AP BIOLOGY

Detailed explanation-1: -Acids that break down the rock and start the process of soil formation are secreted by lichens that colonize bare rock. They provide organic matter to the soil when they die. Mosses will then colonize the thin soil; the soil thickens further when moses die, other hardy species to colonize that land.

Detailed explanation-2: -Lichens are considered as pioneer species in primary succession on rocks because they can easily grow on rocks where other plants cannot grow. They produce oxalic acid which induced the weathering of rocks and thus soil is formed.

Detailed explanation-3: -Spores of lichen or fungus, being the pioneer species, are spread onto a land of rocks. Then, the rocks are broken down into smaller pieces and organic matter gradually accumulates, favouring the growth of larger plants like grasses, ferns and herbs.

Detailed explanation-4: -This process is called primary succession. It begins with organisms such as lichens that can live and grow very slowly on bare rock. Lichens (see the Fungi station) break down rock by secreting acids. The freeze-thaw cycle of winter also contributes to rock destruction.

Detailed explanation-5: -In primary succession, pioneer plants are those that can grow without soil, such as lichens. Lichens begin breaking down a rock. Seasonal cycles of freezing and thawing form cracks in the rock. The dead remains of lichens and dust fall into the cracks.