Important Questions Class 12 Biology Chapter 12

Important Questions Class 12 Biology Chapter 12 are essential for CBSE Class 12 students aiming to score high in the board examination. The Ecosystem chapter is frequently tested through MCQs, short answers, assertion-reason, and long descriptive questions. 

Practising these exam-oriented questions helps students revise core concepts like energy flow, productivity, nutrient cycling, and ecological pyramids while improving answer accuracy and time management.

Topics such as the 10% law of energy transfer, GPP and NPP, decomposition, and ecological pyramids form the backbone of most Ecosystem Class 12 question answers, making this chapter highly scoring when prepared strategically.

Class 12 Biology Chapter 12 Ecosystem

The Ecosystem chapter explores the functional unit of nature where living organisms interact among themselves and with their physical environment. Key concepts include productivity (GPP and NPP), decomposition, and the unidirectional flow of energy following the 10% law. 

It also details ecological pyramids of number, biomass, and energy, while highlighting the limitations of these models and the vital role of nutrient cycling and ecosystem services. Understanding these interactions is crucial for solving Ecosystem class 12 question answers effectively during your board exams.

Important Questions Class 12 Biology Chapter 12

To ensure you are fully prepared, we have compiled a list of important questions  Class 12 Biology chapter 12, ranging from multiple-choice questions to detailed explanations. Practice these to gain confidence for your upcoming finals.

1. In an ecosystem, which one of the following types of entities occupies more than one trophic level?

(1) Frog

(2) Phytoplankton

(3) Zooplankton

(4) Fish

Ans. (4) Fish

2. This ecosystem has the maximum biomass

(1) Grassland ecosystem

(2) Pond ecosystem

(3) Lake ecosystem

(4) Forest ecosystem

Ans. (4) Forest ecosystem

3. These are the primary producers of the deep-sea hydrothermal vent ecosystem

(1) blue-green algae

(2) coral reefs

(3) chemosynthetic bacteria

(4) green algae

Ans. (3) chemosynthetic bacteria

4. In an ecosystem, which is the ultimate source of energy?

Ans. Solar radiation

5. What makes oceans the least productive?

Ans. It is because of the lack of sunlight with increasing depth. Oceans lack nitrogen, which is an important source of nutrient for plants. High salinity offered by oceans does not serve as a favourable condition for all plants. More importantly, the absence of soil is the reason why plants do not sustain.

6. The Tundra desert’s gross primary productivity (GPP) is 800 kilocalories/m2 and respiration losses are about 200 kilocalories.

(a) What is the net primary productivity of the desert? Show calculations.

(b) Why do deserts have the least NPP across most ecosystems?

Ans. (a) 0.5 marks for the correct formula and 0.5 marks for the correct answer:

NPP = GPP – R

NPP = 800 – 200 = 600 kilocalories/m2

(b) The low water availability and other conditions are not unfavourable for rapid photosynthesis.

7. Availability of energy is less for entities at higher trophic levels. Why?

Ans. The 10% energy flow law suggested by Lidman, is followed in the ecosystem. As per this law, only 10% of the energy that is available at every trophic level is transferred to the next trophic level. The remaining is lost in the form of heat (during respiration). As we approach the higher levels, energy keeps declining that is available to entities. Hence the topmost carnivore attains the least amount of energy in a food chain.

8. Why is the number of trophic levels in an ecosystem limited?

Ans. There are not more than 4-5 levels since the energy flow declines as we approach higher levels as only 10% of energy is passed from one to the next progressive trophic level. The remaining energy is lost during respiration and in other crucial activities to the sustenance of life. In case there are more levels, the remaining energy will be limited to an extent that it furthermore would not be able to sustain any trophic level through energy flow. Hence levels are limited.

9. Why does primary productivity vary in different ecosystems?

Ans. The rate at which plants (primary producers) utilize and store solar rays for the formation of chemical energy is referred to as primary productivity. In ecosystems, producers vary and as primary production is dependant on plants, it varies in different ecosystems.

10. In the study of the ecosystem, what are the limitations of ecological pyramids?

Ans. Following are the shortcomings:

• A species can function at two or more trophic levels

• These pyramids represent only simple food chains. But only complex food chains occur in nature.

• Decomposers play a crucial role to maintain stability in an ecosystem which these pyramids do not account for.

Exam Preparation Tips for CBSE Class 12 Biology Chapter 12

Smart revision of Chapter 12 Ecosystem requires conceptual clarity and exam-oriented practice. These tips will help CBSE Class 12 students answer important questions in the Class 12 Biology chapter 12 accurately and score higher.

• Master the 10% Law: Always remember that energy decreases as you move up trophic levels. This is a frequent topic for important questions Class 12 Biology chapter 12.

• Differentiate GPP and NPP: Be clear on the mathematical relationship between Gross and Net Primary Productivity to solve numerical problems.

• Diagram Practice: Draw and label ecological pyramids clearly. Remember that the pyramid of energy is always upright.

Focus on Keywords: When writing Ecosystem class 12 question answers, use terms like "fragmentation," "leaching," "catabolism," and "humification" to impress examiners.