201. An opaque cap is placed over the tip of one coleoptile, while an opaque sleeve covers only the lower part of another coleoptile. Both are exposed to unilateral light. What is the most likely result?
ⓐ. Both bend normally since the tip has no role in the response
ⓑ. The tip-capped coleoptile remains straight, while the lower-covered one bends
ⓒ. The tip-capped coleoptile bends, while the lower-covered coleoptile remains straight
ⓓ. Both remain straight since every region must receive directional light
Correct Answer: The tip-capped coleoptile remains straight, while the lower-covered one bends
Explanation: Covering the tip prevents the essential apical region from receiving unilateral light, so the normal directional response is lost. Covering only the lower region leaves the tip exposed and able to detect or generate the controlling influence. That influence can then move to the lower growth region, allowing curvature even though the lower cells do not receive direct directional illumination. The prediction depends on the difference between the site involved in stimulus perception and the site where differential growth becomes visible. Such a result does not imply that the lower region is unimportant; those cells execute the bending response. The treatments demonstrate that direct illumination of the elongating region is not sufficient to replace the function of an exposed tip. Historical discovery experiments linked a reproducible biological response to a transferable substance before its chemical identity was fully known.
202. Assertion: Covering the coleoptile tip can prevent normal bending towards unilateral light even when the lower growth region remains uncovered.
Reason: The tip is involved in perceiving or supplying a transmittable influence that regulates growth in the region below.
ⓐ. Both are true, and the Reason correctly explains the Assertion
ⓑ. Both are true, but the Reason does not explain the Assertion
ⓒ. Only the Assertion is true; the Reason is a false statement
ⓓ. Only the Reason is true; the Assertion is a false statement
Correct Answer: Both are true, and the Reason correctly explains the Assertion
Explanation: The assertion is true: preventing the tip from receiving the directional light stimulus interferes with normal phototropic curvature. Biologically, the reason is likewise true and provides the required explanation. Experiments with intact, decapitated and selectively covered coleoptiles indicate that the tip has a regulatory role, while the lower region produces much of the curvature through differential growth. If the tip cannot perceive the stimulus or supply the influence, the uncovered lower cells do not independently recreate the normal response. That reason directly connects the apical role with the loss of bending described in the assertion. This evidence established the existence of a transmitted growth influence before its later association with auxin.
203. Which sequence correctly orders the following events in the historical and evidential sequence leading to auxin identification:
P. A chemical growth regulator was isolated from oat coleoptile tips.
Q. Canary-grass coleoptiles were observed bending towards unilateral light.
R. Experiments supported transmission of an influence from the tip to lower regions.
S. The isolated substance was connected with the previously inferred growth influence.
ⓐ. R → Q → P → S
ⓑ. Q → P → R → S
ⓒ. P → Q → S → R
ⓓ. Q → R → P → S
Correct Answer: Q → R → P → S
Explanation: The sequence begins with the Darwin observations of coleoptiles bending towards unilateral light. Follow-up treatments involving the tip established that the response depended on an influence transmitted from the apical region to lower growth tissues. This functional evidence preceded chemical isolation. F.W. Went later isolated auxin from oat-seedling coleoptile tips, providing a chemical connection to the influence inferred from the earlier physiological experiments. The final step is the interpretation that the isolated regulator accounted for the growth-control phenomenon. Observation precedes transfer testing, chemical isolation and finally regulator classification, fixing Q → R → P → S. The order Q → R → P → S preserves the distinction between observing a response, locating a regulatory source, isolating a substance and connecting that substance with the original biological effect. Experimental localisation and transmission evidence must precede chemical isolation and naming, so the history follows increasing strength of identification.
204. A researcher repeats early coleoptile studies and obtains two findings: removal of the tip prevents normal light-directed bending, and an extract prepared from oat coleoptile tips contains a substance that influences growth. Together, these findings most strongly support:
ⓐ. the lower coleoptile has no role in curvature
ⓑ. the tip causes bending only through direct mechanical pressure
ⓒ. a chemical signal from the tip regulates growth below
ⓓ. the tip perceives light, but no chemical influence reaches the lower region
Correct Answer: a chemical signal from the tip regulates growth below
Explanation: The first finding assigns an essential regulatory role to the tip but does not identify the nature of the influence. The second finding supplies chemical evidence by showing that material isolated from oat coleoptile tips can affect growth. When the two results are interpreted together, the most defensible conclusion is that the transmitted influence has a chemical basis associated with auxin. The lower coleoptile remains necessary as the region where unequal growth produces curvature, so it cannot be dismissed as inactive. Mechanical pressure and xylem differentiation do not account for the transfer of growth-regulating activity from tip material. The combined evidence links functional localisation with chemical isolation, moving the explanation beyond observation of bending alone.
205. Four statements describe stages in the auxin discovery pathway.
| Statement | Description |
|---|
| P | Canary-grass coleoptiles bend towards unilateral light |
| Q | The tip is shown to control a response occurring in lower regions |
| R | Auxin is isolated from oat coleoptile tips |
| S | The first bending observation is itself treated as complete chemical identification |
Which evaluation is valid?
ⓐ. P–Q–R is valid, whereas S confuses observation with identification
ⓑ. P and S alone form the complete sequence from observation to isolation
ⓒ. Q shows that the lower region perceives light independently of the tip
ⓓ. R occurred before evidence that a transmittable influence came from the tip
Correct Answer: P–Q–R is valid, whereas S confuses observation with identification
Explanation: Statement P records the initial physiological response. Statement Q adds experimental localisation by showing that the tip controls bending occurring in tissues below. Statement R represents the later chemical stage in which F.W. Went isolated auxin from oat coleoptile tips. These three statements form a coherent progression from observation through functional inference to chemical isolation. Statement S collapses these stages and incorrectly treats visible bending as proof of the regulator's chemical identity. A response can reveal that a controlling influence exists without naming or isolating the molecule responsible. The distinction prevents attribution of Went's isolation to the earlier Darwin experiments and preserves the different kinds of evidence contributed by each stage. The final statement exceeds the evidence because an early bending observation cannot by itself identify the active chemical as auxin.
206. Rice seedlings infected by Gibberella fujikuroi become unusually tall and slender rather than merely showing local tissue damage. This foolish-seedling or bakanae condition first suggested the presence of:
ⓐ. an inhibitory factor that reduces internode elongation
ⓑ. a volatile signal that accelerates fruit ripening
ⓒ. a stress regulator that closes stomata
ⓓ. a fungal factor promoting abnormal shoot elongation
Correct Answer: a fungal factor promoting abnormal shoot elongation
Explanation: The defining observation in bakanae disease is excessive elongation of rice seedlings. The symptom suggested that the fungus affected the plant through an elongation-promoting influence rather than through simple destruction of the infected tissue. At this stage, the biological evidence indicated an active promotory factor but did not yet establish whether living fungal invasion was continuously required or whether a diffusible chemical could act independently. Later sterile-filtrate experiments addressed that distinction. The response is unrelated to stomatal closure or a fruit-ripening volatile, and it is the opposite of permanent elongation inhibition. The unusual phenotype provided the observation from which the gibberellin discovery pathway developed. The abnormal elongation is systemic and reproducible, so the useful inference is a growth-promoting influence associated with the fungus. At this stage, the observation does not yet identify the active molecule; later sterile-filtrate evidence is needed to demonstrate a diffusible factor.
207. Rice seedlings receive the following treatments in \(1926\).
| Treatment | Material applied | Response |
|---|
| P | Sterile nutrient medium | Normal growth |
| Q | Living Gibberella fujikuroi | Abnormal elongation |
| R | Sterile filtrate from a fungal culture | Abnormal elongation |
What is the strongest conclusion?
ⓐ. Living fungal cells must remain in contact with the seedling
ⓑ. The fungus releases a diffusible substance that promotes elongation
ⓒ. The filtrate promotes elongation by supplying additional mineral nutrients
ⓓ. Reduced mineral absorption triggers compensatory shoot elongation
Correct Answer: The fungus releases a diffusible substance that promotes elongation
Explanation: Treatment P supplies the control and shows that the sterile nutrient medium alone does not cause excessive elongation. Living fungus produces the expected symptom in Q. The decisive treatment is R: the sterile fungal filtrate reproduces abnormal elongation even though living fungal cells have been removed. This observation rules out the claim that active invasion is required at the moment the response develops. It supports the presence of a soluble or diffusible substance released into the culture medium by the fungus. The experimental comparison does not yet identify the active molecule chemically, but it narrows the mechanism from infection alone to a transferable chemical influence. That evidence became central to the later recognition of gibberellins. The sterile filtrate reproduces the diseased elongation without living fungal cells, separating a diffusible product from infection as the immediate cause.
208. Assertion: Sterile filtrate from a culture of Gibberella fujikuroi can reproduce bakanae-like elongation in rice seedlings.
Reason: The elongation-promoting effect depends exclusively on living fungal cells remaining inside the treated seedlings.
ⓐ. Both are true, and the Reason correctly explains the Assertion
ⓑ. Both are true, but the Reason does not explain the Assertion
ⓒ. Only the Assertion is true; the Reason is a false statement
ⓓ. Only the Reason is true; the Assertion is a false statement
Correct Answer: Only the Assertion is true; the Reason is a false statement
Explanation: The assertion is supported by Kurosawa's sterile-filtrate evidence. Rice seedlings developed abnormal elongation after receiving filtered fungal culture material from which living fungal cells had been excluded. The stated reason is false, since the response occurring with sterile filtrate demonstrates that living fungal invasion is not exclusively required. A diffusible elongation-promoting substance present in the filtrate can act on the plant. This conclusion still stops short of claiming that every component of the filtrate was known or that the active compound had already been fully identified. Sterile-filtrate evidence supports the assertion while directly opposing the claim made in the reason. The experiment separates the presence of a transferable chemical influence from the presence of the organism that produced it.
209. Arrange the events in the discovery pathway of gibberellins.
P. Sterile fungal filtrate reproduces abnormal elongation in rice seedlings.
Q. Foolish-seedling disease is associated with unusually elongated rice plants.
R. The active elongation-promoting substances are later recognised as gibberellins.
S. A diffusible chemical influence is inferred from the filtrate response.
ⓐ. Q → P → S → R
ⓑ. P → Q → R → S
ⓒ. Q → S → P → R
ⓓ. R → Q → P → S
Correct Answer: Q → P → S → R
Explanation: The sequence starts with the disease phenotype: rice seedlings affected by bakanae show abnormal elongation. Kurosawa then demonstrated that a sterile fungal filtrate could reproduce the symptom, providing an experiment that separated the active influence from living fungal invasion. From this result, a diffusible elongation-promoting substance was inferred. Chemical work later led to recognition of the active substances as gibberellins. The order Q → P → S → R follows the progression from field or disease observation to controlled evidence, functional inference and regulator identification. Abnormal elongation is observed first, reproduction by sterile filtrate follows, a diffusible influence is inferred and the active substances are later recognised as gibberellins, fixing Q → P → S → R. Reversing the order would confuse the later chemical name with the earlier observations that made its discovery possible. The sterile-filtrate result establishes transferability before later isolation and recognition of the gibberellin group.
210. Match each component of the bakanae investigation with its scientific role. A Column II entry is used once.
| Column I | Column II |
|---|
| P. Untreated or sterile-medium seedlings | 1. Demonstrate that the fungus can produce the disease phenotype |
| Q. Seedlings exposed to living fungus | 2. Provide the normal-growth comparison |
| R. Seedlings exposed to sterile fungal filtrate | 3. Support the existence of a transferable chemical influence |
| S. Later chemical investigation | 4. Connect the active substances with gibberellins |
ⓐ. P-1, Q-2, R-4, S-3
ⓑ. P-2, Q-1, R-3, S-4
ⓒ. P-3, Q-4, R-2, S-1
ⓓ. P-4, Q-3, R-1, S-2
Correct Answer: P-2, Q-1, R-3, S-4
Explanation: Untreated seedlings or those receiving sterile medium establish normal growth and supply the comparison needed to recognise abnormal elongation. Seedlings exposed to living fungus demonstrate that Gibberella fujikuroi is associated with the bakanae phenotype. Sterile filtrate is the critical treatment showing that the active influence can persist without living fungal cells, so it supports a transferable chemical substance. Later investigation identifies the active elongation-promoting substances as gibberellins. The mapping distinguishes control, disease reproduction, mechanistic inference and chemical identification. The discovery sequence and evidence types together fix P-2, Q-1, R-3 and S-4. Each stage contributes a different level of evidence, and no single stage alone supplies the entire discovery pathway. The mapping distinguishes an untreated reference, a source of the active influence, evidence that the influence is transferable, and the responsive plant tissue in which elongation is measured.
211. Tobacco internodal callus is grown in four media.
| Medium | Contents | Callus response |
|---|
| P | Basic nutrients without auxin or biological supplement | Very little proliferation |
| Q | Basic nutrients plus auxin | Limited proliferation |
| R | Basic nutrients plus auxin and coconut milk | Strong proliferation |
| S | Basic nutrients plus coconut milk without auxin | Weak response |
Which conclusion best fits the complete pattern?
ⓐ. Auxin alone accounts for the strongest cytokinesis and callus proliferation
ⓑ. Coconut milk acts by removing auxin from the culture medium
ⓒ. Basic nutrients alone support rapid and sustained callus proliferation
ⓓ. Auxin and an additional factor together promote strong callus proliferation
Correct Answer: Auxin and an additional factor together promote strong callus proliferation
Explanation: Medium P shows that basic nutrients alone do not sustain strong proliferation. Medium Q contains auxin but still produces only a limited response, so auxin is not sufficient under these conditions. Medium S supplies coconut milk without auxin and also gives a weak response. Strong proliferation appears in R only when auxin and the biological supplement are present together. The table supports a requirement for an additional cytokinesis-promoting influence acting with auxin. Such a result does not identify coconut milk as the only possible source, since vascular extracts, yeast extract and DNA-related supplements also contributed to the historical investigation. Only the auxin-plus-supplement medium produces strong proliferation, revealing the need for an additional cytokinesis-promoting factor. The experiment established a functional need before the active cytokinin-related substance was crystallised and named. The factorial pattern shows that neither auxin alone nor supplement alone gives the full response; strong proliferation requires their combined presence.
212. Tobacco callus grows poorly in an auxin-containing medium. Addition of several different biological extracts separately restores strong proliferation. What is the most justified next experimental objective?
ⓐ. Increase auxin concentration until the callus divides without extracts
ⓑ. Test the extracts on mature xylem to seek the same division response
ⓒ. Isolate and identify the shared factor that promotes callus cell division
ⓓ. Assume that each effective extract contains the same active molecule
Correct Answer: Isolate and identify the shared factor that promotes callus cell division
Explanation: Auxin is already present in the medium, yet the tobacco callus proliferates poorly until a biological extract is added. Several different extracts restore strong proliferation. Together, these observations suggest that the original medium lacks an additional cell-division-promoting activity. A useful next experiment is to separate an effective extract into components, test which component retains that activity and identify the active factor. The response to several extracts does not prove that every extract contains exactly the same molecule; that question requires further isolation and identification. It also does not show that auxin must be removed from the medium. The evidence provides a reason to search for an additional active substance, connecting the callus response with the investigation that led to cytokinin discovery.
213. A tobacco callus receives auxin throughout an experiment. During Stage P it receives no additional supplement and grows weakly. During Stage Q it receives a DNA-derived supplement and begins proliferating strongly. Removal of that supplement reduces proliferation again. The evidence indicates that:
ⓐ. auxin is unnecessary once callus tissue has formed
ⓑ. a supplement factor acts with auxin to promote cytokinesis
ⓒ. the callus was fully differentiated and incapable of cell division
ⓓ. the supplement promotes only irreversible cell swelling
Correct Answer: a supplement factor acts with auxin to promote cytokinesis
Explanation: Auxin remains present during all stages, so the change in proliferation is linked with addition and removal of the supplement. Weak growth with auxin alone shows that auxin does not provide the complete requirement for strong callus division under the tested conditions. The increased proliferation during Stage Q indicates that the supplement supplies a second activity that acts in the auxin-containing system. The response concerns production of additional cells rather than simple hydration, since callus proliferation is the measured outcome. A callus capable of renewed proliferation is also not a mass of permanently non-dividing mature cells. The case supports cooperative action between auxin and a cytokinesis-promoting factor without requiring identification of every component in the supplement. Experimental evidence should separate production of a signal from responsiveness of the target tissue to that signal.
214. Arrange the events leading from Skoog's callus observations to the naming of kinetin.
P. A cytokinesis-promoting active substance is crystallised.
Q. Tobacco callus proliferates strongly when auxin-containing medium receives certain supplements.
R. The active substance is named kinetin.
S. The supplement is inferred to contain an additional cell-division-promoting factor.
ⓐ. S → Q → P → R
ⓑ. Q → P → S → R
ⓒ. P → R → Q → S
ⓓ. Q → S → P → R
Correct Answer: Q → S → P → R
Explanation: The pathway begins with the biological observation that tobacco callus proliferates strongly only when the auxin-containing medium receives particular supplements. From this contrast, investigators infer that those materials contain an additional factor promoting cytokinesis. The next step is chemical separation and crystallisation of an active substance. Miller and colleagues accomplished this in \(1955\), after which the compound was named kinetin. The order Q → S → P → R preserves the transition from tissue response to functional inference, isolation and naming. The sequence moves from the callus response to inference of an additional factor, then to crystallisation of the active substance and its naming as kinetin. Placing crystallisation first would remove the experimental reason for searching for the active substance, while naming must follow recognition of a distinct compound. Strong callus proliferation first indicates an additional factor; crystallisation and naming can occur only after that activity has been isolated.
215. Review the following statements about the kinetin discovery.
I. The investigation was linked with cytokinesis in tobacco callus.
II. Auxin-containing medium alone gave the full strong proliferation response in the critical observation.
III. Miller and colleagues crystallised an active substance in \(1955\).
IV. The crystallised cytokinesis-promoting substance was named kinetin.
ⓐ. I, III and IV only
ⓑ. I and II only
ⓒ. II, III and IV only
ⓓ. I, II, III and IV
Correct Answer: I, III and IV only
Explanation: Tobacco-callus proliferation supplied the biological system in which an additional cytokinesis-promoting activity was recognised. Auxin was present, but strong proliferation required a supplementary factor, so statement II is not valid. Miller and colleagues later crystallised an active substance in \(1955\) and named it kinetin, making statements III and IV accurate. The progression distinguishes the earlier functional requirement observed in callus from later chemical isolation. Kinetin was not inferred merely from auxin's known growth effects; it was associated with an additional activity promoting cell division. I, III and IV preserve the callus context, 1955 isolation and naming of kinetin; II overstates auxin alone. Statements I, III and IV together describe the biological context, isolation milestone and naming of the substance.
216. Three independently isolated substances are compared during the mid-\(1960\text{s}\).
| Substance | Initial name | Chemical comparison |
|---|
| P | Inhibitor-B | Same structure as Q and R |
| Q | Abscission II | Same structure as P and R |
| R | Dormin | Same structure as P and Q |
Which naming decision is most scientifically justified?
ⓐ. Retain three hormone names since the substances were found independently
ⓑ. Classify only dormin as a regulator and discard the other findings
ⓒ. Recognise one chemical regulator and adopt the common name abscisic acid
ⓓ. Combine the three substances physically to create a new fourth hormone
Correct Answer: Recognise one chemical regulator and adopt the common name abscisic acid
Explanation: Independent discovery and different initial names do not establish different chemical identities. The critical evidence is the structural comparison showing that inhibitor-B, abscission II and dormin are chemically identical. Once this equivalence is established, treating them as three separate final regulators would duplicate one substance under different historical labels. A common name resolves the convergence of the independent studies, and the unified regulator was named abscisic acid. No physical mixing is needed to create the identity; the substances were already the same molecule. Equivalent chemistry across the three isolates justified recognising one regulator and adopting the common name abscisic acid. The table illustrates how chemical analysis can reconcile separate physiological investigations that initially emphasised inhibition, abscission or dormancy. Once chemical comparison establishes identity, three historical names no longer represent three different regulators and can be unified under abscisic acid.
217. Investigators isolate inhibitor-B from one plant system, abscission II from another and dormin from a third. Each produces an inhibitory developmental response. Chemical analysis later shows that all three samples are identical. What is the strongest inference?
ⓐ. Use the shared inhibitory response as sufficient evidence of chemical identity
ⓑ. Retain three hormone identities because the samples came from different systems
ⓒ. Classify the samples as related inhibitors without unifying their identitiesExplanation: The grower's goal is to keep mature fruits marketable on the plant for several more days. Gibberellins can delay senescence in certain fruits, slowing ageing-related changes and extending the period for which fruits may be left on the plant. That effect matches the stated goal more directly than an effect on stalk length or the initiation of fruit development. Delayed senescence does not turn a mature fruit back into a young ovary, and it should not be described as an automatic guarantee for every crop or treatment condition. The relevant reasoning is the direction of the developmental change: slower fruit ageing can lengthen the useful market period, whereas accelerated ageing or abscission would shorten it.
ⓓ. Independent studies converged on the same regulator, later called abscisic acid
Correct Answer: Independent studies converged on the same regulator, later called abscisic acid
Explanation: Inhibitor-B, abscission II and dormin were initially studied in different plant systems and given different names. Their inhibitory effects made comparison worthwhile, but similar biological effects alone could not prove that the samples were the same chemical substance. The question supplies the stronger evidence: later chemical analysis shows that all three samples are identical. That finding permits the separate names to be unified under abscisic acid. Their different original sources describe how the discoveries were made; they do not establish three different final hormone identities. This distinction between a physiological response and chemical identity is central to the inference. The independent investigations converged on one regulator only after the chemical evidence resolved the apparent difference between the samples.
218. Evaluate the following statements about the discovery of abscisic acid.
I. Inhibitor-B, abscission II and dormin were initially obtained in separate investigations.
II. Their chemical identity was established during studies associated with the mid-\(1960\text{s}\).
III. The three names were retained as three principal modern PGR groups.
IV. Their recognised identity led to the common name abscisic acid.
ⓐ. I and III only
ⓑ. I, II and IV only
ⓒ. II and III only
ⓓ. I, II, III and IV
Correct Answer: I, II and IV only
Explanation: The three substances entered the literature through independent investigations and initially received names related to the responses being studied. Chemical comparison during the mid-\(1960\text{s}\) established that inhibitor-B, abscission II and dormin were not three distinct final regulators. They were chemically identical and were unified under the name abscisic acid. Biologically, statements I, II and IV follow this discovery history. Statement III is incorrect since the modern grouping does not preserve them as separate principal PGR classes. The case highlights the difference between an initial descriptive name and a later chemically supported identity. Together, I, II and IV follow the discovery history; III incorrectly preserves three modern regulator groups. Independent isolation can produce multiple labels for one compound until comparative analysis resolves the relationship.
219. In \(1910\), unripe bananas are stored under four conditions.
| Chamber | Storage condition | Ripening response |
|---|
| P | Bananas alone with fresh airflow | Slow |
| Q | Bananas with ripe oranges in a shared closed space | Rapid |
| R | Bananas separated from oranges by an airtight barrier | Slow |
| S | Bananas exposed to air previously surrounding ripe oranges | Accelerated |
Which conclusion is best supported?
ⓐ. Direct contact with orange tissues is required for banana ripening
ⓑ. Ripe oranges remove an inhibitory mineral from the bananas
ⓒ. A volatile substance from ripe oranges accelerates banana ripening
ⓓ. Banana ripening occurs only when light is excluded
Correct Answer: A volatile substance from ripe oranges accelerates banana ripening
Explanation: Chamber Q shows accelerated ripening when ripe oranges and unripe bananas share the same enclosed atmosphere. Chamber R removes atmospheric exchange while retaining the presence of oranges nearby, and the response remains slow, arguing against distance alone or an unrelated storage effect. Chamber S is especially informative: air previously surrounding ripe oranges accelerates ripening without direct fruit contact. The combined evidence points to a transferable volatile substance released by ripe oranges. The experimental comparison does not initially establish its chemical identity, but later work connected the volatile signal with ethylene. Only the chamber sharing air with ripe oranges shows the accelerated response, linking the effect to a volatile substance rather than direct contact. The chamber comparisons distinguish airborne action from direct tissue contact, mineral transfer or a simple effect of darkness.
220. Use the storage arrangement described below. Chamber P contains ripe oranges connected by an open air passage to Chamber Q, which contains unripe bananas. Chamber R contains identical bananas but has no air connection with the oranges. Q ripens faster than R. Which modification would most directly test whether an airborne factor causes the difference?
ⓐ. Close only the P–Q air passage, keeping other conditions constant
ⓑ. Close the passage and simultaneously lower the temperature in Q
ⓒ. Keep the passage open but increase mineral supply to the bananas
ⓓ. Move Q closer to P without controlling the connecting airflow
Correct Answer: Close only the P–Q air passage, keeping other conditions constant
Explanation: The current arrangement associates faster ripening with air exchange from the chamber containing ripe oranges. Closing that passage changes the proposed route of transfer while preserving the fruit types and other storage conditions. If Q then loses its accelerated response, the result would support an airborne or volatile influence. Changing temperature would introduce a second major variable, while altering mineral content or removing peels would not directly test transfer through the connecting atmosphere. The design targets the decisive condition identified by Cousins's observation: a substance emitted by ripe oranges could move through air and affect stored unripe bananas. Later identification of that volatile as ethylene adds chemical identity to the earlier chamber-based inference. Closing the air passage specifically removes transfer of the volatile signal while leaving the fruit groups and their own conditions otherwise comparable.
