LIFE SCIENCE

Detailed explanation-1: -Bacteria were the first organisms to appear on the earth. At that time the environment was devoid of oxygen. Hence, these first bacteria were anaerobic and they were also heterotrophic due to lack of photosynthetic activity.

Detailed explanation-2: -The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things.

Detailed explanation-3: -Prokaryotes were the earliest life forms, simple creatures that fed on carbon compounds that were accumulating in Earth’s early oceans.

Detailed explanation-4: -Organisms that can use oxygen to produce energy are said to be aerobic. Those that cannot are anaerobic. The first bacteria to appear on Earth, some 3.8 billion years ago, had no choice but to be anaerobic, because the atmosphere at that time contained no oxygen.

Detailed explanation-5: -The first life forms were anaerobic as the primitive atmosphere was reducing and oxygen was absent. They were chemoheterotrophs that used the organic component as a source of energy and carbon.