biology : class12 Embryonal Stages : Dicot Embryo, Monocot Embryo, Embryonic Axis, Cotyledons : Embryo Development MCQ Questions and Answers
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Embryonal Stages
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MCQ Questions
1. In the early embryogenesis of a typical dicot, the first transverse division of the zygote produces two unequal cells. Which developmental fate is correctly assigned to them?
A.
The smaller basal cell forms the embryo proper, while the larger terminal cell forms the suspensor
B.
The larger basal cell forms the suspensor, while the smaller terminal cell forms the embryo proper
C.
The larger basal cell forms the embryo proper, while the smaller terminal cell forms the suspensor
D.
Both cells contribute equally and directly to the mature embryo without forming a suspensor
Correct Answer:
The larger basal cell forms the suspensor, while the smaller terminal cell forms the embryo proper
Explanation:
The basal cell is generally larger and develops into the suspensor, whereas the terminal cell is smaller and gives rise to the embryo proper through successive embryonal stages.
2. Which sequence represents the usual morphological progression of a dicot embryo after the proembryo stage?
Explanation:
The embryo initially becomes globular, then develops two cotyledonary primordia producing the heart-shaped stage, and subsequently elongates into the torpedo stage before maturation.
3. The heart-shaped stage of a dicot embryo is distinguished from the preceding globular stage primarily because of the appearance of:
A.
A fully differentiated radicle and plumule
B.
Two lateral cotyledonary outgrowths
C.
A completely elongated hypocotyl
D.
The scutellum and coleoptile
Correct Answer:
Two lateral cotyledonary outgrowths
Explanation:
The heart-shaped appearance results from the initiation and lateral expansion of two cotyledons, a defining event in the transition from the globular to the heart-shaped stage of dicot embryogenesis.
4. Which event most directly accounts for the transition from the heart-shaped stage to the torpedo stage in a dicot embryo?
A.
Loss of the embryo proper through degeneration
B.
Elongation of the embryonic axis between the developing cotyledons
C.
Replacement of both cotyledons by a single scutellum
D.
Formation of the suspensor from the cotyledonary tissue
Correct Answer:
Elongation of the embryonic axis between the developing cotyledons
Explanation:
During the torpedo stage, the embryonic axis elongates and the cotyledons become more developed, giving the embryo its characteristic elongated appearance.
5. A researcher observes a dicot embryo with two recognizable cotyledons, a distinct plumule, hypocotyl, and radicle, but without the protective seedling structures characteristic of monocots. Which stage is being observed?
A.
Globular stage
B.
Heart-shaped stage
C.
Torpedo stage
D.
Mature dicot embryo stage
Correct Answer:
Mature dicot embryo stage
Explanation:
A mature dicot embryo possesses two cotyledons and a differentiated embryonic axis consisting of plumule, hypocotyl, and radicle. The globular, heart-shaped, and torpedo stages precede this organization.
6. In dicot embryogenesis, which pairing correctly relates an embryonal stage to its principal morphological feature?
A.
Globular stage — initiation of two prominent cotyledons
B.
Heart-shaped stage — formation of the suspensor from the zygote's terminal cell
C.
Torpedo stage — elongation of the embryo accompanied by further cotyledon development
D.
Mature stage — absence of recognizable embryonic axis
Correct Answer:
Torpedo stage — elongation of the embryo accompanied by further cotyledon development
Explanation:
The torpedo stage follows the heart-shaped stage and is characterized by elongation of the embryonic axis along with continued development of the cotyledons.
7. Which statement best distinguishes the early monocot embryo from the corresponding dicot embryonal pattern?
A.
The monocot embryo develops two equally prominent cotyledons during the heart-shaped stage
B.
The monocot embryo develops a single cotyledon, called the scutellum, during embryonal differentiation
C.
The monocot embryo lacks an embryonic axis because its embryo remains globular
D.
The monocot embryo forms a suspensor from the scutellum after seed maturation
Correct Answer:
The monocot embryo develops a single cotyledon, called the scutellum, during embryonal differentiation
Explanation:
Unlike the two-cotyledon pattern of dicots, monocots form one cotyledon, the scutellum. This difference is established during the embryonal stages and influences the mature embryo organization.
8. During monocot embryo development, which combination correctly identifies the protective structures associated with the embryonic axis?
A.
Coleoptile protects the radicle, and coleorhiza protects the plumule
B.
Coleoptile protects the plumule, and coleorhiza protects the radicle
C.
Scutellum protects the plumule, and coleoptile protects the radicle
D.
Coleorhiza protects the scutellum, and scutellum protects the radicle
Correct Answer:
Coleoptile protects the plumule, and coleorhiza protects the radicle
Explanation:
In the developing monocot embryo, the plumule is enclosed by the coleoptile, while the radicle is enclosed by the coleorhiza. These structures are characteristic of monocot embryonal organization.
9. An embryo is identified as monocot based on a single cotyledon and a protective sheath surrounding the shoot apex. Which additional observation would most strongly support this identification at the embryonal stage?
A.
The cotyledon is designated as the scutellum and the radicle is enclosed by a coleorhiza
B.
Two cotyledons produce a heart-shaped embryo and the hypocotyl is elongated
C.
The suspensor develops into the plumule and the cotyledons fuse completely
D.
The embryo lacks a radicle but possesses two independent plumules
Correct Answer:
The cotyledon is designated as the scutellum and the radicle is enclosed by a coleorhiza
Explanation:
The scutellum is the single cotyledon of a monocot embryo, and the coleorhiza is the sheath that protects its radicle. Together they provide strong evidence of monocot embryonal organization.
10. If cotyledon initiation is experimentally prevented in a developing dicot embryo, which normal embryonal transition would be most directly disrupted?
A.
The transition from the zygote to the two-celled proembryo
B.
The transition from the globular stage to the heart-shaped stage
C.
The formation of the suspensor from the basal cell
D.
The initial transverse division of the zygote
Correct Answer:
The transition from the globular stage to the heart-shaped stage
Explanation:
The heart-shaped stage is produced by the appearance of two cotyledonary primordia. Preventing cotyledon initiation would therefore block or severely alter this transition.
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