Biotic and Abiotic Factors

An ecosystem is a community of living organisms interacting with each other and their physical environment. Every ecosystem is shaped by two categories of factors:

Biotic Factors

The living components of an ecosystem.

Producers (plants, algae)
Consumers (herbivores, carnivores, omnivores)
Decomposers (bacteria, fungi)
Competition between organisms
Predator-prey relationships
Disease and parasitism

Abiotic Factors

The non-living components of an ecosystem.

Temperature and sunlight
Water availability (precipitation)
Soil type and nutrients
Wind and atmospheric gases
pH levels
Salinity

Key Point: A biome is a large-scale ecosystem defined by its climate, vegetation, and animal life. Examples include tropical rainforests, deserts, tundra, and coral reefs. Australia contains a wide range of biomes, from arid deserts to tropical rainforests.

Energy Flow in Ecosystems

Energy enters most ecosystems as sunlight, which is captured by producers through photosynthesis. This energy is then transferred through the ecosystem via feeding relationships. At each trophic level, approximately 90% of energy is lost as heat through cellular respiration.

Food Chain

Energy flows from the sun through producers to consumers. A food web shows multiple interconnected food chains.

Energy Pyramid (Trophic Levels)

Biogeochemical Cycles

Unlike energy, matter is recycled through ecosystems. Two essential nutrient cycles are the carbon cycle and the nitrogen cycle.

The Carbon Cycle

The Nitrogen Cycle (Key Processes)

Nitrogen fixation: Bacteria (e.g., Rhizobium in root nodules) convert atmospheric N₂ into ammonium (NH₄+).
Nitrification: Soil bacteria convert ammonium into nitrites (NO₂−) and then nitrates (NO₃−), which plants absorb.
Assimilation: Plants use nitrates to build proteins and nucleic acids; animals obtain nitrogen by eating plants.
Decomposition: Decomposers break down dead organisms and waste, releasing ammonium back into the soil.
Denitrification: Anaerobic bacteria convert nitrates back into atmospheric N₂, completing the cycle.

Human Impact and Biodiversity

Human activities have significant impacts on ecosystems worldwide. Understanding these impacts is essential for developing sustainable practices.

Negative Human Impacts

Deforestation and habitat destruction
Burning fossil fuels (increased CO₂)
Pollution (water, air, land)
Overfishing and overhunting
Introduction of invasive species
Urbanisation reducing natural habitats

Conservation Strategies

Protected areas and national parks
Breeding programs for endangered species
Reducing carbon emissions
Sustainable farming and fishing
Habitat restoration projects
Legislation protecting biodiversity

Biodiversity refers to the variety of living organisms within an ecosystem. High biodiversity makes ecosystems more resilient — better able to recover from disturbances. Australia is one of 17 megadiverse countries, home to many unique species found nowhere else (endemic species).

Key Vocabulary

Term	Definition
Ecosystem	A community of living organisms and their non-living environment interacting as a system.
Trophic level	A position in a food chain or energy pyramid (producer, primary consumer, etc.).
Producer	An organism that makes its own food through photosynthesis (autotroph).
Consumer	An organism that obtains energy by eating other organisms (heterotroph).
Decomposer	An organism that breaks down dead organic matter, recycling nutrients.
Biodiversity	The variety of different species and genetic variation within an ecosystem.

Worked Examples

1

Constructing a food chain from given organisms.

Given organisms: Hawk, grasshopper, grass, frog.

Step 1: Identify the producer. Grass is the only organism that photosynthesises → Producer.

Step 2: Identify the primary consumer. Grasshoppers eat grass → Primary consumer.

Step 3: Frogs eat grasshoppers → Secondary consumer.

Step 4: Hawks eat frogs → Tertiary consumer.

Food chain: Grass → Grasshopper → Frog → Hawk

2

Calculating energy transfer between trophic levels.

Question: If producers capture 50,000 kJ of energy from the sun, how much energy is available to secondary consumers?

Step 1: Apply the 10% rule. Energy at primary consumer level = 50,000 × 0.10 = 5,000 kJ.

Step 2: Energy at secondary consumer level = 5,000 × 0.10 = 500 kJ.

Answer: Secondary consumers receive approximately 500 kJ (only 1% of the original energy captured by producers).

3

Analysing the effect of removing a species from a food web.

Scenario: In a food web, rabbits are eaten by foxes and eagles. Rabbits eat grass. If a disease eliminates all rabbits, what happens?

Step 1: Fox and eagle populations decrease due to reduced food supply.

Step 2: Grass populations increase because there are fewer herbivores eating them.

Step 3: Other prey species of foxes and eagles may experience increased predation as predators seek alternative food.

Answer: Removing one species causes a cascade effect throughout the food web, demonstrating the interconnectedness of ecosystems.

Knowledge Check

Select the correct answer for each question. Click “Check Answer” to see feedback.

Question 1

Which of the following is an abiotic factor?

Competition between species Temperature Predation Decomposition

Question 2

If producers in an ecosystem absorb 10,000 kJ of energy, approximately how much energy is available to primary consumers?

10,000 kJ 100 kJ 1,000 kJ 9,000 kJ

Question 3

In the carbon cycle, which process removes CO₂ from the atmosphere?

Respiration Combustion Decomposition Photosynthesis

Question 4

In the nitrogen cycle, which process converts atmospheric nitrogen (N₂) into forms usable by plants?

Nitrogen fixation Nitrification Denitrification Assimilation

Question 5

Why does an energy pyramid get narrower at higher trophic levels?

There are more predators than prey About 90% of energy is lost as heat at each trophic level Energy is created at each level Sunlight only reaches the top level

Ecosystems and Biomes