**Mitochondria and Cristae**

The correct answer is option B: Mitochondria. Cristae are indeed associated with mitochondria.

**Explanation**

Mitochondria are double-membrane-bound organelles found in most eukaryotic cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy.

One important feature of mitochondria is their inner membrane, which is highly folded to form structures called cristae. Cristae are invaginations or inward folds of the inner mitochondrial membrane. These folds increase the surface area of the inner membrane, allowing for more space where ATP synthesis can occur.

**Function of Cristae**

The presence of cristae in mitochondria is crucial for their function. The inner membrane of the mitochondria contains the electron transport chain (ETC) complexes, which play a key role in generating ATP through aerobic respiration. The ETC complexes are responsible for transferring electrons from electron donors to electron acceptors, creating a proton gradient across the inner mitochondrial membrane. This proton gradient is then used to drive the synthesis of ATP.

The highly folded structure of cristae increases the surface area available for the ETC complexes and ATP synthase, which are embedded in the inner membrane. This allows for more efficient ATP production, as there is a higher concentration of these proteins in the cristae. The increased surface area also allows for more efficient electron transfer and proton pumping, further enhancing ATP synthesis.

**Summary**

Cristae are associated with mitochondria. They are invaginations or inward folds of the inner mitochondrial membrane. The presence of cristae increases the surface area of the inner membrane, allowing for more efficient ATP synthesis through the electron transport chain and ATP synthase.