Here's why:

* No cell specialization: In intracellular digestion, there is no specialized digestive system or organs. Instead, food is broken down directly within the cells themselves. This is typical of single-celled organisms like amoebas and some bacteria.

* One opening: Since there's no specialized digestive system, there's only one opening to the organism's body. This opening serves both as the point of entry for food and the exit point for waste.

Here's how it works:

1. The organism engulfs food particles through the single opening.

2. The food is enclosed within a vacuole within the cell.

3. Digestive enzymes are secreted into the vacuole, breaking down the food into smaller molecules.

4. The cell absorbs the nutrients from the broken-down food.

5. Waste products are expelled through the same opening.

In contrast, multicellular organisms have:

* Extracellular digestion: Food is broken down outside of the cells, in a specialized digestive system.

* Specialized cells and organs: Different organs are responsible for different parts of the digestive process, like ingestion, digestion, absorption, and elimination.

* Two openings: One opening for food intake (mouth) and another for waste removal (anus).