What is a mitochondrion responsible for?
MITOCHONDRION is responsible for generating energy for the cellular process as per the cell's requirement.
Mitochondria is a specialized cell organelle which is responsible for generating energy for the cell using a variety of substances. it is called the powerhouse to signify this responsibility.
In plants also, during the breakdown of the glucose for cellular processes mitochondria is the responsible cell organelle which converts the free radicals like NAD+, to energy currency, ATP. It is present to provide energy to the cells at any given time of the day. Chloroplast also can generate ATP but in presence of light. In night ATP required by plant is generated mainly by mitochondria