Ecosystem & Energy Flow
Ecosystem & Energy Flow
Our Environment – Ecosystem Basics
Our environment includes all living (biotic) and non-living (abiotic) things that surround an organism and influence its life.
| Component | Simple meaning | Examples |
|---|---|---|
| Biotic | Living organisms in the environment. | Plants, animals, microorganisms, humans. |
| Abiotic | Non-living physical factors. | Air, water, soil, light, temperature, minerals. |
| Ecosystem | A functional unit where biotic and abiotic components interact. | Pond, crop field, forest, lake, desert, grassland. |
Ecosystem = Biotic community + Physical environment + Interactions.
Major ecosystem types (school level)
- Natural ecosystems – forest, grassland, pond, lakes, rivers, ocean, desert.
- Artificial (man-made) ecosystems – crop fields, gardens, fish ponds, plantation farms.
Trophic levels in an ecosystem
| Trophic level | Role | Examples (India focus) |
|---|---|---|
| Producers | Make food from sunlight by photosynthesis. | Grass, wheat, paddy, trees, phytoplankton. |
| Primary consumers | Herbivores – feed on producers. | Goat, cow, deer, grasshopper, zooplankton. |
| Secondary consumers | Carnivores – feed on herbivores. | Frog, lizard, small fish, birds. |
| Tertiary / top consumers | Top carnivores – no natural predators in that food web. | Tiger, lion, eagle, shark. |
| Decomposers | Break down dead bodies and waste, recycle nutrients. | Bacteria, fungi, some actinomycetes. |
Memory Line: “Environment = biotic + abiotic; Ecosystem = environment with interactions and energy flow.”
Exam Tip: If the question asks “Which is not a component of ecosystem?” – check whether the option is a process (like photosynthesis) instead of a component (like soil, plant, animal, microbe).
Food Chain and Flow of Energy
Food chain is a linear sequence of organisms where each one is eaten by the next.
| Term | Meaning | Simple example |
|---|---|---|
| Food chain | Stepwise transfer of food and energy. | Grass → Goat → Man |
| Grazing food chain | Starts from green plants. | Phytoplankton → Small fish → Big fish → Human |
| Detritus food chain | Starts from dead organic matter. | Leaf litter → Earthworm → Bird → Hawk |
Flow of energy in food chain
- Main source of energy = Sun.
- Plants capture solar energy by photosynthesis → convert to chemical energy (food).
- Energy transfer is unidirectional – from sun → producers → consumers → decomposers → environment (heat).
- At each trophic level, some energy is lost as heat (respiration, movement, life processes).
| Stage | Energy flow highlight | Key point |
|---|---|---|
| Sun → Producer | Only a small fraction of sunlight is captured by plants. | Photosynthesis fixes energy as carbohydrates. |
| Producer → Primary consumer | Herbivore gets part of stored energy. | Much energy used for respiration, growth, movement. |
| Primary → Secondary → Tertiary consumer | Energy decreases at every step. | Animals at higher trophic levels are fewer in number. |
Memory Line: “Energy flow in ecosystem is one-way and decreases at each higher trophic level.”
Exam Tip: If the question asks about direction of energy flow, correct answer is always from producers to various consumers, never backwards.
Food Web and Ecological Stability
Food web is a network of interconnected food chains in an ecosystem.
- In nature, one organism may eat and be eaten by many different organisms.
- Food webs provide stability to ecosystem – if one food source is lost, consumer can shift to another.
| Concept | Food chain | Food web |
|---|---|---|
| Structure | Single straight line | Network of many chains |
| Realism | Ideal, simplified picture | More realistic |
| Stability | Less stable, disturbance at one step affects all directly | More stable, alternatives available |
Example – in an Indian pond ecosystem:
- Phytoplankton → Zooplankton → Small fish → Big fish → Bird
- Phytoplankton → Insect larva → Small fish → Bird
- Decaying plants → Bacteria → Zooplankton → Fish
Memory Line: “Many food chains interlinked = food web; food web = stability of ecosystem.”
Exam Tip: If the diagram shows one straight sequence → mention “food chain”. If it shows many arrows crossing between organisms → mention “food web”.
Ecological Pyramids
Ecological pyramid is a graphical representation of trophic levels of an ecosystem in the form of a pyramid.
| Type of pyramid | What it represents | General pattern |
|---|---|---|
| Pyramid of number | Number of organisms at each trophic level. | Most cases upright (more producers than top consumers). |
| Pyramid of biomass | Total dry weight (biomass) at each trophic level. | Usually upright in forest; can be inverted in aquatic systems. |
| Pyramid of energy | Energy content at each trophic level per unit area per time. | Always upright due to loss of energy at each level. |
Key points for exam
- Producers form the base of all ecological pyramids.
- Pyramid of energy is always upright – because energy cannot be recycled; only nutrients are recycled.
- Top carnivores are few in number and have least energy and biomass.
Memory Line: “Base = producers; top = carnivores; energy pyramid is always upright.”
Exam Tip: If the question says “Which pyramid is always upright?” – answer is pyramid of energy, even if number or biomass can be inverted.
Effects of Human Activities on Ecosystems
Human activities can disturb the balance of ecosystems at local, regional and global levels.
| Human activity | Immediate effect on ecosystem | Long-term impact |
|---|---|---|
| Overuse of chemical fertilisers and pesticides | Soil and water pollution, killing of useful organisms. | Bioaccumulation in food chains, health problems, loss of biodiversity. |
| Deforestation, cutting forests | Loss of habitat for wildlife, soil erosion. | Climate change contributions, loss of biodiversity, disturbed water cycle. |
| Industrial and vehicular pollution | Air and water pollution. | Acid rain, smog, respiratory diseases, global warming. |
| Excessive exploitation of resources | Reduction in natural resource stock. | Resource depletion, conflicts, reduced quality of life. |
Indian context examples
- Pollution in rivers like Ganga, Yamuna, Godavari affecting aquatic life and human health.
- Deforestation in Western Ghats and Eastern Ghats leading to soil erosion and loss of endemic species.
- Urban solid waste mismanagement affecting local ecosystems, stray animals, and groundwater.
Memory Line: “Uncontrolled human activity → disturbed food chains, loss of biodiversity, and weaker ecosystems.”
Exam Tip: When you see words like deforestation, pollution, overgrazing, overfishing in a question, think of impacts on food chain, biodiversity and ecological balance.
Steps Towards Prevention and Conservation
To protect ecosystems, simple preventive and conservation steps are required at individual, community and government levels.
| Level | Action | How it helps ecosystem |
|---|---|---|
| Individual | Save electricity and water, use cloth bags, segregate waste, avoid littering. | Reduces pressure on resources and lowers pollution. |
| Community | Plantation drives, keeping local water bodies clean, awareness campaigns. | Improves local environment and strengthens food chains. |
| Government | Pollution control laws, protected areas (national parks, wildlife sanctuaries), environmental regulations. | Conserves biodiversity and prevents large-scale ecosystem damage. |
Steps towards prevention – simple school-level points
- Reduce, reuse, recycle – especially plastics and metals.
- Afforestation and social forestry to restore degraded lands.
- Use of eco-friendly technologies and renewable energy (solar, wind, biogas).
- Scientific disposal of sewage and solid waste to protect soil and water.
- Environmental education in schools to build responsible citizenship.
Memory Line: “Conservation = wise use of resources + protection of biodiversity for present and future generations.”
Exam Tip: If a question asks for preventive measures, always mention at least one point related to reducing pollution, one about planting/protecting trees, and one about proper waste management.