A microbe recovered from an environmental sample grows on a medium composed of agar and a mix of salts. The agar is not digested during incubation. The growth rate increases in high CO2 conditions. The organism is likely a(n)
heterotroph.
autotroph.
chemotroph.
halophile.
The Correct Answer is B
A. Heterotroph: Heterotrophs obtain carbon from organic compounds; if this organism were a heterotroph it would require organic carbon in the medium (or be able to digest agar or other organics), which the description does not indicate.
B. Autotroph: Autotrophs fix carbon dioxide as their carbon source; increased growth under high CO₂ and growth on a mineral salts medium with no digestible organics strongly suggest a CO₂-fixing autotroph.
C. Chemotroph: Chemotrophs obtain energy from chemical compounds rather than light; this term describes energy source rather than carbon source and can overlap with autotrophy or heterotrophy, so the information given points more directly to carbon fixation (autotrophy).
D. Halophile: Halophiles require or tolerate very high salt concentrations for growth; although the medium contains salts, nothing indicates extreme salinity preference, and the CO₂ response points toward autotrophy rather than halophily.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Temperature and pH affect the rate of substrate binding:
Temperature and pH can influence binding rates indirectly, but this statement does not capture the primary shared mechanism by which extreme temperature or pH reduce enzyme activity.
B. Temperature and pH both induce an enzyme to lose its precise three-dimensional shape:
Both heat and extreme pH disrupt noncovalent interactions (hydrogen bonds, ionic bonds, hydrophobic interactions) that maintain tertiary and quaternary structure, causing loss of the active-site geometry and reduced catalytic activity.
C. Temperature and pH change the activation energy of the reaction:
Activation energy is an inherent property of a given catalyzed reaction; enzymes lower activation energy, but temperature and pH typically affect enzyme structure and kinetics rather than directly altering the chemical activation energy of the catalyzed step.
D. Temperature and pH change the ionization state of cofactors:
pH can change ionization states of cofactors and active-site residues; temperature less directly changes ionization state, so this does not represent a common mechanism for both.
E. There is no common mechanism of temperature and pH effects on enzyme activity:
There is a common mechanism: both can disrupt the weak bonds that maintain native protein structure, leading to loss of function.
Correct Answer is A
Explanation
A. Eurytolerant: Refers to organisms that can survive and grow under a wide range of environmental conditions (e.g., temperature, pH, salinity).
B. Stenotolerant: Opposite of eurytolerant; can survive only within a narrow range of conditions.
C. Obligate: Indicates a strict requirement for a particular condition (e.g., obligate aerobe requires oxygen).
D. Facultative: Indicates flexibility with respect to certain conditions (e.g., facultative anaerobes can
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