CBSE Questions for Class 12 Medical Biology Ecosystem Quiz 4 - MCQExams.com

$$\textbf{Correct option: }$$ A

$$\textbf{ Solution: }$$

$$\textbf{ Option (A): }$$

$$\bullet$$ The rate of energy conversion to the organic substances with the help of producers and chemoautotrophs is known as primary productivity.

$$\bullet$$ The energy obtained from the producers (photoautotrophs) is in the form of light energy whereas the energy is chemical energy obtained from chemoautotrophs through oxidation. 

$$\bullet$$ This primary productivity limiting factor is the carbon element in the form of carbon dioxide gas.  

$$\bullet$$ Carbon dioxide is the gas which is absorbed by plants for the process of photosynthesis.

$$\bullet$$ As a result of photosynthesis, CO2 is converted into glucose, which is the energy produced for the plants as well as the heterotrophs which depend on autotrophic plants. 

$$\bullet$$ The availability of carbon elements determines the rate of photosynthesis, acting as a limiting factor. 

Hence, the correct option is (A).

• In an ecosystem, the rate of production or accumulation of organic matter per unit area per unit time is called productivity. 
• Plants are autotrophic. They perform photosynthesis by using solar energy to synthesize their own food. Hence they are the producers in an ecosystem.
• The rate at which solar energy is stored by producers is called primary productivity. 

• The transition in the species composition of a given area is called ecological succession. 
• During succession, the colonization of species in a particular area increases its population whereas, populations of other species decline and even disappear. 
• The present-day communities in the world have come to be because of succession that has occurred over millions of years since life started on earth.
• Plant succession is a change which passes through definite developmental sequence and proceeds in a definite direction. 

• The gradual changes (succession) of micro-organisms in a microhabitat is known as micro succession or serule e.g., fungi, bacteria. 
• This type of succession occurs within communities, for example in dead trees, animal droppings, etc. 
• It is mainly affected by the conditions available for growth like oxygen, moisture, nutrient etc.

• The transition in the species composition of a given area is called ecological succession. 
• This takes place due to the change in the environmental conditions in a geographical area. 
• During succession, some species colonise an area and their populations become more numerous, whereas populations of other species decline and even disappear. 
• The time scale can be decades (for example, after a wildfire), or even millions of years after a mass extinction. 

• The pyramid of number indicates the number of individual present at each trophic level. 
• The pyramid of numbers can be upright or inverted depending on the number of producers. 
• For example, in a grassland ecosystem, the pyramid of numbers is upright. 
• In this type of a food chain, the number of producers (plants) which is highest is followed by the number of herbivores (mice), which in turn is followed by the number of secondary consumers (snakes) and tertiary carnivores (eagles). .