The cell wall is absent in

The cell wall is a rigid outer layer found in plant cells, fungi, and some bacteria. It helps maintain the shape and provides protection to the cell. However, it is absent in animal cells.

Now, let's break down the options:

1. Cow: Cows are animals, and animal cells do not have a cell wall.
2. Human: Human cells are also animal cells, so they do not have a cell wall.
3. Rat: Like cows and humans, rat cells are animal cells, and they lack a cell wall.