Name the cell organelle found in plant cells only. Write its types and function.

Plastids are the cell organelles found exclusively in plant cells and some protists. These double-membrane-bound organelles are classified into three main types based on the pigments they contain and their specific functions. Chloroplasts are green plastids containing chlorophyll that carry out photosynthesis, converting light energy into chemical energy and producing food for the plant. Chromoplasts are colored plastids (yellow, orange, or red) containing carotenoid pigments that give color to flowers and fruits, attracting pollinators and seed dispersers. Leucoplasts are colorless plastids that primarily function as storage organelles, with subtypes including amyloplasts (storing starch), elaioplasts (storing oils and fats), and aleuroplasts (storing proteins).

Plastids can interconvert depending on the plant's developmental stage and environmental conditions—for example, chloroplasts in ripening tomatoes transform into chromoplasts, changing the fruit from green to red. All plastids develop from undifferentiated proplastids present in meristematic tissues and contain their own DNA and ribosomes, indicating their evolutionary origin from ancient prokaryotic organisms through endosymbiosis. Their primary collective function is to manufacture and store important chemical compounds used by the plant, making them essential for plant nutrition, growth, reproduction, and the ultimate support of nearly all life on Earth through the food chain. Without plastids, plants could not photosynthesize, and terrestrial ecosystems as we know them would not exist.