(a) The advantages of complex structural organisation in higher animals are:
(i) There is cellular differentiation or group of similar cells differentiate to form tissues that carry out similar functions.
(ii) Differential leads to internal structural specialization or the group of similar cells or tissues becomes specialised to carry out one or more functions.
(iii) It increases adaptation to environment.
(v) It leads to mutual interdependence between component cells or division of labour by component cells which leads to efficiency and increase in size.
(b)(i) Differences between colonial organisms and filamentous organisms are:

Colonial organism	Filamentous organisms
-Intercellular cell-wall is absent-Identical cells form a mass. -Cells are linked by cytoplasmic bridges/ connected by cytoplasmic material, i.e., physiologically dependent.	-Inter-cellular cell-wall is present.-Identical cells form end- to -end arrangement/ threadlike filamentous/ linear structure.-All cells are physiologically independent.

(ii) Examples of a colonial organisms are:- Pandorina / Volvox while that of filamentous organism is Spirogyra / Zygnema / Oscillateria