NOVELTY - Producing a photosynthetic product, comprises: either maintaining a photosynthetic plant or algal cell suspension culture, in the presence of water, light and in a carbonic acid-enriched growth medium; or maintaining a photosynthetic plant or algal cell suspension culture, in the presence of water, light and a carbon source comprising carbon dioxide and carbonic acid, where the culture is maintained at a pH of less than 7, preferably 4.5-5.5.    USE - The methods are useful for producing a photosynthetic product, and a biological product, where the photosynthetic product is sugar comprising a mono- and/or a disaccharide, preferably glucose, sucrose and/or fructose, glyceraldehyde, glycerose and/or one or more starches, the biological product is biomass, such as the cells of the second cell culture, and the biological product is at least one fatty acid and/or oil, a proteinaceous product (including recombinantly-encoded proteinaceous products) and a metabolite, such as ethanol. The two-culture system is useful for producing at least one fatty acid and/or oil, comprising a first plant cell suspension culture and a second plant cell suspension culture of oil-producing plant cells. The two-culture system or carbon dioxide capture system is useful to capture carbon dioxide. The extract or a biofuel is useful as a supplementary source of fuel for a carbon dioxide-producing process. The carbonic acid-enriched growth medium is useful for reducing the energetic requirement, e.g. the light energy requirement, for producing a photosynthetic product with a photosynthetic plant or algal cell suspension culture. The carbonic acid is useful as a direct substrate for photosynthesis by a plant or algal cell suspension culture (all claimed).    ADVANTAGE - The method requires a substantially reduced input of energy (primarily in the form of light) compared to conventional photosynthetic processes.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method-1 for the production of a biological product, comprising maintaining a first cell suspension culture of photosynthetic plant or algal cells such that the cultured cells photosynthesize and generate and release photosynthetic product (e.g. sugars, typically mono- and/or disaccharides, preferably glucose, sucrose and/or fructose) into the surrounding culture medium, and maintaining a second cell culture in the presence of the photosynthetic product generated by the first cell suspension culture to allow growth of the second culture and the production of a biological product;    (2) a two-culture system for producing a biological product, comprising a first cell suspension culture and a second cell culture;    (3) a carbon dioxide capture system comprising at least the first plant cell suspension culture, and optionally further the second cell culture;    (4) a carbon dioxide-producing power generating facility comprising the two-culture system, or of the carbon dioxide capture system;    (5) a generating facility for producing a producing biofuel such as bioethanol or other alcohol, comprising the two-culture system, or the carbon dioxide capture system;    (6) an extract of the biological product obtainable by the method;    (7) a extract of at least one fatty acid and/or oil obtainable by the method;    (8) a biofuel obtainable by the processing of the extract of at least one fatty acid and/or oil;    (9) a photosynthetic plant or algal cell suspension culture, comprising carbonic acid-enriched growth medium, or as produced by the method; and    (10) a carbonic acid-enriched growth medium.