Your correct answer is observation
Cyanobacteria were important for Earth's early atmosphere because they produce oxygen.
<u>Explanation</u>:
Cyanobacteria is a Phylum consists of the free living bacteria and endosymbiosis. Cyanobacteria is also called blue green algae which obtain energy through oxygenic photosynthesis and releases Oxygen gas in the atmosphere. Cyanobacteria is responsible for the early oxygen production in environment which changed the early reducing atmosphere of the earth into the oxidizing atmosphere that causes the event of great oxygenation that is rusting of the earth. During this period most of the anaerobes extinct or evolve to live as a parasite or symbol on in other hosts.
Answer:
In the second picture, the answer is A to attach to a host cell.
In the third, the fourth and the fifth the answer is D.
Explanation:
