#botany MCQ

Plant Classification

According to APG IV classification, angiosperms are classified mainly based on

APG IV system published 2016 revises classification using comprehensive plastid rbcL atpB matK ndhF and nuclear 18S gene matrices analyzed via maximum likelihood Bayesian inference, abandoning sole morphological reliance because floral characters highly homoplasious due to pollinator adaptation and convergence. Synapomorphies defined by molecular substitutions support monophyletic orders and families worldwide. Data sources include whole plastome sequencing, transcriptomics, revealing that Amborellales diverges first then Nymphaeales. Fossil record calibrates divergence times but not basis of group circumscription. Thus DNA sequence data provides primary criterion for family delimitation, improving stability compared to Cronquist morphology-based system previously dominant and artificial.

Ref: APG IV 2016, Botanical Journal Linnean Society 181:1-20, DNA sequence classification basis

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Plant Classification

Archaefructus is important because it represents

Archaefructus, recovered from Liaoning Yixian Formation lower Cretaceous about 125 million years, interpreted as herbaceous aquatic early angiosperm bearing reproductive axes with spirally arranged carpels containing seeds and stamens beneath, lacking perianth whorl. Carpels closed yet foliate, ovules enclosed confirming angiosperm status despite primitive organization. It represents extinct stem lineage basal to crown group, not modern angiosperm, not earliest gymnosperm nor primitive bryophyte. Fossil illuminates aquatic herb hypothesis for origin, demonstrating that closed carpel evolved in lacustrine environments preceding showy flower evolution and supporting rapid diversification during Cretaceous.

Ref: Campbell Biology, 12th ed., Chapter 30: Fossil Archaefructus early extinct angiosperm

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Plant Classification

Tepals are characteristic of flowers where

Perianth segments termed tepals when calyx corolla differentiation absent, showing similar pigmentation, size and texture throughout, often both petaloid or sepaloid without clear distinction. Condition common in monocots Liliaceae where outer whorl not green sepaloid but showy, termed petaloid tepals, or in basal angiosperms like tulip, Magnolia where gradual transition from bracts to perianth evident morphologically. Sepals and petals indistinct genetically due to overlapping B-class MADS-box gene expression domain expansion. Presence only petals still corolla, only sepals calyx, absence achlamydeous, whereas tepal concept indicates undifferentiated perianth evolutionarily intermediate.

Ref: NCERT Class 11 Biology, Chapter 5: Perianth differentiation tepals monocot characteristic

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Plant Classification

Amborella trichopoda lacks

Amborella wood anatomy exhibits exclusively tracheid conducting system lacking vessel elements, retaining torus-less circular bordered pits reminiscent of gymnosperms and pteridophytes, considered primitive. This vessellessness represents plesiomorphic retention not secondary loss, as phylogenetic placement suggests vessels evolved independently after Amborella lineage split within core angiosperms. Nonetheless, Amborella possesses angiospermous phloem with companion cells, enclosed ascidiate carpels and double fertilization yielding triploid endosperm confirming flowering plant affinity despite wood. Carpel, flower, endosperm features present, only vessel elements absent, challenging traditional definition of angiosperms requiring vessels and highlighting mosaic evolution.

Ref: Campbell Biology, 12th ed., Chapter 35: Amborella vesselless wood tracheid only plesiomorphy

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Plant Classification

The earliest diverging living angiosperm lineage is

Plastid phylogenomics incorporating rbcL, atpB, matK plus mitochondrial nad and nuclear concatenated genes robustly resolves Amborella trichopoda, shrub endemic New Caledonia with creamy white flowers spirally arranged, as earliest diverging living angiosperm sister to all others with maximal bootstrap support 100 percent. Its placement predates divergence of Nymphaeales water lilies and Austrobaileyales including star anise. Traits like vesselless wood, single aperturate pollen, spirally arranged ascidiate carpels reflect ancestral states useful for reconstructing protoflower ancestral morphology. Magnolia, Nymphaea, Illicium diverge later within mesangiosperms, not basal, making Amborella model organism genome project.

Ref: APG IV 2016, Botanical Journal Linnean Society, Amborella sister to all angiosperms

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Plant Classification

Darwin referred to the rapid diversification of angiosperms as

Charles Darwin correspondence with Joseph Hooker in 1879 lamented abrupt appearance and rapid diversification of flowering plants in Cretaceous fossil record contradicting gradualistic expectation, calling it abominable mystery perplexing evolutionary theory. Mesozoic floras previously dominated by ferns, cycads, conifers were swiftly replaced by angiosperm leaves, flowers and fruits documented in early Cretaceous sediments. Modern explanations invoke co-evolution with insect pollinators, evolution of closed carpel preventing selfing, efficient vessels and fast life cycles herbaceous habit. Green revolution term describes twentieth-century agricultural improvements; adaptive radiation describes pattern but historical phrase specifically identifies angiosperm fossil tempo and diversification explosive nature.

Ref: Campbell Biology, 12th ed., Chapter 30: Darwin abominable mystery rapid angiosperm radiation

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Brassinosteriod

Two biologically active brassinosteroids are:

The right choice is B: Castasterone and brassinolide. In Brassinosteriod, that matches how the process or concept actually works — the other choices mix up related ideas or use the wrong mechanism. Skip these: A) Brassinolide and campesterol; C) Teasterone and cathasterone; D) Dolichol and phytol. A quick check: if an option needs energy, pumps, or the opposite direction of movement, ask whether that really applies.