Cambridge IGCSE Environmental Management (0680): Ecosystems, biodiversity and fieldwork – Study Guide

Living things depend on each other and on their physical surroundings, and this topic gives you the vocabulary to describe those links. It also asks you to explain why biodiversity matters, how forests are lost and protected, and how you would collect reliable data in the field. The fieldwork content is practical, so expect questions that ask you to plan, improve or evaluate an investigation as well as recall facts.

Where this fits in the course

In Cambridge IGCSE Environmental Management (0680) this is the largest topic on living systems. The four sub-topics are ecosystems, forest ecosystems, managing biodiversity and fieldwork investigations. Fieldwork skills can appear anywhere in the written papers, so treat the last section as something to rehearse rather than just read.

Ecosystems

An ecosystem is a community of living organisms interacting with each other and with the non-living (abiotic) environment in a particular area. Key terms to define precisely:

• Producer: an organism, usually a green plant, that makes its own food by photosynthesis.
• Consumer: an organism that obtains energy by eating others; primary consumers eat producers, secondary consumers eat primary consumers.
• Decomposer: bacteria and fungi that break down dead material and return nutrients to the soil.
• Food chain and food web: a chain shows one feeding pathway; a web shows how many chains link together.
• Trophic level: a feeding position in a chain.

Energy flow

Energy enters an ecosystem as sunlight and is passed along a chain, but only a small part is passed on at each step. A common rule of thumb is that about 10 per cent is transferred to the next trophic level. The rest is lost as heat in respiration, in movement, in waste and in parts that are not eaten. This is why food chains rarely have more than four or five levels, and why eating plants directly supports more people per hectare than eating animals.

Nutrients, unlike energy, are recycled. Decomposers return them to the soil, where plants absorb them again.

Forest ecosystems

Tropical rainforests have high rainfall, steady warm temperatures and very high biodiversity. They are layered into emergent trees, canopy, understorey and forest floor, and most of the nutrients are held in the living vegetation and the leaf litter rather than in the soil, which is often thin. When the trees are cleared, the nutrients are quickly lost and the soil can erode, so forest does not recover easily.

Causes of deforestation

• Clearance for farmland, including cattle ranching and plantations such as palm oil.
• Commercial logging for timber and paper.
• Mining, road building and settlement.
• Collection of fuelwood.

Impacts

• Loss of habitat and biodiversity.
• Soil erosion and more flooding, because roots no longer hold the soil or intercept rain.
• Less carbon dioxide absorbed and more released if trees are burned, contributing to climate change.
• Loss of livelihoods for forest communities.

Sustainable management

Options include selective logging with replanting, protected reserves, agroforestry (growing crops among trees), certification of timber, ecotourism and tackling the demand that drives clearance. A balanced answer notes that local people still need income, so management must offer alternatives.

Managing biodiversity

Biodiversity is the variety of living things in an area, including the number of species and the genetic variety within each. It matters because ecosystems with more species are usually more resilient, because species provide food, medicines and materials, and because many people value nature for its own sake.

Threats include habitat loss, overharvesting and hunting, invasive species, pollution and climate change.

Approach	Example idea	Strength	Limitation
Protected areas	National parks and reserves	Protects whole habitats	Needs funding and enforcement
Captive breeding	Zoo breeding then release	Saves very rare species	Expensive; the habitat must still exist
Seed banks	Storing seeds in cold storage	Preserves genetic variety cheaply	Does not protect wild habitats
Laws and treaties	International trade controls on endangered species	Reduces illegal trade	Hard to police
Education and community schemes	Local people share the benefits	Builds long-term support	Slow to show results

Fieldwork investigations

A good investigation begins with a clear aim or hypothesis, for example that the number of daisies decreases with distance from a footpath. Then you plan the method, collect data, present it, analyse it and evaluate it.

Sampling

You cannot count every organism, so you sample. A quadrat is a square frame placed on the ground to count organisms in a known area. A transect is a line along which you sample at regular intervals, useful where conditions change gradually, such as from a shoreline inland. Random sampling avoids bias, while systematic sampling at fixed intervals suits a gradient. Using more quadrats improves reliability.

Variables should be controlled where possible, and abiotic factors such as light, soil moisture and temperature can be measured with a light meter, moisture meter and thermometer. Repeat readings and calculate means.

Evaluation

Typical weaknesses are too few samples, bias in placing quadrats, a single visit that misses seasonal change, and measurement error. Improvements follow directly: more samples, random number tables for placing quadrats, repeats at different times, and calibrated equipment. Safety and ethics also matter: avoid damaging habitats, and return organisms after counting.

Worked example 1: estimating a population

A student places ten 1 m by 1 m quadrats randomly in a grassy field of 600 m squared and counts a plant species. The counts are 3, 8, 5, 6, 2, 7, 4, 5, 9 and 1.

1. Total = 3 + 8 + 5 + 6 + 2 + 7 + 4 + 5 + 9 + 1 = 50.
2. Mean per quadrat = 50 / 10 = 5.
3. Each quadrat is 1 m squared, so the field holds about 5 x 600 = 3,000 plants.

State that this is an estimate; the range of counts, from 1 to 9, shows that the plants are unevenly spread, so a larger sample would improve the estimate.

Worked example 2: energy transfer

A field of grass captures 24,000 kJ per square metre per year in plant biomass. Assuming 10 per cent is transferred at each step, find the energy in secondary consumers.

1. Primary consumers receive 24,000 x 0.10 = 2,400 kJ.
2. Secondary consumers receive 2,400 x 0.10 = 240 kJ.

Percentage left from the original is 240 / 24,000 x 100 = 1 per cent.

Common mistakes

• Saying energy is recycled; nutrients are recycled, energy flows through and is lost as heat.
• Describing biodiversity as only the number of individuals rather than the variety of species.
• Placing quadrats in convenient places and calling the sample random.
• Writing “do more repeats” without saying what would be repeated and why.
• Treating forest conservation as purely about trees, without linking it to people’s needs.

Exam technique

When a question asks you to plan, state the aim, the equipment, how you reduce bias, how many samples you take and how you will process results. When it asks you to evaluate a method, give both a strength and a weakness for the method itself, then an improvement. Calculations in this topic usually need a mean, a total estimate or a percentage; show each line of working. For extended answers on deforestation or conservation, link cause to impact to management, and give at least one limitation.

Check your understanding

1. Define an ecosystem. (A community of living organisms interacting with each other and their non-living surroundings in an area.)
2. Why do food chains usually have few trophic levels? (Only about 10 per cent of energy passes on at each stage, so little is left for higher levels.)
3. Give two reasons deforestation increases flooding and soil erosion. (Roots no longer hold soil, and fewer leaves intercept rainfall, so more runs off.)
4. Give one strength and one limitation of a seed bank. (Preserves genetic variety cheaply; does not protect living habitats.)
5. When is a transect better than random quadrats? (When conditions change gradually along a line, such as inland from a shore.)
6. Five quadrats of 0.25 m squared contain 3, 4, 2, 5 and 1 individuals. What is the mean count per quadrat? (15 / 5 = 3.)
7. Explain why one visit may give an unreliable result. (Populations and conditions change with season and time, so one visit may miss variation.)
8. Suggest one way local people can benefit from forest conservation. (Ecotourism jobs, sustainable harvesting or agroforestry income.)

Frequently asked questions

Why do food chains rarely have more than four or five trophic levels? Only about 10 per cent of energy is passed on to the next trophic level; the rest is lost as heat in respiration, in movement, in waste and in parts that are not eaten. So little energy reaches the top that chains stay short.

Is energy recycled in an ecosystem? No. Nutrients are recycled, as decomposers return them to the soil for plants to absorb again, but energy flows through the ecosystem and is lost as heat. Saying energy is recycled is a common mistake.

Why does biodiversity matter? Ecosystems with more species are usually more resilient, species provide food, medicines and materials, and many people value nature for its own sake. Biodiversity includes the number of species and the genetic variety within each, not just the number of individuals.

How do you improve the reliability of a fieldwork investigation? Take more samples, use random number tables to place quadrats and avoid bias, repeat at different times to catch seasonal change, and use calibrated equipment. Say what each improvement would fix rather than just writing “do more repeats”.

How do I answer a fieldwork planning question in Cambridge IGCSE Environmental Management 0680? State the aim, the equipment, how you will reduce bias, how many samples you will take and how you will process the results. For an evaluation, give a strength and a weakness of the method, then an improvement.