IGCSE Environmental Management Topic 5: Ecosystems, Biodiversity and Fieldwork

5.1 Ecosystems 5.2 Forest Ecosystems 5.3 Managing Biodiversity 5.4 Fieldwork Investigations

Hi Tara. Topic 5 is two different jobs wearing one hat, and it pays to see that before you start. The first three sub-topics — ecosystems, forests, biodiversity — are content: components, causes, impacts, strategies. Then there is 5.4 Fieldwork, which is less content and more a set of moves you perform on a situation you have never seen before. Those moves are not only for 5.4: you use them on every topic.

Look at how the paper is weighted. AO3 — investigation skills and making judgements — is 27% of the whole qualification and 40% of Paper 2. Those marks are spread across every topic: a Paper 2 question on water, farming, ecosystems or population will hand you a source (a table, a graph, a map, an investigation) and ask you to interpret it, judge it or improve it. 5.4 is where the method is taught, so it pays off everywhere. That is why 5.4 is roughly twice the length of anything else here, written as a procedure you can run, not as vocabulary you can recite.

Two sentences to carry through all of 5.1. First: only about 10% of the energy at one trophic level reaches the next, and the other 90% goes on movement, respiration, digestion and excretion. That single number explains why food chains are short, why pyramids of energy are always the right way up, and why eating plants feeds more people than eating meat. Second: pollination is not fertilisation. Pollination is the transfer of pollen from an anther to a stigma. Fertilisation happens afterwards. Writing one when you mean the other loses a mark every time it appears, and it appears often.

One warning about scope. The syllabus keeps saying “limited to:”, and that phrase is a ceiling, not a starting point. For pollination, Cambridge states outright that knowledge of the structure and naming of flower parts is not required — so you will not find them here, and you should not spend a minute on them. Everything in this guide is in the 0680 syllabus for 2027. Nothing that is not in it is here.

5.1 EcosystemsUNIT ASSESSMENT · TUE 22 SEP ▼

▶ Watch: 5.1 Ecosystems

Opens on YouTube in a new tab. The IGCSE 0680 videos follow the OLD chapter numbering — this topic was Chapter 9, and the current coursebook numbers it Chapter 6 — so chapter names in the titles will not match this page. Two are UK GCSE Biology, not 0680: the ecology is the same but check anything extra against this guide. The syllabus decides what is examinable.

Eight words, eight marks (5.1.1)

Objective 5.1.1 is a list of eight terms and it is the cheapest set of marks in Topic 5. Cambridge can ask you to define any of them in one line, or — more often — hand you a paragraph about a wetland and ask you to identify which word applies to which thing in it. Learn them as a ladder, because four of them nest inside each other.

Term	What it means	Worked into a sentence
habitat	the place where an organism lives	The habitat of a mangrove crab is the muddy tidal zone between the roots.
species	a group of organisms that can breed together to produce fertile offspring	All the mangrove crabs in the world are one species.
population	all the organisms of one species living in the same area at the same time	The population of mangrove crabs in this creek is about 400.
community	all the populations of all the species living together in one area	The community includes the crabs, the mangroves, the mudskippers and the herons.
niche	the role an organism plays in its ecosystem — what it eats, what eats it, when it is active, what conditions it needs	The crab’s niche is a night-active scavenger of fallen leaves in the tidal mud.
prey	an organism that is hunted and eaten by another organism	The crab is prey for the heron.
predator	an organism that hunts and eats other organisms	The heron is a predator of crabs and small fish.
apex predator	a predator at the top of a food chain, with no natural predators of its own	The estuarine crocodile is the apex predator of this ecosystem.

The ladder

Habitat → population → community → ecosystem. One place, then one species in it, then all the species in it, then all the species plus the non-living surroundings. Each rung adds exactly one thing. If you can say what each rung adds, you can rebuild all four definitions under pressure.

Habitat is the address; niche is the job

This is the confusion the examiners fish for. Two species can share a habitat and have completely different niches — a bat and an owl both live in the same woodland, but the bat eats flying insects at dusk and the owl eats mice at night. If a question says “describe the niche of…” and you answer with a place, you get nothing. Say what it does.

Biotic and abiotic components (5.1.2)

An ecosystem is the community plus everything non-living around it. Split that into two columns and the objective is done. Biotic means the living part; abiotic means the non-living part. The syllabus gives you the exact lists, so learn the exact lists.

Biotic (living)	What it does
producers	make their own food by photosynthesis; the entry point for all the energy in the ecosystem
primary consumers	eat producers
secondary consumers	eat primary consumers
tertiary consumers	eat secondary consumers
decomposers	feed on dead organisms and waste, breaking them down and releasing nutrients back into the soil or water

Abiotic (non-living)	Why an organism cares	How you would measure it in the field
temperature	controls the rate of every biological process	thermometer
water	needed for photosynthesis and for every reaction in a cell	humidity or moisture meter
oxygen	needed for aerobic respiration	dissolved oxygen probe in water
carbon dioxide	raw material for photosynthesis	gas sensor
salinity	determines which species can control their water balance there	salinity or conductivity meter
light	the energy source for photosynthesis	light meter
pH	affects which plants can take up nutrients and which animals survive	pH meter

This table is secretly a 5.4 table

Every abiotic factor above is something you can measure with a named instrument. Paper 2 loves the question “suggest two abiotic factors the student should have measured, and name the apparatus for each”. That is one mark for the factor and one for the instrument, and it is pure recall from this table. Notice that a light meter, a pH meter and a humidity meter are all on the official fieldwork apparatus list in 5.4 — that is not a coincidence.

Biotic interactions (5.1.3)

Native and invasive species

A native species is one that occurs naturally in an area — it arrived and evolved there without being brought by people. An invasive species is one introduced to an area where it does not occur naturally, which then spreads and causes harm to the species already present.

The reason an invasive species can do so much damage is worth writing as a chain, because “explain why” wants the mechanism: it arrives without the predators, parasites and diseases that limited its numbers at home, so its population grows quickly; it then outcompetes native species for food, light or space, or preys on natives that have no defences against it; native populations fall, and biodiversity is reduced. Note that not every introduced species is invasive — most introduced species never establish. The word invasive is reserved for the ones that spread and cause harm.

Competition

Competition happens when two organisms need the same resource and there is not enough of it to go round. Plants compete for light, water, mineral ions and space. Animals compete for food, water, territory and mates. The consequence to state is that the better competitor obtains more of the resource, so it grows or reproduces more, and the population of the poorer competitor falls. Competition can be between members of the same species or between different species; the syllabus does not ask you to name those two cases, so do not waste words on the terminology.

Predation

Predation is one organism hunting, killing and eating another. What Cambridge really wants is the cycle: prey numbers rise, so there is more food for predators, so predator numbers rise; the increased predators eat more prey, so prey numbers fall; with less food, predator numbers then fall; with fewer predators, prey numbers recover. The predator peak always comes after the prey peak, because the predators have to eat and breed before their numbers can respond. That time lag is the detail that separates a 2-mark answer from a 4-mark one.

Read the peaks left to right and note which colour peaks first. The shape is what matters, not the exact figures.

Pollination (5.1.4)

Cambridge defines pollination in one line and then stops. Here it is: pollination is the transfer of pollen from an anther to a stigma. That is the whole definition, and those two words — anther and stigma — are the only two flower parts you need. The syllabus says in so many words that knowledge of the structure and naming of flower parts is not required. So there is no diagram of a flower in this guide and no list of parts to learn. If a revision site gives you one, close it.

Pollen can be carried in two ways, and the differences all follow from one question: does the plant need to attract an animal, or does it need to throw pollen into moving air?

	Insect pollination	Wind pollination
How pollen travels	stuck to the body of a visiting insect, which carries it to the next flower	blown through the air on the wind
The flower	large, brightly coloured and scented, and it produces nectar as a reward for the visitor	small, dull and unscented, and it produces no nectar
Anthers and stigmas	held inside the flower where the insect must brush past them	held out in the open air where the wind reaches them; stigmas are often feathery to catch grains
The pollen itself	larger, sticky or spiky so it clings to the insect	small, light and smooth so it stays airborne
Amount of pollen	smaller amounts, because delivery is fairly reliable	very large amounts, because most grains never land on a stigma

After the pollen arrives, the sequence continues and you are expected to know the order: pollination → fertilisation → seed formation → fruit formation. Fertilisation is the fusion of the male and female nuclei, and it happens after the pollen has been delivered. So a flower can be pollinated and never fertilised. Getting this order right is worth a mark on its own and it is the single most common slip in 5.1.

Two words, one difference

Pollination is a journey. Fertilisation is a meeting. Pollen travels from an anther to a stigma — that is the journey, and it is all that pollination means. The nuclei fusing is the meeting, and that is fertilisation. Journey first, meeting second, then seed, then fruit.

Photosynthesis and chlorophyll (5.1.5)

Photosynthesis is how energy enters an ecosystem. A green plant takes in carbon dioxide from the air and water from the soil, and uses light energy from the Sun to build them into glucose, releasing oxygen as a waste product. The light energy is captured by chlorophyll, the green pigment in the leaves — without chlorophyll the light simply passes through or is reflected, and no glucose is made.

carbon dioxide + water → glucose + oxygen

energy source: sunlight captured by: chlorophyll

Word equation only

0680 asks for the word equation. It does not ask for a balanced symbol equation, and it does not ask for anything about the stages inside the chloroplast. Write the four words on the two sides in the right order, put sunlight and chlorophyll above or beside the arrow, and stop. Also: a plant does not make energy. It transfers light energy into chemical energy stored in glucose. “Plants make energy” is marked wrong.

Energy flow and the 10% rule (5.1.6)

A food chain shows the path of energy from a producer through a series of consumers. Each arrow means “is eaten by” and points in the direction the energy travels. A food web is several food chains joined together, showing that most organisms eat more than one thing. A trophic level is a feeding position in the chain: producer, primary consumer, secondary consumer, tertiary consumer.

Now the number that runs the whole topic. Only about 10% of the energy at one trophic level is passed on to the next. The other 90% never gets there. The syllabus tells you exactly where it goes, and it names four processes — use its words:

Where the 90% goes	What is happening
movement	energy used to contract muscles as the animal walks, swims or flies is transferred to the surroundings as heat
respiration	glucose is broken down to release energy for life processes; most of that energy ends up warming the organism and then the environment
digestion	not everything eaten can be digested, so the energy in the undigested material passes out in the faeces and never enters the body
excretion	waste products removed from the body still contain some chemical energy, which leaves with them

The same 90% loss happens at every step, so the fall is multiplied, not added.

Worked example A field of wheat fixes 80 000 kJ/m²/year. Assuming 10% transfer at each step, calculate the energy available to a secondary consumer in this ecosystem. [2]

Step 1 — count the steps, not the levels

Producer → primary consumer is one transfer. Primary → secondary is a second transfer. So there are two transfers, not three. Miscounting here is the commonest error, and it is always by one.

Step 2 — apply 10% twice

80 000 × 0.1 = 8 000 kJ at the primary consumer. 8 000 × 0.1 = 800 kJ at the secondary consumer. Show both lines; if the final number is wrong you can still be given the method mark.

800 kJ/m²/year.

Worked example Explain why growing crops to feed people directly supports more people per hectare than growing crops to feed cattle which are then eaten. [3]

The move

This is the 10% rule asked in words. Count the trophic levels in each option. Eating the crop directly: producer → human, one transfer. Eating beef: producer → cattle → human, two transfers.

The explanation, with a because

Only about 10% of energy is passed on at each transfer, because the rest is used in movement and respiration or lost in digestion and excretion. Adding the cattle step therefore removes a further 90% of the energy, so roughly ten times less food energy reaches people from the same area of land.

Fewer trophic levels means fewer 90% losses, so more of the energy fixed by the crop reaches people.

Ecological pyramids (5.1.7)

A pyramid is a food chain drawn as horizontal bars stacked on top of each other, producer always at the bottom. 0680 asks for two kinds: pyramids of numbers and pyramids of energy. It does not ask for pyramids of biomass, so do not spend time on them.

Pyramid of numbers

Each bar shows how many organisms there are at that trophic level. Size is ignored completely — an oak tree counts as one, and so does a single aphid. That is exactly why a pyramid of numbers can come out the wrong shape. If one very large producer supports thousands of small consumers, the bottom bar is narrow and the one above it is wide, and the diagram is inverted at the base. A parasite level can do the same thing at the top: thousands of fleas on a few foxes gives a wide bar at the very top.

Pyramid of energy

Each bar shows how much energy is at that trophic level, usually in kJ per square metre per year. A pyramid of energy is always the right way up. It has to be, because of the 10% rule: energy is lost at every transfer, so the level above can never contain more energy than the level below. If you are ever shown an inverted pyramid of energy, it is wrong.

Three pyramids of numbers, then one pyramid of energy with a scale bar. The scale bar is what makes it “to scale”.

Drawing marks in a pyramid question

If you are asked to draw a pyramid: producer at the bottom, bars horizontal and centred on each other, each bar labelled with the organism and its value, and — for a pyramid of energy — a stated scale. If you are asked to explain why a pyramid of numbers is not pyramid-shaped, the answer is always some version of “because numbers are counted regardless of size, so one large organism can support many small ones”. If you are asked why a pyramid of energy is never inverted, say “because energy is lost at each transfer, so a level can never hold more energy than the one below it”.

Aerobic respiration (5.1.8)

Respiration is the reverse trip. Every living organism — plant, animal and decomposer — breaks down glucose in the presence of oxygen to release the energy stored in it, producing carbon dioxide and water as waste products.

glucose + oxygen → carbon dioxide + water

and: energy is released where: in every living cell, all the time

Two traps in one equation

First, energy is released, not produced or made — it was already in the glucose. Second, plants respire too, all day and all night. A common wrong answer says plants photosynthesise and animals respire. Plants do both; over a whole day a healthy plant photosynthesises more than it respires, which is why it grows.

The carbon cycle (5.1.9)

The carbon cycle is six named processes and you should be able to say, for each one, whether it removes carbon dioxide from the atmosphere or adds it. That framing turns a woolly diagram question into a two-column list.

Process	What happens to the carbon	Effect on atmospheric CO₂
photosynthesis	producers take carbon dioxide from the air and lock the carbon into glucose	removes
respiration	organisms break down glucose and release carbon dioxide	adds
feeding	carbon compounds pass from one organism to the next along the food chain	neither — it moves carbon sideways
decomposition	decomposers break down dead organisms and waste, respiring as they do so	adds
formation of fossil fuels	dead material buried under sediment for millions of years without decomposing becomes coal, oil or natural gas	neither — it stores carbon out of circulation
combustion	fossil fuels or wood are burned, releasing the stored carbon as carbon dioxide	adds

Count the arrows into the atmosphere box and the arrows out of it — that asymmetry is the point of the diagram.

Worked example Explain how burning coal in a power station affects the carbon cycle. [3]

Step 1 — name the process

Burning coal is combustion. Use the syllabus word; “burning” alone is usually accepted but the technical term is safer.

Step 2 — say where the carbon was and where it goes

The carbon in coal was removed from the atmosphere by photosynthesis and locked away when dead material was buried and formed fossil fuels over millions of years. Combustion releases it as carbon dioxide into the atmosphere.

Step 3 — the rate point, which is where the third mark is

The carbon took millions of years to be stored and is returned in seconds, so carbon is added to the atmosphere faster than photosynthesis removes it, and the concentration of carbon dioxide rises.

Combustion returns long-stored carbon to the atmosphere as CO₂, faster than photosynthesis can remove it.

Checkpoint 5.1

Answer, then read the explanation even when you were right.

Your Score 0 / 12

Question 1

A student is asked to describe the niche of a barn owl and writes “an old barn”. Why does this lose the mark?

A Because a barn is a habitat shared by several different species.

B Because the owl hunts outside the barn during the night.

C Because a niche is what an organism does, not where it lives.

D Because a barn is a building and so it counts as abiotic.

A niche is the role: what it eats, what eats it, when it is active. “An old barn” is a habitat answer. A is true but it is not the reason the answer fails — a habitat can be shared and still be a habitat. B is a real fact about owls and tempting because it sounds like niche language, but on its own it does not say why the given answer is wrong. D is a distraction: whether the barn is abiotic has nothing to do with the definition being tested.

Question 2

A pond contains 300 mosquito larvae, 40 frogs and 12 dragonflies. Which of these is a population?

A the 40 frogs living in the pond at that time

B the frogs and the dragonflies taken together

C everything living in the pond, plus its water

D the 300 larvae and the 12 dragonflies

A population is one species in one area at one time, so the 40 frogs qualify. B and D are two species each, which makes them part of a community, not a population. C is the whole ecosystem: all the living things plus the non-living water. The word to test yourself on is “one” — how many species are in the answer?

Question 3

In the food chain seagrass → green turtle → tiger shark, the tiger shark is an apex predator. What does that mean?

A It is the largest organism present in the food chain.

B It eats both producers and consumers in the same chain.

C It gains ten per cent of the energy the seagrass fixed.

D It has no natural predator of its own in this system.

Apex means top of the chain with nothing hunting it. A is usually true of apex predators but it is not the definition — a blue whale is huge and is not an apex predator. B describes an omnivore. C is wrong arithmetic as well as the wrong idea: the turtle gets about 10% of the seagrass energy, and the shark about 10% of that, so roughly 1%.

Question 4

Which of these is an abiotic component of a rocky shore ecosystem?

A the seaweeds growing across the lower rocks

B the salinity of the water in a rock pool

C the barnacles attached to the rock face

D the crabs sheltering under the boulders

Salinity is on the syllabus list of abiotic factors and it is measured with a salinity or conductivity meter. A, C and D are all living things, so they are biotic. Barnacles catch people out because they look like part of the rock; they are animals.

Question 5

A water plant introduced to a lake spreads until it covers the whole surface. Which reason best explains its rapid increase?

A Its niche is wider than that of any native species there.

B It reproduces more quickly than it did in its own range.

C It arrives without the predators that controlled it.

D It is always larger than the native species it replaces.

This is the standard mechanism: no natural predators, parasites or diseases in the new area, so nothing holds the numbers down. B is the same idea stated backwards — its rate of reproduction has not changed, what has changed is what happens to the offspring. A uses the word niche but explains nothing. D is not true of many invasive species, several of which are small.

Question 6

A graph shows two curves rising and falling over 20 years. How can you tell which curve is the predator?

A Its peaks come slightly after the peaks of the other curve.

B Its peaks come slightly before the peaks of the other curve.

C Its curve is smooth while the other curve is quite jagged.

D Its numbers stay constant while the other rises and falls.

The predators can only increase once there is more prey to eat, so the predator peak lags behind the prey peak. B reverses the cause and effect, which is the mistake being tested. C describes a difference in how the data were collected, not in the biology. D describes a species that is not linked to the other at all.

Question 7

Which statement is the definition of pollination?

A the fusion of a male nucleus with a female nucleus

B the growth of a seed into a young plant in the soil

C the movement of an insect between two different flowers

D the transfer of pollen from an anther to a stigma

D is the syllabus wording and it is worth memorising exactly. A is fertilisation, which happens afterwards — this is the swap the examiners want. B is germination. C describes what an insect pollinator does but not what pollination is; wind-pollinated plants have no insect at all.

Question 8

Which shows the correct order of events after a flower opens?

A fertilisation, pollination, seed formation, fruit formation

B pollination, fertilisation, seed formation, fruit formation

C pollination, seed formation, fertilisation, fruit formation

D fertilisation, pollination, fruit formation, seed formation

Pollen has to arrive before nuclei can fuse, so pollination is always first. A and D put fertilisation first, which is impossible. C puts a seed before the fertilisation that creates it. The chain to hold: journey, meeting, seed, fruit.

Question 9

Which is the word equation for photosynthesis?

A glucose + oxygen → carbon dioxide + water

B carbon dioxide + oxygen → glucose + water

C carbon dioxide + water → glucose + oxygen

D glucose + water → carbon dioxide + oxygen

C takes in the two raw materials and produces food plus the waste gas. A is aerobic respiration, which is the same four substances the other way round — that symmetry is exactly why they are confused. B has oxygen going in, which would make it respiration with the wrong products. D is not a real process at all.

Question 10

Producers in a grassland fix 60 000 kJ/m²/year. Assuming 10% transfer at each step, how much energy reaches the tertiary consumers?

A 600 kJ/m²/year

B 60 kJ/m²/year

C 6 kJ/m²/year

D 6 000 kJ/m²/year

Three transfers: 60 000 → 6 000 → 600 → 60. Option D stops after one transfer and A after two, which is the off-by-one slip — count the arrows, not the boxes. C applies a fourth transfer that the question did not ask for.

Question 11

A pyramid of numbers for oak tree → aphids → ladybirds is narrow at the bottom and wide in the middle. Why?

A because energy is lost between each of the trophic levels

B because aphids feed on ladybirds as well as on the oak tree

C because a pyramid of numbers is always drawn to a scale

D because the count ignores the size of each organism

One enormous producer counts as 1, and the thousands of tiny aphids it feeds count as thousands, so the bottom bar is the narrow one. A is a true statement about energy but it would make the pyramid upright, not inverted, so it cannot be the reason. B reverses the food chain given. C is the opposite of the truth: pyramids of numbers are usually drawn for shape only.

Question 12

Which pair of processes both add carbon dioxide to the atmosphere?

A respiration and decomposition

B photosynthesis and respiration

C photosynthesis and decomposition

D feeding and fossil fuel formation

Decomposers respire as they break dead material down, so decomposition adds carbon dioxide just as respiration does. B and C each contain photosynthesis, which is the only process that removes it. D contains the two processes that move carbon around without changing the amount in the air: feeding passes it along a chain, and fossil fuel formation locks it away.

5.2 Forest EcosystemsUNIT ASSESSMENT · TUE 22 SEP ▼

▶ Watch: 5.2 Forest Ecosystems

5.2 is four objectives: why forests are cleared, what happens when they are, one definition to learn word for word, and why sustainable management is worth the effort. Almost every question on it is a describe and explain question, which means a bare list will only ever get you half. Each cause needs a reason people do it; each impact needs a mechanism — a “because” that joins the tree removal to the effect.

Causes of deforestation (5.2.1)

Cause	What is actually happening, and why
logging and timber extraction	Trees are felled for timber, plywood, paper pulp and fuelwood. Hardwoods such as mahogany and teak are valuable, so a small number of trees can make an access road worth building — and the road then opens the forest to everything else on this list.
subsistence and commercial farming	Subsistence farmers clear small plots to grow food for their own families, often by cutting and burning; the ash briefly fertilises poor soil. Commercial farming clears far larger areas for cattle ranching and for cash crops such as soya, oil palm and rubber, which are grown for sale rather than for local food.
roads and settlements	Forest is cleared for the roads that carry timber and crops out, and for the towns that grow along them as people move in to work. A road is a cause and an enabler at the same time.
rock, ore and mineral extraction	Open-cast mines for iron ore, bauxite, gold and coal need the forest above them removed, along with land for spoil heaps, processing plant and access.
hydro-electric power stations	A dam floods the valley behind it, and every tree in the reservoir area is drowned or cleared first. Further forest goes for the dam works and the transmission lines.
climate change	Rising temperatures and changing rainfall dry forests out, so trees die and fires spread more easily and burn larger areas. Here the forest is lost without anyone deliberately clearing it.

Climate change is on both lists

Notice that climate change is a cause of deforestation in 5.2.1 and global warming is an impact of deforestation in 5.2.2. That is not a mistake in the syllabus — it is a feedback loop, and saying so is a good sentence in an extended answer: warming dries and kills forest, the lost forest absorbs less carbon dioxide, so warming increases.

Impacts of deforestation (5.2.2)

Seven impacts, and each one has a chain behind it. Learn the chains, not the labels — “explain” questions are marked on the links.

Impact	The chain that produces it
habitat loss	The trees are the habitat: nesting holes, canopy, shade, leaf litter. Remove them and the species that lived there have nowhere to live, feed or breed, so their populations fall.
loss of biodiversity	Tropical forests hold a very large share of the world’s species, many with small ranges. Clearing an area can remove the entire habitat of a species, so numbers of species as well as numbers of organisms fall.
soil erosion and desertification	Without a canopy, rain hits bare soil directly and washes it away; without roots, nothing binds the soil in place. The fertile topsoil goes first, so the ground cannot support plants, and in dry regions the land can degrade into desert.
silting and flooding	The eroded soil is carried into rivers, where it settles and raises the river bed. A shallower channel holds less water, so the river spills over its banks more often, and reservoirs behind dams fill with sediment and hold less water.
global warming	Two effects at once. Fewer trees means less carbon dioxide removed by photosynthesis; and burning or rotting the felled timber releases the carbon the trees had stored. Both raise atmospheric carbon dioxide, which is a greenhouse gas.
changes to rainfall patterns	Forests return large amounts of water to the air by transpiration. With fewer trees there is less transpiration, so less water vapour, so less cloud and less rainfall downwind — and the region becomes drier.
genetic depletion	As populations shrink and species are lost, the variety of genes held in the forest falls. That variety is the raw material for new medicines, for breeding disease resistance into crops, and for the species themselves to adapt to future conditions.

Interception, water uptake and transpiration all need trees. Surface run-off is the one that increases when they go.

The definition you must be able to write out (5.2.3)

Learn this word for word

Sustainable management of forests is balancing the needs of the environment, wildlife and humans while conserving forests for future generations.

Three groups to balance — environment, wildlife, humans — and one time word, future generations. Students routinely write “using forests without destroying them” and get one mark instead of two, because they name no groups and no timescale.

Why forests need managing sustainably (5.2.4)

Reason	The argument in full
climate regulation	Growing trees absorb carbon dioxide by photosynthesis, so a forest acts as a carbon sink; the carbon held in the wood and soil makes it a carbon store. Managing the forest keeps both working, which slows the rise in atmospheric carbon dioxide.
role in the water cycle	Leaves intercept rain so it reaches the ground slowly. Roots take up water from the soil. Leaves return it to the air by transpiration. All three reduce surface run-off. These four words are the syllabus wording — use them.
flood control	Because run-off is slower and less water reaches the river at once, the river rises more gradually and is less likely to overtop its banks.
prevention of soil erosion	Roots hold soil particles together and the canopy takes the force out of falling rain, so less topsoil is washed or blown away and the land stays productive.
genetic resource	Forests hold varieties of plants and animals whose genes may be needed later — for disease resistance in crops, for new medicines, or to restore a damaged population. Once a species is gone those genes cannot be recovered.
food, medicine and raw materials	Forests supply fruit, nuts, honey, game, medicinal plants, timber, fibres, resins and rubber, both to the people who live in them and to industries elsewhere.
recreation, ecotourism and education	Forests give places to walk and to visit, income from visitors who pay to see wildlife, and living sites for teaching and research.

Worked example Explain how deforestation of a steep hillside can increase the risk of flooding in the valley below. [4]

Step 1 — the water route

There are no leaves to intercept the rain and no roots to take water up, so more rainwater reaches the ground and stays there.

Step 2 — the speed

Surface run-off increases and water reaches the river much more quickly, so the river level rises sharply after rain instead of gradually.

Step 3 — the second, slower route to the same result

Run-off carries eroded soil into the river. The sediment settles and raises the river bed, so the channel holds less water — this is silting, and it makes flooding more likely even in later years.

Step 4 — land the conclusion

More water arriving faster in a channel that holds less means the river overtops its banks more often, so the valley floods more frequently.

Less interception and uptake, faster run-off, silting of the channel, so more frequent flooding.

Checkpoint 5.2

Answer, then read the explanation even when you were right.

Your Score 0 / 8

Question 1

Which of these is given by the syllabus as a cause of deforestation rather than an impact of it?

A the silting of rivers and of the reservoirs behind large dams

B building hydro-electric power stations across valleys

C the depletion of genes held by forest populations

D changes to the pattern of rainfall over the region

A reservoir floods the forested valley behind the dam, so hydro-electric power is listed as a cause. A, C and D are all on the impacts list in 5.2.2. Sorting the two lists is worth doing once on paper, because a question that asks for causes and gets impacts scores nothing however good the science is.

Question 2

Why does clearing forest reduce rainfall in the region downwind?

A Bare soil reflects more sunlight back into the sky.

B Run-off carries the rainwater away to the sea much faster.

C Less transpiration means less water vapour in the air.

D Carbon dioxide released by burning warms the region.

Trees pump water from the soil into the air; take them away and there is less vapour to condense into cloud, so less rain falls downwind. B is true but it is about where surface water goes, not about how much vapour enters the air. A and D are both real consequences of clearing land, but neither is the route the syllabus asks for here.

Question 3

Which best completes the definition: sustainable management of forests is balancing the needs of the environment, wildlife and humans while…

A replanting exactly as many trees as are felled each year.

B preventing all logging inside a national park boundary.

C increasing the income earned by local forest communities.

D conserving forests for future generations.

The syllabus wording is “conserving forests for future generations”, and the timescale is what earns the mark. A is one method of sustainable forestry, not the definition. B goes further than the definition, which allows use as well as protection. C names one of the three groups and drops the other two.

Question 4

A forest is described as both a carbon sink and a carbon store. What is the difference?

A A sink holds carbon; a store keeps absorbing more of it.

B A sink absorbs carbon; a store holds carbon already fixed.

C A sink describes the soil and a store describes the wood in it.

D A sink is natural, and a store is created by replanting.

A growing forest takes carbon dioxide out of the air, which is the sink; the carbon already locked in the wood and soil is the store. A is the same two ideas with the labels swapped, which is the trap. C invents a division between soil and wood that does not exist. D invents a natural-versus-planted division that has nothing to do with the two terms.

Question 5

Deforestation is said to cause genetic depletion. What does that mean?

A Individual trees grow more slowly on the poorer soils.

B The genes of forest species change to suit the new land.

C The variety of genes held by the forest is reduced.

D Fewer seeds are produced by the trees left standing.

Depletion means the pool of genetic variety shrinks as populations fall and species are lost, which matters because that variety is the source of future medicines and crop traits. B describes adaptation, which is a different idea and far slower. A and D are real effects of clearance but they are about growth and reproduction, not about genetic variety.

Question 6

Which sequence correctly explains how deforestation leads to desertification?

A trees removed → more transpiration → wetter soil → desert

B trees removed → silting of rivers → soil dries out → desert

C trees removed → more shade lost → roots rot away → desert

D trees removed → topsoil eroded → nothing grows → desert

Losing the canopy and the roots exposes the fertile topsoil, which is washed or blown away, and land without topsoil cannot support plants. A gets the transpiration direction backwards and ends with wetter soil, which would not give a desert. B mixes in silting, which happens in the river rather than on the slope. C sounds plausible but roots rotting is not what causes the land to degrade.

Question 7

Which pair are the two ways deforestation raises atmospheric carbon dioxide?

A less transpiration, and more surface run-off from slopes

B less photosynthesis, and carbon released by burning wood

C less respiration, and carbon released as the soil is eroded

D less interception, and carbon released by decomposing roots

One route removes less carbon dioxide from the air, the other actively adds it, and a full-mark answer gives both. A and D name real effects of clearing forest, but interception and transpiration are water-cycle processes and neither changes the carbon dioxide level. C is wrong in its first half: less respiration would lower carbon dioxide, not raise it.

Question 8

A government argues that a rainforest is worth conserving even though nobody lives in it. Which reason from 5.2.4 supports that most directly?

A It regulates climate by acting as a carbon sink and store.

B It supplies timber and fibres to industries in other places.

C It gives opportunities for recreation, tourism and teaching.

D It prevents soil erosion on the slopes inside its boundary.

Climate regulation works whether or not anyone is present, and its benefit is global rather than local. B, C and D are all genuine reasons from 5.2.4, but each of them depends on people being there to cut, visit or farm — which is precisely the condition the question removes. Read what the question rules out before choosing.

5.3 Managing Biodiversity ▼

▶ Watch: 5.3 Managing Biodiversity

5.3 is two objectives, and the second one is worth more than the first. 5.3.1 asks you to describe ten conservation strategies — that is recall. 5.3.2 asks you to discuss the benefits and limitations of them, and “discuss” means both sides followed by a judgement. An answer that lists only advantages is capped, however many advantages it lists. Several of these strategies are genuinely argued over by people who study them for a living, so you are not being asked to agree with any of them; you are being asked to weigh them.

The four-part evaluating move

For any strategy, run these four questions and you will always have something to write: What is the benefit? What is the limitation? Who bears the cost? Over what timescale does it work? The third and fourth are the ones most students never think of, and they are where the top band lives. A wildlife corridor benefits the animals, costs the landowner whose field it crosses, and only pays off over decades.

The ten strategies (5.3.1)

Strategy	What it actually involves
sustainable harvesting of wild plant and animal species	Taking only as much as the population can replace — quotas, size limits, closed seasons, banning harvest during breeding. The population keeps supplying a yield indefinitely instead of being fished or collected out.
sustainable forestry	Selective logging rather than clear-felling, replanting after felling, leaving seed trees and buffer strips along rivers, and rotating which areas are cut so each has time to regrow.
national parks and reserves	Areas protected by law where development, hunting and clearance are limited or banned, so whole habitats and communities are conserved together rather than one species at a time.
wildlife corridors	Strips of habitat — hedgerows, replanted forest, underpasses beneath roads — that connect two isolated areas so animals can move between them to feed and breed. Connecting small populations keeps genetic variety up.
seed banks	Seeds collected from many varieties and stored cool and dry, sometimes for decades. Cheap, compact insurance: if a plant is lost in the wild, seed exists to grow it again.
zoos and captive breeding	Breeding threatened animals in captivity, keeping studbooks so related individuals are not paired, and in some cases releasing offspring back into protected habitat.
ecotourism	Small-scale tourism to natural areas that aims to fund conservation and employ local people, so that the wildlife is worth more alive than cleared or hunted.
international cooperation against animal trade	Countries agreeing to share intelligence, patrol borders, train and equip customs officers, and prosecute traffickers — because a smuggled animal crosses several countries and no one country can stop it alone.
regulation of trade in vulnerable and endangered species	Legal controls listing which species may be traded, in what quantities and with what permits, with trade in the most threatened species banned outright.
classifying organisms by threat level	Assessing each species and labelling it threatened, endangered or extinct. This is the step that decides where the money and the legal protection go, which is why the syllabus counts it as a strategy.

The three threat words, in order

Threatened — the population is falling and the species is likely to become endangered if nothing changes. Endangered — numbers are so low that the species is at risk of dying out. Extinct — no individuals of that species remain alive anywhere. Threatened is a warning, endangered is an emergency, extinct is final and cannot be undone.

Benefits and limitations (5.3.2)

This table is the answer to a six-mark “discuss” question. Read across a row and you have two sides of one strategy, which is exactly the shape a mark scheme rewards.

Strategy	Benefits	Limitations
sustainable harvesting	The species survives while people keep the income and the food; local users have a reason to protect it because their livelihood depends on the population lasting.	Quotas must be based on good population data, which is expensive to collect; they need enforcing over large areas; and if the quota is set too high the decline continues while everyone believes it is under control.
sustainable forestry	Timber keeps being produced, soil and water functions are kept, and much of the habitat structure survives compared with clear-felling.	Yields per hectare are lower and costs higher than clear-felling, so unmanaged timber undercuts it on price; replanted forest is often less diverse than the original; and regrowth takes decades.
national parks and reserves	Protects whole communities and abiotic conditions at once, which is far more effective than protecting single species; also generates tourist income and gives a site for research.	Land is taken out of farming or forestry, so local people may lose grazing, fuelwood or hunting rights; patrolling large areas is costly; and boundaries do not stop pollution, fire or climate change crossing them.
wildlife corridors	Lets isolated populations mix, which reduces inbreeding and allows animals to move away from local food shortages or fires; often cheap compared with buying new reserve land.	Uses land that owners want for other things, so agreement is hard; narrow corridors can concentrate animals where poachers and vehicles find them; and they can also help disease and invasive species spread.
seed banks	Very large numbers of varieties stored cheaply in a small space, safe from events in the wild, and available for replanting or for crop breeding.	Seeds of some species will not survive drying and freezing; stored seed loses viability and must be periodically grown on; and it preserves the plant but not the habitat, the pollinators or the species that depended on it.
zoos and captive breeding	Can raise numbers of a species whose wild population is too small to recover on its own, keeps a reserve population if the wild one is lost, and funds research and education. Several species alive today exist because of it.	Expensive per animal compared with habitat protection; captive-bred animals may lack the behaviour to survive release; small captive groups lose genetic variety; and if the original habitat has not been fixed there is nowhere to release them to. Critics argue that money is better spent on the habitat, and supporters reply that for a species down to a few dozen individuals there is no time for that.
ecotourism	Gives wildlife a continuing economic value, so protecting it can pay better than clearing it; provides local jobs and income; and visitors return home better informed.	Visitors need flights, roads, lodges and water, all of which have their own impact; the presence of people can disturb breeding and change animal behaviour; income can leave the region if the operators are based elsewhere; and a site that becomes popular can be damaged by the number of visitors it attracts. Whether a given project is a net benefit depends on how it is run, and the evidence is mixed.
international cooperation and trade regulation	Tackles smuggling across borders, which no single country can do alone; reduces demand by making possession illegal; and a listing brings funding and attention to the species.	Only works if every country signs, enforces and prosecutes, and enforcement varies widely; a ban can raise the price and make smuggling more profitable; and policing borders and ports is expensive.

Worked example A country is deciding between spending its conservation budget on a captive breeding programme for one endangered bird, or on enlarging a national park. Discuss the two options. [6]

The case for captive breeding

If the wild population is very small it may not recover on its own, and captive breeding can raise numbers quickly under controlled conditions. It also holds a reserve population, so a fire or disease in the wild does not end the species, and it funds research and public education.

The case against it

It is expensive per animal, it saves one species rather than a community, captive-bred birds may not survive release, and unless the habitat is protected there is nowhere to release them to.

The case for enlarging the park

A larger protected area conserves the whole community — producers, consumers, decomposers and the abiotic conditions — so many species benefit from one payment. It is usually cheaper per species, and it protects the habitat the bird would eventually need anyway.

The case against it

Land has to be bought or taken out of use, so farmers or foresters lose income and may oppose it; patrolling a bigger area costs more; and if the bird’s population is already below the level at which it can breed successfully, more habitat alone will not save it.

The judgement — do not leave this out

A defensible conclusion: enlarging the park is likely to give more conservation per unit of money because it protects many species at once, unless the bird’s wild population is already too small to recover, in which case captive breeding buys the time that habitat protection needs. Naming the condition that decides it is what lifts a discuss answer into the top band.

Both sides, then a judgement with the condition that decides it. Six marks are rarely three points for one side.

A coastal village earns most of its income from a coral reef that visitors pay to snorkel over. Over ten years visitor numbers have risen from 400 to 9 000 a year. Coral cover on the most visited part of the reef has fallen from 62% to 31%, while a section closed to visitors has stayed at about 60%.

Using the data, discuss whether this ecotourism project is conserving the reef.

▼

Quote the data first

Coral cover on the visited section halved, from 62% to 31%, a fall of 31 percentage points, while the closed section changed very little. The closed section acts as a control, which is what makes the comparison worth anything — without it you could not rule out disease or warming as the cause.

The benefit side

The reef now has a continuing economic value to the village, which gives a strong reason not to fish it out or build over it, and the income supports local jobs.

The limitation side

The twenty-two-fold rise in visitors has coincided with the loss of half the coral where they swim, so the activity is damaging the thing it depends on. Ecotourism is only conservation if visitor numbers stay below what the site can take.

The judgement

On this evidence the project is not currently conserving the visited reef, though it may still be better than the alternative uses of the coast. A sensible next step is to cap daily visitor numbers, rotate which areas are open, and keep monitoring the closed section as a control.

Checkpoint 5.3

Answer, then read the explanation even when you were right.

Your Score 0 / 8

Question 1

What is the main purpose of a wildlife corridor?

A to give visitors a marked route through a reserve

B to keep farm animals out of the protected woodland

C to let animals move between two separated habitats

D to store seed from the plants growing along its edge

A corridor joins habitat that has been split by roads or farmland, so populations can mix, feed more widely and avoid inbreeding. A is a footpath, which is a visitor facility rather than a conservation strategy. B describes a fence, which does the opposite job. D confuses corridors with seed banks.

Question 2

Which is a genuine limitation of storing plant material in a seed bank?

A It saves the plant but not the habitat that supported it.

B It needs a very large area of land for the storage site.

C It can only hold seed from species that are not at risk.

D It reduces the genetic variety within the species stored.

A seed bank preserves the species but nothing it lived with — the soil, the pollinators, the shade. B is the reverse of the truth: seed banks are prized for storing thousands of varieties in a small building. C is invented; threatened species are precisely what they collect. D is wrong if seed is collected from many individuals, which is the whole design.

Question 3

A species is classified as endangered rather than threatened. What does that indicate?

A Its numbers are falling but the fall can still be reversed.

B No individuals of the species remain alive in the wild now.

C Trade in the species has been banned by international law.

D Its numbers are so low that it is at risk of dying out.

Endangered is the emergency level: numbers low enough that extinction is a real prospect. A describes threatened, one step earlier. B describes extinct, one step later. C is a consequence that often follows a listing, but the classification describes the state of the population, not the legal position.

Question 4

Why is protecting a national park often better value than a captive breeding programme?

A Captive breeding always fails when animals are released.

B One payment protects a whole community, not one species.

C Parks need no patrolling once their boundaries are agreed.

D Zoos cannot keep records of which animals are related.

A park conserves producers, consumers, decomposers and the abiotic conditions together, so the cost is spread over many species. A overstates the case — some release programmes have worked, and “always” should make you suspicious of any option. C is false and is one of the real limitations of parks. D is false: studbooks exist precisely to avoid pairing relatives.

Question 5

Which describes sustainable harvesting of a wild fish population?

A catching no more each year than the population replaces

B banning all fishing in the area for a period of ten years

C breeding the fish in tanks and releasing them into the sea

D moving the fleet to a new area when catches begin to fall

Sustainable means the yield can continue indefinitely, so the take must not exceed the replacement. B protects the fish but ends the harvest, so it is protection rather than sustainable use. C is captive breeding, a different strategy. D is the pattern that empties one area after another and is the opposite of what the word means.

Question 6

Why does the trade in endangered species need international cooperation and not just national laws?

A because national governments cannot pass laws about wildlife

B because endangered species migrate between different countries

C because smuggled animals cross several countries on the way

D because trade bans raise the price and increase the profits

A trafficked animal is taken in one country, moved through others and sold in a fourth, so a law in any one of them stops only part of the chain. B is true of some species and is a good reason for cooperation over habitat, but it is not about trade. D is a real limitation of bans, not a reason for cooperation. A is simply false.

Question 7

A student writes that ecotourism is always good for conservation. Why would an examiner not give full marks?

A Ecotourism is not one of the strategies named in 5.3.1.

B A discuss answer needs limitations as well as benefits.

C Tourism income never reaches the local community at all.

D Visitors do not learn anything from seeing wildlife alive.

The command word decides the shape of the answer, and “always good” gives one side only. Real limitations exist — travel emissions, disturbance to breeding, damage at popular sites, income leaving the region — and naming two of them would fix the answer. A is false; ecotourism is on the list. C and D are one-sided in the other direction, and “never” should make you as suspicious as “always”.

Question 8

Which is a limitation of wildlife corridors that is sometimes overlooked?

A They stop populations from mixing across a wide area.

B They cost far more than buying new areas of reserve.

C They increase inbreeding in the populations they join.

D They can also let disease and invasive species spread.

A corridor is a route, and routes do not choose what travels along them — a pathogen or an invasive plant reaches the second area just as easily as the animals do. A and C both state the reverse of what corridors do. B is usually the wrong way round: a strip of habitat is often much cheaper than buying a new block of reserve land.

5.4 Fieldwork Investigations ▼

▶ Watch: 5.4 Fieldwork Investigations

This is the highest-value section in the whole subject and it is worth knowing why before you start. Cambridge assesses AO3 — investigation skills and making judgements — at 27% of the qualification and 40% of Paper 2. The fieldwork methods are taught here, in 5.4, but the marks are not confined to 5.4: Paper 2 sets them in every topic, from river pollution to soil erosion to population surveys. Learn the method here and you use it on all of them.

It is also different in kind. Most sections give you content to explain and apply; this one gives you a procedure you run on a situation you have never seen. The examiner will describe some investigation — snails on a wall, dissolved oxygen down a stream, beetles under leaf litter, people’s opinions about a new reserve — and ask you to plan it, criticise it, or fix it. You will not have met the situation. You will have met the procedure. So learn the procedure until you can run it on anything.

The order the marks come in

Aim → hypothesis → variables → values → strategy → technique → apparatus → risks → repeats → table → process → graph → anomalies → conclusion → evaluation.

Fifteen steps, and a “plan an investigation” question is nothing more than the first nine of them written out. If you are ever stuck in a planning question, work down this list and write a sentence for each — you will hit the mark scheme points because the mark scheme is this list.

Step 1: aims and hypotheses (5.4.1a)

An aim says what you are trying to find out. A hypothesis is a testable prediction that says what will happen and, ideally, why — and the word that matters is testable. A hypothesis you cannot possibly prove wrong with the data you are about to collect is not a hypothesis.

	Weak version	What earns the mark
Aim	“To study the plants near a footpath.”	“To find out how the percentage cover of grass changes with distance from a footpath.”
Hypothesis	“Trampling is bad for plants.”	“The percentage cover of grass will increase as distance from the footpath increases, because trampling damages leaves and compacts the soil.”

Notice what the strong versions contain: both variables, named, with a direction of change, and a reason. That structure works every time. Fill in the blanks: “As [independent variable] increases, [dependent variable] will [increase / decrease], because [mechanism].”

Step 2: variables (5.4.1c, 5.4.1d)

Type of variable	Definition	In the footpath investigation
independent	the one you deliberately change or select	distance from the edge of the footpath, in metres
dependent	the one you measure, to see whether it responds	percentage cover of grass in the quadrat
control variables	everything else that could affect the dependent variable, which you keep the same	quadrat size, time of day, same day so weather is the same, same observer, same slope and aspect, same soil type, same method of estimating cover

“Explain why control variables are kept constant” — the sentence to have ready

Because otherwise a change in the dependent variable could have been caused by the uncontrolled factor rather than by the independent variable, so the result would not be valid.

That single sentence answers the question every time, in any context. And it is worth noticing that the syllabus asks you to describe how as well as explain why. So do not just say “keep the quadrat size the same” — say how: use the same 0.5 m × 0.5 m quadrat for every reading. Do not say “control the weather” — say “collect all readings on the same day, within two hours, so light and temperature are similar”.

Choosing the number and range of values

Two separate decisions and both carry marks. The range is how far the independent variable is spread — it should cover the whole situation you are describing, from the extreme trampled edge to well away from the path. The number of values is how many points you take within that range: aim for at least five, evenly spaced. Fewer than five and you cannot see a trend or spot an anomaly; unevenly spaced and the graph misleads. A good answer states both: “six distances, at 0, 1, 2, 3, 4 and 5 m from the path edge.”

Step 3: planning the method (5.4.1b)

The syllabus lists five things under “plan scientific methods”, and two of them are about people rather than plants. Do not skip those — environmental management asks about human attitudes as well as species.

Planning tool	What it is, and when you would use it
sampling strategy	How you decide where to put your samples: random or systematic. Covered in full below.
sampling technique	The equipment and method you use to catch or count: quadrat, pitfall trap, sweep net and so on. Also below.
questionnaires	A fixed set of written questions given to a number of people. Used when the data you need is about human behaviour or opinion — how often people visit a reserve, whether they would pay an entry fee. Ask closed questions where possible, because they are far easier to process into a graph; keep the wording neutral so it does not lead people to an answer; and sample enough people, chosen in a way that does not favour one group.
surveys	A structured recording of what is actually there, rather than what people say. A traffic survey counts vehicles per hour; a land use survey maps what each field is used for; a litter survey counts items per square metre. The key point is a fixed method applied consistently.
pilot study	A small trial run of the whole method before the real thing. It checks that the apparatus works, that the range and number of values are sensible, that the recording table has the right columns, and how long the work will take. Finding out that your quadrat is too small, or that there are no beetles at all in your chosen field, is very much cheaper on the pilot than on the day.

Step 4: sampling strategies (5.4.2, 5.4.3)

A strategy is where you put your samples. There are exactly two on the syllabus, and the whole comparison turns on one idea: random sampling protects you from bias, systematic sampling shows you a gradient. They answer different questions, so “which is better” is always “better for what?”

Random sampling — how you actually do it

Saying “throw the quadrat over your shoulder” loses the mark, because where you throw is influenced by what you can see and how strong your arm is — that is not random. The method that earns the mark is: lay two tape measures at right angles along two edges of the area to make a grid of coordinates; generate pairs of random numbers (from a calculator, a table or an app); use each pair as an x and a y coordinate; place the quadrat at that point. Repeat for as many samples as you need. Every point in the area then has an equal chance of being chosen, which is what “random” means.

Systematic sampling — how you actually do it

Lay a tape measure (a transect) across the area, running along the gradient you are interested in — up a shore, away from a path, out from a factory. Take a sample at fixed regular intervals along it: every 1 m, every 5 m, whatever the length demands. A continuous transect samples at every interval; an interrupted transect samples at intervals with gaps. You can also sample systematically on a grid, taking a sample at every fifth intersection.

Same field, same quadrat, different question. Left answers “what is here?”; right answers “how does it change?”

Strategy	Benefits	Limitations
random	Removes personal bias, because you cannot unconsciously choose the interesting-looking patches. Gives a fair estimate of the whole area and a mean that can be used to estimate a total population. Results can be treated statistically.	Purely by chance the samples may cluster and miss part of the area, so a rare habitat can be under-represented. It cannot show a gradient, because the samples are not in any order. Generating coordinates and finding each point takes time, and a large area needs many samples before the mean settles down.
systematic	Shows how a community changes along a gradient, in order, which random sampling cannot do. Quick to set out and easy to repeat exactly on another date. Guarantees that the whole length of the gradient is covered evenly.	It is not random, so it can be biased: if the interval happens to match a repeating pattern in the ground — ridges, planted rows, wave marks — every sample lands on the same kind of spot. The choice of where to lay the transect is made by a person, so it may not represent the wider area, and the mean from it should not be treated as an unbiased estimate for the whole site.

The one-line answer to “justify your choice of strategy”

If the question is how much / how many in this area → random, because it gives an unbiased estimate. If the question is how does it change from here to there → systematic along a transect, because it records the order. Say which question you are answering and the justification writes itself. Justify means give a reason for the choice — naming the method alone is only half the mark.

Step 5: sampling techniques (5.4.4, 5.4.5)

A technique is how you catch or count. Seven on the syllabus. The table below is the answer to a six-mark “discuss the benefits and limitations” question, and it is also the answer to “suggest a suitable technique and justify your choice” — which is the most common fieldwork question of all.

Technique	What it is for and how it is used	Benefits	Limitations
pitfall trap	Small ground-living invertebrates such as beetles, spiders and ground bugs. A container is sunk into the soil with its rim level with the surface; animals walking across fall in and cannot climb out. A raised cover keeps rain and birds out.	Works day and night without anyone present, so it catches active night-time species. Cheap, and many traps can be set to compare places.	Only catches animals that walk on the surface, so it misses flying and burrowing species. Catch depends on how active a species is, not just how many there are. Trapped animals may eat each other or die if the trap is left too long, and heavy rain can flood it.
pooter	Collecting small insects singly without harming them. A container with two tubes: you suck on the mouthpiece tube, air is drawn in through the inlet tube and carries the insect into the container. Gauze over the inner end of the mouthpiece stops anything reaching your mouth.	Gentle, so specimens can be identified and released alive. Precise — you choose exactly which animal to collect.	Slow, one animal at a time, so it is impractical for large numbers. Only suits small insects. There is a hygiene risk if the gauze is missing or the pooter is shared.
sweep net	Insects living in long grass and low vegetation. A strong net is swept through the vegetation in a figure-of-eight, a fixed number of sweeps, then the catch is emptied into a tray.	Fast, and collects a large sample from tall vegetation in a few minutes. Standardising the number of sweeps makes places comparable.	Not quantitative in any strict sense — the catch depends on how hard and how fast the person sweeps, so different people get different results. Delicate insects can be damaged, and it does not work on short grass, bare ground or woody plants.
quadrat	Plants and slow-moving animals. A square frame of known area is placed on the ground and what is inside it is counted or estimated. An open frame quadrat is used for counting individuals; a grid quadrat is divided into small squares, which makes estimating percentage cover much easier.	Gives a proper quantitative result per known area, so a population can be estimated for the whole site. Cheap, simple and repeatable.	Useless for anything that moves away. Percentage cover is estimated by eye, so different people give different figures. Too small a quadrat or too few of them gives an unrepresentative result, and species that overlap are hard to score.
transect	Recording change along a gradient. A long tape measure or a string is laid across the area, and samples are taken at fixed intervals along it — usually with a quadrat.	The only technique that shows how a community changes with distance, so it links species to a changing abiotic factor. Cheap and easy to repeat on the same line another year.	Covers a narrow strip only, so it is not representative of the whole site. Where the line is laid is a human choice and can bias the result. Several transects are needed before any conclusion is safe.
aerial photography and drones	Mapping vegetation, land use and large or grouped animals over a wide area from above, and repeating the same flight later to measure change.	Covers ground that is too large, steep, wet or dangerous to walk. No disturbance to the animals on the ground. Images are a permanent record, so the same area can be re-measured years later.	Only sees what is visible from above, so anything under a canopy or underground is missed, and small species cannot be identified. Equipment and trained operators are expensive, flying may need permission, weather can stop work, and drone noise can disturb some birds.
automated sampling	Equipment that records without a person present: camera traps triggered by movement, sound recorders for bats and birds, and data loggers recording temperature, light or pH at set intervals.	Records continuously, day and night, for weeks, which no person could do. Removes observer effects and observer bias, and produces large consistent data sets.	High cost, and the equipment can be stolen, damaged or fail without anyone noticing. It produces enormous quantities of data that take a long time to work through, and it still needs a person to identify what was recorded.

Cambridge can show you either of these unlabelled and ask you to name the parts or say what each does.

The official apparatus list

The syllabus names the equipment you should be able to recognise and use. It is a short list and it is free marks if a diagram comes up: hand lens, humidity or moisture meter, light meter, metre ruler, pH meter, pitfall trap, pooter, quadrat (open frame and grid), 30 cm ruler, sweep net, transect (long tape measure or string), and a tray for hand-sorting. Note that three of them — light meter, pH meter, humidity meter — measure abiotic factors from 5.1.2. That is how a fieldwork question links the two sub-topics together.

Step 6: risks and safety precautions

The syllabus asks you to identify risks and suggest safety precautions, and to describe and explain hazards and safety precautions. A hazard is the thing that could cause harm; the risk is how likely it is and how bad; the precaution is what you do about it. Two marks usually: one for a hazard that genuinely belongs to that site, one for a precaution that actually addresses it. Generic answers like “be careful” get nothing.

Hazard	Why it is a risk here	Precaution
slipping on wet rock or mud	rocky shores and stream banks are wet and uneven	wear boots with a good grip, move slowly, never work alone
deep or fast-moving water	drowning risk when sampling a river or pond	stay out of water above knee depth, work in pairs, an adult supervises
sunburn, heat and dehydration	fieldwork means hours outdoors with no shade	hat, sunscreen, carry water, take breaks in shade
bites, stings and thorns	handling vegetation and invertebrates	use a pooter and a tray rather than fingers, wear gloves and long sleeves
infection from soil or water	bacteria in soil, faeces and untreated water	cover cuts with a waterproof plaster, wash hands before eating
getting lost or separated	large or wooded sites	agree a meeting point and time, carry a charged phone, stay in groups

Make the hazard belong to the site

If the investigation is on a rocky shore, say the incoming tide could cut off the sampling area, so check the tide table and finish before the turn. If it is beside a road, say traffic. Matching the hazard to the described site is what separates a mark from no mark, because the mark scheme is written for that site.

Step 7: repeats, replicates and reliability (5.4.1e)

One reading tells you nothing about how much a measurement varies. The syllabus asks for repeats and replicates, and although the words are often used loosely, keep them apart like this:

A repeat is measuring the same thing again — reading the same quadrat a second time, or taking a second pH reading from the same water sample. It checks your measuring.
A replicate is an independent second sample under the same conditions — a different quadrat at the same distance from the path, a second pitfall trap in the same habitat. It checks your sampling.

Both let you calculate a mean, which reduces the effect of any one odd value, and both make an anomaly visible — with a single reading you would never know it was odd. Three replicates at each value of the independent variable is a sensible standard. If you are asked how to make results more reliable, the answer is almost always: take more replicates and calculate a mean.

Reliable, accurate, valid — three different words

Reliable: repeat readings agree with each other. Fixed by more replicates and a mean. Accurate: the reading is close to the true value. Fixed by better or calibrated apparatus. Valid: the investigation actually tests what it claims to test. Fixed by controlling the other variables. Examiners use these precisely, so match your fix to the word in the question.

Step 8: recording data (5.4.1f)

Marks are given for the design of the table, before a single number goes in it. The rules:

The independent variable goes in the first column, in order, and the dependent variable in the columns to its right.
Units go in the column heading, not beside every number — write “distance / m” at the top and then just 0, 1, 2. Repeating the unit in every cell is a common way to lose the mark.
One column for each replicate, then a column for the mean.
All values in a column to the same number of decimal places.
Draw the whole table with a ruler before you start collecting, so you are not designing it in the field.
For counting things as they pass or as you find them, use a tally and total it afterwards.

Step 9: processing the results (5.4.1g)

Three calculations cover nearly everything Paper 2 asks.

Calculation	How	Watch out for
mean	add the replicates and divide by how many there are	Exclude an anomaly before you take the mean, and say that you have. Give the mean to a sensible number of decimal places — usually one more than the raw data.
percentage cover	with a grid quadrat divided into 100 small squares, the number of squares a species covers is the percentage	Percentages can total more than 100 if plants overlap in layers. That is not an error; say so if asked.
estimating a population	mean number per quadrat ÷ area of quadrat × total area of the site	Get the quadrat area right: a 0.5 m × 0.5 m quadrat is 0.25 m², not 0.5 m². This is the commonest arithmetic slip in the topic.

Worked example A student places ten 0.5 m × 0.5 m quadrats at random in a meadow of area 800 m². The mean number of daisy plants per quadrat is 6.4. Estimate the number of daisy plants in the meadow. [3]

Step 1 — area of one quadrat

0.5 × 0.5 = 0.25 m². Write this line down; it is where most marks are lost.

Step 2 — convert to a density per square metre

6.4 ÷ 0.25 = 25.6 daisy plants per m².

Step 3 — scale up to the whole meadow

25.6 × 800 = 20 480 daisy plants. Because it is an estimate from a sample, it is fair to write it as approximately 20 000.

Why the random placing mattered

Scaling a sample up to a whole area is only valid if the sample was unbiased. Had the quadrats been placed where the student could see daisies, the estimate would be far too high — and a question may well ask you to say so.

About 20 500 daisy plants (20 480).

Step 10: graphs, anomalies and conclusions (5.4.1h, 5.4.1i)

If the independent variable is…	Draw a…	Example
continuous — it can take any value	line graph, points plotted with neat crosses and joined by a line or a smooth curve	distance from path, depth of water, time of day
categoric — it is in separate named groups	bar chart, bars of equal width with gaps between them	habitat type, species name, soil type

Whatever the type: independent variable on the horizontal axis, dependent on the vertical; both axes labelled with units; a scale that is linear and uses more than half the grid; and a key if there is more than one line.

Anomalies

An anomaly is a result that does not fit the pattern of the others. The syllabus wants you to identify and process them, and there is a fixed set of moves:

Identify it — circle it on the graph or ring it in the table, and say which reading it is.
Suggest a cause — and make it specific to the investigation: the quadrat landed on a bare patch of rock, the trap was flooded by rain, the meter was read before it settled.
Repeat that reading if there is time.
Exclude it from the mean, and state that you have excluded it. Quietly dropping data is not acceptable; saying which value you dropped and why is.
Do not draw the line through it. The line of best fit follows the pattern, not the odd point.

Conclusions

A conclusion must do three things: state the relationship, support it with figures from your own data, and explain it with the science. So not “the grass grew better away from the path” but: “Mean percentage cover of grass increased with distance from the path, from 5% at 0 m to 76% at 5 m, because trampling near the path damages leaves and compacts the soil, which reduces the water and air available to roots.” Then say whether that supports your hypothesis. And keep the conclusion inside the data — you tested 0 to 5 m, so you cannot conclude anything about 20 m.

Worked investigation A: trampling beside a footpath

Read this one properly. It is the whole procedure run start to finish on a real question, and almost any quadrat-and-transect question you meet is a repaint of it.

Step	What I would write in the exam
Aim	To find out how the percentage cover of grass changes with distance from a footpath.
Hypothesis	Percentage cover of grass will increase as distance from the footpath increases, because trampling damages the leaves and compacts the soil, reducing the air and water available to roots.
Independent variable	Distance from the edge of the path, in metres.
Dependent variable	Percentage cover of grass inside the quadrat.
Number and range of values	Six distances — 0, 1, 2, 3, 4 and 5 m — evenly spaced, covering the whole gradient from the trampled edge to undisturbed grass.
Control variables, and how	Same 0.5 m × 0.5 m grid quadrat every time; all readings on one morning within two hours so light and temperature are similar; the same person estimates cover each time; the transect kept on the same slope, aspect and soil type; the same method of scoring a partly covered square.
Sampling strategy	Systematic, along a transect running at right angles away from the path. Justified because the question is about how the community changes along a gradient, and only a systematic transect records the samples in order of distance.
Sampling technique and apparatus	A grid quadrat, because percentage cover is far easier and more consistent to estimate when the frame is divided into 100 small squares; a 20 m tape measure as the transect; a metre ruler to place the quadrat accurately at each mark. A light meter and a moisture meter to record two abiotic factors at each point.
Repeats and replicates	Three quadrats at each distance, placed side by side along the 1 m mark, giving three replicates per value; and three parallel transects 10 m apart, so that one unusual line does not decide the result.
Risks and precautions	The path is used by cyclists, so keep the tape flat and work facing oncoming traffic. Kneeling on the ground risks cuts and infection, so cover cuts with a waterproof plaster and wash hands before eating.

The results table, as it should be drawn

Distance from path / m	Cover 1 / %	Cover 2 / %	Cover 3 / %	Mean cover / %
0	4	6	5	5.0
1	18	22	20	20.0
2	35	38	41	38.0
3	54	57	52	54.3
4	68	71	6	69.5
5	78	74	76	76.0

Look at the 4 m row. The third replicate reads 6% where the other two read 68% and 71%, so it is an anomaly. On the day, that quadrat landed on a patch of bare rock. The mean printed for 4 m is 69.5%, which is the mean of 68 and 71 only — the anomalous value has been excluded, and saying so in the answer is part of the mark. Had it been included the mean would have been 48.3%, which would have put a false dip in the graph.

The anomalous replicate is shown and ringed rather than hidden — that is what “identify and process anomalies” means.

Worked example Using the results above, write a conclusion and evaluate the investigation. [6]

Conclusion — relationship, figures, science

Mean percentage cover of grass increased as distance from the path increased, from 5.0% at 0 m to 76.0% at 5 m. The increase was steepest between 0 and 3 m and began to level off after 4 m. This supports the hypothesis. The cause is trampling: feet break the leaves and compact the soil close to the path, which reduces the air spaces and the water available to roots, so fewer grass plants survive there.

Evaluation — what was good

Three replicates at each distance allowed a mean and made the anomaly visible. All readings were taken on one morning by one person, so weather and judgement were kept constant. Six evenly spaced distances covered the full gradient.

Evaluation — sources of error

Percentage cover was estimated by eye, so it is subjective, and overlapping plants are hard to score. The transect was a single narrow line, so it may not represent the whole path. The anomalous quadrat shows that natural variation in the ground — a rock, a hollow — can dominate one reading. And distance from the path is not the only thing changing along the transect: light and soil moisture change too, so trampling has not been isolated.

Evaluation — improvements, matched to those errors

Use a grid quadrat with 100 squares and a fixed rule for scoring part-covered squares, to make the estimate less subjective. Run more transects at several points along the path and take a mean. Increase replicates from three to five at each distance. Measure light and soil moisture at each point so their effect can be considered. Every improvement should answer a named error — “repeat the experiment” on its own earns nothing.

Relationship with figures, science behind it, then errors and improvements that answer those errors one by one.

Worked investigation B: pitfall traps in two habitats

This one uses a categoric independent variable, so almost everything changes: the strategy, the graph and the way the hypothesis is written. Learning both patterns means you are not thrown when the question is about animals rather than plants.

Step	What I would write in the exam
Aim	To compare the number of ground-living invertebrates in leaf litter under trees with the number on bare soil in the open.
Hypothesis	More invertebrates will be caught in traps in leaf litter than in traps on bare soil, because the litter provides dead plant material as food, shelter from predators, and damper, shadier conditions.
Independent variable	Habitat type — leaf litter or bare soil. This is categoric, which is why the results go on a bar chart, not a line graph.
Dependent variable	Number of invertebrates caught per trap in 24 hours.
Control variables, and how	Identical containers of the same diameter and depth; every rim set exactly level with the surface; the same 24-hour period for all traps; the same raised stone cover on each; no bait in any trap; traps at least 2 m apart so they do not compete; the same person identifies and counts the catch using the same key.
Sampling strategy	Random within each habitat: lay two tapes at right angles over each area and use pairs of random numbers as coordinates for the five trap positions. Justified because the question is “how many are there in this habitat”, not “how does it change with distance”, and random placing removes the temptation to set traps where beetles are already visible.
Sampling technique and apparatus	Pitfall traps to catch the animals, a tray for hand-sorting the catch, a pooter to pick up individuals without damaging them, and a hand lens plus an identification key to name them. A humidity meter and a light meter at each trap, to record the abiotic difference the hypothesis depends on.
Repeats and replicates	Five traps in each habitat — ten in all — giving five replicates per habitat, so a mean can be calculated and an odd trap identified. Ideally repeat the whole thing on a second day, because invertebrate activity varies with the weather.
Risks and precautions	Cuts from broken glass in the soil and infection from soil bacteria: wear gloves, cover cuts, wash hands before eating. Use plastic rather than glass containers. Some invertebrates bite or sting, so handle with a pooter and a tray rather than fingers, and release everything where it was caught.
Processing and presentation	Mean number per trap for each habitat, then a bar chart with two bars of equal width and a gap between them, habitat on the horizontal axis and mean number of invertebrates per trap on the vertical axis.
Evaluation points worth having ready	A pitfall trap measures activity as well as abundance, so a fast-moving species is over-represented and a sedentary one under-represented. It catches only surface-walking animals, missing flying and burrowing ones. Twenty-four hours on one date in one place is a narrow basis for a conclusion. A trap flooded by rain gives an anomalously low count and should be identified and excluded.

✎ Run the procedure yourself

Answer each one in your head before you open it. The point is not to recognise the answer — it is to produce it in an unfamiliar setting, which is exactly what AO3 asks.

A student thinks there are more limpets on the sheltered side of a rocky headland than on the wave-exposed side. She has one morning, a quadrat, a tape measure and a notebook.

Name the independent and dependent variables, two control variables, the sampling strategy with a justification, and one hazard with its precaution.

▼

Variables

Independent: side of the headland — sheltered or exposed (categoric). Dependent: number of limpets per quadrat. Control variables: the same quadrat size on both sides; the same height on the shore, measured from the water’s edge, because limpet numbers change up and down a shore as well as around it; the same state of the tide; the same person counting.

Strategy, with the justification

Random within each side, using coordinates from random numbers on a tape grid. Justified because she is comparing how many in two areas rather than tracing a gradient, and random placing prevents her from unconsciously choosing rocks that already have limpets on them. Ten quadrats per side gives a mean worth comparing.

Hazard and precaution

Wet rock and seaweed are slippery, and the tide can cut off part of a headland. Wear boots with a good grip, work in a pair, check the tide table and finish well before the tide turns.

A council wants to know whether residents would support closing a road that runs through a nature reserve. A student is asked to design a questionnaire to find out.

Describe four things she should do to make the results usable, and explain why a pilot study is worth the time.

▼

Use closed questions where possible

Yes/no answers or a fixed scale can be counted and turned into a bar chart. Open questions give richer replies but cannot be processed into data by one student in an evening.

Keep the wording neutral

“Do you agree the road should be closed to protect wildlife?” leads people to yes. “Should the road remain open, be closed, or be closed at weekends only?” does not. A leading question makes the whole data set invalid, and saying so is worth a mark.

Sample enough people, and sample them fairly

A large enough number for a mean or a percentage to mean something, and chosen so one group does not dominate. Asking only inside the reserve reaches people who already use it; asking only in a car park reaches drivers. Ask at several places and at several times of day.

Record systematically

A prepared table with a tally for each possible answer, filled in as you go, rather than notes written up afterwards from memory.

Why the pilot study

Trying it on about ten people first shows which questions are misunderstood, whether any answer options are missing, and how long each interview takes. Fixing the questionnaire after ten replies costs nothing; discovering the problem after two hundred means all two hundred are wasted.

Five pitfall traps in leaf litter caught 24, 27, 22, 3 and 26 invertebrates in 24 hours. The trap that caught 3 was found half full of rainwater.

Calculate the mean the student should report, and explain each decision she has to make.

▼

Identify the anomaly and give it a cause

3 does not fit the pattern of 22 to 27. There is a specific cause on the page: the trap flooded, so animals drowned, floated out or avoided it. Naming that cause is worth more than calling it “an error”.

Decide what to do with it, and say so

Exclude it from the mean and state clearly that it has been excluded and why. Including it: (24+27+22+3+26) ÷ 5 = 20.4. Excluding it: (24+27+22+26) ÷ 4 = 24.75, which is about 24.8. The 4.4 difference between the two shows how much one anomaly can distort a small data set.

What she should do next time

Repeat that trap if there is time. For future work, give each trap a raised cover to keep rain out, and check the traps more often. Note that the improvement addresses the specific cause — that is what makes it a real improvement rather than a wish.

Checkpoint 5.4

Answer, then read the explanation even when you were right.

Your Score 0 / 12

Question 1

A student measures dissolved oxygen in a stream at six points downstream of a sewage outfall. What is the dependent variable?

A the distance downstream from the sewage outfall

B the concentration of dissolved oxygen in the water

C the temperature of the water at each of the points

D the number of sampling points chosen along the stream

The dependent variable is the one you measure to see whether it responds — here, the oxygen. A is the independent variable, the thing she selected. C should be a control variable, or at least recorded, because temperature affects how much oxygen water can hold. D is a decision about the method, not a variable at all.

Question 2

Why must control variables be kept constant during an investigation?

A so that the readings can be collected more quickly in the field

B so that any anomalous results become easier to spot afterwards

C so that the apparatus gives readings closer to the true value

D so that any change measured is caused by the one being tested

This is the validity sentence: without controls, the change in the dependent variable might have been caused by something else. B is the job of replicates, C is the job of better apparatus, and A is not a scientific reason at all. Matching the fix to the right word — valid, reliable, accurate — is what the question is really testing.

Question 3

Which method correctly produces a random sample of quadrat positions in a field?

A using pairs of random numbers as coordinates on a tape grid

B throwing the quadrat over your shoulder without looking round

C placing a quadrat every five metres along a tape across the field

D choosing ten spots that look typical of the field as a whole

Random means every point has an equal chance, and only coordinates from random numbers achieve that. B feels random but the throw is affected by strength, wind and slope, and it is a safety risk; examiners mark it wrong. C is systematic sampling, which is a valid strategy but not a random one. D is the definition of bias, however honestly it is done.

Question 4

A student wants to show how plant species change from the water’s edge up a sand dune. Which strategy should she justify choosing?

A random, because it removes bias from the placing of quadrats

B random, because a mean can then be scaled to the whole dune

C systematic, because it records the samples in order of distance

D systematic, because it takes far less time than random sampling

The question is about change along a gradient, and only a transect records position in order. D picks the right strategy for the wrong reason and would not score the justification mark — speed is a convenience, not a scientific justification. A and B give genuine benefits of random sampling, but neither can show a gradient.

Question 5

Which technique is most suitable for estimating the number of ground beetles active at night in a woodland?

A a sweep net drawn through the low vegetation

B pitfall traps sunk level with the soil surface

C a grid quadrat placed on the woodland floor

D aerial photographs taken from a drone flown at dusk

Pitfall traps work unattended through the night, which is exactly what a night-active ground animal needs. A catches insects in tall vegetation, not on the ground. C is designed for plants and other things that stay put; a beetle simply walks out. D cannot see under a canopy or resolve an animal that size.

Question 6

Why does a pooter have gauze over the inner end of the mouthpiece tube?

A to slow the airflow so insects are not injured

B to filter soil particles out of the collected air

C to hold the insects still while they are counted

D to stop anything being drawn into your mouth

The gauze is a safety feature: air passes through it, insects and dust do not. A is a real benefit of a gentle technique but it is not what the gauze does. B is half right — particles are stopped — but the reason is the operator, not the sample. C describes what the container does.

Question 7

What is the main purpose of carrying out a pilot study before the real investigation?

A to check the method works before time is spent on it

B to collect a first set of results to include in the mean

C to give the group practice at using the apparatus safely

D to prove the hypothesis is right before the main study

A pilot tests the method: is the range sensible, is the quadrat the right size, does the table have the right columns, how long does it take. B is wrong because pilot data were collected with a method you were still changing. C is a useful side effect, not the purpose. D misunderstands what a hypothesis is — the point is to test it, not to prove it in advance.

Question 8

Three readings at one point are 41, 44 and 9. What should the student do?

A include all three, because raw data must never be altered

B delete the 9 from the table so it cannot affect the graph

C keep the 9 in the table, exclude it from the mean, and say so

D take the mean of all three and then round it to the nearest ten

Anomalies are recorded, identified, explained and then excluded from the mean with a statement that they have been. B loses the record of what happened, which is the one thing you must not do. A drags the mean from 42.5 down to 31.3 and hides the problem. D is arithmetic dressed up as a solution and changes nothing about the anomaly.

Question 9

Twelve 0.25 m² quadrats give a mean of 3 buttercup plants each. The field is 600 m². What is the estimated population?

A 1 800 plants

B 450 plants

C 21 600 plants

D 7 200 plants

3 ÷ 0.25 = 12 plants per m²; 12 × 600 = 7 200. Option A is what you get by forgetting to convert to a density per square metre and just multiplying 3 by 600 — the commonest slip in the topic. C multiplies by the number of quadrats as well. B divides where it should multiply.

Question 10

A student compares mean invertebrate counts in four named habitats. Which graph should she draw?

A a line graph, with the four habitats along the bottom axis

B a bar chart, with equal bar widths and gaps between them

C a histogram, with the bars drawn touching one another

D a pie chart, showing each habitat as a share of the total

Habitat is categoric — separate named groups — so a bar chart with gaps is right. A is wrong because joining the points implies values exist between two habitats, which is meaningless. C is for continuous data grouped into classes. D would show proportions of a total, which is not what a comparison of four means asks.

Question 11

Which of these is a testable hypothesis?

A Pollution in the river is a serious problem for the town.

B To investigate the effect of the factory on the river water.

C Nitrate concentration will be higher downstream of the pipe.

D The river should be tested for nitrate at ten sampling points.

A hypothesis is a prediction you could show to be wrong by measuring something. C names both variables and a direction, so a measurement can contradict it. A is an opinion with no measurable quantity in it. B is an aim, not a prediction. D is a method — useful, but nothing in it could turn out false.

Question 12

Results vary widely between replicates at the same point. Which improvement addresses that directly?

A take more replicates at each point and calculate a mean

B extend the range of the independent variable by five metres

C use a larger scale on the vertical axis of the finished graph

D write the conclusion using the median instead of the mean

Wide spread between replicates is a reliability problem, and reliability is improved by more replicates and a mean. B changes what is covered, not how consistent it is. C changes only how the same data look. D is a reasonable way to handle an outlier but it does nothing about the underlying variation, and the syllabus asks for means.

▶ Revise the whole topic

Whole-topic run-throughs, for when you have worked through every sub-topic above and want one sweep before a paper. Opens on YouTube in a new tab. The IGCSE 0680 videos follow the OLD chapter numbering — this topic was Chapter 9, and the current coursebook numbers it Chapter 6 — so chapter names in the titles will not match this page. Two are UK GCSE Biology, not 0680: the ecology is the same but check anything extra against this guide. The syllabus decides what is examinable.