In the diagram of a mitochondrion, the letter 'A' is most likely used to indicate which structure?

• A. Nuclear envelope
• B. Ribosome
• C. Cristae
• D. Golgi apparatus

Answer: (C)

Verified step by step guidance

1. Understand the context of the question: The mitochondrion is a double-membraned organelle responsible for energy production in eukaryotic cells. The question asks about identifying a structure labeled 'A' in a diagram of a mitochondrion.
2. Review the key structures of a mitochondrion: These include the outer membrane, inner membrane, intermembrane space, cristae (folds of the inner membrane), and the matrix (the innermost compartment).
3. Focus on the term 'cristae': Cristae are the folds of the inner mitochondrial membrane that increase the surface area for energy production processes like the electron transport chain and ATP synthesis.
4. Eliminate incorrect options: The nuclear envelope surrounds the nucleus, not the mitochondrion. Ribosomes are involved in protein synthesis and are not specific to the mitochondrion's structure. The Golgi apparatus is a separate organelle involved in protein modification and sorting.
5. Conclude that the correct answer is 'cristae,' as it is a defining feature of the mitochondrion and is likely labeled 'A' in the diagram to indicate the folded inner membrane structure.