Why are there no multicellular anaerobic organisms?

Answer 1

I'm not sure how old this question is, but in fact three species multicellular anaerobic organisims were found in deep-sea sediments in April 2010. If you do a search for 'multicellular anaerobic organisms' you can see the details.

Answer 2

The most accepted theory of the born of life on Earth is related to anaerobic organisms which could grow in absence of oxygen. It has being postulated that the first living cells appeared more than 3.5 x 109 years ago. At that time, the atmospheric and environmental conditions on the planet lacked of molecular oxygen but rich in geochemically produced organic molecules. Under these basis, it's well accepted by the scientific community that the earliest living forms should have had such a metabolic pathways for producing ATP, that presumably resembled present-day forms of fermentation process.

Answer 3

Multicellular organisms have higher energy demands and anaerobic metabolism is less efficient in producing energy compared to aerobic metabolism. As a result, multicellular organisms have evolved to rely on aerobic respiration to meet their energy needs. Additionally, the lack of oxygen in anaerobic environments may limit the size and complexity of multicellular organisms due to constraints on metabolism and gas exchange.

Answer 4

The early organisms on Earth were anaerobic because there was no oxygen available.