Revision: Energy Flow in an Ecosystem Science SSC (English Medium) 9th Standard Maharashtra State Board

A series of organisms where one is eaten by the next and energy flows from producers to consumers is called a food chain.

A network of interconnected food chains showing how various organisms are related through feeding relationships is called a food web.

A predator is any consumer that kills and eats another living organism in order to obtain energy. The organism being eaten is called the prey.

Food chain, in ecology, the sequence of transfers of matter and energy in the form of food from organism to organism. Food chains intertwine locally into a food web because most organisms consume more than one type of animal or plant. Plants, which convert solar energy to food by photosynthesis, are the primary food source. In a predator chain, a plant-eating animal is eaten by a flesh-eating animal. In a parasite chain, a smaller organism consumes part of a larger host and may itself be parasitized by even smaller organisms. In a saprophytic chain, microorganisms live on dead organic matter.

It refers to relationships between organisms of different species that show on intimate association with each other. Symbiotic relationships provide atleast one of the participating species with a nutritional advantage.
Examples of Symbiosis Relationships are of Fungus and photosynthestic alga and Microbes and cattle.

The circular movement of nutrients between living organisms and the physical environment of an ecosystem is called biogeochemical cycle.

Chemoautotrophs are those who make their own food by deriving the energy from chemical reactions. e.g., Nitrifying bacteria, Iron bacteria etc.

• 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).

• 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.

• A food web is a network of interconnected food chains operating within an ecosystem.
• It shows multiple feeding relationships, as organisms may have more than one food source.
• Food webs represent the flow of energy and nutrients among producers and consumers.
• The complexity of a food web depends on the diversity of organisms and the number of alternative food choices.

• Meaning → Movement of nutrient elements through the various components of an ecosystem is called Nutrient Cycling or Biogeochemical Cycles.
• Two Types → Nutrient cycles are of two types — Gaseous and Sedimentary.
• Gaseous Cycle → Reservoir is the atmosphere. Examples: Nitrogen cycle and Carbon cycle.
• Sedimentary Cycle → Reservoir is the Earth's crust. Examples: Sulphur cycle and Phosphorus cycle.
• Importance → Nutrient cycling ensures the continuous recycling of nutrients between the biotic (living) and abiotic (non-living) components of an ecosystem, unlike energy, which flows unidirectionally.

• Carbon is a key element of living organisms and is found in air, water, soil, rocks, and oceans (major reservoirs).
• The carbon cycle is the movement of carbon between the atmosphere, organisms, and the Earth through natural processes.
• Photosynthesis fixes CO₂ into organic matter, which passes through food chains.
• CO₂ returns to the atmosphere through respiration, decomposition, and combustion.
• Carbon sinks & humans: Fossil fuels and rocks store carbon, but human activities increase CO₂, causing global warming.

• Nitrogen Fixation — N₂ → Ammonia/nitrogenous salts. Types: Biological (microbes) and Non-biological (lightning/industrial).
• Nitrification — NH₃ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter). Nitrates absorbed by plants.
• Ammonification — Dead organic matter → NH₃, by ammonifying bacteria in soil.
• Denitrification — NO₃⁻ → N₂ (back to atmosphere), by Bacillus, Paracoccus, Pseudomonas denitrificans.
• Cyclic Flow — Atmosphere → Soil → Plants → Animals → Soil → Atmosphere. Nitrogen is continuously recycled.