An ecological succession is a gradual change in the biological community due to changes in the non-living or abiotic factors of the ecosystem and with respect to time until the ecosystem attains stability. Primary succession occurs in region which is not previously inhabitat by any floral or faunal species. It occurs specifically in barren and lifeless landforms. This includes regions where soil is incapable for plant growth. Hot lava released after volcanic eruption will make the soil unsuitable for plant growth also rocks found in these regions are compact. Therefore, pioneer or primitive species act on such rocks and soil like lichen and produces acids which remove the compaction from these soils and make them suitable for growth of plants in that region.
<span>The word from the pick list that fits here is "enzyme". Enzymes are normally spcialised protein molecules and they act as catalyst ie agents to speed up a reaction in causing traits to develop in the genes of organisms in reaction to chemical stimulants.</span>
