Abiotic and Biotic Factors
- Junessa Masaya
- Apr 15
- 4 min read
Updated: May 20
HSC Biology | Free Study Notes
In this lesson
what abiotic factors are
what biotic factors are
how temperature, rainfall and light affect ecosystems
how competition, predation and disease affect populations
why these factors matter in ecosystem dynamics
What are abiotic factors?
Abiotic factors are the non-living parts of an ecosystem.
These are physical and chemical conditions in the environment that affect where organisms can live and how well they survive. Module 4 specifically includes studying the impact of abiotic factors in ecosystems.
Examples of abiotic factors
temperature
rainfall
light
water availability
soil type
salinity
On this page, the main focus is temperature, rainfall and light.
What are biotic factors?
Biotic factors are the living parts of an ecosystem and the interactions between organisms.
These include how organisms affect one another through feeding, competition, disease and other relationships. Module 4 specifically includes biotic factors such as predation, competition, symbiotic relationships, and the consequences of disease in populations.
Examples of biotic factors
competition
predation
disease
symbiosis
food availability caused by other organisms
On this page, the main focus is competition, predation and disease.
Temperature
Temperature is an important abiotic factor because it affects survival, activity and reproduction.
How temperature affects organisms
Temperature can influence:
enzyme activity
metabolic rate
growth
breeding success
distribution of species
Why temperature matters in ecosystems
Some species are adapted to hot conditions, while others are adapted to cooler conditions. If temperature changes, some organisms may survive better than others, which can change population sizes and food web relationships.
Example idea
A prolonged rise in temperature may reduce the abundance of species that are not well adapted to heat, while favouring more heat-tolerant species.
Rainfall
Rainfall is an abiotic factor that affects water availability in an ecosystem.
How rainfall affects organisms
Rainfall influences:
plant growth
availability of drinking water
breeding conditions
habitat structure
Why rainfall matters in ecosystems
If rainfall is low:
plants may grow less
herbivores may have less food
predator numbers may later decline
If rainfall is high:
plant productivity may increase
more food may become available
some populations may grow
Key idea
Rainfall often affects ecosystems indirectly by first changing producer abundance.
Light
Light is an abiotic factor that is especially important for photosynthetic organisms.
How light affects organisms
Light affects:
the rate of photosynthesis
plant growth
flowering in some species
habitat conditions such as shade and temperature
Why light matters in ecosystems
If light availability changes, the abundance and distribution of producers can change. This then affects herbivores and higher consumers.
Example idea
Plants growing under dense forest canopy receive less light than plants in open grassland, so different species may be favoured in each habitat.
Competition
Competition is a biotic factor that occurs when organisms require the same limited resources.
What organisms compete for
Organisms may compete for:
food
water
light
shelter
territory
mates
Why competition matters
Competition can reduce population growth because not all individuals get the resources they need.
Types of competition
Competition may happen:
between individuals of the same species
between different species
Example idea
Plants in a crowded area may compete for light and soil nutrients, while animals may compete for food or nesting sites.
Predation
Predation is a biotic factor in which one organism kills and eats another.
Why predation matters
Predation affects:
population size of prey
food supply of predators
selection pressures within populations
How predation changes ecosystems
If predator numbers rise:
prey numbers may fall
If prey numbers fall too far:
predator numbers may later decrease because food becomes limited
This shows the interdependence of species in ecosystems.
Disease
Disease is a biotic factor that can influence population size and ecosystem balance.
Why disease matters
Disease can:
reduce survival
reduce reproductive success
spread through populations
alter competition between species
How disease affects populations
If disease spreads through a population:
abundance may decrease
some age groups may be affected more than others
food webs may be disrupted if the affected species has an important role
The Module 4 syllabus specifically includes predicting consequences for populations due to disease.
Abiotic and biotic factors work together
In real ecosystems, abiotic and biotic factors do not act separately.
Example
Low rainfall, which is an abiotic factor, may reduce plant growth. This can then increase competition for food among herbivores, which is a biotic factor.
Another example
A temperature change may favour one predator species over another, changing predation pressure on prey populations.
Key idea
Ecosystem dynamics are shaped by interactions between non-living conditions and living relationships.
Comparison table
Type of factor | Example | How it affects organisms |
Abiotic | Temperature | Affects metabolism and survival |
Abiotic | Rainfall | Affects water availability and plant growth |
Abiotic | Light | Affects photosynthesis and habitat conditions |
Biotic | Competition | Limits access to resources |
Biotic | Predation | Changes prey and predator numbers |
Biotic | Disease | Reduces survival and population size |
Worked example
Exam-style question
Explain the difference between an abiotic factor and a biotic factor, using one example of each.
Worked answer
An abiotic factor is a non-living part of the environment, such as rainfall, which affects water availability and plant growth. A biotic factor is a living interaction in an ecosystem, such as predation, where one organism kills and eats another, affecting population size.
Why this works
This answer:
defines both terms clearly
gives one example of each
links each example to its effect on the ecosystem
Common mistakes
Calling all environmental factors abiotic, even when they involve living organisms.
Forgetting that disease is a biotic factor.
Listing factors without explaining how they affect populations.
Confusing predation with competition.
Describing light only as heat, rather than as a factor affecting photosynthesis and plant growth.
Quick quiz
What is an abiotic factor?
What is a biotic factor?
How can rainfall affect an ecosystem?
Why is predation important in population dynamics?
How can disease change biodiversity in a community?
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