301. Seed-viability records are summarised below.
| Record | Reported viable-seed age |
|---|
| P. Lupinus arcticus | about \(10{,}000\,\text{years}\) |
| Q. Phoenix dactylifera | about \(2{,}000\,\text{years}\) |
| R. A recently harvested crop sample | less than \(1\,\text{year}\) |
Which conclusion is justified by these records alone?
ⓐ. All seeds possess a minimum natural lifespan of \(2{,}000\,\text{years}\)
ⓑ. Seed age alone proves that metabolic activity remained high throughout storage
ⓒ. Every recently harvested crop seed will eventually remain viable for \(10{,}000\,\text{years}\)
ⓓ. Exceptional longevity can occur, but these records do not define a universal seed lifespan
Correct Answer: Exceptional longevity can occur, but these records do not define a universal seed lifespan
Explanation: The table contains examples with very different reported ages, including two exceptionally old viable-seed records. The strongest defensible inference is limited: certain seeds under particular circumstances can retain viability for remarkably long periods. The data do not establish a minimum lifespan shared by all species, nor do they show that recently harvested seeds will eventually match the oldest record. Viability also does not require continuous high metabolic activity; mature seeds commonly exist in a low-metabolism state. The correct interpretation respects the difference between an exceptional observation and a biological universal. Longevity records demonstrate what can occur, not what must occur in every species or under every storage environment. Where several mechanisms coexist, the strongest conclusion is the one supported by the supplied developmental evidence without assuming an unstated pathway.
302. An orchid fruit is found to contain several thousand tiny seeds. No information is available about how long those seeds remain viable or whether any exceptional reproductive pathway occurred. Which inference is strongest?
ⓐ. High seed output is shown, but not longevity or fertilisation status
ⓑ. The seeds must remain viable for thousands of years because their number is high
ⓒ. The fruit must be parthenocarpic because the seeds are very small
ⓓ. The seeds must be apomictic because one fruit contains so many embryos
Correct Answer: High seed output is shown, but not longevity or fertilisation status
Explanation: The supplied evidence concerns seed number and size: one orchid fruit contains many very small seeds. That observation supports a conclusion about reproductive output, namely that a single fruit can generate thousands of propagules. It does not provide information about how long those seeds remain viable, so exceptional longevity cannot be inferred. Similarly, seed number does not reveal whether fertilisation occurred or whether an apomictic route was used. Parthenocarpy would ordinarily concern fruit formation without fertilisation and commonly seedlessness, which is not what the observation establishes. The case illustrates the importance of keeping seed output, seed longevity and reproductive origin as separate biological variables even when all are discussed in relation to successful plant reproduction.
303. Assertion: Exceptional records of seed viability should not be treated as the normal lifespan of every flowering-plant seed.
Reason: Every mature seed has the same fixed viability period regardless of species or storage conditions.
ⓐ. Both are true; Reason correctly explains Assertion
ⓑ. Both are true; Reason does not explain Assertion
ⓒ. Assertion is false, whereas the stated Reason is true
ⓓ. Assertion is true, whereas the stated Reason is false
Correct Answer: Assertion is true, whereas the stated Reason is false
Explanation: The Assertion is true as very old viable seeds represent exceptional observations rather than a universal rule for all flowering plants. Seed longevity can vary greatly among species and is influenced by the conditions under which seeds mature and are stored. The Reason is false since it claims exactly the opposite: a single fixed viability period for all mature seeds. Records such as those associated with Lupinus arcticus and Phoenix dactylifera demonstrate that extreme persistence is possible, but they do not establish that every seed shares those durations. Interpreting exceptional biological records correctly requires preserving their status as examples of potential longevity rather than converting them into mandatory lifespan limits.
304. An ovary contains \(8\) ovules. Exactly \(6\) ovules are successfully fertilised, and assume that only fertilised ovules form seeds while the ovary itself develops normally into a fruit. What outcome is expected?
ⓐ. \(8\) seeds, with the seed coat formed from the ovary wall
ⓑ. \(6\) seeds, with the pericarp formed from the integuments
ⓒ. \(6\) seeds, with the pericarp formed from the ovary wall
ⓓ. \(8\) seeds, with the pericarp formed from the fertilised egg
Correct Answer: \(6\) seeds, with the pericarp formed from the ovary wall
Explanation: Only successfully fertilised ovules are stated to become seeds. Since \(6\) of the \(8\) ovules are fertilised, the expected seed count is \(6\). Fruit-wall origin must then be considered separately from seed number. The ovary develops into the fruit, and its wall forms the pericarp. The biological interpretation combines a count with the correct developmental transformation. The remaining \(2\) unfertilised ovules do not form normal seeds under the supplied assumption. Seed coats, when seeds form, arise from ovular integuments rather than from the ovary wall. The calculation is meaningful only when linked to the distinction between ovule-to-seed development and ovary-wall-to-pericarp development. The seed count follows successful ovules, not the original ovule number: \(6\) fertilised ovules give \(6\) seeds under the stated assumption, while the two unsuccessful ovules contribute none. The pericarp is counted differently since it develops from the ovary wall of the single ovary, so its origin is unaffected by whether every ovule formed a seed.
305. Three fruit-development records are shown below.
| Record | Major mature tissue contribution | Fertilisation |
|---|
| P | Ovary | Occurs |
| Q | Ovary plus substantial thalamus contribution | Occurs |
| R | Ovary | Does not occur |
Which classification correctly distinguishes the three developmental routes?
ⓐ. P-false fruit, Q-parthenocarpic fruit, R-true fruit
ⓑ. P-parthenocarpic fruit, Q-true fruit, R-false fruit
ⓒ. P-true fruit, Q-accessory fruit, R-parthenocarpic fruit
ⓓ. P-true fruit, Q-apomictic product, R-accessory fruit
Correct Answer: P-true fruit, Q-accessory fruit, R-parthenocarpic fruit
Explanation: Record P shows the ordinary true-fruit condition: the ovary is the principal fruit-forming structure and fertilisation has occurred. Record Q includes a substantial contribution from the thalamus in addition to the ovary, so it represents a false or accessory fruit despite fertilisation being present. Record R differs along another axis. The fruit develops from the ovary even though fertilisation does not occur, which identifies parthenocarpy. The table requires two independent criteria: tissue origin and fertilisation status. False-fruit classification is based on contribution from non-ovarian floral tissue, whereas parthenocarpy is based on fruit development without fertilisation. Keeping those axes separate prevents accessory fruits and seedless fertilisation-independent fruits from being treated as the same phenomenon.
306. A transverse section of a typical mature angiosperm anther shows two distinct lobes and four pollen-containing chambers arranged near the corners, with two chambers associated with each lobe. Which structural interpretation best fits the observation?
ⓐ. The anther is bilobed, dithecous and tetrasporangiate
ⓑ. The anther is monolobed, monothecous and bisporangiate
ⓒ. The anther is bilobed, tetrathecous and monosporangiate
ⓓ. The anther is tetralobed, dithecous and bisporangiate
Correct Answer: The anther is bilobed, dithecous and tetrasporangiate
Explanation: A typical angiosperm anther has two lobes and is described as bilobed and dithecous. In transverse section, four microsporangia or pollen sacs are commonly visible, with two associated with each anther lobe. The presence of four microsporangia makes the anther tetrasporangiate. The structural terms refer to different organisational features and should not be interchanged: bilobed describes the two-lobed external architecture, whereas tetrasporangiate refers to the four microsporangial chambers in section. These microsporangia contain the tissues from which pollen ultimately develops. Reading all three levels together prevents a common error in which the number of pollen sacs is incorrectly treated as the number of anther lobes. The usual tetrasporangiate anther contains four microsporangia arranged as two in each of two lobes, linking sectional anatomy with pollen-producing capacity. Male gametophyte development remains distinct from anther tissue identity: pollen is haploid gametophytic material surrounded and supported by diploid sporophytic tissues.
307. In a developing anther, the epidermis, endothecium and middle layers are experimentally impaired, but the tapetum remains structurally and metabolically functional. Developing microspores receive adequate nutrition. Which defect is most directly expected later?
ⓐ. Failure of the megaspore mother cell to enter meiosis
ⓑ. Conversion of microspores into female gametophytes
ⓒ. Impaired anther protection and inefficient dehiscence
ⓓ. Failure of the generative cell to remain haploid
Correct Answer: Impaired anther protection and inefficient dehiscence
Explanation: The young microsporangium is surrounded by epidermis, endothecium, middle layers and the innermost tapetum. The outer three layers contribute mainly to protection and to the mechanical events associated with anther dehiscence, whereas the tapetum provides nutritive support to developing pollen. In this experiment, tapetal function remains intact, so the primary nutritional pathway for microspore development is preserved. Damage to the outer wall-layer system instead predicts weakness in protection and pollen-release mechanics as the anther matures. The defect should not be transferred to female sporogenesis or interpreted as a change in gametophytic ploidy. Selective layer damage reveals that successful pollen production and successful pollen release depend on related but functionally different anther tissues. The tapetum is the innermost microsporangial wall layer and supports developing microspores, whereas the sporogenous lineage gives rise to pollen mother cells.
308. Histological examination of a young microsporangium reveals Layer P as the innermost wall layer composed of cells with dense cytoplasm, some containing more than one nucleus. Tissue Q occupies the centre as a compact homogeneous mass whose cells can become pollen mother cells. P and Q are respectively:
ⓐ. endothecium and tapetum
ⓑ. tapetum and sporogenous tissue
ⓒ. sporogenous tissue and middle layers
ⓓ. epidermis and endothecium
Correct Answer: tapetum and sporogenous tissue
Explanation: Layer P is identified by both position and cellular appearance. The tapetum is the innermost microsporangial wall layer and its cells characteristically possess dense cytoplasm; they may also become multinucleate. Its major role is nutritional support of developing pollen. Tissue Q lies centrally rather than forming part of the wall. This compact homogeneous sporogenous tissue contains cells that are potentially capable of becoming pollen or microspore mother cells. Those mother cells later undergo meiosis to produce haploid microspores. The distinction separates supporting tissue from reproductive precursor tissue. Although both occupy the same young microsporangium, the tapetum nourishes the developing male lineage, while the sporogenous tissue supplies the cells that actually enter the meiotic pathway.
309. An anther contains \(18\) pollen mother cells that all complete normal meiosis, and every meiotic product survives as a separate microspore. What is the expected number and ploidy of the resulting microspores?
ⓐ. \(72\) haploid microspores
ⓑ. \(36\) diploid microspores
ⓒ. \(72\) diploid microspores
ⓓ. \(18\) haploid microspores
Correct Answer: \(72\) haploid microspores
Explanation: Each pollen mother cell is diploid and undergoes one meiotic event that normally produces a tetrad of four haploid microspores. The number of products is:
\[
18\times4=72
\]
Meiosis also reduces chromosome-set number from \(2n\) in each pollen mother cell to \(n\) in every resulting microspore. The correct outcome is \(72\) haploid microspores. This calculation integrates product number with the biological nature of the division. A numerical answer alone would be incomplete if ploidy were misassigned. Later development of these microspores into pollen involves mitotic divisions of the haploid male gametophytic lineage rather than another meiotic reduction, so the transition established here is the key \(2n\rightarrow n\) step of microsporogenesis. Both parts of the answer need independent verification. Product number comes from \(18\times4=72\), while ploidy comes from the reduction division that changes each \(2n\) pollen mother cell into \(n\) meiotic products. A count of \(72\) with diploid status would fail the meiotic check, and a haploid count of \(18\) would ignore the four products formed by each successful mother cell.
310. A mutant anther completes normal meiosis in all pollen mother cells, producing haploid microspore tetrads, but the four microspores within each tetrad fail to separate during maturation. Which conclusion best follows?
ⓐ. The microspores must remain diploid because tetrad separation failed
ⓑ. Normal meiosis can occur despite impaired separation of mature pollen units
ⓒ. Failure of tetrad separation proves that meiosis never occurred
ⓓ. Each retained tetrad should develop into a single diploid female gametophyte
Correct Answer: Normal meiosis can occur despite impaired separation of mature pollen units
Explanation: Meiosis is explicitly stated to be completed normally with production of haploid tetrads. Ploidy reduction has already occurred before the defect appears. The abnormality affects a later developmental step: microspores of a tetrad normally separate as the anther matures, then continue maturation as individual pollen grains before release following dehiscence. Failure of separation does not reverse meiosis or restore diploidy. The biological contrast is useful since microsporogenesis and pollen maturation are sequential but different processes. A plant can form genetically appropriate haploid meiotic products yet still fail to release normal individual pollen grains if a later maturation event is disrupted. The defect is post-meiotic rather than a failure of reduction division itself. A pollen mother cell is diploid, but its meiotic products are haploid microspores; later pollen cells belong to the haploid male gametophyte.
311. A pollen mutant produces a chemically resistant sporopollenin-rich exine over nearly the entire grain, including the region that would normally remain a germ pore. The intine and internal cells are otherwise normal. What is the most direct predicted consequence?
ⓐ. Pollen-tube emergence is impaired despite resistant exine
ⓑ. The pollen becomes diploid because the exine is continuous
ⓒ. The generative cell undergoes meiosis instead of mitosis
ⓓ. The pollen loses the resistant character of the exine
Correct Answer: Pollen-tube emergence is impaired despite resistant exine
Explanation: Sporopollenin forms the highly resistant exine, but germ pores are specialised regions where sporopollenin is absent. During pollen germination, the pollen tube emerges through such an aperture rather than breaking randomly through the resistant exine. In the mutant, the protective chemical property of the exine remains intact, but the normal structural discontinuity required for efficient tube emergence has been eliminated. The expected defect is functional rather than meiotic or ploidy-related. This case illustrates an important structure-function trade-off within one pollen wall: sporopollenin provides exceptional durability, while its local absence at germ pores permits reproductive outgrowth. Successful pollen must combine both protection and an appropriate site for germination. Exine and intine differ in both position and composition: the sporopollenin-rich exine is external, while the inner intine is chiefly cellulose and pectin.
312. A viable pollen grain has a normal sporopollenin-rich exine and normal germ pores, but its thin inner wall has been severely disrupted before it reaches a compatible stigma. Which effect is most directly expected?
ⓐ. The pollen loses the four microsporangia of the original anther
ⓑ. The pollen is converted from haploid to diploid before germination
ⓒ. The tapetum reforms around the pollen after deposition on the stigma
ⓓ. Pollen-tube growth may fail even with an intact resistant exine
Correct Answer: Pollen-tube growth may fail even with an intact resistant exine
Explanation: The thin continuous inner pollen wall is the intine, composed mainly of cellulose and pectin. It lies beneath the sporopollenin-rich exine and participates in the living wall system from which the pollen tube develops through a germ pore. Severe disruption of the intine can interfere with normal germination and tube outgrowth even if the outer exine remains chemically resistant and structurally recognisable. The defect does not change the haploid status of the male gametophyte or recreate anther tissues such as tapetum. This comparison separates the two pollen-wall layers by function and composition: exine primarily provides exceptional external resistance, whereas the intine is a thinner inner wall more directly continuous with growth during germination.
313. Pollen grains are exposed experimentally to harsh conditions that destroy most ordinary cellular material. After treatment, sculptured outer walls remain recognisable even though the internal contents are no longer functional. Which property most directly explains persistence of the outer walls?
ⓐ. The intine is made entirely of lignin and cannot be degraded
ⓑ. The generative cell secretes a permanent cellulose capsule
ⓒ. The exine contains exceptionally resistant sporopollenin
ⓓ. The tapetum remains attached permanently to mature pollen
Correct Answer: The exine contains exceptionally resistant sporopollenin
Explanation: The decisive observation is selective persistence of the outer pollen wall after harsh treatment. The exine is composed largely of sporopollenin, an exceptionally resistant material capable of withstanding high temperatures and strong acids or alkalis. This durability also helps explain why pollen-wall structures may be preserved for long periods even when internal biological viability has been lost. The intine is chemically different, consisting mainly of cellulose and pectin, and does not account for the extraordinary resistance described. Tapetal cells are anther tissues involved during pollen development and are not permanent coverings of shed pollen. Structural preservation must be separated from functional viability: a resistant exine can remain identifiable long after the living contents can no longer germinate. Germ pores are regions where sporopollenin is absent from the exine, providing sites through which the pollen tube can emerge during germination.
314. Use the arrangement described below. A two-celled pollen grain contains Cell P, which occupies most of the grain, has abundant food reserve and an irregular nucleus. Cell Q is smaller, spindle-shaped and lies within the cytoplasm of P. Which interpretation is correct?
ⓐ. P is the vegetative cell and Q is the generative cell
ⓑ. P is a male gamete and Q is the large vegetative cell
ⓒ. P is the generative cell and Q is the tapetum
ⓓ. P is the intine and Q is the generative nucleus
Correct Answer: P is the vegetative cell and Q is the generative cell
Explanation: The larger pollen cell with abundant food reserve and an irregularly shaped nucleus is the vegetative cell. The smaller spindle-shaped cell embedded within its cytoplasm is the generative cell. These identities are functionally important, not merely descriptive. The vegetative cell supports pollen-tube development, whereas the generative cell later divides mitotically to produce the two male gametes if that division has not already occurred before pollen shedding. Both cells belong to the haploid male gametophyte. The arrangement distinguishes the supportive vegetative component from the reproductive precursor. Cell size, nuclear form, location and later fate all point to the same identification, making the figure interpretable without requiring an unseen microscopic image. Three-celled pollen already contains the vegetative cell and two male gametes at shedding, whereas two-celled pollen completes generative-cell division later. Microspore formation follows meiosis, while maturation into functional pollen adds wall differentiation and gametophytic organisation without another reduction division.
315. Pollen from two species is examined at the instant of shedding.
| Species | Cells present at shedding | Post-shedding generative mitosis required to obtain two male gametes |
|---|
| P | Vegetative cell + generative cell | Yes |
| Q | Vegetative cell + two male gametes | No |
A treatment blocks generative-cell mitosis only after pollen shedding. Which interpretation is correct?
ⓐ. Q is more strongly affected because its generative cell must still divide
ⓑ. Both are equally affected because male gametes always form after shedding
ⓒ. P is more strongly affected because Q has already formed its two male gametes
ⓓ. Neither is affected because generative-cell mitosis occurs during meiosis
Correct Answer: P is more strongly affected because Q has already formed its two male gametes
Explanation: Species P sheds pollen in the two-celled condition. Its generative cell has not yet completed the mitosis that produces two male gametes, so a treatment blocking that division after shedding prevents an essential later developmental step. Species Q is already three-celled at shedding: one vegetative cell and two male gametes are present. The relevant mitosis has already occurred, so a treatment beginning only after shedding cannot prevent formation of male gametes that already exist. The comparison shows that pollen stage at shedding determines when male-gamete production must occur. It also reinforces that the generative division is mitotic and preserves haploidy rather than being a second meiotic event. Three-celled pollen already contains the vegetative cell and two male gametes at shedding, whereas two-celled pollen completes generative-cell division later. The shedding stage therefore records whether generative-cell mitosis has already occurred, not a difference in the haploid ploidy of the male lineage.
316. Assertion: The two-celled pollen condition should not be described as an exceptional shedding stage among angiosperms.
Reason: More than \(60\%\) of angiosperms commonly shed pollen with one vegetative cell and one generative cell.
ⓐ. Both are true; Reason does not explain Assertion
ⓑ. Both are true; Reason correctly explains Assertion
ⓒ. Assertion is true, whereas the stated Reason is false
ⓓ. Assertion is false, whereas the stated Reason is true
Correct Answer: Both are true; Reason correctly explains Assertion
Explanation: The Assertion is valid since the two-celled condition is actually the more common shedding stage described for angiosperms. The Reason supplies the supporting quantitative fact: more than \(60\%\) of angiosperms commonly shed pollen while it still contains a vegetative cell and an undivided generative cell. In the remaining species, the generative cell has already divided before shedding, producing three-celled pollen. The Reason explains why two-celled pollen cannot be treated as an unusual exception. At the same time, the percentage must not be converted into a universal rule. A substantial minority of species shed pollen after generative mitosis has already produced the two male gametes. The percentage supports the explanatory relation while still leaving room for the substantial group that sheds three-celled pollen.
317. Historical records indicate that Parthenium became established in an area after introduction as a contaminant associated with imported wheat. During its flowering season, exposure to its pollen is associated with severe allergic and bronchial symptoms in susceptible people. Which conclusion follows from the supplied evidence?
ⓐ. Imported wheat pollen itself must be the allergen responsible for every recorded symptom
ⓑ. Parthenium can be treated as a hydrophilous plant because it arrived through imported grain
ⓒ. The observation establishes that all angiosperm pollen causes severe bronchial disease
ⓓ. Parthenium pollen is allergenic; imported wheat explains its introduction, not the symptoms
Correct Answer: Parthenium pollen is allergenic; imported wheat explains its introduction, not the symptoms
Explanation: The evidence contains two different relationships that should not be merged. The imported-wheat context concerns how Parthenium was introduced as a contaminant, whereas the reproductive-biological relevance of the plant is that its pollen is associated with serious allergic and bronchial responses in susceptible individuals. The historical route of introduction does not demonstrate that wheat pollen produced the symptoms. Nor does one allergenic example justify a universal claim that all angiosperm pollen causes severe disease. The strongest interpretation preserves both parts of the evidence at their proper level: introduction history identifies the contaminant route, while the reproductive biology example concerns allergenic pollen produced by Parthenium. Pollen therefore has both reproductive significance and practical health relevance: a grain that functions normally for the plant can still act as an allergen in a susceptible person.
318. Pollen grains from a plant are shown to contain several nutrients, and a commercial product made from such pollen is marketed with a claim that it improves athletic performance. No controlled performance data are supplied. Which conclusion is most scientifically appropriate from the supplied evidence?
ⓐ. Nutrient-rich pollen necessarily increases athletic performance in every consumer
ⓑ. Pollen may be nutrient-rich, but supplement performance claims need independent evidence
ⓒ. Any marketed pollen product must be biologically inactive because pollen is a gametophyte
ⓓ. Nutrient-rich pollen cannot be used in food products unless fertilisation has occurred
Correct Answer: Pollen may be nutrient-rich, but supplement performance claims need independent evidence
Explanation: The evidence supports two limited statements: pollen grains can contain nutrients, and pollen products may be marketed as food supplements. Those facts do not by themselves establish every physiological or performance claim made about a commercial preparation. A claim of improved athletic performance would require evidence designed specifically to test that outcome. The biological identity of pollen as the male gametophyte does not prevent its components from being used in food products, nor does such use depend on fertilisation. The correct reasoning separates an established compositional fact from an unverified causal claim. This boundary keeps the reasoning within reproductive biology while avoiding conversion of marketing language into unsupported physiology. Pollen viability sets a time limit on successful use of a grain, but viability alone does not guarantee that the recipient pistil will accept it.
319. Equal samples of freshly shed pollen from the same species are kept under two environmental conditions.
| Time after shedding | Condition P viable pollen | Condition Q viable pollen |
|---|
| \(15\,\text{min}\) | \(92\%\) | \(90\%\) |
| \(60\,\text{min}\) | \(76\%\) | \(41\%\) |
| \(180\,\text{min}\) | \(58\%\) | \(8\%\) |
The conditions differ in temperature and humidity. What is the strongest inference?
ⓐ. Species identity cannot influence pollen viability in any flowering plant
ⓑ. Temperature and humidity can alter the rate of pollen-viability loss
ⓒ. Condition Q must always have higher humidity than P
ⓓ. Every pollen grain remains viable for exactly \(180\,\text{min}\)
Correct Answer: Temperature and humidity can alter the rate of pollen-viability loss
Explanation: Both samples come from the same species and begin with very similar viability, but their later trajectories diverge strongly. At \(180\,\text{min}\), Condition P retains \(58\%\) viable pollen whereas Condition Q retains only \(8\%\). Since the experimental conditions differ in temperature and humidity, the data support an environmental influence on the rate of viability loss. The table does not identify which specific temperature or humidity value caused the difference, so no directional claim about higher or lower humidity is justified. It also does not eliminate species-level variation, which is independently important in pollen longevity. The appropriate inference is limited to the supplied comparison: environmental conditions can substantially alter viability duration within a species.
320. Pollen of one species remains highly viable for about \(20\,\text{min}\) after shedding but loses most viability by \(45\,\text{min}\). Flower P has a receptive stigma \(10\,\text{min}\) after pollen release, while Flower Q first becomes receptive \(50\,\text{min}\) after release. No fresh pollen arrives later. Which flower has the stronger opportunity for successful pollination leading toward fertilisation?
ⓐ. Q, because delayed stigma receptivity always improves pollen viability
ⓑ. Q, because dead pollen can regain viability on a receptive stigma
ⓒ. P and Q equally, because pollen viability is irrelevant once pollen has been shed
ⓓ. P, because its stigma is receptive while the pollen remains highly viable
Correct Answer: P, because its stigma is receptive while the pollen remains highly viable
Explanation: Successful pollination requires more than physical contact between pollen and stigma. The pollen must still be viable when it encounters a receptive stigma. Flower P becomes receptive at \(10\,\text{min}\), well within the interval when the pollen remains highly viable. Flower Q does not become receptive until \(50\,\text{min}\), after most viability has already been lost according to the supplied condition. Since no fresh pollen arrives later, Q has a much smaller opportunity for successful pollen germination and subsequent tube growth. This case integrates two time-dependent requirements that are often studied separately: pollen longevity and stigma receptivity. Reproductive success is favoured when those functional windows overlap. Pollination identifies pollen transfer to a stigma; it does not by itself prove that the pollen is compatible or that fertilisation will follow.
