1. Have their own DNA: Both mitochondria and chloroplasts have their own DNA, which is separate from the nuclear DNA of the host cell. This suggests that they were once independent organisms that were engulfed by a host cell.

2. Replicate independently: Mitochondria and chloroplasts have the ability to replicate independently within the host cell. This is similar to how free-living bacteria reproduce.

3. Possess double membranes: Mitochondria and chloroplasts have double membranes, which is believed to be a result of the engulfment process. The outer membrane is thought to have originated from the host cell's plasma membrane, while the inner membrane is believed to be derived from the membrane of the engulfed organism.

4. Have similar ribosomes: The ribosomes found in mitochondria and chloroplasts are similar to those found in prokaryotic cells (bacteria), rather than eukaryotic cells (host cells). This suggests that they have retained their own protein synthesis machinery from their bacterial ancestry.

5. Produce energy: Both mitochondria and chloroplasts are involved in energy production within the cell. Mitochondria are responsible for cellular respiration, which generates ATP, the energy currency of the cell. Chloroplasts are involved in photosynthesis, which converts sunlight into chemical energy in the form of glucose.

These characteristics support the endosymbiotic theory, which proposes that mitochondria and chloroplasts were once free-living bacteria that were engulfed by ancestral host cells. Over time, they formed a mutually beneficial relationship, where the host cell provided protection and nutrients, while the endosymbionts provided energy and other essential functions.