Ecosystem Test - 54

Secondary succession occurs in the areas where there occurred some natural disasters like hurricane, forest fire which reduces the ecosystem. It includes abandoned farm lands.

Primary succession takes place in a newly formed area like new ponds and bare rocks and the areas where the soil is unable to develop sustainable lives like newly cooled lava and retreated glacier areas.

So the correct option is A.

The pioneer species in xerarch and hydrarch succession are lichens and phytoplanktons respectively. Xerarch is a plant succession starting on bare ground or rock and culminating in a mature climax forest. The pioneer species, such as lichens and mosses, result in the gradual accumulation of soil. Hydrarch is a plant succession which starts in relatively shallow water, such as ponds and lakes and culminating in a mature forest, e.g. phytoplankton, Hydrilla, Vallisneria.

• An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems.
•  The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems.
  
• Maximum productivity (on a global basis) is shown by the aquatic ecosystem because 90% of total photosynthesis occurs in oceans and lakes by algae.
  
• So, the correct answer is 'Aquatic ecosystem'.

• If succession takes place on rock, it is called Lithosere.
• If succession takes place on sand, it is called Psammosere.
• If succession takes place in a saline environment, it is called Halosere.

In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. In secondary succession, an area that was previously occupied by living things is disturbed, then re-colonized following the disturbance.

• Phosphorus moves in a cycle through rocks, water, soil and sediments, and organisms, called the 'phosphorus cycle', which is an imperfect nutrient cycle.
• Gaseous cycles are cycles like water cycle, carbon cycle, nitrogen cycle, etc. where the reservoir is a natural atmosphere or the hydrosphere.  
• In a perfect nutrient cycle, nutrients are replaced as fast as they are utilized. So all the gaseous cycles are usually considered perfect cycles. 
• Sedimentary cycles are considered relatively imperfect cycles. The Earth’s crust elements are the reservoir of sedimentary cycles. They are called imperfect cycles because some nutrients that are lost from the cycle get locked into sediments and thus, become unavailable for immediate cycling. Eg.:  Cycles of phosphorous, sulfur, calcium, magnesium, etc.
  
• So, the correct answer is option D.