In plants, dead cells are not excreted, rather, they form key structural elements which support and protect living tissue as the organism grows. Two examples of useful functions are the formation of (1.) xylem vessels and (2.)sclerenchyma.
Explanation:
Xylem vessel: mature xylem vessel is made up of dead cells called <em>vessel elements</em> aligned end-to-end; here, the ends are dissolved and the protoplasm is absent. These form long, continuous tubes that facilitate the unobstructed flow of water and minerals to other areas within plants.
Sclerenchyma are comprised of dead cells which have secondary walls reinforced with lignin. In plants, they provide key structural support and greater mechanical strength to prevent damage or tears within the plant tissue.
Unlike the light reactions, which take place in the thylakoid membrane, the reactions of the Calvin cycle take place in the stroma (the inner space of chloroplasts).
