The correct answer is option 3 i.e. both unicellular and multicellular organisms .

Division of labour refers to the specialization of functions within a biological system. While it's most apparent in multicellular organisms, where different cells or groups of cells perform specific tasks, some unicellular organisms also exhibit a form of division of labour.

• In multicellular organisms, division of labour is evident as cells differentiate into specialized tissues and organs, each performing specific functions. This specialization allows for increased efficiency and complexity in biological processes.

• In unicellular organisms, division of labour occurs within the single cell. Different organelles perform specialized functions, such as energy production by mitochondria, protein synthesis by ribosomes, and waste processing by lysosomes. Additionally, some unicellular organisms, like certain algae, can form colonies where individual cells specialize in different tasks, demonstrating a more complex form of division of labour at the organismal level.

 Other options explained:

• Only unicellular organisms:  while unicellular organisms exhibit internal division of labour, multicellular organisms also display this phenomenon.

• Only multicellular organisms:  unicellular organisms also demonstrate division of labour, albeit in a different form.

• Neither unicellular nor multicellular organisms: both types of organisms exhibit division of labour, though in different ways.