Prokaryotic cells are characterized by:
Lack of membrane-bound organelles
Presence of mitochondria
Multiple nuclei
The Correct Answer is A
A. Lack of membrane-bound organelles: Prokaryotic cells do not have membrane-bound organelles such as mitochondria, endoplasmic reticulum, or Golgi apparatus. All cellular processes, including energy production, protein synthesis, and DNA replication, occur in the cytoplasm or at the plasma membrane, which allows for rapid metabolic activity but limits compartmentalization.
B. Presence of mitochondria: Mitochondria are membrane-bound organelles responsible for aerobic respiration and ATP production in eukaryotic cells. Prokaryotes lack mitochondria and instead carry out energy-producing processes across the plasma membrane.
C. Multiple nuclei: Prokaryotic cells contain a single, circular chromosome located in the nucleoid region, not multiple nuclei. Multiple nuclei are characteristic of certain eukaryotic cells, such as skeletal muscle fibers or some fungal hyphae.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Secreted protein toxins: Exotoxins are proteins actively secreted by certain bacteria into their surrounding environment. They are highly potent and can cause specific damage to host cells or tissues, such as neurotoxins (Clostridium tetani), enterotoxins (Vibrio cholerae), or cytotoxins (Corynebacterium diphtheriae). Being protein in nature, they are often heat-labile and can stimulate strong immune responses, making them targets for toxoid vaccines.
B. Lipid toxins: Lipid-based toxins, such as lipopolysaccharides (LPS), are characteristic of endotoxins, not exotoxins. Endotoxins are part of the outer membrane of Gram-negative bacteria and are released mainly when the bacterial cell dies, producing systemic effects like fever and inflammation rather than specific cellular targeting.
C. DNA toxins: There are no naturally occurring bacterial toxins that are composed of DNA. While bacterial DNA can be transferred via plasmids or phages to spread virulence factors, DNA itself does not function as a secreted toxin causing direct cellular damage.
Correct Answer is D
Explanation
A. Halophile: Halophiles are organisms that thrive in high-salt environments. The description of temperature-based growth does not indicate a preference for saline conditions, so this term would not apply to the observed growth pattern.
B. Anaerobe: Anaerobes are organisms that grow in the absence of oxygen. The scenario focuses on temperature preferences, not oxygen requirements.
C. Mesophile: Mesophiles grow optimally at moderate temperatures, typically between 20°C and 45°C, with 37°C being ideal for many human-associated mesophilic bacteria. Because this species did not grow at 37°C or 50°C, it does not fit the definition of a mesophile.
D. Psychrophile: Psychrophiles are organisms that thrive at cold temperatures, usually with optimal growth at 0–15°C and survival at temperatures below 20°C. The abundant growth in the refrigerator and minimal growth at room temperature, with no growth at 37°C or higher, indicates that this species is adapted to cold environments, fitting a psychrophile definition.
E. Capnophile: Capnophiles require elevated levels of carbon dioxide for optimal growth. The growth pattern described is based on temperature rather than carbon dioxide levels, so this term is not applicable.
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