---
title: "Ecosystem, ecology and trophic levels"
subject: "Technology, Environment and Society"
chapter: 4
key: "semester_7/technology_environment_and_society:ecosystem-ecology-trophic"
source: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/ecosystem-ecology-trophic
site: BCT Engineering
---

# Ecosystem, ecology and trophic levels

Technology, Environment and Society · Chapter 4: Environment

- Asked in: 2082 Bhadra, 4 marks
- Video: [Ecosystem Ecology: Links in the Chain - Crash Course Ecology #7](https://www.youtube.com/watch?v=v6ubvEJ3KGM) — CrashCourse
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/technology_environment_and_society/ecosystem-ecology-trophic
- Whole chapter: https://www.bctengineer.com/md/semester_7/technology_environment_and_society/chapter-4

## Question

Define and discuss ecosystem and ecology with flow of materials or energy in each trophic levels.

## Short answer

Ecology studies the relationships of living organisms with each other and their physical environment. An ecosystem is a functional unit where biotic and abiotic components interact through unidirectional energy flow—only about 10% passes between trophic levels—while nutrients cycle through biogeochemical cycles.

## Answer

**Ecology** is the branch of science that studies the relationships of living organisms with each other and with their physical environment (the term was coined by Ernst Haeckel, 1866).

An **ecosystem** is a functional unit of nature in which a community of living things (biotic components) interacts with the non-living environment (abiotic components) through flow of energy and cycling of materials. Examples: forest, pond, grassland, river, Phewa Lake.

#### Components of an ecosystem

- **Abiotic:** sunlight, water, air, soil, temperature, minerals.
- **Biotic:**
  - **Producers (autotrophs)** – green plants, algae; make food by photosynthesis.
  - **Consumers (heterotrophs)** – primary (herbivores), secondary (carnivores), tertiary (top carnivores).
  - **Decomposers** – bacteria and fungi that break dead matter into nutrients.

#### Flow of energy and materials through trophic levels

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

```text
Sun
 |
 v
Producers (grass)        10,000 kJ   T1
 v
Herbivores (deer)         1,000 kJ   T2
 v
Carnivores (fox)            100 kJ   T3
 v
Top carnivores (tiger)       10 kJ   T4
     \    dead matter    /
      --> Decomposers --> nutrients back to soil
```

- **Energy flow is one-way (unidirectional):** sunlight → producers → consumers, and is finally lost as heat. Only about **10%** of energy passes from one level to the next (Lindeman's 10% law); the rest is used in respiration and lost as heat. That is why food chains are usually short (4–5 levels) and the energy pyramid is always upright.
- **Materials (nutrients) cycle:** carbon, nitrogen, phosphorus and water move from the environment into producers, through consumers, and back to soil and air through decomposers (biogeochemical cycles). Matter is reused; energy is not.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does ecology study?
   A. Relationships of organisms with each other and their environment
   B. Only plants
   C. Only climate
   D. Only rocks
   Answer: A. Ecology studies relationships of living organisms with each other and their physical environment. (Key point: Definition)

2. According to Lindeman's 10% law, how much energy passes to the next trophic level?
   A. About 90%
   B. About 50%
   C. About 10%
   D. About 1%
   Answer: C. About 10% passes on; the rest is lost in respiration and as heat. (Key point: 10% law)

3. How do energy and materials differ in an ecosystem?
   A. Both cycle
   B. Energy flows one way and is lost as heat; materials cycle via decomposers
   C. Energy cycles; materials flow one way
   D. Neither moves
   Answer: B. Energy is unidirectional, nutrients are recycled. (Key point: Energy vs matter)

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