CBSE Questions for Class 12 Medical Biology Ecosystem Quiz 15 - MCQExams.com

• The given pyramid best represents Pyramid of numbers in forest ecosystem.
•  The given pyramid best represents pyramid of numbers in forest ecosystem as it is spindle-shaped. The producers are giant size trees in the forest ecosystem, and they form the base of the pyramid. The producers are usually less in number, but they support a higher number of herbivores such as deer, birds and elephants. The number goes down at each succeeding level as the primary consumers support very fewer numbers of carnivores. This results in a spindle-shaped structure of the pyramid of numbers in the forest ecosystem.
• Thus, Option D is correct.

Correct Option: B

Explanation:

•  The pyramid of numbers tends to represent the organism number across each trophic level.
• In a forest ecosystem, As the trophic level increase, the number of organisms decreases.

Hence, the pyramid of numbers is upright.

• Gross Primary Production, GPP, is the total amount of CO$$_2$$ that is fixed by the plant in photosynthesis.
• Respiration (R) is the amount of CO$$_2$$ that is lost from an organism or system from metabolic activity. 
• Net Primary Production (NPP) is the net amount of primary production after the costs of plant respiration are included. Therefore, NPP = GPP - R.
  
• It is the amount of energy that a plant stores as biomass, which is then available to heterotrophs.
  
• Primary productivity is the rate of formation of new organic matter by producers i.e. Plants and other photosynthetic organisms. 
• Secondary productivity is the rate of formation of new organic matter by consumers.
  

A.Correct option C

B.Explanation for the correct option:

1. Biomass is the standing amount of weight an area holds of all the organisms with respect to time.

2. Trophic levels are the parameters that define the source through which the producers and consumers acquire their food.

3. Producers are one that is autotrophs. Primary consumers are the herbivore of that ecosystem. Secondary consumers are those that feed upon the primary consumers hence; they follow carnivores’ pattern of feeding.

4. Generally, the pyramid of biomass is upright, but there exists an exception of the pond ecosystem where the pyramid is inverted.

5. In the pond ecosystem the biomass of plants is comparatively less than other trophic level organisms because as we go up the body biomass increases exponentially in this case.

• The number of primary consumers is always less than the producers in a pyramid of numbers that represent an ecosystem with a large freshwater pond. In a large freshwater pond, the producers are always higher in number. The number of primary consumers is less than the producers, and secondary consumers are even less in number. The top consumers in a pond ecosystem are least in number.

• The Rivet Popper hypothesis given by Paul Ehlrich tries to explain the importance of key species in an ecosystem. 
• The hypothesis compares the ecosystem with an aeroplane and the rivets with the species that are joining the parts of the aeroplane/ecosystem together. 
• If the passengers start taking out the rivets, then initially there will be no issue in flight but later, the aeroplane will not be capable to maintain its flight.
• Similarly, if the key species are exploited, they would be extinct, which would not harm the ecosystem initially but later, the ecosystem will collapse.
• However, those rivets which are the parts of the wings are more important because they are directly involved with the flight function. 
• These rivets on wings are compared to the key species of an ecosystem. 

A.Primary production – The amount of biomass product per unit area over a time period by plant during photosynthesis is called Primary production.

B.Net primary production - s the rate at which all the plants in an ecosystem produce net useful chemical energy; it is equal to the difference between the rate at which the plants in an ecosystem produce useful chemical energy (GPP) and the rate at which they use some of that energy during respiration.

C.Gross primary production - the amount of chemical energy as biomass that primary producers create in a given length of time

D.secondary production - the generation of biomass of heterotrophic (consumer) organisms in a system. This is driven by the transfer of organic material between trophic levels, and represents the quantity of new tissue created through the use of assimilated food.

$$\textbf{Solution}$$

$$\bullet$$ This ecological pyramid shows that the primary producers are less in number than the primary consumers.

Xerosere is a plant succession that is limited by water availability. It includes the different stages in a xerarch succession. The xerarch succession of ecological communities originated in an extremely dry situation such as sand deserts, sand dunes, salt deserts, rock deserts etc. A xerosere may include lithosere (on rock) and psammoseres (on sand).

The stages in order are -