Maharashtra Class 7 Answered
The excretion mechanism in plants is completely different from animals. Different plants use different types of strategies.
Oxygen can be cinsidered as a waste product of photosynthesis and carbon dioxide a waste product of respiration; water is a waste product of both. Oxygen and carbon dioxide diffuse out through openings in the leaves (stomata) or through the cell walls of roots and other plant structures. Water will be lost through transpiration and guttation or just used for maintaining turgor in cells.
Some trees deposit waste chemicals in their branches and trunks, especially in old xylem which is probably no longer used for water transport. Materials that are exuded by some plants—resins, saps, latexes, etc.—are forced from the interior of the plant by hydrostatic pressures inside the plant and by absorptive forces of plant cells. These forces are passive in nature, and exudation requires no energy expenditure on the part of the plant.
Plant cells have large vacuoles, and these can be used for either storage of useful compounds, or the storage of waste substances - often accumulating at concentrations that lead to crystal formation in the vacuole.
Plants can also store the waste in organs that are destined to fall off (like autumn leaves) or die off (like the leaves and stalk of a bluebell which is dying back in the summer,leaving the bulb underground.
Some plants will actively secrete waste compounds into the soil, occasionally using them as chemical weapons against other competing plants.
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