GSEB Class 12 Biology Solutions Chapter 14 Ecosystem

GSEB Class 12 Biology Ecosystem Text Book Questions and Answers

Question 1. Fill in the blanks.
1. Plants are called as .................... because they fix carbon dioxide.
2. In an ecosystem dominated by trees, the pyramid (of numbers) is .................... type.
3. In aquatic ecosystems, the limiting factor for productivity is ....................
4. Common detritivores in our ecosystem are ....................
5. The major reservoir of carbon on earth is....................
Answer:
1. Autotrophs
2. Upright
3. Light
4. Bacteria and earthworms.
5. Oceans
In simple words: This section tests basic ecological terminology and concepts, identifying key roles and components within an ecosystem, such as producers, pyramid types, limiting factors, decomposers, and carbon reservoirs.

🎯 Exam Tip: Remember these fundamental ecological definitions and examples as they often appear in multiple-choice questions or short answer formats. Pay close attention to the specific characteristics of different ecosystem types.

Question 2. Which one of the following has the largest population in a food chain?
a. Producers
b. Primary consumers
c. Secondary consumers
d. Decomposers
Answer: (d) Decomposers
In simple words: Decomposers, like bacteria and fungi, are generally the most numerous organisms in an ecosystem because they break down dead organic matter from all trophic levels, making their population size vast and essential for nutrient recycling.

🎯 Exam Tip: Understand the role of each trophic level and decomposers in an ecosystem. Decomposers are crucial for nutrient cycling, and their populations are typically the largest due to their ubiquitous presence and function.

Question 3. The second trophic level in a lake is
a. phytoplankton
b. zooplankton
c. benthos
d. fishes
Answer: (b) zooplankton
In simple words: In a lake ecosystem, phytoplankton are the primary producers (first trophic level); zooplankton feed on phytoplankton, thus occupying the second trophic level as primary consumers.

🎯 Exam Tip: Clearly identify the organisms at each trophic level in different ecosystems, especially aquatic ones. Primary producers form the base, followed by primary consumers (herbivores) at the second level.

Question 4. Secondary producers are
a. herbivores
b. producers
c. carnivores
d. None of the above
Answer: (d) None of the above
In simple words: The term "secondary producers" is not standard in ecology; producers (like plants) are primary, and consumers are heterotrophs. No organism is typically labeled a "secondary producer" in the context of creating organic matter from inorganic substances.

🎯 Exam Tip: Be precise with ecological terminology. Producers synthesize organic matter, while consumers derive energy from consuming other organisms. The term "secondary producer" is not commonly used in standard ecological models.

Question 5. What is the percentage of photosynthetically active radiation (PAR), in incident solar radiation?
a. 100%
b. 50%
c. 1-5%
d. 2-10%
Answer: (b) 50%
In simple words: Approximately 50% of the total incident solar radiation falls within the photosynthetically active radiation (PAR) spectrum, which plants can use for photosynthesis.

🎯 Exam Tip: Know the typical percentage of solar radiation that is photosynthetically active. This value is fundamental to understanding energy capture in ecosystems.

Question 6. Distinguish between
a. Grazing food chain and detritus food chain
b. Production and decomposition
c. Upright and inverted pyramid
d. Food chain and Food web
e. Litter and detritus
f. Primary and secondary productivity
Answer:
a. **Grazing food chain:** This food chain initiates with plant biomass, which is consumed by herbivores. These herbivores are then subsequently eaten by various carnivores, forming a series of energy transfers.
**Detritus food chain:** In contrast, this food chain starts with the dead organic matter, such as dead animal bodies and fallen leaves, which are commonly referred to as detritus.

b. **Production:** This term refers to the process of synthesizing organic compounds from inorganic substances, like CO2, H2O, and minerals, primarily utilizing sunlight. Plants are the main organisms responsible for this process.
**Decomposition:** This is the process where substances are broken down into their constituent parts, mainly carried out by reducer organisms like bacteria and fungi.

c. **Upright pyramid:** An upright pyramid occurs when the number or biomass of producer organisms is maximal in an ecosystem, and these values progressively diminish at each subsequent trophic level in a food chain.
**Inverted pyramid:** An inverted pyramid arises when the number of individuals or the biomass at the producer level is minimal, and these values progressively increase at higher trophic levels within a food chain.

d. **Food chain:** This describes the sequential inter-linking of organisms where food energy is transferred from producers through a series of organisms that eat and are eaten in turn.
**Food web:** A food web represents a complex network of interconnected food chains at various trophic levels, forming multiple feeding connections among different organisms within a biotic community.

e. **Detritus:** This comprises the dead remains of plants and animals, categorized into litterfall and below-ground detritus.
**Litter:** Specifically, litter is the above-ground detritus, consisting of dead plant remains, dead animal remains, and their fecal matter that falls onto the Earth's surface in terrestrial ecosystems.

f. **Primary productivity:** This refers to the rate at which producers in an ecosystem generate biomass or organic matter per unit area over a specific time period.
**Secondary productivity:** This describes the rate at which consumers in an ecosystem produce biomass or organic matter over a specific time period.
In simple words: This question differentiates various key ecological terms, covering energy flow pathways (grazing vs. detritus food chains), fundamental processes (production vs. decomposition), structural representations (upright vs. inverted pyramids), feeding relationships (food chain vs. food web), organic matter categories (litter vs. detritus), and rates of organic matter creation (primary vs. secondary productivity).

🎯 Exam Tip: For "distinguish between" questions, provide clear, concise definitions for each term and highlight their key differences. Using comparative language (e.g., "in contrast," "whereas") can help clarify the distinctions effectively.

Question 7. Describe the components of an ecosystem.
Answer:
An ecosystem's components can be categorized into two primary types: the biotic component, which includes various organisms, and the abiotic component, consisting of environmental factors.

a. **Biotic components:** These are the living organisms within an ecosystem, forming interconnected relationships primarily through food. Based on how they obtain food, organisms in an ecosystem are categorized into three main groups:
i. **Producers:** These organisms create food materials. They are divided into two types:
**Photoautotrophs:** These are green plants containing chlorophyll. They capture light energy and convert it into chemical energy through photosynthesis.
**Chemoautotrophs:** These are certain bacteria, such as sulfur bacteria and iron bacteria, which capture energy released from chemical reactions to synthesize organic food.
ii. **Consumers:** These are mainly animals that cannot produce their own food. They obtain materials and energy by consuming producers or other consumers. Consumers are further classified into primary, secondary, and tertiary consumers.
iii. **Decomposers:** These organisms break down the dead organic remains of producers and consumers. Primarily bacteria and fungi, they are also known as saprotrophs.

b. **Abiotic factors:** These encompass the non-living, physicochemical elements of the environment. These components influence the distribution, structure, behavior, and relationships of organisms. Abiotic factors include inorganic substances, organic compounds, and climatic factors.
In simple words: Ecosystems are made up of living (biotic) and non-living (abiotic) parts. Biotic parts include producers (like plants making their own food), consumers (animals eating other organisms), and decomposers (bacteria and fungi breaking down dead matter). Abiotic parts are environmental factors like sunlight, water, and soil that affect living things.

🎯 Exam Tip: When describing ecosystem components, clearly define and provide examples for both biotic and abiotic factors. For biotic components, elaborate on the roles of producers, consumers, and decomposers.

Question 8. Define ecological pyramids and describe with examples, pyramids of number and biomass.
Answer:
An ecological pyramid is a graphical representation illustrating the numbers, biomass, or accumulated energy at different trophic levels within an ecosystem's food chain.

a. **Pyramid of numbers:** This graphical representation shows the arrangement of individuals at various trophic levels in an ecosystem's food chain. These pyramids are frequently observed in animal communities. Their shape can be upright, as seen in grassland or pond ecosystems, or inverted, as in parasitic food chains.

b. **Pyramid of biomass:** This pyramid graphically represents the biomass present per unit area at different trophic levels. Examples include grassland and forest ecosystems.
In simple words: Ecological pyramids are visual tools that show how much energy, biomass, or how many organisms exist at each level of a food chain. A pyramid of numbers counts individuals, while a pyramid of biomass measures the total weight of living matter at each level. They can be upright (most at the bottom) or inverted (most at the top in some cases).

🎯 Exam Tip: When defining ecological pyramids, specify the three types (number, biomass, energy). For pyramids of number and biomass, remember to include examples of both upright and inverted forms, explaining why they occur.

Question 9. What is primary productivity? Give a brief description of the factors that affect primary productivity.
Answer:
Primary productivity denotes the rate at which producers in an ecosystem generate biomass or organic matter per unit area over a specific duration.

Various factors influencing primary productivity include light, temperature, water availability, and nutrients. For instance, in desert environments, sunlight is plentiful, yet water is scarce, and nutrients may be deficient. Consequently, in such regions, the supply of water and essential nutrients becomes the limiting factor for primary productivity.
Productivity generally increases from polar regions toward the tropics due to higher levels of sunlight and warmer temperatures.
In simple words: Primary productivity is how fast plants (producers) create new organic material in an area. Factors like light, temperature, water, and nutrients all impact this rate. If any of these are scarce, like water in a desert, they can limit how much plants can grow.

🎯 Exam Tip: Clearly define primary productivity and then systematically list and explain the key environmental factors that influence it. Providing examples, like deserts, helps illustrate the concept of limiting factors.

Question 10. Define decomposition and describe the processes and products of decomposition.
Answer:
Decomposition is the physical and chemical breakdown of complex organic remains into inorganic raw materials, such as CO2, H2O, and minerals, facilitating their recycling. The initial organic matter undergoing this process is termed detritus.
Several processes are involved in decomposition:
• Fragmentation
• Leaching
• Catabolism

(a) **Fragmentation of Detritus:** Small invertebrate animals, known as detritivores, break down detritus into smaller, highly pulverized particles, often found in their feces.

(b) **Leaching:** Soluble substances from the fragmented and decomposing detritus are carried into the upper layers of the soil by percolating water.

(c) **Catabolism:** Saprotrophic bacteria and fungi secrete digestive enzymes that degrade the remaining complex organic compounds in the detritus into simpler inorganic compounds.
Catabolic action results in two main products: humus and inorganic substances. The processes involved in forming these products are respectively called humification and mineralization.
In simple words: Decomposition is the natural process where complex dead organic matter is broken down into simple inorganic substances, like carbon dioxide, water, and minerals, by organisms such as bacteria and fungi. This process involves steps like fragmentation (breaking into smaller pieces), leaching (soluble substances washing away), and catabolism (chemical breakdown), eventually forming humus and releasing minerals.

🎯 Exam Tip: When defining decomposition, emphasize its role in nutrient recycling. Describe the main steps—fragmentation, leaching, and catabolism—and mention the final products: humus (via humification) and inorganic nutrients (via mineralization).

Question 11. Give an account of energy flow in an ecosystem.
Answer:
The ultimate source of all energy utilized by living organisms is sunlight. This radiant energy is converted into chemical energy, stored in the bonds of organic substances, through photosynthesis by green plants, which act as producers.

When a primary consumer (an animal) consumes a plant, the plant's organic substances are oxidized in the animal's body to release energy. A portion of this energy dissipates as heat, while another part is used for building animal tissues. When a secondary consumer eats the primary consumer, further energy loss occurs as heat when the secondary consumer oxidizes the primary consumer's organic substances.

Upon death, organisms are decomposed by decomposers, which break down the dead bodies and release chemical energy. Consequently, energy flow in an ecosystem is unidirectional: it moves from sunlight to plants, then from plants to animals, and finally to decomposers.
In simple words: Energy in an ecosystem starts with sunlight, which plants convert into chemical energy. This energy then moves through the food chain as animals eat plants or other animals. At each transfer, a significant amount of energy is lost as heat, meaning energy flow is one-way, from producers to consumers and decomposers, and decreases at higher trophic levels.

🎯 Exam Tip: Focus on the unidirectional nature of energy flow and the 10% law. Explain how energy is captured by producers, transferred through trophic levels, and lost as heat at each step, ultimately reaching decomposers.

Question 12. Write the important features of a sedimentary cycle in an ecosystem.
Answer:
In sedimentary cycles, the primary reservoir for nutrient elements resides in the Earth's sediments. Elements such as phosphorus, sulfur, potassium, and calcium follow a sedimentary cycle. These cycles are typically slow and less efficient, as elements can become locked in the reservoir pool, staying out of circulation for extended periods.

Important features:
(i) **Input of Nutrients:** Nutrients enter the nutrient pool through the weathering of rocks. Soil formation also occurs through rock weathering, making nutrients available to plants. Wind and mining activities can also transport nutrients from various areas, depositing them onto the soil.

(ii) **Internal Nutrient Cycling:** This involves the circulation of nutrients within the ecosystem. Plants absorb soil nutrients, incorporating them into organic matter. These nutrients then transfer from producers to herbivores and subsequently to carnivores as organic matter. This process is called transfer. All trophic levels eventually contribute some organic matter as detritus.
Detritivores (decomposers) act on detritus, releasing nutrients back into the cycling pool. In stable ecosystems, over 80% of nutrient requirements for biotic components are met through this internal cycling.

(iii) **Output of Nutrients:** This refers to the movement of nutrients out of an ecosystem, which reduces their availability in the cycling pool. Outputs can occur through soil erosion, runoff water, and economic activities like harvesting crops or removing wood from forests. Crop fields often exhibit a negative nutrient budget due to these outputs.
In simple words: Sedimentary cycles involve nutrients like phosphorus and calcium stored mainly in rocks and soil, unlike gaseous cycles in the atmosphere. These cycles are slow because elements can get stuck in rocks. Nutrients enter the system from weathered rocks, circulate through living organisms, and can leave through erosion or harvesting.

🎯 Exam Tip: When describing sedimentary cycles, highlight their geological reservoir (sediments/rocks) and slow nature. Detail the three phases: input (weathering), internal cycling (through food webs and decomposition), and output (erosion, harvesting).

Question 13. Outline the salient features of carbon cycling in an ecosystem.
Answer:
All living organisms require nutrient elements in relatively large quantities, which they obtain from the biosphere. These elements, derived from Earth for growth and metabolism, are termed biogeochemical or biogenetic nutrients. The movement of nutrient elements through living and non-living components of the biosphere is known as the biogeochemical cycle.

In gaseous cycles, the atmosphere serves as the reservoir for nutrient elements. The four most abundant elements in living systems—hydrogen, carbon, oxygen, and nitrogen—primarily have gaseous cycles. The carbon cycle is notably efficient and relatively rapid, ensuring continuous circulation of its elements.

Carbon is fundamental to life, acting as the backbone for complex organic molecules such as carbohydrates, lipids, proteins, and nucleic acids.

The primary sources of carbon include the air (CO2), water (dissolved CO2), fossil fuels, and rocks. Carbon dioxide is obtained from the biosphere through:
• green plants for photosynthesis
• corals for creating calcareous skeletons

Carbon is added to the biosphere through:
• respiration in organisms
• decay of organic wastes and dead organisms
• burning of fossil fuels
• weathering of rocks
• volcanic activity
In simple words: The carbon cycle describes how carbon moves through Earth's atmosphere, oceans, land, and living things. Plants take carbon dioxide from the air, animals get carbon by eating plants, and carbon returns to the air through respiration, decomposition, and burning of fossil fuels. Oceans also store a lot of carbon.

🎯 Exam Tip: When discussing the carbon cycle, emphasize its role as the backbone of life and its main reservoirs (atmosphere, oceans, fossil fuels, rocks). Detail the key processes of carbon exchange, including photosynthesis, respiration, decomposition, and combustion.

GSEB Class 12 Biology Ecosystem Additional Important Questions and Answers

Question 1. Mention the technical term for expressing an animal's place of living in abiotic environment and its functional relationship with other organisms in an ecosystem.
Answer:
Trophic level and food chain
In simple words: An animal's living space and how it interacts with its environment and other creatures is described by its trophic level (its position in the food chain) and its role within the food chain itself.

🎯 Exam Tip: Differentiate between "habitat" (place of living) and "niche" (functional role). The question specifies both, so "trophic level and food chain" encompasses the functional relationships in an ecosystem.

Question 2. Give 2 man-made ecosystems.
Answer:
Pond, crop fields
In simple words: Man-made ecosystems are environments created or significantly modified by humans, such as fish ponds or agricultural fields.

🎯 Exam Tip: Examples of man-made ecosystems are common. Think of any environment directly managed or constructed by humans, like aquariums, gardens, or urban parks, in addition to ponds and crop fields.

Question 3. In a particular climatic condition, which components of detritus determine its
a. slower decomposition
b. quicker decomposition?
Answer:
a. Decomposition rate is slower if detritus is rich in lignin and chitin.
b. Decomposition rate is quicker if detritus is rich in nitrogen and water-soluble substances like sugars.
In simple words: The speed of decomposition depends on what the detritus is made of. It breaks down slowly if it contains tough materials like lignin and chitin, but quickly if it's rich in easily digestible substances like nitrogen and sugars.

🎯 Exam Tip: Remember the chemical composition factors influencing decomposition rates. Complex, tough molecules (lignin, chitin) slow it down, while simple, nutrient-rich components (nitrogen, sugars) speed it up.

Question 4. Break down of complex organic matter into inorganic substances by decomposers is called decomposition. Some terms related to decomposition are given. Detritus, detritivores, fragmentation, leaching, catabolism, humification, mineralisation. Explain the above terms to give an outline of the decomposition process.
Answer:
• **Detritus:** This includes dead plant remains (e.g., leaves, bark, flowers) and dead animal remains, including fecal matter.
• **Detritivores:** These are organisms that break down detritus into smaller particles.
• **Fragmentation:** The process by which detritus is broken down into smaller pieces.
• **Leaching:** This is when water-soluble inorganic nutrients seep down into the soil horizon and precipitate as unavailable salts.
• **Catabolism:** The degradation of the remaining detritus into simpler inorganic substances by bacterial and fungal enzymes.
• **Humification:** This process leads to the accumulation of a dark-colored amorphous substance known as humus.
• **Mineralisation:** This involves the further degradation of humus by microbes, resulting in the release of inorganic nutrients.
In simple words: Decomposition is the process where dead organic matter (detritus) is broken down. Detritivores start by fragmenting it. Soluble nutrients can then leach into the soil. Bacteria and fungi cause catabolism, breaking it down further. This leads to humification, forming stable humus, and finally mineralization, releasing simple inorganic nutrients back into the ecosystem.

🎯 Exam Tip: Clearly define each term related to decomposition and explain its role in the overall process. Understanding the sequence from detritus to fragmentation, leaching, catabolism, humification, and mineralization is crucial.

Question 5. Lindeman proposed law of 10%. How will you explain this law in relation to food chain?
Answer:
The 10% Law, proposed by Lindeman, states that only about 10% of the energy from one trophic level is transferred to the next higher trophic level, while the remaining 90% is lost, primarily as heat, during metabolic activities and incomplete consumption.
For example, in a food chain:
Producers \(\rightarrow\) Herbivores \(\rightarrow\) Consumer-1 \(\rightarrow\) Consumer 2
(100 kcal) \( \implies \) (10 kcal) \( \implies \) (1 kcal) \( \implies \) (0.1 kcal)
When plants (producers) are consumed by an animal (herbivore), only about 10% of the energy stored in the plant biomass is fixed into the animal's flesh. Similarly, when a carnivore (Consumer-1) eats that herbivore, only about 10% of the energy from the herbivore is transferred and fixed into the carnivore's tissues. This successive loss explains why food chains rarely extend beyond three to four trophic levels, as insufficient energy remains to support higher levels.
In simple words: Lindeman's 10% Law explains that only about one-tenth of the energy from one level of a food chain moves to the next. The rest (90%) is lost as heat or used up by the organism. This means there's much less energy available at higher levels, which is why food chains are usually short.

🎯 Exam Tip: When explaining Lindeman's 10% law, clearly state the percentage transferred and the reason for the loss (heat, metabolism). Provide a simple numerical example to illustrate energy transfer across trophic levels.

Question 6. The number of individuals in an ecosystem is given. Construct the pyramid of number and energy. Producer – 1, Herbivores – 50, Carnivores – 75
Answer:

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक उल्टे संख्या पिरामिड (Pyramid of Number) और एक सीधे ऊर्जा पिरामिड (Pyramid of Energy) को दर्शाता है। संख्या पिरामिड में उत्पादक (Producer) सबसे नीचे एक इकाई (1) के साथ सबसे छोटा आधार बनाते हैं, उसके ऊपर शाकाहारी (Herbivores) 50 की संख्या में, और शीर्ष पर मांसाहारी (Carnivores) 75 की संख्या में सबसे बड़ा ब्लॉक बनाते हैं, जो एक उल्टा आकार दिखाता है। इसके विपरीत, ऊर्जा पिरामिड में उत्पादक सबसे नीचे सबसे चौड़ा आधार बनाते हैं, उसके ऊपर शाकाहारी और फिर मांसाहारी, प्रत्येक स्तर पर ऊर्जा में कमी दिखाते हुए एक सीधा आकार बनाते हैं।

**Pyramid of Number (Inverted):**
Given: Producer = 1, Herbivores = 50, Carnivores = 75.
Since the number of producers (1) is less than the herbivores (50), and herbivores are less than carnivores (75), the pyramid of number will be inverted. This is a typical example in some ecosystems, such as a single large tree supporting many insects.

**Pyramid of Energy (Upright):**
The pyramid of energy is always upright. Producers, being at the base, always have the maximum amount of energy, which decreases progressively at successive trophic levels due to energy loss (as per the 10% law). Therefore, for the given numbers, the energy pyramid will have a wide base for producers, narrowing towards carnivores.
In simple words: For the given data (1 producer, 50 herbivores, 75 carnivores), the pyramid of number would be inverted because there are more consumers than producers. However, the pyramid of energy would always be upright, as producers always have the most energy, and energy decreases as it moves up each trophic level.

🎯 Exam Tip: Understand that pyramids of number can be inverted (e.g., a single tree supporting many insects), but pyramids of energy are *always* upright because energy is lost at each trophic transfer. Be ready to construct and explain both types of pyramids.

Question 7. The mean net productivity of two biomes are given. Analyse them and answer the following questions. Tropical rain forest – 450 kg/sq.km Desert – 15 kg/sq.km
a. Why does the productivity of deserts become less than that of the tropical rain forest?
b. From the above data analyse the importance of plants in the existence of life.
Answer:
a. In deserts, the annual rainfall is typically less than 10 inches, and day temperatures can range from 100°F to 135°F. This creates the driest environment, making water a severely limiting factor for plant growth. Consequently, the productivity of desert ecosystems is much lower.
b. In tropical rainforests, the vegetation consists of a luxuriant mass of trees and other plants. Plants are the primary producers in any ecosystem. Their abundance and high productivity in tropical rainforests underscore their crucial role in supporting diverse life forms by converting solar energy into usable organic matter, which forms the base of all food chains.
In simple words: Deserts have low productivity (15 kg/sq.km) because they are very dry and hot, severely limiting plant growth. Tropical rainforests, with high rainfall and suitable temperatures, have very high productivity (450 kg/sq.km) due to abundant plant life. This shows that plants, as producers, are essential for creating the food and energy that support all other life forms.

🎯 Exam Tip: Connect productivity levels directly to environmental factors. For high productivity, consider abundant water, suitable temperature, and nutrient availability. For low productivity, identify the key limiting factors (e.g., water in deserts). Emphasize the role of producers (plants) as the foundation of all ecosystems.

Question 8. Consider a pond ecosystem.
a. Draw a pyramid of energy in that ecosystem.
b. Compare three types of pyramidal relationships found among the organisms in the pond ecosystem.
c. Is there any difference between nutrient flow and energy flow in an ecosystem? Substantiate.
Answer:
a.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक तालाब पारिस्थितिकी तंत्र में ऊर्जा के सीधे पिरामिड (Pyramid of Energy) को दर्शाता है। सबसे नीचे का आधार उत्पादक (Producers) द्वारा बनाया जाता है, जिसमें अधिकतम ऊर्जा होती है। इसके ऊपर प्राथमिक उपभोक्ता (Consumers) होते हैं, जिनमें ऊर्जा का स्तर कम होता है, और सबसे ऊपर अपघटक (Decomposers) होते हैं, जो ऊर्जा पिरामिड के शीर्ष पर सबसे संकरा हिस्सा बनाते हैं क्योंकि वे मृत कार्बनिक पदार्थों से ऊर्जा प्राप्त करते हैं। यह पिरामिड दर्शाता है कि ऊर्जा एकतरफा बहती है और प्रत्येक पोषण स्तर पर कम होती जाती है।

b. In a pond ecosystem:
**Pyramid of Number:** This is typically upright, with a large number of phytoplankton (producers) supporting fewer zooplankton (primary consumers) and even fewer small fish (secondary consumers), etc.
**Pyramid of Biomass:** This is often inverted. Phytoplankton (producers) have a small total biomass at any given moment, but they reproduce rapidly. They are consumed by a larger biomass of zooplankton, which are then consumed by an even larger biomass of fish. The standing crop biomass of phytoplankton is lower than that of zooplankton.
**Pyramid of Energy:** This is always upright. The energy captured by phytoplankton at the base is highest and decreases progressively at each subsequent trophic level (zooplankton, fish, etc.).

c. Yes, there is a significant difference between nutrient flow and energy flow in an ecosystem. Energy flow is unidirectional and non-cyclic; it decreases with successive trophic levels as much of it is lost as heat. In contrast, nutrient flow is cyclic; nutrients are continually recycled within the ecosystem (e.g., carbon, nitrogen, phosphorus cycles) without significant loss from the system, although they may change forms or locations. The amount of energy decreases with each transfer, but nutrient elements are reused.
In simple words: In a pond, the pyramid of energy is always upright, showing decreasing energy at higher levels. The pyramid of number is usually upright (many small producers to fewer large consumers). However, the pyramid of biomass can be inverted, with a smaller mass of fast-reproducing producers supporting a larger mass of consumers. Crucially, energy flows in one direction and is lost, while nutrients cycle continuously within the ecosystem.

🎯 Exam Tip: For pond ecosystems, highlight the unique inverted biomass pyramid (due to small, rapidly reproducing producers). Emphasize the universal upright nature of the energy pyramid and the fundamental distinction between unidirectional energy flow and cyclic nutrient flow. Provide clear reasons for each pattern.

Question 9. Observe the figures given below and answer the following questions.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र जलक्रमण (Hydrarch Succession) के विभिन्न क्रमिक चरणों को दर्शाता है, जो एक नग्न जल निकाय से शुरू होकर एक स्थिर वन समुदाय में समाप्त होता है। पहला चित्र एक खाली जल निकाय को दिखाता है, उसके बाद दूसरे चित्र में प्लवक (phytoplankton) जैसे अग्रदूत समुदाय, फिर तीसरे में जलीय वनस्पति और अंततः चौथे और पांचवें चित्रों में झाड़ियाँ और वृक्ष शामिल होते हैं, जो एक चरम समुदाय (climax community) की ओर बढ़ते हैं। यह एक पारिस्थितिकीय अनुक्रमण की प्रगति को चित्रित करता है।

a. Identify the ecological concept converged through the given figures.
b. Name the group of organisms coming as a pioneer community in this ecological process.
c. Given any two characteristic features of climax community.
Answer:
a. The ecological concept depicted by the figures is seral stages of hydrarch succession (succession in a water body).
b. The pioneer community in this process comprises phytoplanktons.
c. Two characteristic features of a climax community are:
• It consists of large-sized individual organisms.
• It possesses a complex food chain and food web, high nutrient conservation, and high efficiency of energy use.
In simple words: The diagrams show ecological succession starting in water (hydrarch succession), where pioneer organisms like phytoplankton first colonize. A climax community, the stable end stage of succession, has large organisms, complex food chains, good nutrient recycling, and efficient energy use.

🎯 Exam Tip: Recognize ecological succession, especially hydrarch (water) vs. xerarch (dry) succession. Identify pioneer species (first colonizers) and understand the defining characteristics of a stable climax community (diversity, complexity, nutrient cycling efficiency).

Question 10. It is stated that the pyramid of energy is always upright. Justify
Answer:
• The base of the pyramid of energy is occupied by producers, which inherently possess the maximum amount of energy captured from the sun.
• When energy flows from one trophic level to the next, only about 10% is transferred, while the remaining 90% is lost, primarily as heat, during metabolic processes and incomplete consumption.
• Consequently, the amount of energy available at a higher trophic level will always be less than that at the lower trophic levels. This consistent decrease ensures that the pyramid of energy will always be upright, never inverted.
In simple words: The pyramid of energy is always upright because producers at the bottom capture the most energy from the sun. At each step up the food chain, about 90% of this energy is lost as heat, meaning there is progressively less energy available to support higher trophic levels.

🎯 Exam Tip: The upright nature of the energy pyramid is a fundamental principle. Justify it by explaining the high energy content of producers and the significant energy loss (90%) as heat at each trophic level due to the second law of thermodynamics.

Question 11. The products of ecosystem processes are named ecosystem services. Give any five services of the ecosystem.
Answer:
Ecosystem services are the numerous benefits that human beings receive from ecosystems. Five key services include:
• Purification of air and water
• Mitigation of drought and flood events
• Cycling of essential nutrients
• Maintenance of biodiversity
• Provision of wildlife habitat
In simple words: Ecosystem services are the many benefits nature provides us. These include cleaning our air and water, controlling droughts and floods, recycling important nutrients, protecting different types of plants and animals (biodiversity), and providing homes for wildlife.

🎯 Exam Tip: Be able to list and briefly describe several key ecosystem services. Focus on functions that directly benefit human well-being and environmental stability, such as clean air/water, climate regulation, and biodiversity support.

Question 12. Why does secondary succession is faster than primary succession?
Answer:
Secondary succession is generally faster than primary succession for several reasons:
• Secondary succession occurs in an area where life previously existed but was subsequently disturbed or wiped out (e.g., after a forest fire or flood).
• Crucially, some soil and organic sediments are already present in the disturbed area, providing a pre-existing substrate with nutrients. This allows for quicker colonization and plant growth.
• In contrast, primary succession occurs in areas where no life existed before (e.g., newly formed volcanic islands or bare rock). It takes a significant amount of time for soil to form and accumulate organic matter, which is a slow process, thus making primary succession much slower.
In simple words: Secondary succession is quicker because it happens in places where life used to be and some soil or organic matter is already present, making it easier for new species to grow. Primary succession starts from bare ground, where there's no soil, so it takes a very long time for soil to form before plants can colonize.

🎯 Exam Tip: Distinguish between primary and secondary succession by focusing on the initial conditions. The presence of existing soil and residual life forms significantly speeds up secondary succession compared to primary succession, which starts from barren ground.

Question 13. Cite an example of an inverted ecological pyramid. What kind of pyramid of energy would it have?
Answer:
Example of an inverted ecological pyramid: The pyramid of biomass in the sea (or a pond ecosystem where phytoplankton biomass is less than zooplankton biomass).
Kind of pyramid of energy: The energy pyramid would always be upright.
In simple words: An example of an inverted ecological pyramid is the biomass pyramid in the ocean, where the small, fast-reproducing phytoplankton (producers) have less total biomass than the larger, longer-lived zooplankton and fish (consumers) they support. However, the energy pyramid for this or any ecosystem will always be upright because energy decreases at each step up the food chain.

🎯 Exam Tip: Remember that while biomass pyramids can be inverted (especially in aquatic environments with rapidly reproducing producers), energy pyramids are universally upright. Always provide a specific example when asked for an inverted pyramid.

Question 14. Name the pioneer species on a bare rock. How do they help in establishing?
Answer:
Lichens are the pioneer species in succession on bare rock.
Lichens play a crucial role in establishing the ecosystem by secreting specific acids. These acids corrode the rock surface, contributing to the weathering process and aiding in the formation of initial soil particles. This soil formation then creates a suitable substrate, paving the way for other plant species, such as bryophytes, to colonize the area. The ultimate climax community established through this succession will typically be a mesic (moderately moist) forest.
In simple words: On bare rock, lichens are the first species to grow (pioneer species). They help create new soil by releasing acids that break down the rock, making it possible for other plants like mosses to grow later, eventually leading to a forest.

🎯 Exam Tip: Identify lichens as classic pioneer species on bare rock. Explain their mechanism (acid secretion, weathering) in creating soil, which is a critical step in primary succession and allows subsequent, more complex plant communities to establish.

Gujarat Board Textbook Solutions Class 12 Chapter 14 Ecosystem

GSEB Class 12 Biology Ecosystem Text Book Questions and Answers

Question 1. Fill in the blanks:
1. Plants are called as .................... because they fix carbon dioxide.
2. In an ecosystem dominated by trees, the pyramid (of numbers) is .................... type.
3. In aquatic ecosystems, the limiting factor for productivity is ....................
4. Common detritivores in our ecosystem are ....................
5. The major reservoir of carbon on earth is....................
Answer:
1. Autotrophs
2. Upright
3. Light
4. Bacteria and earthworms.
5. Oceans
In simple words: This section identifies fundamental ecological concepts like producers (autotrophs), pyramid shapes, limiting factors, detritivores, and major carbon reservoirs, which are essential for understanding ecosystem structure and function.

🎯 Exam Tip: Understanding these basic ecological definitions and examples is crucial for foundational knowledge and often appears in multiple-choice or short-answer questions.

Question 2. Which one of the following has the largest population in a food chain?
a. Producers
b. Primary consumers
c. Secondary consumers
d. Decomposers
Answer: (d) Decomposers
In simple words: Decomposers, such as bacteria and fungi, typically have the largest populations in a food chain because they break down organic matter at all trophic levels, making them vital for nutrient cycling.

🎯 Exam Tip: Remember the critical role of decomposers in nutrient recycling and their pervasive presence across all ecosystem types for competitive exams.

Question 3. The second trophic level in a lake is
a. phytoplankton
b. zooplankton
c. benthos
d. fishes
Answer: (b) zooplankton
In simple words: In a lake ecosystem, phytoplankton are primary producers (first trophic level), and zooplankton consume them, thus occupying the second trophic level as primary consumers.

🎯 Exam Tip: Accurately identifying trophic levels in different ecosystems, especially aquatic ones, is a common exam requirement.

Question 4. Secondary producers are
a. herbivores
b. producers
c. carnivores
d. None of the above
Answer: (d) None of the above
In simple words: Secondary producers are a misnomer in standard ecological terminology; organisms that produce biomass are producers (plants), while consumers convert biomass but do not "produce" it in the same sense.

🎯 Exam Tip: Distinguish clearly between producers (autotrophs) and consumers (heterotrophs) and avoid confusion with terms like "secondary producers."

Question 5. What is the percentage of photosynthetically active radiation (PAR), in incident solar radiation?
a. 100%
b. 50%
c. 1-5%
d. 2-10%
Answer: (b) 50%
In simple words: Roughly half of the total incoming solar radiation consists of wavelengths that photosynthetic organisms can effectively use for photosynthesis.

🎯 Exam Tip: Knowing the approximate percentage of PAR in solar radiation is important for understanding ecological energy flow and primary productivity calculations.

Question 6. Distinguish between
a. Grazing food chain and detritus food chain
b. Production and decomposition
c. Upright and inverted pyramid
d. Food chain and Food web
e. Litter and detritus
f. Primary and secondary productivity
Answer:
a. **Grazing food chain:** This food chain begins with plant biomass being consumed by herbivores, which are then subsequently eaten by various carnivores. **Detritus food chain:** This food chain initiates from the dead organic matter of animals and fallen leaves, collectively referred to as detritus.
b. **Production:** This term refers to the synthesis of organic compounds from inorganic substances, such as carbon dioxide and minerals, typically using sunlight. This process is primarily carried out by plants. **Decomposition:** This is the process where a substance is broken down into its fundamental constituent parts, a task performed by reducer organisms.
c. **Upright pyramid:** An upright pyramid occurs when the quantity of producer organisms or their biomass is at its maximum within an ecosystem, gradually decreasing at each successive trophic level in a food chain. **Inverted pyramid:** Conversely, an inverted pyramid is observed when the number of individuals or their biomass at the producer level is minimal, progressively increasing at each subsequent trophic level in a food chain.
d. **Food chain:** This describes the sequential connection of organisms through which food energy is transferred from producers, through a series of organisms that consume and are consumed. **Food web:** A food web is a complex network formed by inter-connected food chains at various trophic levels, creating multiple feeding connections among diverse organisms in a biotic community.
e. **Detritus:** This comprises the dead remnants of plants and animals. It is typically categorized into litterfall and below-ground detritus. **Litter:** This specifically refers to above-ground detritus, encompassing dead plant remains, animal carcasses, and faecal matter that accumulate on the earth's surface in terrestrial ecosystems.
f. **Primary productivity:** This denotes the rate at which biomass or organic matter is produced per unit area over a specific period by producers within an ecosystem. **Secondary productivity:** This refers to the rate of biomass or organic matter production by consumers over a given period.
In simple words: This question differentiates key ecological concepts, highlighting how energy flows (food chains/webs), organic matter is processed (production/decomposition), and populations or biomass are structured (pyramids), alongside specific forms of organic matter (litter/detritus) and productivity types.

🎯 Exam Tip: Clearly defining and contrasting these paired ecological terms is vital; focus on the starting point, energy source, or structural implications for each distinction.

Question 7. Describe the components of an ecosystem.
Answer:
Ecosystem components can be broadly categorized into two primary types: the biotic component, which includes various living organisms, and the abiotic component, consisting of environmental factors.
a. **Biotic components:** These encompass all living organisms within an ecosystem and form interconnected relationships through food. Based on their nutritional mode, these organisms are grouped into three main categories: producers, consumers, and decomposers.
(i) **Producers:** These organisms synthesize food materials. They are divided into photoautotrophs and chemoautotrophs.
**Photoautotrophs:** These are green plants containing chlorophyll. They capture light energy and convert it into chemical energy.
**Chemoautotrophs:** Certain bacteria, such as sulfur bacteria and iron bacteria, derive energy from chemical reactions to synthesize organic food.
(ii) **Consumers:** Primarily animals, these organisms cannot produce their own food. Instead, they obtain energy and materials by utilizing substances stored by producers. Consumers are classified into primary, secondary, and tertiary categories.
(iii) **Decomposers:** These organisms are responsible for breaking down the dead organic remains of producers and consumers. They are mainly bacteria and fungi, also known as saprotrophs.
b. **Abiotic factors:** These include the non-living, physicochemical elements of the environment. Such components influence the distribution, structure, behavior, and relationships among organisms. Abiotic factors comprise inorganic substances, organic compounds, and climatic elements.
In simple words: An ecosystem comprises living (biotic) elements like producers, consumers, and decomposers, and non-living (abiotic) elements such as physical and chemical environmental factors, all interacting to maintain balance.

🎯 Exam Tip: When describing ecosystem components, ensure you explain both biotic and abiotic factors thoroughly, providing specific examples for each sub-category to demonstrate comprehensive understanding.

Question 8. Define ecological pyramids and describe with examples, pyramids of number and biomass.
Answer:
An ecological pyramid serves as a graphical representation illustrating the numbers, biomass, or accumulated energy at different trophic levels within an ecosystem's food chain.
a. **Pyramid of numbers:** This graphical representation illustrates the arrangement of individual organisms at different trophic levels in an ecosystem's food chain. These pyramids are typically found in animal communities. Their shape can be upright (e.g., in grassland or pond ecosystems) or inverted (e.g., in parasitic food chains).
b. **Pyramid of biomass:** This pyramid graphically represents the total biomass present per unit area at various trophic levels. Examples include grassland and forest ecosystems.
In simple words: Ecological pyramids visually show the structure of an ecosystem by illustrating the quantity of organisms (number), total living matter (biomass), or energy at each feeding level, which can be upright or inverted depending on the ecosystem type.

🎯 Exam Tip: When defining ecological pyramids, specify that they represent numbers, biomass, or energy at *each trophic level*. Providing clear examples of both upright and inverted pyramids is crucial for full marks.

Question 9. What is primary productivity? Give a brief description of the factors that affect primary productivity.
Answer:
Primary productivity refers to the rate at which producers in an ecosystem generate biomass or organic matter per unit area over a specific time period.
Several factors influence primary productivity, including light, temperature, water, and essential nutrients. For instance, in desert environments, sunlight is abundant, but water is scarce, and nutrients may be deficient. Consequently, in such regions, the availability of water and nutrients becomes the primary limiting factor for productivity. Productivity generally increases from polar regions towards tropical areas due to higher sunlight and temperature.
In simple words: Primary productivity is the rate at which plants create organic matter, influenced by factors like sunlight, temperature, water, and nutrients, often increasing in warmer, wetter climates.

🎯 Exam Tip: Define primary productivity clearly, then elaborate on the main environmental factors (light, temperature, water, nutrients) that can limit or enhance it, giving examples for clarity.

Question 10. Define decomposition and describe the processes and products of decomposition.
Answer:
Decomposition is the process involving the physical and chemical breakdown of complex organic remains into simpler inorganic raw materials, such as CO₂, H₂O, and minerals, facilitating their recycling within the ecosystem. This process is carried out by organisms that break down detritus.
There are several types of decomposition processes:
• Fragmentation
• Leaching
• Catabolism
(a) **Fragmentation of Detritus:** Small invertebrate animals, known as detritivores, break down detritus into highly pulverized matter, often in their faeces.
(b) **Leaching:** Soluble substances present in the fragmented and decomposing detritus are leached into the upper soil layers by percolating water.
(c) **Catabolism:** This process is carried out by saprotrophic bacteria and fungi. They secrete digestive enzymes over the fragmented detritus, which transform complex organic compounds into simpler inorganic compounds.
Catabolic action results in two main products: humus and inorganic substances. The processes involved in forming these products are respectively termed humification and mineralization.
In simple words: Decomposition is the breakdown of dead organic matter into simpler inorganic substances by detritivores and microbes, involving fragmentation, leaching, and catabolism, ultimately forming humus and releasing minerals.

🎯 Exam Tip: When defining decomposition, highlight its role in nutrient recycling. Detail the three main steps (fragmentation, leaching, catabolism) and their respective products (humus, minerals) for a comprehensive answer.

Question 11. Give an account of energy flow in an ecosystem.
Answer:
The ultimate source of all energy utilized by living organisms is sunlight. This radiant energy from the sun is converted into chemical energy, stored in the bonds of organic substances, by green plants through photosynthesis. These green plants are designated as producers.
When an animal (primary consumer) consumes a plant, the plant's organic substances are oxidized within the animal's body to release energy. Only a portion of this energy is used to build animal tissues, while the rest dissipates as heat. Similarly, when a second animal (secondary consumer) consumes the first, further energy loss occurs as heat when the secondary consumer oxidizes the primary consumer's organic substances.
Upon the death of organisms, decomposers break down their dead bodies, releasing chemical energy. Thus, energy flow in an ecosystem is unidirectional: from sunlight to plants, then from plants to animals, and finally to decomposers.
In simple words: Energy in an ecosystem originates from sunlight, is captured by producers (plants) through photosynthesis, and then flows unidirectionally through consumers, with significant amounts lost as heat at each transfer, eventually reaching decomposers.

🎯 Exam Tip: Emphasize the unidirectional nature of energy flow and the consistent energy loss at each trophic level, often quantified by the 10% law, as these are core concepts.

Question 12. Write the important features of a sedimentary cycle in an ecosystem.
Answer:
In a sedimentary cycle, the primary reservoir for nutrient elements is found in the Earth's sediments. Elements such as phosphorus, sulfur, potassium, and calcium follow a sedimentary cycle. These cycles are typically slow and less efficient, as elements can become locked in the reservoir pool, remaining out of circulation for extended periods.
Important features include:
(i) **Input of Nutrients:** Nutrients enter the nutrient pool primarily through the weathering of rocks. Soil formation also occurs through rock weathering, making nutrients available to plants. Wind also carries nutrients from mining areas and industrial zones, depositing them over the soil.
(ii) **Internal Nutrient Cycling:** This refers to the circulation of nutrients within the ecosystem. Plants absorb nutrients from the soil, incorporating them into organic matter. These nutrients, in the form of organic matter, then transfer from producers to herbivores and from herbivores to carnivores. This movement is called transfer. All trophic levels contribute organic matter as detritus. Decomposers act on detritus, releasing nutrients back into the cycling pool. In stable ecosystems, internal nutrient cycling fulfills over 80% of the biotic community's nutrient requirements.
(iii) **Output of Nutrients:** This describes the movement of nutrients out of an ecosystem, which reduces their availability in the cycling pool. This occurs through processes like soil erosion, runoff water, and economic activities such as harvesting crops or removing wood from forests. Crop fields, for example, often operate under a negative nutrient budget.
In simple words: Sedimentary nutrient cycles store elements like phosphorus and sulfur in rocks and soil, involving slow processes of input (weathering), internal cycling through living organisms, and output (erosion or harvesting).

🎯 Exam Tip: Focus on distinguishing sedimentary cycles from gaseous ones by highlighting the reservoir (earth's sediments), the slow nature of the cycle, and the processes of input, internal cycling, and output of nutrients.

Question 13. Outline the salient features of carbon cycling in an ecosystem.
Answer:
All living organisms require nutrient elements in relatively large quantities, obtaining them from the biosphere's components. Nutrient elements from the Earth used by living organisms for growth and metabolism are termed biogeochemical or biogenetic nutrients. The movement of nutrient elements through both living and non-living parts of the biosphere is referred to as a biogeochemical cycle.
In gaseous cycles, the atmosphere serves as the reservoir for nutrient elements. Hydrogen, carbon, oxygen, and nitrogen - the four most abundant elements in living systems - predominantly follow gaseous cycles. The carbon cycle is notably efficient and relatively rapid, ensuring elements remain in circulation.
Carbon is widely considered the foundation of life, with carbon atoms forming the backbone of complex organic molecules such as carbohydrates, lipids, proteins, and nucleic acids.
The main sources of carbon include air, water, fossil fuels, and rocks. Carbon dioxide is acquired from the biosphere by:
• Green plants through photosynthesis.
• Corals for forming calcareous skeletons.
Carbon is reintroduced into the biosphere through:
• Respiration in organisms.
• Decay of organic wastes and dead organisms.
• Burning of fuel.
• Weathering of rocks.
• Volcanic activity.
In simple words: The carbon cycle involves the continuous movement of carbon through living organisms and the environment, with its primary atmospheric reservoir as CO2, utilized by plants for photosynthesis and released back through respiration, decomposition, and combustion.

🎯 Exam Tip: When describing the carbon cycle, clearly outline its main reservoirs, the key biological processes (photosynthesis, respiration, decomposition), and anthropogenic activities that influence its balance.

GSEB Class 12 Biology Ecosystem Additional Important Questions and Answers

Question 1. Mention the technical term for expressing an animal's place of living in abiotic environment and its functional relationship with other organisms in an ecosystem.
Answer:
Trophic level and food chain
In simple words: An animal's position in the abiotic environment and its interactions with other organisms are defined by its trophic level and its role within the food chain.

🎯 Exam Tip: Understand that "trophic level" indicates an organism's feeding position, and "food chain" describes the energy transfer, collectively defining its ecological role.

Question 2. Give 2 man-made ecosystems.
Answer:
Pond, crop fields
In simple words: Man-made ecosystems are environments created or significantly modified by humans, such as artificial ponds and agricultural fields.

🎯 Exam Tip: Be able to identify common examples of both natural and artificial ecosystems.

Question 3. In a particular climatic condition, which components of detritus determine its
a. slower decomposition
b. quicker decomposition?
Answer:
a. Decomposition rate is slower if detritus is rich in lignin and chitin.
b. Decomposition rate is quicker if detritus is rich in nitrogen and water-soluble substances like sugars.
In simple words: The rate of detritus decomposition depends on its chemical composition: high lignin and chitin slow it down, while high nitrogen and soluble sugars speed it up.

🎯 Exam Tip: Remember that complex, tough compounds (lignin, chitin) inhibit decomposition, while simpler, nutrient-rich compounds (nitrogen, sugars) accelerate it.

Question 4. Break down of complex organic matter into inorganic substances by decomposers is called decomposition. Some terms related to decomposition are given. Detritus, detritivores, fragmentation, leaching, catabolism, humification, mineralisation. Explain the above terms to give an outline of the decomposition process.
Answer:
• **Detritus:** This term encompasses dead plant remains, such as leaves, bark, and flowers, along with dead animal remains, including faecal matter.
• **Detritivores:** These are organisms responsible for breaking down detritus into smaller particles.
• **Fragmentation:** This process refers to the physical breakdown of detritus into smaller fragments.
• **Leaching:** This is the process where water-soluble inorganic nutrients seep downwards into the soil horizon, where they may precipitate as unavailable salts.
• **Catabolism:** This involves the degradation of the remaining detritus into simpler inorganic substances through the action of bacterial and fungal enzymes.
• **Humification:** This leads to the accumulation of humus, a dark-colored, amorphous substance.
• **Mineralisation:** This is the further degradation of humus by microbes, resulting in the release of inorganic nutrients.
In simple words: Decomposition is the multi-step process where detritus (dead organic matter) is fragmented by detritivores, leached of soluble nutrients, catabolized by microbes, then transformed into humus (humification), and finally releases inorganic nutrients (mineralization).

🎯 Exam Tip: Systematically explain each term related to decomposition, focusing on the sequence of events and the role of different organisms and processes in breaking down organic matter and cycling nutrients.

Question 5. Lindeman proposed law of 10%. How will you explain this law in relation to food chain?
Answer:
The 10% law, proposed by Lindeman, states that the transfer of energy from one trophic level to the next in a food chain is accompanied by a significant loss of energy. At each successive higher trophic level, only about 10% of the energy fixed in the preceding level is transferred, while the remaining 90% is lost, primarily as heat, during metabolic processes.
For example:
Producers \(\longrightarrow\) Herbivores \((100 \text{ kcal}) \longrightarrow (10 \text{ kcal})\)
\(\implies\) Consumer-1 \(\longrightarrow\) Consumer 2 \((1 \text{ kcal}) \longrightarrow (0.1 \text{ kcal})\)
In simple words: Lindeman's 10% law explains that only about 10% of energy is transferred from one feeding level to the next in a food chain; the rest is lost, primarily as heat, which limits the number of trophic levels an ecosystem can support.

🎯 Exam Tip: Explain the 10% law clearly by defining energy transfer and loss, and illustrate it with a numerical example to show the drastic reduction in energy at higher trophic levels.

Question 6. The number of individuals in an ecosystem is given. Construct the pyramid of number and energy.
Producer – 1, Herbivores – 50, Carnivores – 75
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह अनुभाग एक पारिस्थितिकी तंत्र में संख्याओं और ऊर्जा के पिरामिडों को दर्शाता है। संख्या का पिरामिड उल्टा है, जिसमें उत्पादक (जैसे एक पेड़) कम संख्या में होते हैं, लेकिन बड़ी संख्या में शाकाहारी (जैसे कीड़े) उसका सेवन करते हैं, जिसके बाद और भी अधिक मांसाहारी होते हैं। ऊर्जा का पिरामिड हमेशा सीधा होता है, जिसमें उत्पादकों के पास सबसे अधिक ऊर्जा होती है, और प्रत्येक क्रमिक पोषण स्तर पर ऊर्जा की मात्रा घटती जाती है।
The provided data suggests an inverted pyramid of numbers (e.g., a single large tree supporting many herbivores) and an upright pyramid of energy.
**Pyramid of Number (Inverted):**
The base (Producer) would be 1 (e.g., a large tree).
The next level (Herbivores) would be 50 (e.g., insects feeding on the tree).
The top level (Carnivores) would be 75 (e.g., birds feeding on the insects).
This results in a structure where the number of individuals increases at higher trophic levels.
**Pyramid of Energy (Always Upright):**
Regardless of the number of individuals, the energy content at the producer level is always the highest. Energy decreases significantly at each successive trophic level due to the 10% law. Therefore, the pyramid of energy will always be upright, with producers at the widest base, followed by herbivores, and then carnivores at the narrowest top.
In simple words: With one producer supporting many herbivores and even more carnivores, the number pyramid is inverted, while the energy pyramid always remains upright because energy decreases at each higher trophic level.

🎯 Exam Tip: Understand that pyramids of number can be inverted, but pyramids of energy are always upright, reflecting the fundamental law of energy transfer (10% law) and the inevitable energy loss at each trophic level.

Question 7. The mean net productivity of two biomes are given. Analyse them and answer the following questions.
Tropical rain forest – 450 kg/sq.km Desert – 15 kg/sq.km
a. Why does the productivity of deserts become less than that of the tropical rain forest?
b. From the above data analyse the importance of plants in the existence of life.
Answer:
a. In deserts, the annual rainfall is less than 10 inches, and day temperatures can range from 100°F to 135°F. This makes deserts the driest ecosystems. Consequently, the productivity in deserts is significantly lower due to extreme aridity and high temperatures limiting plant growth.
b. In tropical rainforests, the vegetation consists of a rich mass of trees and other plants. Plants, as producers, form the foundation of an ecosystem's productivity. The high productivity of tropical rainforests directly reflects the abundance and diversity of its plant life, underscoring their critical role in sustaining life by converting solar energy into biomass.
In simple words: Deserts have low productivity due to scarce water and extreme temperatures, while tropical rainforests thrive with high productivity thanks to abundant plants (producers) that are essential for life.

🎯 Exam Tip: When comparing biomes, relate productivity directly to limiting factors like water availability and temperature, and always emphasize the fundamental role of producers (plants) in ecosystem energy flow.

Question 8. Consider a pond ecosystem.
a. Draw a pyramid of energy in that ecosystem.
b. Compare three types of pyramidal relationships found among the organisms in the pond ecosystem.
c. Is there any difference between nutrient flow and energy flow in an ecosys-tem? Substantiate.
Answer:
a.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक तालाब पारिस्थितिकी तंत्र में ऊर्जा के पिरामिड को दर्शाता है। यह पिरामिड हमेशा सीधा होता है, जिसमें उत्पादक (जैसे शैवाल) आधार पर सबसे अधिक ऊर्जा रखते हैं। प्राथमिक उपभोक्ता (जैसे ज़ूप्लवक) अगले स्तर पर आते हैं, उसके बाद द्वितीयक उपभोक्ता (जैसे छोटी मछली) और शीर्ष पर तृतीयक उपभोक्ता (जैसे बड़ी मछली या अपघटक) आते हैं, ऊर्जा प्रत्येक स्तर पर घटती जाती है।
b. In a pond ecosystem:
• **Pyramid of Number:** Can be upright (many phytoplankton, fewer zooplankton, even fewer fish) or inverted (few large producers like big trees or single large plants supporting many primary consumers).
• **Pyramid of Biomass:** Is typically inverted (e.g., small biomass of phytoplankton supporting a larger biomass of zooplankton at a given time).
• **Pyramid of Energy:** Is always upright, as energy decreases at each successive trophic level.
c. Yes, there is a fundamental difference between nutrient flow and energy flow in an ecosystem. Energy flow is unidirectional, meaning it moves in one direction from producers to consumers, with substantial loss at each trophic level (e.g., 10% law). In contrast, nutrient flow is cyclic; nutrients are reused and recycled within the ecosystem through processes like decomposition. While energy dissipates, nutrients are conserved and continuously circulated.
In simple words: In a pond, biomass pyramids are often inverted, but energy pyramids are always upright, showing unidirectional energy flow. Nutrient flow, however, is cyclic, meaning nutrients are recycled rather than lost from the ecosystem.

🎯 Exam Tip: Be able to differentiate the shapes of number, biomass, and energy pyramids for various ecosystems. Critically, remember that energy flow is one-way and dissipates, while nutrient cycling is a closed loop, recirculating elements.

Question 9. Observe the figures given below and answer the following questions.
ℹ️ चित्र व्याख्या (Diagram Explanation): ये चित्र एक पारिस्थितिक अनुक्रमण की प्रगति को दर्शाते हैं। पहला चित्र शुरुआती जलीय चरण को दिखाता है, संभवतः सूक्ष्मजीवों के साथ। दूसरा चित्र पानी में डूबे हुए पौधों और कीचड़ के संचय को दर्शाता है, जबकि तीसरा चित्र उभयचर पौधों और एक अधिक विकसित स्थलीय समुदाय की ओर प्रगति को दिखाता है, जो एक अधिक जटिल पारिस्थितिकी तंत्र के गठन की ओर अग्रसर है।
a. Identify the ecological concept converged through the given figures.
b. Name the group of organisms coming as a pioneer community in this ecological process.
c. Given any two characteristic features of climax community.
Answer:
a. The ecological concept depicted in the figures is ecological succession, specifically hydrarch succession (succession in a water body leading to a terrestrial community).
b. In this ecological process, phytoplankton typically form the pioneer community.
c. Two characteristic features of a climax community are:
• It consists of large-sized individual organisms.
• It exhibits a complex food chain and food web structure.
• It possesses high nutrient conservation efficiency.
• It demonstrates high efficiency in energy utilization.
In simple words: The figures illustrate hydrarch succession, starting with pioneer phytoplankton. A climax community, the stable end-stage, features large organisms, complex food webs, efficient nutrient use, and high energy efficiency.

🎯 Exam Tip: Be able to identify diagrams representing ecological succession (especially hydrarch or xerarch). Understand the concept of pioneer and climax communities and their distinct characteristics.

Question 10. It is stated that the pyramid of energy is always upright. Justify
Answer:
The pyramid of energy is invariably upright for the following reasons:
• The base of the energy pyramid is occupied by producers, which capture the maximum amount of energy directly from the sun.
• When energy flows from one trophic level to the next, only about 10% of the energy is transferred, while the remaining 90% is lost, primarily as heat, during metabolic activities and incomplete consumption.
• Consequently, the amount of energy available at a higher trophic level will always be less than that at the lower trophic levels. This progressive decrease in available energy ensures that the energy pyramid always maintains an upright configuration and can never be inverted.
In simple words: The energy pyramid is always upright because producers have the most energy, and at each higher trophic level, about 90% of the energy is lost as heat, meaning less energy is available for successive levels.

🎯 Exam Tip: The upright nature of the energy pyramid is a fundamental principle in ecology; thoroughly explain the 10% law and the concept of energy loss at each trophic transfer to justify it.

Question 11. The products of ecosystem processes are named ecosystem services. Give any five services of the ecosystem.
Answer:
Five crucial services provided by ecosystems include:
• Purification of air and water.
• Mitigation of drought and flood conditions.
• Cycling of essential nutrients.
• Maintenance of biodiversity.
• Provision of wildlife habitat.
In simple words: Ecosystem services are the benefits humans receive from ecosystems, such as clean air and water, flood control, nutrient cycling, biodiversity support, and wildlife habitats.

🎯 Exam Tip: List a diverse range of ecosystem services, classifying them broadly into supporting, provisioning, regulating, and cultural services to demonstrate a comprehensive understanding.

Question 12. Why does secondary succession is faster than primary succession?
Answer:
Secondary succession progresses more rapidly than primary succession for several key reasons:
• Secondary succession occurs in an area where life previously existed but was somehow disturbed or wiped out (e.g., by fire or flood).
• In these areas, existing soil and organic sediments are often already present, providing a fertile substrate for new growth. This pre-existing soil structure and nutrient content accelerate the recolonization process.
• Primary succession, conversely, begins in areas devoid of life and soil (e.g., bare rock or newly formed volcanic islands). It requires a prolonged period for soil formation to occur, which significantly slows down the entire succession process.
In simple words: Secondary succession is quicker because it starts in areas where soil and organic matter already exist after a disturbance, unlike primary succession, which begins on barren land and first needs to build soil.

🎯 Exam Tip: The main distinguishing factor is the presence or absence of soil at the outset; highlight how pre-existing soil and seeds accelerate secondary succession compared to primary succession.

Question 13. Cite an example of an inverted ecological pyramid. What kind of pyramid of energy would it have?
Answer:
**Example of an inverted ecological pyramid:** The pyramid of biomass in the sea. In marine environments, the biomass of phytoplankton (producers) at any given moment can be less than the biomass of the zooplankton (primary consumers) that feed on them, because phytoplankton have very high turnover rates.
**Kind of pyramid of energy:** The energy pyramid in this, or any, ecosystem will always be upright.
In simple words: An inverted pyramid of biomass can occur in the sea where phytoplankton biomass is low but rapidly reproducing, supporting a larger zooplankton biomass. However, the energy pyramid will always be upright due to energy loss at each trophic transfer.

🎯 Exam Tip: Remember that while biomass pyramids can be inverted (especially in aquatic ecosystems with high producer turnover), energy pyramids are universally upright due to the laws of thermodynamics and energy transfer efficiency.

Question 14. Name the pioneer species on a bare rock. How do they help in establishing?
Answer:
Lichens are the pioneer species on a bare rock during primary succession. They play a crucial role in establishing subsequent communities by secreting specific acids. These acids corrode the rock surface, contributing to its weathering and initiating the formation of soil. This newly formed, rudimentary soil then creates suitable conditions, paving the way for the growth of other plants, such as bryophytes, and ultimately leading towards a climax community like a mesic forest.
In simple words: Lichens are pioneer species on bare rock; they secrete acids that break down rock, creating the first layers of soil, which allows other plants like mosses to grow and continue the process of ecological succession.

🎯 Exam Tip: Identify lichens as key pioneer species on bare rock and explain the mechanism (acid secretion and weathering) by which they initiate soil formation, a critical step in primary succession.