Concept:Unicellular organisms perform all physiological activities using specialized structures called organelles.
Explanation:At the cellular level of organization, the organism consists of a single cell.
All life processes such as digestion, respiration, and excretion happen inside this cell.
These activities are carried out by specialized structures within the cell.
These specialized structures are known as organelles.
The cell membrane and cytoplasm provide support, but the actual physiological functions depend on organelles.
Thus, a cellular-level organism uses its organelles to carry out physiological activities.
Answer:B. organelles