Definitions [5]
Define a consumer.
A consumer is an organism that obtains energy by feeding on other organisms. As it cannot produce its own food, consumers rely on plants or other animals for nourishment, which are a vital part of the food chain. Consumers are further classified into primary consumers, secondary consumers, and tertiary consumers.
Define decomposition.
Decomposition is the process that involves the breakdown of complex organic matter or biomass from the bodies of dead plants and animals with the help of decomposers into inorganic raw materials such as carbon dioxide, water, and other nutrients.
Definition: Decomposition
Decomposition is the process by which decomposers break down complex organic matter into simple inorganic substances like carbon dioxide, water, and nutrients.
Definition: Food Chain
A series of organisms where one is eaten by the next and energy flows from producers to consumers is called a food chain.
Define ecological pyramids.
An ecological pyramid is a graphical representation of various environmental parameters, such as the number of individuals present at each trophic level, the amount of energy, or the biomass present at each trophic level. Ecological pyramids represent producers at the base, while the apex represents the top-level consumers present in the ecosystem.
Formulae [1]
Formula: Net Primary Productivity (NPP)
Net Primary Productivity (NPP) = Gross Primary Productivity (GPP) - Respiratory loss by plants (R)
Key Points
Key Points: Concept of Ecosystem
- An ecosystem is a self-regulating and self-sustaining unit of nature that includes both living (biotic) and non-living (abiotic) components interacting with each other.
- The term ecosystem was given by A.G. Tansley in 1935, and ecosystems can vary in size from a small pond to the entire biosphere.
- Ecosystems are mainly of two types: terrestrial (forest, grassland, desert) and aquatic (lakes, rivers, oceans), and can also be natural or artificial.
- Producers, consumers, and decomposers are the main biotic components; producers make food, consumers depend on them, and decomposers break down waste and recycle nutrients.
- All organisms, including small or unnoticed ones like insects and microbes, play an important role in maintaining balance and cleanliness in the ecosystem.
Key Points: Structure and Function of an Ecosystem
- Two Structural Features → Species Composition (identifying species) + Spatial Pattern (distribution of biotic/abiotic components).
- Two Spatial Patterns → Stratification (vertical, e.g., trees→shrubs→herbs) + Zonation (horizontal, e.g., inter-tidal, littoral zones).
- Types → Terrestrial (forest, grassland, desert) + Aquatic (lakes, rivers, seas, oceans).
- Classification → Natural (self-sustainable) + Artificial (needs human input, e.g., farmland, fish tank).
- Components → Biotic (living) + Abiotic (non-living).
- 4 Functions → Productivity + Decomposition + Energy Flow + Nutrient Cycling (PDEN).
Key Points: Productivity
- Productivity is the rate of formation of biomass (organic matter) at any trophic level per unit area over time, mainly through photosynthesis or chemosynthesis. Unit: g m⁻² yr⁻¹ or g m⁻² day⁻¹.
- Primary productivity is the amount of biomass produced by plants; it includes Gross Primary Productivity (total production) and Net Primary Productivity (usable biomass left after plant respiration).
- Net Primary Productivity (NPP) is important because it represents the energy available to herbivores and other consumers in the ecosystem.
- Secondary productivity is the rate of formation of organic matter by consumers (heterotrophs) and depends on primary productivity.
- Productivity varies across ecosystems depending on factors like plant species, nutrient availability, climate, and photosynthetic efficiency; globally, oceans contribute a significant share.
Key Points: Decomposition
- Decomposition is the process of breaking down complex organic matter into simpler inorganic substances like carbon dioxide, water, and nutrients by decomposers.
- Detritus (dead plants, animals, and fecal matter) is the raw material for decomposition.
- 5 Steps → Fragmentation → Leaching → Catabolism → Humification → Mineralisation.
- Fragmentation is done by detritivores (like earthworms), while bacteria and fungi carry out catabolism by breaking down organic matter into simpler substances.
- Humification forms humus (dark, nutrient-rich substance) that improves soil fertility and water-holding capacity, and mineralisation releases inorganic nutrients back into the soil.
- Factors affecting decomposition include temperature, moisture, oxygen, and the nature of detritus; warm and moist conditions speed it up, while cold and anaerobic conditions slow it down.
Key Points: Trophic Levels of The Ecosystem:
| Trophic Level | Meaning | Examples | Role in Energy Flow |
| Producers (Autotrophs) | Organisms that synthesise their own food using sunlight through photosynthesis. | Green plants, algae, phytoplankton | Convert solar energy into chemical energy, forming the base of the food chain. |
| Primary Consumers (Herbivores) | Organisms that directly depend on producers for their food. | Grasshopper, squirrel, elephant, deer | Consume plant material, store energy for the next trophic level, and act as a link to higher consumers. |
| Secondary Consumers (Carnivores) | Carnivores that feed on herbivores to obtain energy. | Frog, owl, fox, snake | Transfer energy from herbivores to higher levels and help control herbivore populations. |
| Apex or Top Consumers (Carnivores) | Predators at the highest level of the food chain, feeding on herbivores and carnivores. | Tiger, lion, eagle, crocodile | Regulate populations of secondary consumers, maintain ecosystem stability, and have no natural predators. |
| Omnivores (Mixed Consumers) | Organisms that consume both plants (producers) and animals (herbivores and carnivores). | Humans, bears, raccoons | Diversify energy flow by feeding across multiple levels and connecting various parts of the food chain. |
Key Points: Energy Flow in Ecosystem
- PAR → Less than 50% of total incident solar radiation is Photosynthetically Active Radiation (PAR) — the only portion usable by plants.
- Energy Captured by Plants → Plants use only 2–10% of PAR to sustain the entire living world through photosynthesis.
- Energy Flow is Unidirectional → Energy flows from producers → consumers in one direction only; it is never recycled back.
- Trophic Levels → Organisms are arranged in a feeding hierarchy called trophic levels — Producers (1st) → Primary Consumer/Herbivore (2nd) → Secondary Consumer/Carnivore (3rd) → Tertiary Consumer/Top Carnivore (4th).
- Two Types of Food Chains → GFC (Grazing Food Chain) starts with producers (e.g., Grass → Goat → Man); DFC (Detritus Food Chain) starts with dead organic matter and involves decomposers (e.g., Dead leaves → Wood louse → Blackbird).
- Food Web → A network of interconnected food chains involving producers, consumers, and decomposers is called a Food Web.
- 10% Law → Only 10% of energy is transferred from one trophic level to the next. Given by Lindemann (1942). This limits food chains to usually 4–5 trophic levels. A species can occupy more than one trophic level (e.g., a sparrow eats seeds as a primary consumer and insects as a secondary consumer).
Key Points: Food Chain
- A food chain is a linear sequence of organisms in which food energy is transferred from producers to consumers.
- Every food chain begins with producers (green plants) and usually ends with top consumers that are not preyed upon.
- Energy decreases at each trophic level, so food chains are usually short (not more than five levels).
- Shorter food chains are more stable and efficient, as less energy is lost at each step.
Key Points: Ecological Pyramids
| Type of Pyramid | What it Represents | Unit | Shape | Example / Key Feature |
|---|---|---|---|---|
| Pyramid of Energy | Energy flow across trophic levels | Joules (J) | Always upright | Energy decreases at each level due to heat loss (e.g., 10,000 J → 1,000 J → 100 J → 10 J) |
| Pyramid of Numbers | Number of organisms at each trophic level | Individuals per unit area | Upright or inverted | Upright in grassland; inverted in parasitic chains or when one tree supports many insects |
| Pyramid of Biomass | Total dry mass of organisms at each trophic level | kg m⁻² | Upright or inverted | Upright in terrestrial ecosystems; inverted in aquatic ecosystems (phytoplankton < zooplankton) |
