What term best describes the following organism: the so-called blue-green algae, they are photosynthetic bacteria; producing oxygen, they contain sheets of plasma membranes that contain photosystems; they utilize chlorophyll-a; just like plants; but contain phycolibin pigments that are not found in plant chloroplasts; form heterocysts that are nitrogen fixing; form akinetes (spores); and heterocysts (n-fixing cells); some have separation discs (hormonogonia) that cause filaments to fragment (dispersal); prochloronta a subclade that is ancestral to plant chloroplasts?
a) methanogen.
b) spirochaeta.
c) enteric bacteria.
d) extreme halophile.
e) cyanobacteria.

The correct answer will be option E.

Explanation:

The features given in the question are the characteristics features of the group of bacteria belonging to Cyanobacteria.

These Cyanobacteria are the prokaryotes which are capable of synthesizing the food through a process called photosynthesis. These bacteria use sunlight as their energy, use water and air to synthesize food. They under anaerobic condition synthesize the nitrogen in special structures called heterocyst, a characteristic feature of cyanobacteria.

Thus, the features given in the question are:  

1. contain photosystems to carry out photosynthesis.

2. producing oxygen

4. contain phycobilins

6. Hetrocysts: nitrogen-fixing structures.

7. The ancestor of plant chloroplasts.

Thus, option E is the correct answer.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.