The unit of photosynthesis is the photosynthetic unit. Thylakoids contain photosynthetic units. The photosynthetic unit consists of 300-400 molecules of chlorophyll-a, chlorophyll-b, carotene and xanthophyll. It contains various enzymes, phospholipids, sulfolipids, metal ions, quinones, etc. Photosynthetic units absorb light energy and cause photophosphorylation.