Chapter 5: Our Environment

Solution

Green plants (and other autotrophs like algae and photosynthetic bacteria) are called producers because they produce their own food through photosynthesis, converting solar energy into chemical energy (glucose). They form the base (first trophic level) of all food chains. All other organisms depend on producers directly or indirectly for food.

Solution

Plastic bags are non-biodegradable — they cannot be broken down by bacteria, fungi, or other biological processes. They persist in the environment for hundreds of years, polluting soil and water, and harming wildlife. Vegetable peels, paper, and cotton cloth are all biodegradable — they can be decomposed by microorganisms into simpler substances within weeks to months.

Solution

A deer is a primary consumer (herbivore) — it feeds directly on plants (producers). An eagle is a tertiary/top consumer, a frog is a secondary consumer (eats insects which eat plants), and a mushroom is a decomposer (breaks down dead organic matter).

Solution

In the food chain: Plants -> Deer -> Tiger

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The secondary consumer is: Tiger

Solution

In the food chain: Grass -> Grasshopper -> Frog -> Snake -> Eagle

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The secondary consumer is: Frog

Solution

In the food chain: Plants -> Deer -> Tiger

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The primary consumer is: Deer

Solution

In the food chain: Phytoplankton -> Zooplankton -> Small fish -> Large fish

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The primary consumer is: Zooplankton

Solution

In the food chain: Algae -> Tadpole -> Dragonfly -> Fish -> Crane

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The tertiary consumer is: Fish

Solution

In the food chain: Phytoplankton -> Zooplankton -> Small fish -> Large fish

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The secondary consumer is: Small fish

Solution

In the food chain: Grass -> Grasshopper -> Frog -> Snake -> Eagle

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The tertiary consumer is: Snake

Solution

In the food chain: Grass -> Grasshopper -> Frog -> Snake -> Eagle

Producer = first organism. Primary consumer = 2nd, secondary = 3rd, etc.

The primary consumer is: Grasshopper

Solution

In this food chain, grass is the producer (T₁). The deer eats the grass directly, making it a primary consumer (herbivore) at the second trophic level (T₂). The lion eats the deer, making it a secondary consumer (carnivore) at T₃. Primary consumers always eat producers directly.

Solution

According to the 10% law:
Producers: 10,000 J
Primary consumers get 10% of 10,000 = 1,000 J
Secondary consumers get 10% of 1,000 = 100 J
At each trophic level, only 10% of the energy is transferred to the next level. The remaining 90% is used for the organism's own life processes and lost as heat during respiration.

Solution

Chlorofluorocarbons (CFCs) are the primary chemicals responsible for ozone depletion. Used in refrigerators, air conditioners, and aerosol sprays, CFCs rise to the stratosphere where UV radiation breaks them down, releasing chlorine atoms. Each chlorine atom can destroy thousands of ozone molecules through a catalytic chain reaction. The Montreal Protocol (1987) successfully phased out CFC production globally.

Solution

Decomposers (bacteria and fungi) play a crucial role by breaking down dead plants, animals, and waste matter into simple inorganic substances (nutrients, minerals). These nutrients are released back into the soil, where they become available for producers (plants) to use again. Without decomposers, dead organisms and waste would accumulate, and essential nutrients would be locked away, eventually making the ecosystem collapse.

Solution

The Montreal Protocol (1987) is the international agreement that successfully phased out the production and consumption of ozone-depleting substances, primarily CFCs. It is considered one of the most successful environmental treaties. The Kyoto Protocol and Paris Agreement deal with climate change (greenhouse gas emissions), while the Rio Declaration covers broader sustainable development principles.

Solution

Waste segregation at source — separating biodegradable waste (kitchen waste, garden waste) from non-biodegradable waste (plastic, glass, metal) — is a fundamental practice for effective waste management. Biodegradable waste can be composted, while non-biodegradable waste can be recycled or disposed of properly. Open burning causes air pollution, dumping in water bodies causes water pollution, and unlined landfills can contaminate groundwater.

Solution

The three Rs are: Reduce (use fewer resources, avoid unnecessary consumption), Reuse (use items again instead of discarding them — e.g., cloth bags instead of plastic), and Recycle (process waste materials into new products — e.g., recycling paper, glass, metals). Following the three Rs hierarchy — reduce first, then reuse, then recycle — minimises waste and environmental impact.

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 50000 x (0.1)^(4-1) = 50.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 1000 x (0.1)^(2-1) = 100.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 5000 x (0.1)^(3-1) = 50.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 10000 x (0.1)^(2-1) = 1000.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 2000 x (0.1)^(3-1) = 20.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 1000 x (0.1)^(4-1) = 1.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 10000 x (0.1)^(3-1) = 100.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 20000 x (0.1)^(3-1) = 200.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 2000 x (0.1)^(4-1) = 2.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 5000 x (0.1)^(4-1) = 5.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 50000 x (0.1)^(2-1) = 5000.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 10000 x (0.1)^(4-1) = 10.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 20000 x (0.1)^(2-1) = 2000.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 5000 x (0.1)^(2-1) = 500.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 1000 x (0.1)^(3-1) = 10.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 2 = 2000 x (0.1)^(2-1) = 200.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 3 = 50000 x (0.1)^(3-1) = 500.0 kJ

Solution

By the 10% rule, only 10% of energy passes to next trophic level.

Energy at trophic level 4 = 20000 x (0.1)^(4-1) = 20.0 kJ

Solution

At each trophic level, approximately 90% of energy is lost as heat through respiration. By the fourth trophic level, only about 0.1% (1/1000) of the original energy remains. This is insufficient to sustain another population of organisms. For example, starting with 10,000 J: T₂ gets 1,000 J, T₃ gets 100 J, T₄ gets 10 J — too little for a T₅. This progressive energy loss limits the length of food chains.

Solution

In biological magnification (biomagnification), non-biodegradable chemicals like DDT accumulate progressively at each trophic level. Since organisms at higher levels eat many organisms from the level below, they accumulate larger and larger amounts of the chemical. The top-level consumer (tertiary consumer) has the highest concentration because it has consumed many organisms that each had accumulated the toxin. This is why DDT caused the most damage to birds of prey like eagles, which are top predators.

Solution

The ozone layer absorbs most of the sun's harmful ultraviolet (UV) radiation. If depleted, increased UV radiation would reach Earth's surface, causing: (1) Higher rates of skin cancer (especially melanoma). (2) More cases of cataracts (eye damage). (3) Weakened immune systems. (4) Damage to phytoplankton and reduced crop yields. While ozone depletion and global warming are related environmental issues, they are caused by different chemicals — CFCs deplete ozone; CO₂ and methane cause global warming.

Solution

A food web is more stable than a single food chain because it consists of multiple interconnected food chains. If one species declines or goes extinct, predators can switch to alternative food sources from other connected chains. In a simple food chain, the loss of one species could collapse the entire chain. Greater interconnection and biodiversity make the ecosystem more resilient to disturbances.

Solution

In this aquatic food chain:
T₁ (Producers): Phytoplankton
T₂ (Primary consumers): Zooplankton
T₃ (Secondary consumers): Small fish
T₄ (Tertiary consumers): Big fish
T₅ (Quaternary consumers): Shark
The small fish is at the third trophic level as a secondary consumer.

Solution

The ozone layer is found in the stratosphere, approximately 15–35 km above the Earth's surface. Here, UV radiation from the sun drives the formation of ozone (O₃) from oxygen (O₂). The stratospheric ozone layer absorbs 97–99% of the sun's harmful UV-B and UV-C radiation, protecting life on Earth from DNA damage, skin cancer, and other harmful effects.

Solution

The statement that 'energy can be recycled and reused' is incorrect. Unlike nutrients (like carbon, nitrogen, phosphorus), energy follows a one-way flow through an ecosystem. Energy enters as sunlight, is captured by producers, flows through consumers, and is eventually lost as heat at each trophic level. It cannot be recycled — once used for metabolism and lost as heat, it is gone from the ecosystem. Nutrients, on the other hand, are recycled through biogeochemical cycles.

Solution

Both are true and R correctly explains A. Because only 10% of energy passes from one trophic level to the next, higher trophic levels receive progressively less energy. This means each successive level can support fewer organisms. For example, many grass plants are needed to support fewer deer, and even fewer lions. This energy constraint is the reason for the decrease in organism numbers at higher trophic levels, creating the characteristic pyramid of numbers.

Solution

The Assertion is true — DDT concentration is indeed highest in top predators like fish-eating birds due to biological magnification. However, the Reason is false — DDT is non-biodegradable, NOT biodegradable. This is precisely why it accumulates. DDT cannot be broken down by biological processes, so it persists in fatty tissues and its concentration increases at each trophic level instead of being reduced.

Solution

If all decomposers were removed, dead organisms and organic waste would not be broken down. They would accumulate in the environment. More critically, essential nutrients (nitrogen, phosphorus, carbon, etc.) would remain locked in the dead matter and would not be recycled back into the soil. Over time, the soil would become nutrient-depleted, producers would lack nutrients and decline, and the entire ecosystem would eventually collapse.

Solution

From an ecological perspective, when humans eat plants directly (T₁ → T₂), only one step of energy loss occurs. When humans eat animals that ate plants (T₁ → T₂ → T₃), two steps of energy loss occur. Since 90% of energy is lost at each transfer, eating plants directly is far more efficient — you get 10% of the plant's energy vs. only 1% if it went through an animal first. To produce 1 kg of beef, approximately 10 kg of grain is needed. This is why growing crops for direct human consumption can feed more people than growing crops to feed livestock.

Solution

This dramatic concentration increase is a classic example of biological magnification (biomagnification). Mercury, like DDT, is non-biodegradable and not easily excreted. At each trophic level — from water → phytoplankton → zooplankton → small fish → large fish → tuna — the concentration of mercury increases because: (1) Organisms consume many prey from the level below. (2) Mercury accumulates in tissues faster than it is excreted. (3) The predator accumulates mercury from all the prey it has ever eaten. A tuna (top predator) has consumed millions of organisms indirectly, concentrating mercury to dangerous levels. This is why health advisories recommend limiting consumption of large predatory fish.