Question

In prokaryotes, chromatophores are
A. Specialised granules responsible for the colouration of cells
B. Structures responsible for organising the shape of the organism
C. Inclusion bodies lying free inside the cells for carrying out various metabolic activities
D. Internal membrane systems that may become extensive and complex in photosynthetic bacteria

Answer 1

Hint: In photosynthetic prokaryotes, chromatophores arise from the cell membrane. These structures are extensively found in some photosynthetic bacteria as a coloured, membrane-associated vesicle containing pigments of different colours.

Complete answer: In photosynthetic prokaryotes, chromatophores are internal membrane systems present. These arise from the plasma membrane as membrane-lined sacs or thylakoids. Thylakoid membranes in cyanobacteria and purple bacteria contain photosynthetic pigments.
In photosynthetic prokaryotes, chromatophores are internal membrane systems present and should become extensive and sophisticated in photosynthetic bacteria. These grow from the cell wall as membrane lined sacs or thylakoids. Thylakoid membranes in cyanobacteria and phototrophic bacteria contain photosynthetic pigments. Small pigment-containing sacs or granules of phycobilin remain attached to these membranes. These structures are usually protected by a non-lipid proteinaceous membrane in green bacteria and are often referred to as 'chlorosomes'. In photosynthetic bacteria, internal membrane systems that may become detailed and complex. Chromatophores are one of a number of cell types produced in the neural crest during vertebrate embryonic development, a paired strip of cells that emerge at the margins of the neural tube. These cells have the ability to move over long distances, allowing several body organs, including the skin, eye, ear, and brain, to be inhabited by chromatophores.
Hence, the correct answer is option D.

Additional information: Chromatophores take either a dorsolateral route through the dermis, entering the ectoderm through small holes in the basal lamina, or a ventromedial route through the somites and the neural tube. The eye's retinal pigmented epithelium melanophores are the exception to this. Chromatophores can be regionally or completely absent if the proteins are defective, resulting in a leucistic condition.

Note: Chromatophores also include bacteriochlorophyll and carotenoid pigments. The light-harvesting proteins are intrinsic to the chromatophore membranes in phototrophic bacteria, including the Rhodospirillum rubrum. However, they are organised into specialised antenna complexes called chlorosomes in green sulphur bacteria.