Mitochondria, nucleus, chloroplast

The correct answer is option 'A': Mitochondria, nucleus, chloroplast.

Mitochondria, nucleus, and chloroplast are cellular organelles that contain DNA. Let's understand each of these organelles and their functions:

1. Mitochondria:
- Mitochondria are often referred to as the "powerhouses" of the cell because they produce the majority of the cell's energy in the form of ATP (adenosine triphosphate) through a process called cellular respiration.
- They have their own DNA, known as mitochondrial DNA (mtDNA), which is separate from the nuclear DNA. Mitochondrial DNA is circular in shape, similar to bacterial DNA, and is inherited maternally.
- The DNA present in mitochondria is responsible for encoding certain proteins necessary for the mitochondria to function.

2. Nucleus:
- The nucleus is considered the control center of the cell as it contains the majority of the cell's genetic material in the form of DNA.
- The DNA in the nucleus is organized into structures called chromosomes, which carry the genes that determine an organism's traits.
- The nucleus is involved in important cellular processes such as DNA replication, transcription, and regulation of gene expression.

3. Chloroplast:
- Chloroplasts are organelles found in plant cells and some algae. They are responsible for photosynthesis, the process by which plants convert sunlight, water, and carbon dioxide into glucose and oxygen.
- Like mitochondria, chloroplasts also contain their own DNA, known as chloroplast DNA (cpDNA). This DNA is circular and contains genes that encode proteins involved in photosynthesis.
- Chloroplast DNA is inherited from the maternal parent, similar to mitochondrial DNA.

In conclusion, all three organelles - mitochondria, nucleus, and chloroplast - contain DNA. The mitochondria and chloroplasts have their own DNA, separate from the nuclear DNA found in the nucleus.