Question

why mitochondria termed as semi autonomous

Answer 1

Mitochondria is considered as autonomous cell organelle due to the following counts :
Mitochondria have their own DNA which can replicate independently. The mitochondrial DNA produces its own mRNA, tRNA and rRNA.
The organelles posses their own ribosomes, called mitoribosomes.
Mitochondria synthesize some of their own structural proteins. However, most of the mitochondrial proteins are synthesized under instructions from cell nucleus.
The organelles synthesize some of the enzymes required for their functioning. e.g. succinate dehydrogenase.
They show hypertrophy .i.e. internal growth.

Answer 2

Mitochondria are capable of self duplication. they have DNA ,RNA, ribosomes and enzymes. they are able to synthesise some of their own proteins. Hence they are regarded as semi autonomous organelles.