Exercise Solutions (From Screenshot Page 128)

Q1: Fill in the blanks.

1. The functional unit of nature where living organisms interact with their non-living environment is called an ecosystem.
2. The living components of an ecosystem are called biotic components.
3. The non-living components of an ecosystem are called abiotic components.
4. Organisms that produce their own food are called producers.
5. Organisms that depend on producers for food are called consumers.
6. Organisms that break down dead organic matter are called decomposers.
7. A sequence showing energy transfer through feeding relationships is a food chain.
8. A network of interconnected food chains is a food web.
9. Energy flow in an ecosystem is always unidirectional.
10. Only about 10% of energy is transferred from one trophic level to the next.
11. The continuous cycling of elements between living and non-living components is called a biogeochemical cycle.
12. Atmospheric nitrogen is converted to usable forms by nitrogen-fixing bacteria.
13. The continuous movement of water on, above, and below Earth's surface is the water cycle.
14. Excessive or unwanted sound is called noise pollution.
15. Planting trees helps in controlling noise pollution and maintaining environmental balance.

Q2: Match the pairs.

(Note: As an AI, I cannot create interactive matching. I will provide the correct pairs.)

• Producers - Green plants
• Primary Consumers - Herbivores
• Secondary Consumers - Carnivores
• Decomposers - Bacteria and fungi
• Abiotic components - Sunlight, water, soil
• Forest ecosystem - Natural ecosystem
• Crop land - Artificial ecosystem
• Carbon cycle - Photosynthesis and respiration
• Nitrogen fixation - Rhizobium bacteria
• Water cycle - Evaporation and precipitation

Q3: Give scientific reasons.

1. Decomposers are essential for an ecosystem.
   Reason: Decomposers (like bacteria and fungi) play a crucial role in an ecosystem by breaking down dead organic matter (dead plants, animals, and waste products) into simpler inorganic substances. This process, called decomposition, returns vital nutrients (like carbon, nitrogen, phosphorus) back to the soil, water, and atmosphere. These nutrients are then made available for producers to reuse, thus completing the nutrient cycles and ensuring the continuous flow of matter in the ecosystem. Without decomposers, nutrients would be locked up in dead organic matter, and the ecosystem would eventually run out of essential resources.
2. Energy flow in an ecosystem is unidirectional.
   Reason: Energy flow in an ecosystem is unidirectional (one-way) because energy enters the ecosystem primarily from the sun (captured by producers), then flows from producers to various levels of consumers. At each transfer, a significant portion of energy (about 90%) is lost as heat during metabolic processes or is used for life activities. This lost energy cannot be recycled back to the lower trophic levels. Therefore, a continuous input of energy from the sun is required to sustain an ecosystem.
3. Excessive human interference leads to ecological imbalance.
   Reason: Excessive human interference, through activities like deforestation, pollution (air, water, soil), over-exploitation of natural resources, and the introduction of invasive species, disrupts the delicate balance between the biotic and abiotic components of an ecosystem. These activities can lead to habitat destruction, loss of biodiversity, disruption of natural cycles (like the carbon and nitrogen cycles), and climate change. Such disturbances can severely impact the health and stability of ecosystems, reducing their ability to provide essential services and potentially leading to the extinction of species.
4. Planting trees helps in maintaining environmental balance.
   Reason: Planting trees (afforestation) helps maintain environmental balance in several ways:
   • Carbon Cycle: Trees absorb large amounts of carbon dioxide from the atmosphere during photosynthesis, helping to reduce greenhouse gases and mitigate global warming.
   • Oxygen Cycle: They release oxygen into the atmosphere during photosynthesis.
   • Water Cycle: Trees play a crucial role in the water cycle by promoting transpiration and increasing local rainfall, and by preventing soil erosion.
   • Biodiversity: Forests provide habitats for a vast array of plant and animal species, thus preserving biodiversity.
   • Soil Conservation: Tree roots hold soil together, preventing soil erosion.
   All these contribute to a healthier and more balanced environment.

Q4: Answer the following questions.

1. Explain the components of an ecosystem.
   Answer: An ecosystem consists of two main interacting components:
   • Biotic Components (Living): These include all living organisms. They are categorized based on their role in nutrient cycling and energy flow:
     • Producers (Autotrophs): Primarily green plants and algae that produce their own food using sunlight through photosynthesis. They form the base of the food chain.
     • Consumers (Heterotrophs): Organisms that obtain food by feeding on other organisms. They are further divided into:
       • Primary Consumers (Herbivores): Eat producers (e.g., deer, cow).
       • Secondary Consumers: Eat primary consumers (e.g., lion, wolf).
       • Tertiary Consumers: Eat secondary consumers (e.g., tiger, eagle).
     • Decomposers (Saprotrophs): Microorganisms like bacteria and fungi that break down dead organic matter (dead plants, animals, waste) into simpler inorganic substances, returning nutrients to the soil.
   • Abiotic Components (Non-living): These are the physical and chemical factors of the environment that influence the living organisms.
     • Physical Factors: Sunlight, temperature, rainfall, wind, humidity, atmospheric pressure, soil type, topography.
     • Chemical Factors: Water, oxygen, carbon dioxide, nitrogen, minerals (e.g., phosphorus, potassium), pH of soil/water.
2. Explain food chain and food web with examples.
   Answer:
   • Food Chain: A food chain is a simple, linear sequence that illustrates how energy is transferred from one organism to another through feeding relationships. It always starts with a producer, followed by various levels of consumers.
     Example: Grass (Producer) → Deer (Primary Consumer) → Tiger (Secondary Consumer)
   • Food Web: A food web is a more complex and realistic representation of feeding relationships in an ecosystem. It consists of multiple interconnected food chains. In a food web, most organisms feed on more than one type of organism, and they can also be eaten by more than one type of organism. This interconnectedness provides alternative food sources, making the ecosystem more stable.
     Example: In a forest, grass is eaten by deer, rabbits, and insects. Deer are eaten by tigers and wolves. Rabbits are eaten by foxes and eagles. Insects are eaten by birds and frogs. This creates a complex network of feeding relationships rather than a single linear chain.
3. Explain the energy flow in an ecosystem.
   Answer: Energy flow in an ecosystem is unidirectional, meaning it moves in one direction, primarily from the sun to producers, and then through various trophic levels of consumers.
   • Producers: Green plants (producers) capture solar energy through photosynthesis and convert it into chemical energy (food). They form the base of the energy pyramid.
   • Consumers: Energy is then transferred to primary consumers (herbivores) when they eat producers. Secondary consumers get energy by eating primary consumers, and tertiary consumers get energy by eating secondary consumers.
   • Energy Loss: A crucial aspect of energy flow is that only about 10% of the energy is transferred from one trophic level to the next. The remaining 90% is lost as heat during metabolic activities (respiration, movement, etc.) or is used for life processes at that trophic level. This significant energy loss means that the amount of available energy decreases progressively at higher trophic levels.
   • Pyramid of Energy: This unidirectional flow and energy loss are why the pyramid of energy is always upright, with the largest energy base at the producer level and decreasing energy at successive consumer levels. Continuous input of solar energy is required to sustain the ecosystem.
4. Explain any two biogeochemical cycles.
   Answer: Biogeochemical cycles are the continuous cycling of essential chemical elements between the living (biotic) and non-living (abiotic) components of the ecosystem.
   • Carbon Cycle: This cycle involves the movement of carbon through the atmosphere, oceans, land, and living organisms.
     • Photosynthesis: Green plants absorb carbon dioxide (CO₂) from the atmosphere to make food.
     • Respiration: Plants and animals release CO₂ into the atmosphere during respiration.
     • Decomposition: Decomposers break down dead organic matter, releasing CO₂ back into the atmosphere and soil.
     • Combustion: Burning of fossil fuels (coal, oil, gas) and wood releases large amounts of CO₂ into the atmosphere.
     This cycle maintains the balance of carbon dioxide in the atmosphere.
   • Nitrogen Cycle: This cycle describes the circulation of nitrogen, which is a vital component of proteins and nucleic acids. Although atmospheric nitrogen (N₂) is abundant, most organisms cannot use it directly.
     • Nitrogen Fixation: Atmospheric N₂ is converted into usable forms (ammonia, nitrates) by nitrogen-fixing bacteria (e.g., Rhizobium) or by lightning.
     • Nitrification: Ammonia is converted to nitrites and then to nitrates by nitrifying bacteria.
     • Assimilation: Plants absorb nitrates from the soil and convert them into proteins.
     • Ammonification: Decomposers break down nitrogenous waste and dead organisms into ammonia.
     • Denitrification: Denitrifying bacteria convert nitrates back into atmospheric N₂, completing the cycle.
     This cycle ensures the continuous availability of nitrogen for living organisms.

Q5: Differentiate between.

1. Producers and Consumers
   

   Feature	Producers (Autotrophs)	Consumers (Heterotrophs)
   Food Production	Produce their own food (e.g., via photosynthesis)	Depend on producers or other consumers for food
   Energy Source	Primarily sunlight (chemical energy)	Obtain energy by eating other organisms
   Trophic Level	First trophic level (base of food chain)	Higher trophic levels (primary, secondary, tertiary)
   Examples	Green plants, algae	Animals (herbivores, carnivores, omnivores)

2. Food Chain and Food Web
   

   Feature	Food Chain	Food Web
   Structure	Linear sequence of feeding relationships	Network of interconnected food chains
   Complexity	Simple, shows single pathway of energy flow	Complex, shows multiple pathways of energy flow
   Realism	Less realistic (organisms rarely eat only one type)	More realistic (shows diverse feeding relationships)
   Stability	Less stable (break in chain affects all above)	More stable (alternative food sources available)