Understanding Ecosystem, Biodiversity and Conservation requires you to connect concepts such as productivity, energy flow, trophic levels, ecological relationships and biodiversity with their applications in different ecosystems. Questions can test definitions, numerical relationships, examples and statements based on ecological principles.

The PW Ecosystem, Biodiversity and Conservation Complete Chapter One-Shot Revision Video For NEET brings these concepts together for quick revision. You can use it to revise important terms, concepts and question patterns before practising more NEET questions.

Ecosystem And Ecological Hierarchy

An ecosystem is the functional unit of ecology. It consists of:

• Biotic Components: Living organisms

• Abiotic Components: Non-living physical and chemical factors

Plants depend on sunlight, water, soil, and temperature. Animals depend on plants and other animals for food. Therefore, an ecosystem can function only when its biotic and abiotic components interact.

The ecological hierarchy is:

1. Organism: The basic level at which ecology begins

2. Population: Members of the same species living in an area and capable of producing fertile offspring

3. Community: All living organisms in a particular area

4. Ecosystem: Biotic and abiotic components interacting with one another

Size, Origin, And Types Of Ecosystems

Ecosystems can be small or very large. An aquarium, fish tank, or garden may represent a small ecosystem. The biosphere is the largest ecosystem and is formed by the combined effect of many local ecosystems.

A man-made ecosystem is controlled by humans. Examples include:

• Aquarium: Humans select the fish, plants, and other organisms.

• Cropland: Humans select crops such as wheat, rice, gram, maize, or sugarcane.

• Basis: Terrestrial ecosystems are based on land, while aquatic ecosystems are based on water.
• Examples: Terrestrial ecosystems include forests, deserts and grasslands; aquatic ecosystems include ponds, lakes, rivers and seas.
• Man-Made Example: Cropland is a terrestrial example, while an aquarium is an aquatic example.

Structure Of An Ecosystem

Abiotic factors determine which plants can grow in a region. In a desert, limited water prevents the growth of very large trees. Plants such as cacti and CAM plants are adapted to these conditions.

In tropical rainforests, abundant water and moisture support tall trees, thick trunks, and dense vegetation.

The sequence is:

1. Abiotic factors determine the plants present.

2. Herbivores that feed on those plants become established.

3. Carnivores that feed on herbivores become established.

4. A complete ecosystem develops.

Thus, vegetation influences the distribution of animals. For example, a carrot-dominated field is more likely to support herbivores that feed on carrots.

Species Composition And Stratification

Species composition means identifying and counting the species present in an ecosystem. It includes:

• Species Identification: Determining which species are present

• Species Enumeration: Counting individuals of each species

Stratification refers to the vertical distribution of organisms into layers, or strata. A forest may contain:

1. Ground Layer: Herbs and grasses

2. Shrub Layer: Shrubs

3. Medium-Tree Layer: Medium-sized trees

4. Tall-Tree Layer: Tall trees

Four Essential Aspects Of An Ecosystem

Every functioning ecosystem includes:

1. Productivity

2. Decomposition

3. Energy Flow

4. Nutrient Cycling

Productivity

Plants capture sunlight and convert light energy into chemical energy stored in food. They are called producers.

Decomposition

Bacteria and fungi break down dead plants, animals, leaves, and branches into simpler inorganic substances. These organisms are called decomposers.

Energy Flow

Energy moves through organisms in the sequence:

Plants, Herbivores, Carnivores, Top Carnivores

Nutrient Cycling

Decomposition releases inorganic nutrients into the soil. Plants absorb these nutrients, herbivores consume plants, and carnivores consume herbivores. After death, the nutrients return to the soil through decomposition.

Pond Ecosystem

A pond demonstrates the interaction between biotic and abiotic components.

Abiotic Components

• Sunlight

• Temperature

• Water

• Soil

Biotic Components

Producers include phytoplankton, algae, cyanobacteria, floating plants, submerged plants, and marginal plants.

Consumers follow a simple food chain:

Phytoplankton, Zooplankton, Small Fish, Large Fish

Fungi, bacteria, and flagellates act as decomposers. A pond therefore shows all four essential ecosystem processes: productivity, decomposition, energy flow, and nutrient cycling.

Primary Productivity

The Sun is the ultimate source of energy for most ecosystems. According to the first law of thermodynamics, energy can neither be created nor destroyed; it can only be converted from one form to another.

Production And Productivity

• Production: Total amount of biomass or energy produced

• Productivity: Rate of biomass or energy production

Productivity must include time in its unit.

(*Memory Tip: If the unit includes “per year” or another time term, it represents productivity.)*

Primary And Secondary Productivity

Primary productivity is the first production of food and biomass by plants or other autotrophs through photosynthesis.

Secondary productivity is biomass formed by consumers after they feed on organisms at a lower trophic level.

• Primary Productivity: Produced directly by autotrophs using light energy

• Secondary Productivity: Produced by consumers using already-formed biomass

Gross And Net Primary Productivity

• Gross Primary Productivity (GPP): Total energy produced during photosynthesis

• Respiratory Loss: Energy used by the plant for respiration and maintenance

• Net Primary Productivity (NPP): Energy remaining after respiratory loss

NPP = GPP − Respiratory Loss

NPP is available to herbivores and higher trophic levels. Animals receive NPP, not GPP.

Decomposition And Its Steps

Detritus is dead organic matter on which decomposers act. Earthworms are called the “friends of farmers” because they fragment dead matter, loosen soil, and improve aeration.

The five steps of decomposition are:

1. Fragmentation: Physical breakdown of detritus into smaller particles

2. Catabolism: Chemical breakdown of complex organic matter

3. Leaching: Downward movement of water-soluble nutrients with water

4. Humification: Formation of dark, amorphous humus

5. Mineralisation: Release of inorganic minerals from humus

(*Memory Tip: Remember F-C-L-H-M: Fragmentation, Catabolism, Leaching, Humification, Mineralisation.)*

Warm, moist conditions and oxygen increase decomposition. Sugars decompose easily, while lignin and chitin decompose very slowly.

Trophic Levels And Food Chains

A trophic level is the feeding position of an organism in a food chain.

1. First Trophic Level: Producers

2. Second Trophic Level: Herbivores or primary consumers

3. Third Trophic Level: Carnivores or secondary consumers

4. Fourth Trophic Level: Top carnivores

A food chain is linear, while a food web contains interconnected food chains. Omnivores may occupy different trophic levels in different food chains.

Types Of Food Chains

• Grazing Food Chain: Begins with living producers

• Detritus Food Chain: Begins with dead organic matter

(*Memory Tip: DFC is more prominent on land because dead matter remains in soil; GFC is relatively more prominent in aquatic ecosystems.)*

Lindeman’s 10% Rule

According to Lindeman’s 10% rule, only about 10% of energy passes from one trophic level to the next. Approximately 90% is lost as heat.

(*Memory Tip: At every trophic transfer, 10% moves forward and 90% is lost as heat.)*

Because energy decreases sharply, ecosystems usually contain about four trophic levels and rarely more than five.

Ecological Pyramids

Ecological pyramids represent trophic levels through:

• Pyramid Of Numbers

• Pyramid Of Biomass

• Pyramid Of Energy

The pyramid of energy is always upright because energy decreases at every trophic transfer. The pyramid of biomass is usually upright in forests but may be inverted in aquatic ecosystems, where phytoplankton have lower biomass than zooplankton and fish.

Limitations include poor representation of omnivores, food webs, and decomposers. Decomposers act on dead matter from every trophic level.

Biodiversity And Its Levels

Biodiversity means the variety of living organisms. It occurs at three major levels:

1. Genetic Diversity: Variation within a species

2. Species Diversity: Variation in the number and types of species

3. Ecological Diversity: Variation among ecosystems and biomes

Examples of genetic diversity include rice strains and mango varieties. Species diversity differs between regions, such as the greater amphibian diversity of the Western Ghats compared with the Eastern Ghats. India has high ecological diversity because it contains deserts, rainforests, rivers, beaches, snowy regions, and oceans.

Tropical regions generally have greater species richness than temperate regions because they receive more solar energy, have stable climates, and provide more time for diversification and speciation.

Species–Area Relationship

Alexander von Humboldt proposed the species–area relationship. As the area of study increases, species richness also increases, but eventually approaches a limit.

The relationship is written as:

S = C A raised to the power Z

Where:

• S: Species richness

• A: Area

• C: Constant

• Z: Slope or regression coefficient

The logarithmic form is:

Log S = Log C + Z Log A

This produces a straight-line relationship. The value of Z is generally lower for small areas and higher for very large areas.

Importance Of Biodiversity Conservation

Biodiversity improves ecosystem stability by providing:

• Lower variation in biomass production

• Greater resistance to disturbance

• Greater resilience after disturbance

• Greater resistance to alien species

The rivet-popper hypothesis, proposed by Paul Ehrlich, compares species with rivets in an aeroplane. Removing a few rivets may not cause immediate failure, but removing a critical rivet can destabilise the entire structure.

Evil Quartet Of Biodiversity Loss

The four major causes of biodiversity loss are:

1. Habitat Loss And Fragmentation

2. Overexploitation

3. Alien Species Invasion

4. Co-Extinction

Habitat loss and fragmentation destroy or divide natural habitats. Overexploitation removes organisms faster than they can reproduce. Alien species compete with or consume native species. Co-extinction occurs when the loss of one closely dependent species causes the loss of another.

Biodiversity Conservation Methods

In Situ Conservation

In situ conservation protects organisms in their natural habitats. Examples include:

• Biosphere Reserves

• National Parks

• Wildlife Sanctuaries

• Sacred Groves

Biosphere reserves contain:

• Core Zone: Strict protection

• Buffer Zone: Limited human activity

• Transition Zone: Greater human activity

Sacred groves are protected by local communities because of religious and cultural beliefs.

Ex Situ Conservation

Ex situ conservation protects organisms outside their natural habitats. Examples include:

• Zoos

• Botanical Gardens

• Wildlife Safari Parks

• Seed Banks

• Cryopreservation

Cryopreservation stores biological material such as seeds, pollen, sperm, gametes, or tissues in liquid nitrogen at approximately minus 196 degrees Celsius.

Biodiversity Hotspots And Bioprospecting

A biodiversity hotspot contains many species and endemic organisms within a small area. The Western Ghats and Sri Lanka, Indo-Burma, and the Himalayan region are associated with India.

Bioprospecting means searching living organisms for useful products, medicinal compounds, fibres, timber, fragrances, or other resources.

Watch the complete PW video to revise the chapter and practise important PYQs and must-do questions for NEET.

Most Important Questions from Ecosystem, Biodiversity and Conservation

Q1. Match the trophic levels with their correct species examples in a grassland ecosystem. [2020]

List-I

A. Fourth trophic level
B. Second trophic level
C. First trophic level
D. Third trophic level

List-II

I. Crow
II. Vulture
III. Rabbit
IV. Grass

Options:

A. A-III, B-II, C-I, D-IV
B. A-IV, B-III, C-II, D-I
C. A-I, B-II, C-III, D-IV
D. A-II, B-III, C-IV, D-I

Answer: D. A-II, B-III, C-IV, D-I

The fourth trophic level is represented by the vulture, the second by the rabbit, the first by grass and the third by the crow.

Q2. Given below are two statements:

Statement I: The primary source of energy in an ecosystem is solar energy.

Statement II: The rate of production of organic matter during photosynthesis in an ecosystem is called net primary productivity (NPP).

In the light of the above statements, choose the most appropriate answer from the options given below. [2025]

A. Both Statement I and Statement II are correct
B. Both Statement I and Statement II are incorrect
C. Statement I is correct but Statement II is incorrect
D. Statement I is incorrect but Statement II is correct

Answer: C. Statement I is correct but Statement II is incorrect

Solar energy is the primary source of energy for most ecosystems. The rate of production of organic matter through photosynthesis is gross primary productivity (GPP), not NPP.

Q3. Who is known as the father of Ecology in India?

A. S. R. Kashyap
B. Ramdeo Misra
C. Ram Udar
D. Birbal Sahni

Answer: B. Ramdeo Misra

Ramdeo Misra is known as the father of Ecology in India.

Q4. Which of the following is the unit of productivity of an ecosystem?

A. g m⁻²
B. kcal m⁻²
C. kcal m⁻³
D. kcal m⁻² yr⁻¹

Answer: D. kcal m⁻² yr⁻¹

Productivity represents the rate of production of biomass or organic matter. Therefore, its unit includes an area and a time component, such as kcal m⁻² yr⁻¹.

Q5. Given below are two statements:

Statement I: In an ecosystem, there is unidirectional flow of energy from the Sun through producers to consumers.

Statement II: Ecosystems are exempt from the second law of thermodynamics.

In light of the above statements, choose the most appropriate answer from the options given below. [2025]

A. Both Statement I and Statement II are correct
B. Both Statement I and Statement II are incorrect
C. Statement I is correct but Statement II is incorrect
D. Statement I is incorrect but Statement II is correct

Answer: C. Statement I is correct, but Statement II is incorrect

Energy flow in an ecosystem is unidirectional, moving from the Sun to producers and then through different trophic levels. Ecosystems are not exempt from the second law of thermodynamics.

 Revising Ecosystem, Biodiversity and Conservation requires attention to trophic levels, productivity, energy flow, biodiversity and conservation concepts. The PW Ecosystem, Biodiversity and Conservation Complete Chapter One-Shot Revision Video for NEET can be used for quick revision before solving more chapter-wise questions

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