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Heart-Shaped Embryo Stage
MCQ questions and answers.
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MCQ Questions
1. The heart-shaped stage of a typical dicot embryo is produced primarily by which developmental event?
A.
Elongation of the suspensor without any cotyledon formation
B.
Lateral initiation and outward growth of two cotyledonary primordia
C.
Fusion of the plumule with the radicle
D.
Differentiation of the endosperm into vascular tissue
Correct Answer:
Lateral initiation and outward growth of two cotyledonary primordia
Explanation:
The heart-shaped appearance arises when two cotyledonary primordia develop laterally from the globular embryo, creating two lobes and a central notch.
2. In a dicot embryo at the heart-shaped stage, the indentation between the two cotyledonary lobes most directly indicates the future position of the:
A.
Suspensor
B.
Radicle
C.
Plumule
D.
Root cap
Correct Answer:
Plumule
Explanation:
The notch between the two developing cotyledons is associated with the embryonic shoot region, or plumule, which lies between the cotyledonary primordia.
3. Which positional relationship is characteristic of a dicot embryo at the heart-shaped stage?
A.
The radicle lies between two cotyledons at the distal end
B.
The plumule lies between two laterally expanding cotyledonary primordia
C.
The suspensor surrounds the developing cotyledons
D.
The cotyledons arise from the basal end below the radicle
Correct Answer:
The plumule lies between two laterally expanding cotyledonary primordia
Explanation:
At the heart-shaped stage, the two cotyledons expand laterally, while the plumule or shoot apex occupies the region between them.
4. A globular dicot embryo changes into a heart-shaped embryo when the apical region begins to show:
A.
Two distinct lateral cotyledonary outgrowths
B.
A single central root outgrowth
C.
Complete loss of the embryonic axis
D.
Conversion of the suspensor into endosperm
Correct Answer:
Two distinct lateral cotyledonary outgrowths
Explanation:
The transition from the globular to the heart-shaped stage is marked by the appearance of two lateral cotyledonary outgrowths.
5. If one cotyledonary primordium fails to develop normally during the heart-shaped stage, the most immediate morphological effect would be:
A.
Formation of a perfectly symmetrical heart-shaped embryo
B.
Loss of the embryonic root pole
C.
Asymmetry of the two-lobed embryo
D.
Transformation of the embryo into a monocot embryo
Correct Answer:
Asymmetry of the two-lobed embryo
Explanation:
The heart-shaped form depends on relatively balanced development of two cotyledonary primordia; unequal growth produces an asymmetric embryo.
6. Which observation would best distinguish a heart-shaped dicot embryo from an earlier globular embryo?
A.
Presence of a suspensor at the basal end
B.
Visible bilateral cotyledonary lobes separated by a notch
C.
Presence of actively dividing embryonic cells
D.
Attachment of the embryo to surrounding nutritive tissue
Correct Answer:
Visible bilateral cotyledonary lobes separated by a notch
Explanation:
The defining visual feature of the heart-shaped stage is the emergence of two cotyledonary lobes with a distinct notch between them.
7. During the heart-shaped stage, the two cotyledonary primordia are best interpreted as structures that will later become the:
A.
First pair of leaves of the mature shoot
B.
Root cap and root hairs
C.
Vascular cambium and secondary xylem
D.
Endosperm layers surrounding the embryo
Correct Answer:
First pair of leaves of the mature shoot
Explanation:
The cotyledonary primordia visible at the heart-shaped stage develop into the two seed leaves of a dicot embryo.
8. Which sequence correctly represents the morphological progression involving the heart-shaped stage in a typical dicot embryo?
A.
Heart-shaped, globular, torpedo-shaped, mature embryo
B.
Globular, heart-shaped, torpedo-shaped, mature embryo
C.
Torpedo-shaped, globular, heart-shaped, mature embryo
D.
Globular, torpedo-shaped, heart-shaped, mature embryo
Explanation:
In typical dicot embryogenesis, cotyledon initiation changes the globular embryo into the heart-shaped stage, followed by elongation into the torpedo stage.
9. The central notch of a heart-shaped dicot embryo is formed mainly because:
A.
The two cotyledonary primordia grow laterally while the intervening shoot region remains distinct
B.
The radicle splits into two independent roots
C.
The suspensor divides the embryo into two equal halves
D.
The endosperm mechanically cuts the embryo into two lobes
Correct Answer:
The two cotyledonary primordia grow laterally while the intervening shoot region remains distinct
Explanation:
Lateral expansion of the cotyledons on either side of the shoot apex creates the characteristic two-lobed outline and central notch.
10. A researcher observes an embryo with two prominent lateral lobes, a notch at the apical region, and a developing embryonic axis between the lobes. This embryo is most likely at the:
A.
One-celled zygote stage
B.
Globular stage
C.
Heart-shaped stage
D.
Fully mature seedling stage
Correct Answer:
Heart-shaped stage
Explanation:
Two lateral cotyledonary lobes separated by an apical notch, with the embryonic axis developing between them, are diagnostic features of the heart-shaped stage.
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Heart-Shaped Embryo Stage
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