity of Golgi transport. The order links vesicle origin, face geometry and movement through the stack into one directional pathway. Newly received material enters the cis face, passes through Golgi cisternae and leaves from the trans face in transport vesicles. Golgi polarity fixes the route, since the cis surface receives ER-derived material and the trans surface dispatches processed products.
218. A stack of flattened cisternae lies near the nucleus. Surface P is convex and receives vesicles arriving from the ER, while surface Q is concave and releases processed material. P and Q are:
ⓐ. trans face and cis face, respectively
ⓑ. cis face and trans face, respectively
ⓒ. RER surface and SER surface, respectively
ⓓ. outer and inner nuclear membranes, respectively
Correct Answer: cis face and trans face, respectively
Explanation: The Golgi apparatus has a distinct structural polarity. Its convex cis face is the forming or receiving side and commonly faces incoming ER-derived material. The concave trans face is the maturing or releasing side from which processed products leave in vesicles. The two faces differ structurally and functionally but remain interconnected through the Golgi stack. The description of flattened cisternae near the nucleus also supports Golgi identification rather than an ER or nuclear-envelope structure. P is the cis face, while Q is the trans face. Their geometry provides a reliable guide to the direction in which material enters and exits the organelle.
219. Consider the following statements about the Golgi apparatus.
I. It commonly occurs near the nucleus.
II. It consists of parallel stacks of flattened cisternae.
III. Its cis face is convex and receiving, while its trans face is concave and releasing.
IV. Its two faces are structurally identical and completely disconnected.
ⓐ. I, III and IV only
ⓑ. I, II and IV only
ⓒ. II, III and IV only
ⓓ. I, II and III only
Correct Answer: I, II and III only
Explanation: The Golgi apparatus commonly occupies a position near the nucleus and is composed of stacks of flattened membrane-bound cisternae. Its polarity is reflected in two distinguishable faces. The convex cis face receives material, particularly vesicles arriving from the ER, while the concave trans face releases processed and packaged products. Although the faces differ in form and role, they belong to one interconnected organelle. Statement IV incorrectly removes both their structural distinction and their continuity. Statements I, II and III together describe location, cisternal architecture and directional polarity. A complete Golgi polarity and transport mapping requires every pair to satisfy its own biological relation. These features allow the Golgi to receive, process and dispatch cellular material in an organised sequence.
220. Labelled ER-derived vesicles are followed near a Golgi stack. They first fuse with convex face P. Hours later, labelled products leave from concave face Q. When fusion at P is blocked, vesicles accumulate outside P and output from Q declines. The experiment identifies:
ⓐ. P is the trans receiving face; Q is the cis releasing face
ⓑ. P and Q are non-polar receiving and releasing surfaces
ⓒ. P is the cis receiving face; Q is the trans releasing face
ⓓ. P is an ER receiving region; Q is an ER releasing region
Correct Answer: P is the cis receiving face; Q is the trans releasing face
Explanation: The time-course observation establishes direction rather than relying only on organelle shape. Incoming ER-derived vesicles first interact with P, so P functions as the receiving face. Its convex geometry further identifies it as the cis face. Products later leave from the concave surface Q, placing Q at the trans or releasing side. Blocking fusion at P causes incoming vesicles to accumulate and reduces later output from Q, showing that entry at the cis face is required for normal passage through the stack. The treatment, accumulation site and downstream reduction collectively demonstrate Golgi polarity from cis toward trans. The decisive evidence concerns how the named components are arranged and coordinated within Golgi polarity and transport. The accumulation outside P identifies it as the receiving side, while reduced departure from Q reveals the downstream effect of blocking entry.
