chloroplast defined in 1951 yearchloroplast - chloroplast;
chloroplast - Plastid containing chlorophyll; occurring (one to many) in cells of algae (excepting blue-green algae) and higher plants. Site of photosynthesis. In higher plants usually disc shaped, arranged in single layer in cytoplasm; changing shape and position in cell in relation to light intensity; in algae variously shaped, cup-shaped, spiral, stellate, or in form of a network, one to several per cell, often accompanied by pyrenoids. Develop from pro-plastids; and in some algae, bryophytes, lycopods, multiply by division. Consist of a double membrane enclosing a homogenous stroma in which are embedded a number of grana, each consisting of a series of membrane-bounded, flattened, disc-shaped vesicles forming lamellae known as thylakoids, closely arranged like coins in a pile. The membranes of the thylakoids bear the photosynthetic pigments. Grana are linked with each other by similar lamellae lying parallel one with another but farther apart than those of the grana and lacking chlorophyll. Reactions involved in absorption of light energy and its conversion to chemical energy go on in grana. Subsequent utilization of chemical energy in reduction of carbon dioxide to form carbohydrates occurs in stroma.
In algae grana do not occur and the thylakoids traverse the stroma of the chloroplast as a whole, roughly parallel to each other. Chloroplasts do not occur in blue-green algae or photosynthetic bacteria, thylakoids lying free in the cytoplasm, many per cell, varying in arrangement and shape in different forms - vesicular, tubular, lamellate or irregular.
near chloroplast in Knolik
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