kloroplastid

Kloroplastid is a plastid that carries out photosynthesis in plants, algae, and many protists. It contains chlorophyll and other pigments that capture light energy, enabling the conversion of carbon dioxide and water into sugars while releasing oxygen. Chloroplasts are typically located in photosynthetic cells and are essential for carbon fixation and biomass production.

Structure: A chloroplast is enclosed by a double membrane and contains an internal membrane network of thylakoids, often arranged in stacks called grana, surrounded by the fluid stroma. The organelle also contains its own DNA and ribosomes and can divide within the cell.

Metabolism: Light-dependent reactions occur in the thylakoid membranes, producing ATP and NADPH. The Calvin cycle, in the stroma, uses these energy carriers to fix CO2 into sugars. Beyond photosynthesis, chloroplasts participate in the synthesis of fatty acids, certain amino acids, pigments, and other essential metabolites.

Origin and genetics: Chloroplasts are believed to have originated from ancient cyanobacteria via endosymbiosis. They retain a circular genome and gene expression machinery, though many genes have migrated to the host nucleus and are imported back into the organelle. Chloroplasts are inherited in various patterns among species and can show genetic variation within lineages.

Variation: In non-photosynthetic tissues, chloroplasts may differentiate into other plastid types or become reduced to leucoplasts. The term chloroplastid is commonly used in some languages to refer to this organelle family, with plastids representing the broader group including chloroplasts, chromoplasts, and leucoplasts.