A Level Biology Practice Exam

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Which structure is composed of microtubules and is found in most eukaryotic cells?

Mitochondria
Nucleus
Centrioles
Ribosomes

The correct answer is: Centrioles

The correct choice highlights centrioles, which are critical structures composed of microtubules found in most eukaryotic cells. Centrioles play a key role in cell division, particularly in the formation of the spindle fibers that segregate chromosomes during mitosis and meiosis. Their arrangement as a pair and their role in organizing the microtubules are vital for the proper functioning of the cytoskeleton and cellular infrastructure. Mitochondria, while essential for energy production through cellular respiration, are not composed of microtubules; they have their own double membrane structure and are involved primarily in metabolic processes. The nucleus stores genetic material and controls various cellular activities, but it does not contain microtubules as a principal component. Ribosomes are responsible for protein synthesis and are made of ribosomal RNA and proteins, lacking any microtubule composition. Thus, centrioles are uniquely characterized by their microtubule composition and functional role in cell division, making them the correct answer.