Environmental Factors Affecting Ecosystems Revision Notes | GCSE AQA Higher Biology

1. Why Environmental Factors Matter

Why can polar bears only live in the Arctic, while camels thrive in deserts? The answer lies in environmental factors - the non-living conditions that determine where organisms can survive.

These abiotic factors act like invisible barriers and gateways in nature. Get the conditions right, and life flourishes. Get them wrong, and organisms struggle or disappear entirely. Understanding these factors helps us predict how ecosystems respond to changes like climate change or pollution.

Three key abiotic factors shape every ecosystem on Earth: temperature, water availability, and atmospheric gas composition. Let's see how each one controls life's possibilities.

2. Temperature - The Universal 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 proteins denature, killing the organism.

Picture enzymes as molecular machines with moving parts. At low temperatures, they move sluggishly. As temperature rises, they speed up - but only to a point. Beyond their optimum temperature, the enzyme's shape changes permanently, like a lock that's been melted. The key no longer fits.

Trap: Many students think organisms can adapt to any temperature if given time. Actually, each species has genetic limits - their tolerance range - that cannot be exceeded regardless of time.

Temperature affects ecosystems in three main ways. First, it determines which species can survive in an area - Arctic foxes have thick fur and counter-current blood flow, while desert lizards can tolerate body temperatures that would kill most mammals. Second, it controls activity levels - cold-blooded animals become sluggish in winter, affecting food webs. Third, it influences reproduction timing - many plants and animals use temperature cues to trigger breeding seasons.

3. Water Availability - Life's Essential Resource

Water isn't just something organisms drink - it's the medium where life happens. Every cell is mostly water, and all biochemical reactions occur in aqueous solutions. Without adequate water, organisms face a cascade of problems.

Think of a plant cell like a water balloon. When water is plentiful, the cell stays firm and upright - this is turgor pressure. As water becomes scarce, the balloon deflates. The plant wilts, photosynthesis slows, and growth stops. In extreme cases, the cell membrane pulls away from the cell wall in a process called plasmolysis.

Different organisms have evolved remarkable strategies to cope with water scarcity. Cacti store water in thick stems and have waxy coatings to reduce water loss. Desert animals like kangaroo rats can survive without drinking, obtaining all their water from metabolic processes. Camels can lose 25% of their body water and still survive - a loss that would kill most mammals.

Water availability shapes entire ecosystem structures. Rainforests, with abundant water, support incredible biodiversity and complex food webs. Deserts, with limited water, have fewer species but highly specialised adaptations. Seasonal water availability creates migration patterns - wildebeest follow the rains across African savannas.

4. Atmospheric Gases - The Invisible Ecosystem Drivers

The air around us contains a precise mixture of gases that makes life possible. Change these concentrations, and ecosystems transform dramatically. Three gases have the biggest impact: oxygen, carbon dioxide, and water vapour.

Oxygen concentration determines which organisms can survive and how active they can be. At sea level, air contains about 21% oxygen - perfect for most life forms. Climb a mountain, and oxygen levels drop. Above 3000 metres, many lowland species struggle. Some high-altitude animals have evolved larger lungs and more red blood cells to cope.

Carbon dioxide levels affect plant growth directly through photosynthesis. Higher CO₂ concentrations can boost plant growth - the 'fertilisation effect'. However, this only works if other factors like water and nutrients aren't limiting. Many plants also respond to rising CO₂ by closing their stomata more, which saves water but can reduce cooling.

Water vapour in the atmosphere - humidity - affects how easily organisms can lose water. In humid conditions, sweat doesn't evaporate efficiently, making temperature regulation harder for mammals. Plants in humid environments often have different leaf structures compared to those in dry air.

Trap: Students often think more CO₂ always means more plant growth. Actually, plants need balanced nutrition - if nitrogen or phosphorus is limited, extra CO₂ won't help much.

5. How Environmental Factors Interact

Environmental factors don't work in isolation - they interact in complex ways. A change in one factor often triggers changes in others, creating cascading effects throughout ecosystems.

Consider a warming climate. Higher temperatures increase evaporation rates, potentially reducing water availability. This forces plants to close their stomata to conserve water, which reduces CO₂ uptake and slows photosynthesis. Meanwhile, warmer air holds more water vapour, increasing humidity in some regions but creating droughts in others.

The concept of limiting factors helps us understand these interactions. Imagine a plant in a desert greenhouse. You could pump in extra CO₂, but if water is scarce, growth won't increase. Water is the limiting factor. Add water, and suddenly the plant responds to the extra CO₂. Now temperature might become limiting if it gets too hot.

This principle explains why ecosystems are so sensitive to environmental change. Alter one factor, and you might shift which factor becomes limiting, completely changing how the ecosystem functions.

6. Exam Technique - Environmental Factors Questions

Environmental factor questions appear frequently in GCSE exams, often worth 4-6 marks. Examiners test your ability to link environmental conditions to organism survival and ecosystem changes.

Worked example: Worked Example: Applying Environmental Factors Affecting Ecosystems

Use this method to answer an exam-style question about why environmental factors matter.

1. Underline the key term in the question and write a one-line definition linked to environmental factors affecting ecosystems. — This prevents vague answers and anchors the response in required terminology.
2. Describe the process in logical order using scientific vocabulary and direction words (increase/decrease, faster/slower). — Examiners award marks for clear causal chains, not isolated facts.
3. If data is provided, show each step of working and include units. — Method marks depend on visible working, even if the final answer is not fully correct.
4. Finish with a sentence explaining what the result shows about environmental factors affecting ecosystems. — Interpretation secures higher-band marks.

Answer: A complete response links mechanism, evidence, and conclusion for environmental factors affecting ecosystems.

For 'explain' questions, use this structure: State the environmental factor → Explain how it affects biological processes → Describe the consequence for the organism or ecosystem. For example: 'Low temperature reduces enzyme activity because enzymes have less kinetic energy, so metabolic reactions slow down and the organism becomes less active.'

Watch out for questions asking about 'optimum conditions'. Don't just list ideal values - explain why these conditions are optimum by referring to biological processes. Remember that optimum conditions for one process might not be optimum for another.

When discussing limiting factors, only one factor can be limiting at any time. If a question asks which factor is limiting, look for the one that's in shortest supply or at the most extreme level compared to the organism's needs.