In plant cells, which organelles contain their own DNA and ribosomes, reflecting a degree of genetic and metabolic independence?

Introduction / Context:
Some organelles in eukaryotic cells have their own genetic material and protein synthesis machinery. This is an important clue to their evolutionary origin and functional independence. In plant cells, both energy producing and photosynthetic organelles show this feature. This question asks you to identify which organelles in plant cells contain their own DNA and ribosomes, supporting the endosymbiotic theory.

Given Data / Assumptions:

• The focus is on plant cell organelles.
• Options mention mitochondria, chloroplasts, both, and vacuoles.
• We assume awareness of the endosymbiotic theory, which proposes that some organelles evolved from free living bacteria.

Concept / Approach:
Mitochondria are present in nearly all eukaryotic cells and are responsible for aerobic respiration and ATP production. Chloroplasts are present in plant cells and some algae and carry out photosynthesis. Both mitochondria and chloroplasts have double membranes, their own circular DNA, and their own ribosomes that resemble bacterial ribosomes. They can synthesise some of their own proteins and replicate independently of the nucleus, although they still rely on nuclear genes for many components. Vacuoles, on the other hand, are membrane bound sacs for storage and do not contain their own DNA or ribosomes.

Step-by-Step Solution:
Step 1: Recall that mitochondria are often called the powerhouses of the cell and contain their own mitochondrial DNA and ribosomes. Step 2: Remember that chloroplasts, the site of photosynthesis in plants, also contain their own chloroplast DNA and ribosomes. Step 3: Recognise that vacuoles are storage organelles and do not possess their own genome or ribosomes. Step 4: Choose the option stating that both mitochondria and chloroplasts have their own DNA and ribosomes.

Verification / Alternative check:
Cell biology studies show that mitochondrial and chloroplast DNA are circular and share similarities with bacterial genomes. These organelles also have 70S type ribosomes, more like those of bacteria than the 80S ribosomes of the eukaryotic cytoplasm. Observations of their reproduction show that they divide by a process similar to binary fission, independently of the cell cycle. This evidence strongly supports the idea that both mitochondria and chloroplasts contain their own DNA and ribosomes.

Why Other Options Are Wrong:

• Mitochondria only: This ignores the fact that chloroplasts also contain their own DNA and ribosomes in plant cells.
• Chloroplasts only: This ignores mitochondria, which are present in plant cells and have their own genetic material.
• Vacuoles: Vacuoles are storage compartments and lack their own genome and ribosome population.

Common Pitfalls:
Some students may think that only mitochondria are special because they have their own DNA, forgetting that chloroplasts share this feature in photosynthetic organisms. Others may wrongly assume that any large organelle has its own genome. It helps to memorise that mitochondria and chloroplasts are the two organelles strongly linked to the endosymbiotic theory and are the ones known to contain their own DNA and ribosomes.

Final Answer:
In plant cells, both mitochondria and chloroplasts contain their own DNA and ribosomes.