**Plastids: A Cell Organelle Found Only in Plants**

**Introduction to Plastids:**
Plastids are a group of membrane-bound organelles found in plant cells. They are unique to plants and are absent in animal cells. Plastids are double-membraned organelles that have their own DNA and are involved in various functions, such as photosynthesis, storage of pigments, and synthesis of essential molecules.

**Types of Plastids:**
Plastids can be classified into three main types based on their functions and characteristics:

1. **Chloroplasts:** These are green-colored plastids that contain chlorophyll and are responsible for photosynthesis. Chloroplasts capture light energy and convert it into chemical energy in the form of glucose.

2. **Chromoplasts:** Chromoplasts are plastids that contain pigments other than chlorophyll, such as carotenoids and anthocyanins. They are responsible for the synthesis and storage of pigments that give fruits and flowers their vibrant colors.

3. **Leucoplasts:** Leucoplasts are colorless plastids that are involved in the synthesis and storage of various molecules, such as starch, oils, and proteins. They are found in non-photosynthetic tissues, such as roots, tubers, and seeds.

**Functions of Plastids:**
Plastids play crucial roles in plant cells and are involved in various functions, including:

1. **Photosynthesis:** Chloroplasts are the primary sites of photosynthesis in plants. They contain chlorophyll pigments that capture light energy and convert it into chemical energy, which is used to synthesize glucose.

2. **Pigment Synthesis:** Chromoplasts are responsible for the synthesis and storage of pigments, such as carotenoids and anthocyanins, which give fruits and flowers their characteristic colors.

3. **Storage of Essential Molecules:** Leucoplasts are involved in the synthesis and storage of important molecules, such as starch, oils, and proteins. They store these molecules in non-photosynthetic tissues, where they are required for energy storage and growth.

4. **Conversion of Plastids:** Plastids can interconvert between different types based on the requirements of the plant. For example, when a green fruit ripens, chloroplasts in the fruit's cells may convert into chromoplasts, leading to a change in color.

**Conclusion:**
Plastids are organelles unique to plant cells and are involved in various crucial functions. They are classified into three main types: chloroplasts, chromoplasts, and leucoplasts, each with its specific roles. Chloroplasts are responsible for photosynthesis, chromoplasts synthesize and store pigments, and leucoplasts are involved in the synthesis and storage of essential molecules. Therefore, the correct answer to the given question is option C - Plastids.