Abiotic and biotic factors
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of key terms in Ecology.
What does ‘abiotic’ mean?
Non-living parts of an ecosystem.
What does ‘biotic’ mean?
Living parts of an ecosystem.
What is a ‘community’?
All of the living organisms / species in a habitat.
Topic Explainer Video
Check out these @JoeDoesBiology and @Lauradoesbiology videos that explain abiotic and biotic factors, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What Are Abiotic and Biotic Factors?
Abiotic factors are the non-living parts of a habitat that can affect where organisms live and how well they survive.
Examples include:
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Light intensity: More light means more photosynthesis for plants.
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Temperature: Affects enzyme activity in plants and animals.
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Moisture levels: Needed for plants to grow and for animals to find drinking water.
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Soil pH and mineral content: Some plants grow best in acidic or alkaline soil; minerals such as nitrates are needed for plants to make amino acids and proteins.
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Wind intensity and direction: Can affect seed dispersal and temperature.
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Carbon dioxide concentrations: Needed by plants for photosynthesis.
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Oxygen concentrations: Needed by aquatic animals in water for respiration, and required in the soil for plants to grow well.
Biotic factors are the living parts of a habitat that can affect where organisms live and how well they survive.
Examples include:
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Numbers of predators.
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Diseases caused by pathogens.
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Competition between species.
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Availability of food / prey.
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Number of herbivores (animals that eat plants).
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Shade provided by trees: Light intensity is obviously an abiotic factor, but as a tree is a living thing, if it shades a particular area, this can be classed as a biotic factor too.
How These Factors Affect a Community
How Abiotic Factors Affect a Community
A change in an abiotic factor can affect the population sizes in a community:
Example 1: If light intensity decreases in a woodland, plants needing lots of light may not grow as well as they absorb less light for photosynthesis. This can affect animals that rely on those plants for food.
Example 2: If oxygen concentrations drop in a pond (e.g. due to pollution), fish and other aquatic animals may die due to a lack of oxygen for aerobic respiration, reducing the population.
Example 3: If mineral ion concentration in the soil decreases, plants may grow more slowly, be smaller, or develop deficiencies (e.g. yellow leaves from lack of magnesium). Poor plant growth means less food for herbivores, so populations of animals that feed on these plants may also decrease.
How Biotic Factors Affect a Community
Example 1: If a new predator is introduced into an area it can cause the population of prey species to decrease. For example, if more foxes move into an area, rabbit numbers may fall because more rabbits are hunted. This can also affect other species that rely on the rabbits for food or compete with them for grass.
Example 2: If two species compete for the same resource, one species may be better adapted and outcompete the other. For example, grey squirrels are larger and more adaptable than red squirrels. They compete with red squirrels for food like nuts and seeds. Because grey squirrels outcompete them, red squirrel numbers have declined in many areas of the UK.
Key Terms
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Abiotic factor – A non-living factor in a habitat that affects organisms (e.g., temperature, light).
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Biotic factor – A living factor in a habitat that affects organisms (e.g., predators, competition).
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Community – All the different species living in a habitat.
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Ecosystem – All the living organisms plus abiotic factors, interacting together in a habitat.
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Exam Tips
- If giving oxygen concentration as an abiotic factor – always say oxygen concentration in the soil for plants or in the water for aquatic organisms.
- Never use the term nutrients! Always say mineral ion concentration in the soil as an abiotic factor that affects plant growth.
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Practice Question
A scientist measured the light intensity in two areas of a woodland: an open clearing and a shaded area under trees. Explain how the difference in light intensity might affect the plants found in each area. (4 marks)
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Light intensity is an abiotic factor needed for photosynthesis.
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Plants in the open clearing absorb more light, so can photosynthesise more.
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This means they can make more glucose and grow faster and outcompete other species.
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In the shaded area, only shade-tolerant plants will survive well.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!