Question

Where do certain symbiotic microorganisms normally occur in the human body
A. Oral lining and tongue surface
B. Vermiform appendix and rectum
C. Duodenum
D. Caecum

Answer 1

Symbiosis is usually defined as a relationship between two organisms where both the living beings are completely different from each other from every facet. But they stick together for the work to have functioned that helps them to complete the task. The symbiotic relationship between them can benefit both of the organisms or it can also benefit only one organism(commensalism) or parasitic. Symbiotic microorganisms also help in the digestive system as they break down complex foods into simple food that contains fibre. They additionally produce vitamins. These symbiotic microorganisms are also present in ruminants.

Complete answer:
Caecum in the large intestine is the only place in the digestive system which hosts independent symbiotic microorganisms. It's a small blind sac-like structure which helps in the synthesis of Vitamin B-12 and helps indigestion. The caecum is connected to the colon(which is the largest part of the large intestine). Colon doesn’t contain digestive glands but harbours plenty of microorganisms some of which are symbiotic.
The Oral Lining and also tongue surface produces enzymes and secretive juices which helps in digestion, they don’t unleash any microorganisms. Also, the vermiform appendix helps in providing the mucosal immune system and rectum releases the nitrogenous wastes of the body. At duodenum, the absorption of food takes place by enzymes. Hence only Caecum remains where symbiotic microorganisms are hosted and synthesis of vitamins take place.

Hence, the correct answer is option (D).

Additional information:
Symbiosis is any kind of a detailed and long-term biological interaction between two different biological organisms, be it mutualistic, commensalism, or parasitic. The relationship may be positive, negative, or neutral. An example of this would be a remora being attached to a shark throughout their life and getting food from what the shark eats. Symbiosis was first defined by Marko de Bary.
Symbiotic bacteria refers to those groups of microorganisms which work in association with either plant life, animal life or fungus in which bacteria as well as the host to which it is attached, both are benefited. Symbiotic bacteria are bacteria living in symbiosis or biological interaction with another organism or host body. Some of the examples of symbiotic bacteria are:-
-Rhizobium fixes with leguminous plants
-Frankia with dicotyledonous plants
-Azospirillum with some cereal grasses.

Note: symbiotic association between plants and prokaryotes are beneficial for plant productivity and growth , plant community structure and acquisition of limiting resources in legume-rich grassland communities. As symbiosis not only helps the plants but also the environment for nitrogen-fixation.