Plastids are organoids characteristic of plant cells.
There are leukoplasts – colorless plastids, chromoplasts with a red-orange color, and chloroplasts – green plastids. All of them have a single plan of structure and are formed by two membranes: the outer (smooth) and the inner, forming the septum thylakoid stroma. On thylakoid stroma grana are located, consisting of flattened membrane vesicles – thylakoid grana. They are stacked on top of each other by type of coin posts. Inside these vesicles is chlorophyll. The light phase of photosynthesis takes place in the thylakoids of gran, I dark in the stroma. In plastids, there is a circular DNA molecule similar in structure to the prokaryotic chromosome; there are many small ribosomes on which protein synthesis is partially independent of the nucleus. Plastids can move from one species to another: chloroplasts in the fall turn into chromoplasts, and those, in turn, can become leukoplasts. The increase in the number of plastids is due to their halving and budding, which is preceded by the reduction of the ring DNA molecule. In their structure, plastids differ from each other by the presence of various types of pigments. So leukoplasts are generally devoid of pigments and are responsible for the synthesis of starch and the storage of nutrients. Chloroplasts contain a green pigment – chlorophyll. They are processes of photosynthesis. Chromoplasts contain yellow-orange carotenoid pigments.
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