CBSE Questions for Class 12 Medical Biology Ecosystem Quiz 9 - MCQExams.com

• 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'.

a) Primary succession happens in a bare rock and pond areas whereas the secondary succession occurs in the areas affected by natural calamities.

b) Hydrarch succession occurs only in water areas.

c) When a community becomes stable and is in equilibrium with the environmental conditions, it is called the climax community.

d)The areas such as lava flow in which the soil is incapable of developing sustainable lives undergo primary succession.

So the correct option is B.

• Phytoplankton is a diverse group of single-celled organisms capable of performing photosynthesis. They are responsible for a significant portion of the oxygen we breathe and hence called lungs of the world.
• Pioneer species are the first species to colonize barren environments or previously biodiverse steady-state ecosystems that have been disrupted, such as by fire. The pioneer species are the first stages of ecological succession. Some lichens grow on rocks without soil, so are the pioneer species, and break down the rocks into soil for plants.
  
• The plants which grow best at lower light intensities are called sciophytes. They have developed many adaptations for displaying their foliage to light. They may be twiners, climbers or epiphytes.
  
• Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. Examples include areas which have been cleared of existing vegetation such as abandoned farmlands.

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.

• 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.

• 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.

• A forest pyramid of umber shows secondary consumers on the top.
• As we move down, there are the primary consumers and then, the producers.