Mitochondria is a double-membraned organelle found in most eukaryotic cells. It is responsible for producing energy in the form of ATP through cellular respiration. The discovery of mitochondria is attributed to Richard Altamann, making option D the correct answer.

The discovery of mitochondria can be attributed to Richard Altamann, a German pathologist, who first described and named these organelles in 1886. Altamann studied the structure of cells using various staining techniques and observed distinct granules within the cytoplasm of cells. He named these granules "bioblasts," which were later identified as mitochondria.

Mitochondria's discovery by Richard Altamann paved the way for further research on their structure and function, and their importance in cellular metabolism and energy production was gradually uncovered.

Key Points:
- Mitochondria were discovered by Richard Altamann in 1886.
- Altamann observed distinct granules within the cytoplasm of cells and named them "bioblasts."
- These granules were later identified as mitochondria.
- Altamann's discovery led to further research on the structure and function of mitochondria.
- Mitochondria are responsible for cellular respiration and energy production in cells.

In conclusion, the discovery of mitochondria is credited to Richard Altamann. His observation of distinct granules within cells and subsequent naming of these granules as "bioblasts" laid the foundation for the study of mitochondria and their essential role in cellular metabolism and energy production.