Examkin

Soru

Zorluk: OrtaInferences from the Text

In carbonaceous chondrite meteorites such as the Murchison meteorite, several non-proteinogenic alpha-amino acids exhibit slight left-handed (L-enantiomer) excesses, ranging from 2% to 18%. Because terrestrial biological contamination exclusively yields standard proteinogenic amino acids, the presence of L-excesses in non-terrestrial, non-proteinogenic amino acids indicates that abiotic chiral asymmetry originated prior to the emergence of terrestrial biochemistry. The leading astrophysical model posits that this enantiomeric bias was induced by asymmetric photolysis driven by ultraviolet circularly polarized light (UV-CPL) in the protoplanetary nebula. Laboratory irradiations of racemic amino acid ices with synchrotron UV-CPL have successfully reproduced small enantiomeric excesses; however, the magnitude of the photo-induced excess is strictly constrained by the total degree of photochemical destruction, with high enantiomeric excesses requiring over 99% molecular degradation. Consequently, researchers propose that secondary aqueous alteration within the meteorite's parent asteroid must have subsequently amplified these initial modest asymmetries via solid-solution phase equilibria without requiring catastrophic photolytic depletion.

Based on the passage, which of the following statements are logically supported by the text? (Select all that apply.)

  1. The chiral bias observed in non-proteinogenic amino acids from carbonaceous chondrites cannot be attributed to contamination from living terrestrial organisms.Cevap
  2. B
    Secondary aqueous alteration inside parent asteroids generated the initial chiral asymmetry without any prior exposure to ultraviolet circularly polarized light.
  3. C
    Synchrotron radiation is emitted naturally by protoplanetary nebulae and serves as the primary environmental driver of chiral selection in deep space.
  4. Producing a substantial enantiomeric excess through UV-CPL photolysis alone would necessitate the destruction of almost all of the precursor amino acid molecules.Cevap
  5. E
    Every amino acid extracted from the Murchison meteorite displays an L-enantiomer excess greater than 18%.

Cevap

The statements confirming that terrestrial contamination cannot account for the chiral bias in non-proteinogenic amino acids and that generating substantial enantiomeric excess via UV-CPL alone requires destroying over 99% of the starting molecules are both logically entailed by the passage.
The text directly establishes two valid inferences: first, because terrestrial contamination is strictly restricted to standard proteinogenic amino acids, the chiral bias in non-proteinogenic amino acids cannot stem from Earth organisms; second, achieving high enantiomeric excess purely through UV-CPL photolysis requires over 99% degradation, meaning almost all original molecules must be destroyed.

Adım Adım Çözüm

1
Evaluate claims regarding terrestrial biological contamination against the explicit premises in the text.
The text states that terrestrial contamination yields only proteinogenic amino acids, which guarantees that non-proteinogenic chiral imbalances must be non-terrestrial in origin.
This establishes the truth of the statement regarding terrestrial contamination.
2
Assess the relationship between photolysis yield, molecular destruction, and enantiomeric magnitude.
The text explicitly links high photo-induced enantiomeric excesses to over 99% molecular degradation.
This establishes that achieving high enantiomeric excess solely through photolysis requires destroying nearly all original molecules.
3
Evaluate the remaining options against quantifier precision and causal scope.
The claims about aqueous alteration acting without initial UV-CPL, synchrotron radiation being a natural astrophysical source, and all amino acids exceeding 18% excess either distort textual modifiers or introduce unsupported causal links.
Eliminating unsupported logical leaps and external facts confirms the correct pair of inferences.

Anahtar Kavram

Drawing strictly supported inferences from scientific prose by tracking quantifier scope and causal mechanisms
Tahmini Süre:1m 30s
Bu soruyu puanla

Konular

Inferences from the Text

Bu konudan daha fazla soru