Question

Why in the case of single celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed?

Answer 1

heya............

Heya folk !!!
Here's the answer you are looking for
In unicellular organisms there is only one cell which governs the all the activities of the cell so only through diffusion materials like gases, water etc can exchange between the environment and the cell. 
It does not require any special system through which exchange takes place.
But in case of a multicellular organisms there is separate system for separate function. Many cells clustered together to form tissues, tissues to organs and organs to organ system. So through diffusion the process of exchange of materials between the organism and the environment is not fulfilled Multicellular organisms have a complicated system so diffusion is not the process which can fulfil the requirements of the organisms.
For instance, in human beings diffusion of gas from the head to the feet can take up to 3 years. 
Therefore, diffusion is not efficient in performing different functions that are required for a multicellular organism to live.

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tysm.....@kundan

Answer 2

Answer:

In the case of a single-celled organism, no specific organs for taking in food, exchange of gases or removal of wastes may be needed because the entire surface of the organism is in contact with the environment.

Explanation: