Top 200 Vocabulary Word List for AP Environmental Science | Must Know Words for Common Examination Instructions

The 200-word examination instruction list

AP Environmental Science prompts ask you to identify a problem, explain a mechanism, propose a solution or calculate a result. Name the exact action first, then check the site, population, time period and units in the question.

Start with the list below, or jump to exam requirements, worked examples, the Fencing Method or practice. The list combines command words with terms that tell you how to read a question or format an answer.

Environmental science instructions and concepts

No.	Instruction or term	Meaning or action
1	Design an investigation	State what changes, what gets measured, what stays fixed and how the results test the prediction.
2	Propose a solution	Name a feasible action that directly addresses the problem in the scenario.
3	Justify a solution	Connect the action to the mechanism by which it reduces the stated problem.
4	Identify a drawback	Name a specific negative consequence of the proposed action.
5	Trade-off	Explain what improves and what may worsen when the same option is adopted.
6	Environmental indicator	Use a measurable feature as evidence about environmental condition.
7	Ecosystem service	Name a benefit people receive from ecosystem processes.
8	Food web	Use feeding links to follow energy transfer or predict indirect effects.
9	Trophic level	Identify an organism’s feeding position in the stated pathway.
10	Primary productivity	Express the rate at which producers form organic matter or store energy.
11	Gross primary productivity	Give total producer energy capture before subtracting respiration.
12	Net primary productivity	Subtract producer respiration from gross primary productivity.
13	Energy transfer efficiency	Divide production at the higher trophic level by production at the lower level.
14	Carrying capacity	Identify the population that the environment can sustain under stated conditions.
15	Limiting resource	Identify the resource whose scarcity restricts growth or abundance.
16	Exponential growth	Recognise growth at a constant proportional rate under the model.
17	Logistic growth	Explain slowing growth as population size approaches carrying capacity in the model.
18	Density-dependent factor	Identify a process whose per-capita effect changes with population density.
19	Species richness	Count the distinct species in the specified area or sample.
20	Species evenness	Compare how equally individuals are distributed among species.
21	Ecological succession	Describe how the composition of a community changes after formation or disturbance.
22	Invasive species	Identify an introduced species whose spread causes or is likely to cause harm.
23	Habitat fragmentation	Explain how dividing continuous habitat can isolate populations or change edge exposure.
24	Habitat corridor	A link between habitat patches that can support movement.
25	Island biogeography	Use isolation and area to reason about immigration, extinction and richness.
26	Watershed	Identify the land area draining to a named water body or outlet.
27	Runoff	Track water moving over land and the substances it can carry.
28	Infiltration	Describe water entering the soil surface.
29	Aquifer recharge	Describe water replenishing a groundwater reservoir.
30	Impervious surface	Identify a surface that substantially limits infiltration.
31	Water table	Identify the upper boundary of the saturated zone in an unconfined aquifer.
32	Point-source pollution	Identify pollution discharged from a recognisable, discrete source.
33	Nonpoint-source pollution	Identify diffuse pollution carried from many locations.
34	Eutrophication	Trace nutrient enrichment and its consequences for an aquatic system.
35	Dissolved oxygen	Use oxygen concentration in water to assess conditions for aquatic organisms.
36	Biochemical oxygen demand	Relate oxygen consumed by microbial decomposition under test conditions to organic pollution.
37	Hypoxia	Identify unusually low dissolved oxygen in the given environment.
38	Bioaccumulation	Describe a substance building up within an organism over time.
39	Biomagnification	Describe a substance reaching higher concentrations at successively higher trophic levels.
40	Persistent pollutant	Identify a pollutant that remains in the environment for a long time.
41	Photochemical smog	Connect sunlight and precursor pollutants to products such as ground-level ozone.
42	Temperature inversion	Explain how warmer air above cooler surface air can limit vertical mixing.
43	Particulate matter	Identify suspended solid or liquid particles in air.
44	Acid deposition	Connect emissions such as sulphur dioxide or nitrogen oxides to acidic deposition.
45	Stratospheric ozone	Explain how upper-atmosphere ozone absorbs much incoming ultraviolet radiation.
46	Greenhouse gas	Identify a gas that absorbs and emits infrared radiation.
47	Carbon sink	Identify a reservoir taking up more carbon than it releases over the stated period.
48	Carbon source	Identify a process or reservoir releasing net carbon over the stated period.
49	Ocean acidification	Explain how increased dissolved carbon dioxide lowers seawater pH.
50	Albedo	Compare the fraction of incoming radiation reflected by a surface.
51	Positive feedback	Trace a response that amplifies the initial change.
52	Negative feedback	Trace a response that counteracts the initial change.
53	Renewable resource	Identify a resource replenished on the relevant human timescale.
54	Nonrenewable resource	Identify a finite resource replenished too slowly for the relevant human timescale.
55	Capacity factor	Divide actual energy production by the amount possible at full rated output for the same period.
56	Energy efficiency	Divide useful energy output by total energy input.
57	Per capita	Divide the total by the number of people represented.
58	Ecological footprint	Estimate the biologically productive area needed to support specified consumption and absorb associated wastes under the method used.
59	Life-cycle assessment	Consider impacts across production, use and disposal within the defined scope.
60	Integrated pest management	Combine monitoring and targeted controls to limit pest damage.
61	Crop rotation	Change which crops grow in a field across seasons or years.
62	Soil erosion	Describe soil being removed or transported by water, wind or another agent.
63	Desertification	Identify land degradation in drylands.
64	Overgrazing	Explain how grazing faster than vegetation can recover damages land.
65	Clear-cutting	Identify the removal of most or all trees in a designated area.
66	Maximum sustainable yield	Under the model, find the largest long-run harvest that can be maintained.
67	Bycatch	Identify organisms caught unintentionally in fishing operations.
68	Primary wastewater treatment	Remove settleable or floatable solids using physical separation.
69	Secondary wastewater treatment	Use biological processes to reduce biodegradable organic matter.
70	Tertiary treatment	Apply additional treatment, such as nutrient removal, to meet specified discharge goals.
71	Landfill leachate	Identify contaminated liquid draining through or from deposited waste.
72	Source reduction	Reduce waste generation before treatment or disposal becomes necessary.
73	Environmental justice	Examine how environmental risks, benefits and decision-making are distributed.
74	Mitigation	Reduce a harmful impact or its underlying cause.
75	Adaptation	Adjust practices or systems to manage existing or expected effects.
76	Baseline scenario	Use the stated reference case against which an intervention is compared.
77	Reference site	Use a comparable site to interpret the condition at the site under study.
78	Upstream versus downstream	Compare positions relative to water flow and the possible pollution source.
79	Percent removal	Divide the reduction by the initial amount or concentration and multiply by 100%.
80	Population doubling time	Estimate the time for a population to double under a stated growth model.

Laboratory, graph and evidence instructions

No.	Instruction or term	Meaning or action
81	Hypothesis	State a testable prediction about a relationship.
82	Research question	Specify the focused question that the investigation will answer.
83	Independent variable	Identify what the investigator changes deliberately.
84	Dependent variable	Identify the measured outcome of the investigation.
85	Controlled variable	Identify a factor kept constant to help isolate the tested relationship.
86	Control group	Use the baseline comparison to interpret the treatment effect.
87	Experimental design	Use the stated groups, conditions and measurements to judge the experiment.
88	Sample size	Check how many observations, individuals or trials contribute to the result.
89	Random assignment	Use the assignment procedure to assess whether treatment groups support a causal conclusion.
90	Representative sample	Check whether the selected cases reflect the population of interest.
91	Raw data	Use the measurements as originally collected.
92	Processed data	Use values calculated, combined or transformed from the original readings.
93	Outlier	Identify an observation unusually far from the general pattern.
94	Uncertainty	State or interpret the estimated doubt associated with a measurement or value.
95	Error bars	Read their meaning from the figure legend before interpreting them.
96	Repeatability	Consider agreement when the same method is repeated under the same conditions.
97	Reproducibility	Consider whether results agree when the method is repeated under changed conditions.
98	Validity	Consider whether the evidence or method answers the intended question.
99	Reliability	Consider whether a result or method gives consistent findings.
100	Confounding factor	Identify a factor that could contribute to the apparent relationship.
101	Operational definition	Use the measurable rule the study gives for the concept.
102	Correlation	Describe how variables vary together within the data.
103	Causation	Explain how one factor produces a change in another when evidence supports it.
104	Trend	The broad direction or pattern over a range.
105	Pattern	A regularity visible across observations or examples.
106	Scatterplot	Describe form, direction, strength and unusual points when relevant.
107	Line of best fit	Draw a line representing the overall pattern of plotted data.
108	Interpolate	Estimate within the range covered by the data.
109	Extrapolate	Estimate outside the observed range using an assumed pattern.
110	Read the axes	Identify the quantities, units and intervals on a graph before using a value.
111	Gradient from a graph	Calculate change in the vertical quantity per change in the horizontal quantity.
112	Area under a graph	Use the area only where the graph’s quantities make it the requested accumulated value.
113	Baseline measurement	Use the reading taken before the stated intervention or change.
114	Identify the reference group	Find the comparison used to isolate the change attributed to the intervention.
115	Explain a limitation	Identify the assumption or data issue that restricts the conclusion.
116	Keep the comparison fair	Compare quantities on the same stated basis and units.
117	Control treatment	Use the treatment intended to provide a reference comparison.
118	Positive control	Use the comparison expected to show that the procedure can detect an effect.
119	Negative control	Use the comparison expected to show what happens without the target effect.
120	Residual	Subtract the predicted response from the observed response.
121	Significant figures	Give the requested number of meaningful digits.
122	Decimal places	Count the required digits to the right of the decimal point.
123	Dimensional analysis	Track units through the calculation to see whether the result has the requested dimension.
124	Order of magnitude	Estimate the relevant power-of-ten scale.
125	Calculate the percentage change	Divide the change by the starting value and multiply by 100.
126	Rate of change	Find the change in one quantity per unit change in another.
127	Unit rate	Calculate the amount corresponding to one unit of the other quantity.
128	Parameter	Use the fixed or adjustable quantity that defines a family of cases.
129	Model	Use a simplified mathematical or conceptual representation to address the task.
130	Table	Information arranged in rows and columns.
131	Graph	A visual display of data or a mathematical relationship.
132	Diagram	A drawing showing features, structure or relationships.
133	Scale	The intervals or measurement relationship used in a display.
134	Unit	The standard attached to a measurement, such as minutes or metres.

Command words, quantities and exam directions

No.	Instruction or term	Meaning or action
135	Identify	Name the requested item or feature directly.
136	State	Give the requested fact or result in a concise form.
137	Describe	Report the relevant features, sequence or pattern.
138	Explain	Connect the result to a cause, mechanism or principle.
139	Compare	Use the same basis for both cases and state the relevant relationship.
140	Contrast	State a difference between the named cases on a common basis.
141	Determine	Use the information given to reach the requested result.
142	Predict	State the outcome expected under the supplied conditions.
143	Justify	Connect specific evidence or a rule to the answer you give.
144	Calculate	Use the supplied values and the relevant relationship to produce a result.
145	Estimate	Give a reasonable approximate value from the information provided.
146	Interpret	Explain what the result means in the scenario.
147	Analyze	Break the information into relevant parts and explain how they relate.
148	Evaluate	Judge the claim, design or result against a stated or relevant criterion.
149	Support	Give evidence that strengthens the named claim.
150	Select	Choose the option that meets the stated condition.
151	Define	State the meaning of the term with its essential features.
152	Give one	Supply one relevant answer that meets the task.
153	Indicate	Point to or state the feature the prompt asks for.
154	Complete	Fill the missing parts while preserving the given structure.
155	Label	Attach clear names, units or symbols to the requested features.
156	Construct	Produce the specified representation using the information given.
157	Sketch	Show the required shape, relationships and labels.
158	Plot	Place the supplied points on the correct axes and scale.
159	Outline	Give the main steps or features in a logical order.
160	Infer	Draw a conclusion supported by the clues or evidence supplied.
161	Suggest	Offer a plausible answer that fits the scenario and constraints.
162	Distinguish	Name the feature that separates two easily confused ideas.
163	Demonstrate	Show that a stated claim follows by giving appropriate steps or an example.
164	Check	Test the proposed result against the original conditions.
165	Quantify	Give the magnitude of the change or relationship with units where relevant.
166	Represent	Express the same information in the requested form.
167	Evidence	A relevant observation, value, result or example that supports a claim.
168	Claim	A statement that can be tested or supported.
169	Assumption	A condition treated as true for the purpose of the reasoning.
170	Constraint	A restriction the answer must satisfy.
171	Criterion	The rule or standard used to judge whether a choice works.
172	Condition	A requirement or circumstance that affects the conclusion.
173	Conclusion	The result of the reasoning stated in the question’s context.
174	Exception	A case that departs from the stated rule.
175	Counterexample	A case that disproves a general claim.
176	Magnitude	The size of a quantity, considered separately from direction.
177	Direction of change	State whether the quantity increases, decreases or stays unchanged.
178	Initial value	The value at the stated starting point.
179	Final value	The value at the stated end point.
180	Signed change	Subtract the initial value from the final value and retain the sign.
181	Relative change	Divide the difference by the initial value when that baseline is meaningful.
182	Sequence	Give the steps or outputs in their required order.
183	Order of operations	Apply operations in the sequence indicated by grouping and precedence.
184	Exact value	Give the value without rounding or estimation.
185	Approximation	A value or model used as a close representation within stated limits.
186	Unit conversion	Use a conversion factor to change the units while keeping the quantity the same.
187	Ratio	Compare two quantities by division in the order specified.
188	Proportional reasoning	Use the way quantities scale to connect two cases.
189	Direct relationship	As one quantity increases, the other increases under the stated conditions.
190	Inverse relationship	As one quantity increases, the other decreases under the stated conditions.
191	Boundary condition	A requirement that applies at a specified boundary of the system or task.
192	Reference value	A comparison value against which the result is interpreted.
193	Domain	The inputs or values for which the model or operation applies.
194	Range of values	Identify the values between the specified limits and check endpoint inclusion.
195	At least	Includes the named value and every larger eligible value.
196	At most	Includes the named value and every smaller eligible value.
197	Exactly one	Allow one qualifying case and exclude zero and all cases with two or more.
198	Each	Apply the instruction separately to every item named.
199	All	Cover every eligible item in the group.
200	Any	Check whether the wording means one eligible item or any eligible choice.

What the AP Environmental Science exam requires

College Board lists the regular 2027 exam for 13 May 2027. Fully digital. Complete both sections in Bluebook, including typed free-response answers.

Section	Format and weight
I · Multiple choice	80 questions in 90 minutes, worth 60%. Expect standalone items and sets drawing on numerical data, models or maps, and texts.
II · Free response	3 questions in 70 minutes, worth 40%. Practise planning an investigation, interpreting numerical evidence, and using calculations to analyse an environmental problem.
Calculator policy	Both sections permit a handheld four-function calculator with square root or a scientific nongraphing calculator. Bluebook has a built-in scientific calculator. College Board excludes handheld graphing calculators in 2027.

AP is a U.S.-based subject examination programme taken by students in the United States and internationally. Practise with the College Board materials for the exact course. If you are taking the exam outside the U.S., confirm registration and local reporting time with your school or test centre. The same vocabulary strategy transfers to other national exams by matching the verb, scope and answer format to that exam’s own sample paper and scoring guidance.

Give a named mechanism when the task asks why. When asked to propose a solution, specify the action and where it operates. When asked to justify it, trace the action to the environmental result it is meant to achieve.

Choose the denominator before calculating

A percent change needs an initial value. An emission rate per person needs the number of people represented. A removal efficiency compares the amount removed with the initial amount. Write the denominator with a unit or label first so you can tell whether the calculation answers the question.

Separate describing data from explaining the data

Describe a trend by naming its direction, time span or difference between groups. Explain the trend by connecting it to an environmental process. If an investigation cannot isolate a cause, describe the evidence it provides and state what would make the causal interpretation stronger.

Match an intervention to the scale of the problem

A school can change purchasing or install local water-saving equipment. A watershed intervention may require action at several sources. If the prompt asks for a solution, choose the scale of action that fits the location, sources and constraints in the scenario.

Worked examples for common exam instructions

Explain a mechanism and propose a response

Prompt. After storm runoff enters a lake, nitrate rises and a large algal bloom appears. Explain how this could reduce dissolved oxygen and propose one way to reduce nitrate loading.

Answer. As bloom biomass dies, microbes decompose it and use dissolved oxygen in respiration. A vegetated buffer between fertilised land and the lake can intercept runoff and take up some nutrients before they reach the water.

Match the action to the route described. A buffer can reduce nutrient delivery in surface runoff, and its effectiveness depends on placement, design and flow paths.

Design an investigation

Prompt. Test whether shade from streamside plants reduces stream water temperature.

Answer. Use multiple comparable reaches or experimental channels, assign shade treatments where possible, measure water temperature at fixed depths and times, and compare the mean temperatures for shaded and unshaded treatments. Keep flow and measurement procedures comparable.

Shade is the treatment and water temperature is the measured response. Repeated readings in a single reach are not the same as independent replicated reaches.

Calculate an annual benefit

Prompt. A school uses 120,000 kWh per year. A project cuts use by 15%, and electricity emissions are estimated at 0.40 kg CO₂ per kWh. Calculate annual avoided emissions.

Answer. The project saves 120,000 × 0.15 = 18,000 kWh per year. Multiplying by 0.40 kg CO₂/kWh gives 7,200 kg CO₂ per year, or 7.2 metric tonnes per year.

This estimate uses the supplied emissions factor as constant. Preserve the time unit and distinguish tonnes from kilograms.

Interpret data without overclaiming

Prompt. The average nitrate concentration was 3 mg/L upstream and 8 mg/L downstream of a farm on one sampling day. Describe the comparison and give one limitation.

Answer. Downstream nitrate was 5 mg/L higher on that day. One day of sampling does not establish a persistent difference, and the comparison alone does not separate farm runoff from other upstream-to-downstream inputs.

If asked for an improvement, sample both locations on multiple days and add monitoring near plausible inputs. That produces evidence for a more specific explanation.

Use the Fencing Method to build an answer

Start within a small boundary. Answer one instruction correctly in a short sentence or a small piece of code. Add one detail at a time, checking that each addition helps satisfy the prompt. Finish by transferring the same skill to a nearby case.

Start. Runoff can carry nitrogen.

Add context. Rain can carry nitrate from fertilised soil into a lake.

Add the reasoning or operation. More nitrate can stimulate algal growth where nitrogen limits growth. Decomposition of the resulting biomass can then lower dissolved oxygen.

Transfer. Try the same structure with sediment runoff. Change the mechanism and explain what happens to light penetration.

Practice with the 200 terms

Choose three terms with different answer shapes. Cover the meaning column and say what an examiner would expect to see. Write one answer to each, then underline the exact number, evidence, explanation or code that fulfils the instruction.

Describe versus justify

Try it. A county reduced landfill disposal from 60 tonnes per week to 45 tonnes after starting separate food-scrap collection. Calculate the percentage reduction and explain one possible mechanism.

Check. Disposal fell by 15/60 × 100% = 25%. Diverting food scraps to composting can lower the mass entering the landfill. The before-and-after figures alone cannot quantify how much of the fall the scheme caused.

On a second pass, change one number or condition and predict how the answer changes before calculating. Then use a released question and its scoring guidelines to check which parts of your reasoning were visible.

Frequently asked questions

What makes a proposed solution specific?

Name the action, the place or source where it applies, and, if requested, the process that reduces the stated harm. Practise writing each part separately so the evidence and mechanism stay visible.

Do I have to memorise every definition?

Use the terms in small groups. For each one, practise identifying the required answer and producing it. The exact instructions and official scoring guidelines for an individual item determine what that response needs.

Official sources and next reading

College Board AP Environmental Science exam format, course description and released questions · College Board AP calculator policy

AP exam command words · eduKateSG vocabulary learning guide · How to build a sentence with the Fencing Method