Q.Define ecosystem services, giving pollination as an example.

Ecosystem services are the benefits that plant communities and the wider ecosystems they form provide to the environment and to human life, typically delivered continuously by ordinary, healthy plant communities without any deliberate human effort.

One of the clearest such services is pollination. A very large proportion of flowering plants — including many crop species humans rely on for food — cannot set seed or fruit without their flowers being pollinated, and this pollination is carried out largely by animal pollinators such as bees, butterflies, and certain birds. By offering nectar and pollen as a reward, plants sustain stable pollinator populations, and in return those pollinators enable the reproduction of both wild plant species and cultivated crops — a two-way ecological relationship in which each side depends on the other's continued survival.

Two further vital services flow directly from photosynthesis: carbon fixation and oxygen release. During photosynthesis, green plants absorb atmospheric carbon dioxide and use it to build organic compounds within their tissues, effectively locking away, or "fixing," carbon that would otherwise remain in the atmosphere as a greenhouse gas. Carried out across entire forests, grasslands, and other plant communities, this fixation of atmospheric carbon dioxide is one of the most important natural processes moderating greenhouse-gas levels in the atmosphere and mitigating climate change. At the same time, photosynthesis releases oxygen as a byproduct, and it is this continuously replenished atmospheric oxygen that sustains the aerobic respiration of virtually all animal and plant life, humans included. …