Cells are just biological automata, they are dead thing, just a bunch of robots exchanging messages, no more alive than a chair. However, when many types of cells come together, they form a living being.
Consciousness, or life, is an emrgent property that appeared due a collection of cells working together, it's more than the sum of its parts.
Where is the boundary? When do these automata become alive? We don't know, but we can be sure that monkeys and mice are alive, and they feel things. They feel pain, which is a property of the neural system.
To use another analogy, let's imagine a conscious robot. It's made of various metallic things, of nuts, bolts, alloys, wires, sensors, and let's assume it feels pain.
Performing stress testing on the individual bolts that make up its body (just bolts, like spare parts, from a toolbox) would not cause anything to feel pain.
I really recommend watching this kurzgesagt video [1] about cells, proteins, and how they interact.
[1] https://youtu.be/TYPFenJQciw