Part 5 — Double fertilization; pollen tube growth; fertilization events & barriers (25 MCQs)

Q86. Double fertilization in angiosperms results in formation of:

a) One zygote only
b) One zygote and one diploid endosperm
c) One zygote and a primary endosperm nucleus (usually triploid)
d) Two zygotes

Answer: c) One zygote and a primary endosperm nucleus (usually triploid)

(c) Correct. One sperm fuses with egg → zygote (2n); other sperm fuses with two polar nuclei → primary endosperm nucleus (3n in most angiosperms).
(b) Endosperm is normally triploid (not diploid) in Polygonum type.

Q87. The condition where both fertilizations occur but one fails later is:

a) Cryptic double fertilization
b) Partial double fertilization leading to seed abortion or abnormal endosperm
c) No such event occurs
d) Apomixis

Answer: b) Partial double fertilization leading to seed abortion or abnormal endosperm

(b) Correct. If one fusion fails or endosperm development fails, embryo development disturbed, seed may abort.

Q88. During pollen tube growth the generative cell divides:

a) Before pollen grain germination always
b) After pollen germination usually to form two sperms in the tube as it grows (in bicellular pollen)
c) Never divides
d) During megasporogenesis

Answer: b) After pollen germination usually to form two sperms in the tube as it grows (in bicellular pollen)

(b) Correct. In bicellular pollen, generative cell divides in tube to produce two sperms.

Q89. In angiosperms, one sperm fertilizes egg and the other fuses with:

a) Egg as well (double zygote)
b) Central cell polar nuclei forming primary endosperm nucleus (PEN)
c) Synergid always to form embryo sac
d) None — only egg is fertilized

Answer: b) Central cell polar nuclei forming primary endosperm nucleus (PEN)

(b) Correct. This is hallmark of double fertilization.

Q90. If pollen tube enters ovule through chalaza rather than micropyle, this phenomenon is called:

a) Porogamy
b) Chalazogamy
c) Mesogamy
d) Funiculogamy

Answer: b) Chalazogamy

(b) Correct. Chalazogamy = pollen tube enters through chalaza (e.g., some members like Ficus?).
Porogamy = micropyle entry.

Q91. Fertilization in angiosperms generally occurs when pollen tube reaches:

a) Nucellus only
b) Embryo sac, delivering two sperms for double fertilization
c) Integuments directly
d) Receptacle

Answer: b) Embryo sac, delivering two sperms for double fertilization

(b) Correct. Pollen tube discharges two sperms into synergid/egg region.

Q92. What is the fate of synergid that receives pollen tube?

a) It divides and forms antipodals
b) It degenerates to facilitate sperm release and fertilization
c) It becomes endosperm
d) Forms zygote

Answer: b) It degenerates to facilitate sperm release and fertilization

(b) Correct. One synergid often degenerates to aid sperm discharge.

Q93. Which type of barrier prevents hybridization after zygote formation?

a) Pre-zygotic barrier
b) Post-zygotic barrier (e.g., hybrid inviability or sterility)
c) Floral isolation only
d) Mechanical barrier only

Answer: b) Post-zygotic barrier (e.g., hybrid inviability or sterility)

(b) Correct. Post-zygotic barriers act after fertilization (e.g., hybrid embryo aborts or is sterile).

Q94. In most angiosperms the primary endosperm nucleus is:

a) Diploid (2n)
b) Triploid (3n)
c) Haploid (n)
d) Tetraploid (4n)

Answer: b) Triploid (3n)

(b) Correct. Fusion of one sperm (n) with two polar nuclei (n+n) typically yields 3n. Exceptions exist.

Q95. The pollen tube usually discharges contents into:

a) Egg cell directly
b) One of the synergids (micropylar entry), and sperms reach egg/central cell subsequently
c) Antipodals always
d) Chalaza directly

Answer: b) One of the synergids (micropylar entry), and sperms reach egg/central cell subsequently

(b) Correct. Synergid targets facilitate sperm release; actual fusion occurs with egg/polar nuclei.

Q96. Secondary messenger molecules in pollen tube guidance include:

a) Sugars only
b) Peptides, calcium gradients, small signaling molecules & chemoattractants from synergids
c) RNA only
d) Lipids exclusively

Answer: b) Peptides, calcium gradients, small signaling molecules & chemoattractants from synergids

(b) Correct. Complex signaling environment guides tube growth; Ca²⁺ crucial.

Q97. Endosperm formation in most cereals (monocots) results in:

a) No endosperm present
b) Persistent endosperm (storage tissue) in mature seed (e.g., wheat)
c) Endosperm is absorbed completely before seed maturity
d) Endosperm forms only in gymnosperms

Answer: b) Persistent endosperm (storage tissue) in mature seed (e.g., wheat)

(b) Correct. Many monocots retain endosperm in seed; many dicots absorb it (cotyledons store instead).

Q98. Which is true about fertilization in angiosperms:

a) It is always chalazogamous
b) Double fertilization is unique to angiosperms (though some gymnosperms show analogous events)
c) Only one sperm is produced per pollen grain
d) Egg cell provides pollen tube guidance

Answer: b) Double fertilization is unique to angiosperms (though some gymnosperms show analogous events)

(b) Correct. Double fertilization (egg + polar nuclei) is characteristic of angiosperms.
(c) Two sperms produced in angiosperms; (d) egg is passive; synergids guide.

Q99. Autogamy, geitonogamy and xenogamy are types of:

a) Differing embryo sac types
b) Pollination based on source of pollen
c) Seed dispersal mechanisms
d) Fertilization modes

Answer: b) Pollination based on source of pollen

(b) Correct. These are pollination types based on where the pollen comes from.

Q100. Which of the following statements about double fertilization is false?

a) Two fertilization events occur — one forming zygote and one forming primary endosperm nucleus
b) Both sperm nuclei always fuse with egg to give diploid zygotes
c) It leads to formation of nutritive tissue (endosperm) for embryo
d) It ensures coordinated development of embryo and endosperm

Answer: b) Both sperm nuclei always fuse with egg to give diploid zygotes (False)

(b) False. One sperm fuses with egg, the other with polar nuclei; not both with egg.

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Part 5 — Double fertilization; pollen tube growth; fertilization events & barriers (25 MCQs)