Communities & Abiotic factors

SPEC 4.7.1.1 & 4.7.1.2 • PAPER 2

The ecology vocabulary mark schemes test relentlessly — and the seven named non-living factors that shape every community. Lesson 7.01.

The Word You Pick Is The Mark

The AQA spec uses specific terms in a specific hierarchy: individual → population → community → ecosystem. Mark schemes catch students who muddle them — writing "ecosystem" where "community" is correct, or "habitat" where "population" is needed.

The trap

Use the wrong word at the wrong level and the examiner cannot award the mark — even if the biology underneath is right. Module 7 examiner reports flag ecology vocabulary as a recurring failure mode.

In the next 10 minutes, you'll know the four named levels, the seven named abiotic factors (verbatim spec wording), and how to write 4-mark "explain how abiotic factor X affects population Y" answers using PEE.

What You'll Be Able To Do

By the end of this lesson:

Objective 1

Define the four named levels of ecological organisation — and the distinction between habitat and ecosystem.

Objective 2

Explain interdependence and what plants vs animals compete for in a community.

Objective 3

Recall the seven named abiotic factors and apply them to "explain the effect of factor X on community Y" exam questions using PEE.

The Four Levels — In Order

Memorise this hierarchy. The exam tests which term applies at which level.

The exam trick

Population = same species only. Community = multiple species. Ecosystem = community + the non-living parts (water, soil, air, light).

Definitions — Spec Wording

Use these exact phrases in 2-mark definition questions. Mark schemes accept paraphrases but reject vague substitutes ("group of animals", "everything in nature").

Ecosystem

The interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

Community

All the populations of different species living together in a habitat, interacting with each other.

Population

All the individuals of one species living in a habitat.

Stable community

A community where all the species and environmental factors are in balance so that population sizes remain fairly constant. (Verbatim spec language — use it.)

Habitat vs Ecosystem — The Mix-Up

These two terms are routinely confused. The distinction is sharp.

HABITATECOSYSTEM

The place where an organism livesThe whole system — community + abiotic factors

Location-focused: for one organism or populationSystem-focused: organisms and their physical environment together

e.g. a pond (for a frog) , a rotting log (for woodlice)e.g. an entire pond ecosystem — fish, plants, microbes, water, oxygen, light, temperature

Mark-scheme trap

If a question asks "name the habitat", do not answer "the ecosystem". A pond is both a habitat (for individual organisms) and the basis of an ecosystem — but if the question asks for one, give the right one.

Interdependence — Why Removing A Species Hurts

Within a community, each species depends on other species for food, shelter, pollination, seed dispersal. If one species is removed, it can affect the whole community.

Worked example

Remove the bee → plants aren't pollinated → fewer seeds → fewer plants → less food for the rabbit → rabbit population falls → fox population falls. One species removed; the whole community shifts.

Competition — Plants vs Animals

To survive and reproduce, organisms require a supply of materials from their surroundings and from the other living organisms there(verbatim spec wording). When those materials are limited, organisms compete. The spec lists exactly what plants and animals compete for.

PLANTS COMPETE FORANIMALS COMPETE FOR

Light — for photosynthesisFood — for energy

Space — to growMates — to reproduce

Water — for photosynthesis and transportTerritory — defended area for feeding/breeding

Mineral ions from the soil — e.g. nitrates for protein synthesis

Exam tip

"Suggest factors organisms compete for" questions expect items from the correct column. Plants don't compete for "mates"; animals don't compete for "mineral ions". Match resource to organism type.

The 7 Named Abiotic Factors

An abiotic factor is a non-living factor affecting a community. The spec lists exactly seven — memorise them in this form.

01Light intensityAffects rate of photosynthesis in plants → plant growth

02TemperatureAffects enzyme activity → metabolic rate, growth

03Moisture levelsWater availability for all organisms

04Soil pH and mineral contentDetermines which plants can grow / uptake nutrients

05Wind intensity and directionAffects transpiration, pollination, seed dispersal

06Carbon dioxide levels (for plants)Affects rate of photosynthesis

07Oxygen levels (for aquatic animals)Required for aerobic respiration in fish, invertebrates, etc.

Memory hook

The last two have qualifiers in the spec — CO₂ for plants, O₂ for aquatic animals. Don't drop the qualifier.

How An Abiotic Factor Affects A Community

Exam questions don't just test recall — they test mechanism. You need to explain why a change in light, temperature, or oxygen changes a population. Build the chain.

Worked mechanism — light intensity falls

Light intensity decreases (abiotic factor change).

Rate of photosynthesis in plants decreases.

Plants produce less glucose; growth slows, plant population may fall.

Herbivores have less food → herbivore population decreases.

Knock-on: predators have fewer prey → predator population decreases too.

The chain rule

Always link the abiotic factor to a biological process the spec names (photosynthesis, respiration, enzyme activity), then to the population. Skipping the middle step costs the mark.

Worked Example — Apply PEE

A typical Paper 2 question on abiotic factors, modelled on the spec content and the recurring "explain effect on community" question style.

Question: A pond becomes contaminated with pollution that lowers the oxygen concentration in the water. Explain how this could affect the fish population in the pond. 4 marks

P

Point: Oxygen concentration is an abiotic factor affecting aquatic animals. (spec language)

E

Evidence: Fish need oxygen for aerobic respiration to release energy for movement, growth, and reproduction.

E

Explain: A reduction in oxygen means fish cannot respire as efficiently, so some fish die and surviving fish may grow more slowly or fail to reproduce — the fish population decreases.

Mark scheme map

Four creditable points: (1) identify abiotic factor; (2) name the biological process (aerobic respiration); (3) link process to consequence for individuals; (4) consequence for the population. Hit all four = 4/4.

Synoptic Links — Where This Recurs

Module 7 is the most synoptic module on Paper 2. Examiners reward students who connect ecology back to mechanisms from earlier modules.

← Module 2: Enzymes

Temperature affects communities because it affects enzyme activity. Above optimum, enzymes denature; below, kinetic energy is too low for collisions.

← Module 4: Photosynthesis

Light intensity, CO₂ and temperature are the limiting factors for photosynthesis. Plant population size traces this directly.

← Module 4: Respiration

Oxygen drives aerobic respiration. Drop O₂ in a pond, and fish energy production crashes — Module 4 mechanism applied to ecology.

← Module 6: Natural selection

Abiotic stress is a selection pressure. Variants better adapted to the new condition survive, breed, pass alleles on. Ecology meets evolution.

Examiner Alerts — The Precision Traps

Three recurring vocabulary errors flagged across AQA biology examiner reports for Module 7 ecology questions.

Alert 1

The hierarchy is named. Organism → population → community → ecosystem. Mark schemes test which term applies at which level. Get them mixed up and the answer voids.

Alert 2

Community ≠ ecosystem. Community = populations of different species. Ecosystem = community plus abiotic factors. Don't substitute one for the other.

Alert 3

Always name the biological process. For "explain how an abiotic factor affects this population" questions, your chain MUST include the named process — photosynthesis, aerobic respiration, or enzyme activity. "Less light, so fewer plants" jumps the gap and loses the middle mark. The process name is the mark.

Common Errors — Wrong vs Right

Mark-scheme language matters. Here's the substitution table.

Wrong

"A population is all the organisms in an area."

Right

A population is all the individuals of the same species in a habitat.

Wrong

"An ecosystem and a community are the same."

Right

Ecosystem = community + abiotic factors.

Wrong

"Temperature is a biotic factor."

Right

Temperature is abiotic (non-living).

Wrong

"Light is low so fewer rabbits."

Right

Light is low → less photosynthesis → fewer plants → less food for rabbits → fewer rabbits. Name the process.

Your Turn

Question:

4 marks

Hint: identify the abiotic factor, link it to a biological process, then to the population.

P

Point: Temperature is an abiotic factor. As temperature rises, the concentration of dissolved oxygen in the water decreases (warm water holds less oxygen).

E

Evidence: Trout need oxygen for aerobic respiration to release energy; higher temperatures also increase their metabolic rate, raising oxygen demand.

E

Explain: Oxygen demand rises while supply falls, so trout cannot respire fast enough — some die, others fail to grow or reproduce. The trout population decreases.

✓

Marks: abiotic factor named (1) · biological process named (1) · effect on individuals (1) · effect on population (1) = 4/4.

Recap — Three Takeaways

The hierarchy.

Organism → population (same species) → community (all species) → ecosystem (community + abiotic).

The 7 abiotic factors.

Light · temperature · moisture · soil pH / minerals · wind · CO₂ (plants) · O₂ (aquatic animals).

Build the chain.

Abiotic factor → biological process (photosynthesis/respiration/enzymes) → individual → population.

One sentence to remember

An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment. That sentence covers three definitions at once.

Up Next

Next lesson

7.02 — Biotic Factors

The four named living factors affecting a community: availability of food, new predators, new pathogens, and one species outcompeting another. Spec 4.7.1.3, Paper 2.

Before you move on

Make sure you can list the seven abiotic factors verbatim, and write the PEE chain for one of them (light, temperature, or oxygen). That's the foundation for everything else in Module 7.

Lesson Summary Card

Key Definitions

Ecosystem = interaction of a community (biotic) with non-living (abiotic) parts of the environment.

Community = all populations of different species in a habitat.

Population = all individuals of one species in a habitat.

Habitat = the place where an organism lives.

Stable community = species + environmental factors in balance; population sizes fairly constant.

What Plants & Animals Compete For

Plants: light · space · water · mineral ions from soil

Animals: food · mates · territory

The 7 Abiotic Factors

Light intensity · temperature · moisture levels · soil pH and mineral content · wind intensity and direction · CO₂ (plants) · O₂ (aquatic animals)

Top exam tip

For "explain the effect of [abiotic factor] on [population]" questions, the chain is always: factor → biological process → individual → population. Name the process or lose the mark.