Definitions [7]
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.
Define the term predation.
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.
Define the food chain and give two examples.
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.
Define the following term and give two examples:
Symbiosis
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.
Define chemoautotrophs.
Chemoautotrophs are those who make their own food by deriving the energy from chemical reactions. e.g., Nitrifying bacteria, Iron bacteria etc.
Key Points
- Energy flow in an ecosystem is strictly unidirectional, moving from the sun through producers to consumers and decomposers.
- Unlike physical matter, energy within an ecosystem is never recycled and is progressively lost as heat at every trophic step.
- Less than 50% of incident solar radiation is Photosynthetically Active Radiation (PAR), and plants capture merely 2–10% of this PAR to sustain the living world.
- Grazing Food Chains (GFC) originate with living plants and dominate aquatic ecosystems, while Detritus Food Chains (DFC) originate with dead organic matter and dominate terrestrial ecosystems.
- Interconnected food chains create complex food webs that provide ecosystems with essential stability, resilience, and alternative energy pathways.
- Within a complex food web, a single organism has the ecological flexibility to occupy more than one trophic level simultaneously.
- Organisms are structured into sequential trophic levels, from producers (T1) to apex predators (T4), with available energy drastically decreasing at each successive tier.
- Decomposers act systematically across all trophic levels to break down dead organic matter, forming a critical biological link for continuous nutrient recycling.
- 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.
