General chloroplast structure

Plastids are a family of genetically-identical organelles that have many manifestations--the most familiar of which is the chloroplast. Photosynthesis is confined to chloroplasts. A typical chloroplast of a photosynthesizing (chlorenchyma) cell from a jade plant leaf is shown here. Photosynthesizing membranes are sites of all the chlorophyll in the green cells and they form thylakoids (flattened sacs) in which photochemical (light) reactions of photosynthesis occur. Thylakoids form a highly ordered internal membrane system which is comprised of grana and intergranal elements. In this chloroplast the thylakoid system occupies the largest part of its internal space. Grana (singular = granum) refers to stacks which are made of variable number of thylakoids.

The amorphous matrix in which the thylakoid system is immersed is called the stroma. The stroma is the site of light-independent reactions of photosynthesis resulting in sugar formation. Also seen are black lipid bodies (L), two small starch grains (S), and several tiny plastoglobuli (P) which are lipids containing pigments such as carotenoids or lycopenes.

IS = intercellular space, M = mitochondrion, PM = plasma membrane, CW = cell wall, T = tonoplast (limiting membrane of the vacuole), V = vacuole

Illustration from: Ledbetter & Porter, 1970, Introduction to the Fine Structure of Plant Cells, Springer-Verlag