The appressed areas are called partitions. These are hydrophobic in nature the space between the two membranes of thylakoid (fret membrane) is called fret channel.
The space between two thylakoids is called loculus while the ends of disc shaped thylakoids are called margins. These areas (loculus, fret channel) are hydrophilic.
The chlorophyll molecules are concentrated in the fret channel i.e., in the space between the two membranes of thylakoids.
The chlorophyll molecules may be entirely in the space or the heads may be in the fret channel while the tails are buried in the sub units occasionally the entire chlorophyll molecule may be found in the fret membrane. Other pigments like cytochromes, carotenoids, etc-, are also found in the fret membranes.
Four sub units of the partition constitute a photosynthetic unit or a quantosome. Ribosomes and RNA have also been isolated from the chloroplasts indicating machinery for protein-synthesis.
Since the chloroplasts, have their own RNA, DNA ribosome’s and protein synthesis, according to Deviln (1975) “One might be inclined to view the chloroplast as a cell within a cell”. De Robertis (1980) suggests.
“It has been suggested that chloroplasts may have resulted from a symbiotic relationship between an autotrophic microorganism, able to transform energy from light, and a heterotrophic host cell” But Bogorad (1977) opines that the chloroplast components depend to a great extent on the nuclear genes for their assembly into an integrated organelle.