These are green plastids. They have green pigment the chlorophyll. Chloroplast takes part in photosyn­thesis. They are found in mesophyll cells of leaf and chlorenchyma cells in stem. Many algae have only single Chloroplast in their cells but other advanced groups of plants have 20-40 chloroplasts per cell. Their size and shape varies in different groups of plants. In algae they are stellete, ribbon-like, cup-like, reticulate, spiral, sheet like, disc or tablet like. In mosses, ferns and seed plants chloroplasts are flat, circu­lar, ovate, elliptical.

Their detailed structure has been revealed by electron microscope. Each chloroplast has two unit membranes made up of lipoprotein. Inside the membranes is the proteinaceous ground substance called stroma . Stroma contains a variety of particles, osmiophilic droplets, ribosomes, strands of DNA and RNA, dis­solved salts, enzymes. Embedded in the stroma are many membranes, running paral­lel to each other throughout the length of the chloroplast. These are called lamellae, Each lamella is made up of two unit membranes. At some intervals the lamellae have 10-100 rounded flat sac like structures stacked one above the other. Such rounded flat structure is called thylakoid.

One stack of thylakoids is called granum. Different grana are connected with grana of other lamella with the help of tubular connections called stroma lamellae or frets. Each chloroplast contains 40-60 grana. Membrane of grana lamellae are made up of proteins