Cambridge O Level Environmental Management (5014): Ecosystems, biodiversity and fieldwork – Study Guide

This topic joins together four ideas that Cambridge O Level Environmental Management 5014 treats as a sequence. First you learn how an ecosystem works (5.1), then you study forests as a major example (5.2), then you look at how biodiversity is protected (5.3), and finally you learn how to collect and analyse your own data in the field (5.4). The final sub-topic is the practical skill that supports the others, so it is worth learning even if you rarely meet it in a direct recall question.

Where this fits in the specification

Ecosystems link back to Topic 1 (natural resources) and Topic 2 (land), because soil, water and energy supply all shape which organisms can live somewhere. They also lead forward to human population (Topic 7), since population growth drives habitat loss. Questions on this topic often ask you to apply a general idea to a named place, so build your own short case study of one forest and one protected area.

5.1 Ecosystems

An ecosystem is a community of living organisms (the biotic part) interacting with each other and with the non-living (abiotic) environment, such as light, temperature, water and soil. A habitat is the place where an organism lives; a population is all the members of one species in a habitat; a community is all the populations together.

Food chains, webs and trophic levels

A food chain shows who eats whom, with arrows pointing in the direction of energy flow.

• Producers (green plants and algae) make food by photosynthesis.
• Primary consumers are herbivores; secondary consumers eat them; tertiary consumers eat the secondary consumers.
• Decomposers (bacteria and fungi) break down dead material and return nutrients to the soil.

A food web is several linked food chains. Its value in an exam answer is that you can show how removing one species affects many others. If a web shows frogs eating both beetles and flies, losing the beetles may mean the frogs eat more flies, but losing a producer affects every level above it.

Energy flow and pyramids

Only a small share of energy passes from one trophic level to the next. The rest is lost as heat from respiration, in movement, in waste and in parts that are not eaten. This is why food chains rarely have more than four or five links, and why a pyramid of energy is always the correct shape (wide base, narrow top). Pyramids of numbers and biomass can sometimes look odd (for example, one large tree supporting thousands of insects), so explain the reason if you are asked.

Worked example: energy transfer

A pond receives sunlight, and producers fix 20 000 kJ per square metre per year. The primary consumers store 2 000 kJ m-2 yr-1, and the secondary consumers store 240 kJ m-2 yr-1.

Efficiency from producers to primary consumers = 2 000 / 20 000 x 100 = 10%.

Efficiency from primary to secondary consumers = 240 / 2 000 x 100 = 12%.

Energy not passed on from the producers = 20 000 - 2 000 = 18 000 kJ m-2 yr-1, which is 90% of what the producers fixed. A good explanation names where it goes: respiration (released as heat), uneaten plant parts, and waste passed to decomposers.

Nutrient recycling

Unlike energy, nutrients are recycled. Decomposers release nutrients from dead matter, which plants take up again through their roots. Learn the carbon cycle (photosynthesis removes carbon dioxide, respiration, combustion and decay return it) and be ready to link it to climate change.

5.2 Forest ecosystems

Forests, especially tropical rainforest, are very productive and hold a large share of the world’s species. Know the layers of a rainforest (emergent, canopy, understorey, forest floor) and why the canopy shades the floor, so few plants grow there.

Why forests matter: they store carbon, regulate the water cycle (leaves release water vapour by transpiration; roots hold soil), provide timber, food, medicines and habitat, and support local and Indigenous communities.

Causes of deforestation: commercial logging, clearing for farming (cattle, palm oil, crops), mining, road building, fuelwood collection and settlement.

Impacts: loss of habitat and biodiversity, soil erosion and landslides on cleared slopes, more flooding downstream, less transpiration and so less local rainfall, and more carbon dioxide in the atmosphere.

Sustainable management: selective logging instead of clear-felling, replanting and reforestation, protected reserves, agroforestry (growing crops among trees), certification of timber, and involving local people in decisions. A balanced answer always notes the cost: protection can reduce short-term income, so alternatives such as ecotourism need to be offered.

5.3 Managing biodiversity

Biodiversity is the variety of living things in an area: the number of species (species richness), the genetic variety within each species, and the variety of habitats. Higher biodiversity usually makes an ecosystem more resilient, because if one species declines others can fill its role.

Threats: habitat loss and fragmentation, overharvesting and poaching, pollution, invasive non-native species, and climate change. Small, isolated populations are especially vulnerable because they lose genetic variety.

Ways to protect biodiversity

Method	How it works	Limitation
National parks and reserves	Legal protection of whole habitats	Costly to patrol; boundaries can be ignored
Captive breeding and zoos	Keeps endangered species breeding for later release	Does not save the habitat; limited numbers
Seed banks	Store seeds of rare plants for the future	Does not protect wild populations
Laws and treaties	Ban trade or hunting of protected species	Hard to enforce across borders
Education and community schemes	Local people benefit from conservation	Takes time and funding

A strong answer joins protection of the habitat with action on the cause of the threat. Protecting a reserve while ignoring poaching, for example, protects very little.

5.4 Fieldwork investigations

Fieldwork means collecting first-hand data outdoors. The usual sequence is: state a question or hypothesis, plan the method, collect data, present it, analyse it, draw a conclusion and evaluate.

Sampling is needed because you cannot count every organism. Random sampling (for example, quadrats placed using random co-ordinates) avoids bias. A transect (a line across a habitat, with samples at regular intervals) is better for showing change along a gradient, such as from shade into open ground.

Measuring abiotic factors might include light intensity, soil pH, soil moisture, temperature or water quality. Repeat readings and take a mean so that one unusual reading does not mislead you.

Worked example: quadrat sampling

A meadow measures 400 m2. A student places ten 1 m2 quadrats at random and counts the daisies: 4, 7, 3, 6, 5, 9, 2, 4, 8, 6.

Total = 54. Mean per quadrat = 54 / 10 = 5.4.

Estimated population = mean per m2 x total area = 5.4 x 400 = 2 160 daisies.

Evaluation: ten quadrats is a small sample, so repeating with more quadrats would make the estimate more reliable.

Worked example: capture-mark-recapture

For mobile animals, 40 beetles are caught, marked and released. A later sample of 30 beetles contains 6 marked ones.

Population estimate = (first sample x second sample) / number recaptured = (40 x 30) / 6 = 200 beetles.

The method assumes the marked beetles mix evenly, no marked animals are lost or gained, and the marking does not harm them.

Common mistakes

• Drawing food-chain arrows from the consumer to the food. They show the direction of energy flow, so they point to the consumer.
• Saying that energy is “used up”. Energy is transferred or lost as heat, not destroyed.
• Treating biodiversity as the same as the number of individuals. It is about variety.
• Giving one-sided answers on deforestation. Cambridge questions often reward both the economic benefit and the environmental cost.
• Forgetting to repeat measurements or to use a random method in a fieldwork plan.

Exam technique

Command words matter. Describe needs what you see or what happens; explain needs a reason (use “because”); suggest means apply your knowledge to an unfamiliar situation; evaluate or assess needs strengths, weaknesses and a judgement. For data questions, quote figures with units from the table or graph, and show your calculation steps. In fieldwork questions, comment on reliability (repeats, sample size) and on safety.

Check your understanding

1. State the difference between a habitat and an ecosystem. A habitat is where an organism lives; an ecosystem includes all the organisms there plus the non-living environment and their interactions.
2. Why do food chains rarely have more than five trophic levels? Energy is lost at each level, mainly as heat from respiration, so too little remains to support more levels.
3. Producers fix 15 000 kJ m-2 yr-1 and primary consumers store 1 200. Calculate the percentage transferred. 1 200 / 15 000 x 100 = 8%.
4. Give two ways deforestation can increase flooding. Less interception and transpiration so more runoff; bare soil is eroded and silts up rivers.
5. Explain why a seed bank does not fully protect a rare plant. It preserves seeds but does not protect the wild habitat or population.
6. A 200 m2 field has a mean of 3.5 plants per m2 from random quadrats. Estimate the population. 3.5 x 200 = 700 plants.
7. Why is random placement of quadrats better than choosing where to put them? It avoids bias, such as picking areas that look richer.
8. Suggest one limitation of the capture-mark-recapture method. Marked animals may not mix evenly with the rest, or marking may make them easier for predators to catch.

Frequently asked questions

How do you calculate energy transfer efficiency between trophic levels? Divide the energy at the higher trophic level by the energy at the level below and multiply by 100. For example, 2 000 kJ reaching primary consumers from 20 000 kJ fixed by producers is an efficiency of 10%.

How does capture-mark-recapture estimate a population? Multiply the number in the first sample by the number in the second sample, then divide by the number of marked animals recaptured. The method assumes marked animals mix evenly, none are lost or gained, and marking does not affect survival.

Which way should food chain arrows point? Arrows point in the direction of energy flow, from the organism eaten to the organism that eats it. Drawing them from consumer to food is a common mistake.

Why are forests important in Cambridge O Level Environmental Management 5014? Forests store carbon, help regulate the water cycle through transpiration and hold a large share of the world’s species. Deforestation causes loss of habitat, soil erosion and more flooding.