I don't know what you mean by "cut plants". Plants respire when they can't get enough energy to subsist on via photosynthesis. This usually happens at night or, for plants that shut down for part of the year, during the cold/dry season. If you mean cutting a plant down, the reason why plants die when cut is because they can no longer transport water, so they dehydrate to death;all of the chemistry that allows plants to live, either when photosynthesizing or when respiring, takes place in water, so without water a plant is dead.

Respiration is something living plants and animals do. Cut plants will usually die, unless they're plants that can grow roots and have enough light, water, and soil.

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