The correct answer is option 1. This means that the statement "They require a separate organ for food uptake" is not correct for single-celled organisms. Let`s explore each option to understand why this is the correct answer.

Option 1: The statement is incorrect because single-celled organisms, such as bacteria or amoebas, do not require a separate organ for food uptake. They have structures like cell membranes or specialized organelles that allow them to take in and process nutrients.

Option 2: This statement is correct. Single-celled organisms do not need a separate organ for respiration. They exchange gases directly with the environment through their cell membrane or other respiratory structures.

Option 3: This statement is also correct. Single-celled organisms produce waste or excretory material, just like multicellular organisms do. They eliminate waste through processes like diffusion or exocytosis.

Option 4: This statement is correct. Single-celled organisms remain in direct contact with the external environment, as they do not have complex internal systems or organs like multicellular organisms.

In conclusion, option 1 is the correct answer because single-celled organisms do not require a separate organ for food uptake.