Question

First photosynthetic organisms to appear on earth were

• A. Bacteria
• B. Cyanobacteria
• C. Bryophytes
• D. Green algae

Answer 1

The correct option is B Cyanobacteria

Evolution of mode of nutrition

• The earliest prokaryotes were heterotrophs that obtained energy from the organic matter that was present in the sea.
• As the temperature dropped the anoxygenic bacteria (purple bacteria) evolved where they manufactured organic compounds, using light as source of energy and hydrogen sulphide as the electron source. They did not release oxygen.
• Cyanobacteria then evolved that used water as a source of hydrogen electrons and light as a source of energy, releasing oxygen as a by-product.
• The atmosphere now contained oxygen, supporting the growth of algae and then bryophytes

Final answer
(c) Cyanobacteria