Plants generally don't have special mechanisms for elimination of unwanted products from their body. However they do so by the following ways:

1. The oxygen produced during photosynthesis as a by-product is released out into the atmosphere through tiny pores called stomata.

2. Stomata are also the site of release of the water vapours during transpiration.

3. Some excess water may also be eliminated through pores called hydathodes present on the leaf margins of some plants during the process of guttation.

4. Some plants even exude wastes in the form of gums, resins, saps and latex, etc. which are forced out through hydrostatic forces acting within the plants.