Physical Abiotic Factors in Ecosystems Revision Notes | GCSE AQA Higher Biology

1. Why Physical Factors Control Life

Walk into a forest and you'll notice something obvious: different plants grow in different places. Ferns thrive in the shady undergrowth while oak trees dominate the sunny canopy. This isn't random — it's controlled by physical factors in the environment.

These non-living factors are called abiotic factors. They act like invisible filters, determining which organisms can survive where. Get the conditions wrong, and species can't establish themselves.

Trap: Many students think abiotic means 'dead things like fallen logs'. Actually, abiotic factors are environmental conditions — they were never alive in the first place. A rotting log is biotic because it was once living.

2. Light Intensity - The Energy Controller

Light intensity determines how much energy is available for photosynthesis. Think of it as the power supply for the entire ecosystem — without enough light, plants can't make glucose, and the whole food web collapses.

Different plants have evolved different light requirements. Shade-tolerant species like moss can photosynthesise in low light conditions, while sun-loving plants like sunflowers need intense, direct sunlight to thrive.

This creates distinct zones in ecosystems. Forest floors receive only 2-5% of the light that hits the canopy. That's why you find completely different plant communities at different heights — each adapted to their light environment.

3. Temperature - The Rate Controller

Temperature controls the speed of life itself. Every chemical reaction in living organisms — from photosynthesis to respiration — depends on temperature. Too cold, and reactions slow to a crawl. Too hot, and enzymes denature.

Most organisms have an optimal temperature range where they function best. Outside this range, they struggle to survive. This is why you find polar bears in the Arctic and camels in deserts — each is adapted to their temperature environment.

Temperature also affects water availability. Higher temperatures increase evaporation rates, making water scarcer even in areas with adequate rainfall. This double effect — direct temperature stress plus water stress — makes temperature a powerful ecological filter.

4. Moisture Levels - The Life Sustainer

Water is life. Every cell needs water for chemical reactions, transport, and structural support. Moisture levels in the environment determine which organisms can establish and maintain populations in an area.

Plants lose water constantly through transpiration — water evaporating from their leaves. In dry conditions, they must either reduce water loss (by closing stomata) or increase water uptake (with deeper roots). Each strategy comes with trade-offs.

Animals face similar challenges. Desert animals like kangaroo rats have evolved to need very little water, while amphibians like frogs require moist environments because they lose water rapidly through their permeable skin.

5. Wind Intensity and Direction - The Invisible Force

Wind might seem less important than light or water, but it's a major ecological force. Strong winds create physical stress, increase water loss, and can prevent certain species from establishing themselves.

On exposed hillsides and coastlines, constant wind creates stunted, wind-sculpted vegetation. Trees grow low and bent, shaped by years of wind pressure. Only the most wind-tolerant species survive in these harsh conditions.

Wind direction matters too. In the UK, prevailing south-westerly winds bring moist air from the Atlantic. The western sides of hills receive more rainfall (orographic precipitation), creating different plant communities on west-facing versus east-facing slopes.

Wind also affects seed dispersal and pollination. Some plants rely entirely on wind to spread their offspring, while others need calm conditions for insect pollinators to operate effectively.

6. How Abiotic Factors Work Together

Here's where it gets complex: abiotic factors don't work in isolation. They interact with each other to create unique environmental conditions. High temperature plus low moisture creates desert conditions. Low temperature plus high moisture creates bog conditions.

These interactions explain why ecosystems are so diverse. A small change in one factor can shift the entire balance, allowing new species to colonise while forcing others to retreat.

Worked example: Analysing Abiotic Factor Interactions

A student investigates why heather grows on acidic moorland but not in neutral grassland, even though both areas have similar temperature and rainfall. Explain the interaction of abiotic factors.

1. Soil pH: moorland is acidic (pH 4-5), grassland is neutral (pH 6-7) — This is the main abiotic factor that differs between the two habitats
2. Acidic soils have low nutrient availability due to reduced bacterial decomposition — Low pH slows down decomposer activity, reducing nutrient cycling
3. Heather is adapted to low-nutrient, acidic conditions with specialised root associations — Heather has mycorrhizal fungi that help extract nutrients from poor soil
4. In neutral grassland, fast-growing grasses outcompete heather for light and space — Higher nutrient availability favours rapid growth, giving grasses an advantage

Answer: Soil pH interacts with nutrient availability to create conditions that favour different plant communities. Heather thrives in low-nutrient, acidic conditions where it faces less competition, but cannot compete with faster-growing species in nutrient-rich, neutral soils.

7. Exam Technique - Mastering Abiotic Factor Questions

Exam questions on abiotic factors often ask you to explain distribution patterns or predict how changes might affect communities. The key is linking the factor to its biological effect, then to the ecological outcome.

Common mistake: Students often describe what happens without explaining why. 'Plants grow better in higher light intensity' gets no marks. 'Plants grow better in higher light intensity because the rate of photosynthesis increases, providing more glucose for growth' gets full marks.