Command Words (AQA A Level Biology): Revision Note
Exam code: 7402
Command words
Command words are the instruction words in an exam question
Command words show what the examiner wants you to do, such as describing data, explaining reasons, or evaluating evidence
They also tell you the skill being assessed, for example recall, application, or analysis, which guides how detailed and structured your answer should be
Not responding to the command word correctly will cause you to lose marks in an exam even if your biological knowledge is sound
Learning what each command word is asking for will allow you to use your biological knowledge effectively to gain marks in exams
The table below contains a list of command words that have appeared in recent AQA A Level Biology exams
Command word | Requirement |
|---|---|
Assess | Make an informed judgement |
Calculate | Use numbers provided to work out the value of something |
Compare | Describe the similarities and/or differences between things |
Complete | Finish a task by adding to given information |
Consider | Review and respond to given information |
Contrast | Identify differences between things |
Deduce | Draw a logical conclusion from information provided |
Define | Specify meaning |
Describe | Recall facts, events or a process |
Determine | Use given data or information to obtain an answer |
Discuss | Present key points, often including different viewpoints or evidence |
Draw | Produce, or add to, a diagram |
Evaluate | Judge from available evidence, considering arguments for and against |
Explain | Give reasons |
Give | Produce an answer from recall or from given information, without explanation or description |
Justify | Support a case with evidence |
Name | Identify using a recognised technical term |
Outline | Set out main characteristics |
Predict | Give a plausible outcome |
State | Express in clear terms |
Suggest | Apply knowledge and understanding to a new situation |
Interpreting command words
While students are often aware of the importance of command words, mistakes relating to command word interpretation appear year after year
The following command words frequently cause problems for students:
explain and describe
evaluate
suggest
compare and contrast
Explain vs describe
Confusing "explain" and "describe" is the most common command word error
Remember that:
describe = recall a structure or process, or describe a pattern in data
explain = give a biological reason for an event or observation
Read questions carefully so that you know whether you need to describe, explain, or both, before starting to write an answer
Worked Example
Figure 1 shows the effect of increasing substrate concentration on enzyme activity with and without a competitive and non-competitive inhibitor.
Figure 1
Explain the difference between the effects of the competitive and non-competitive inhibitors.
[2]
Mark scheme
Increasing substrate concentration reduces the effect of the competitive inhibitor / competitive inhibition can be overcome by adding more substrate (so the curve reaches the same Vmax as without inhibitor) [1 mark]
The non-competitive inhibitor changes the active site shape / reduces the function of the active site (so the curve plateaus at a lower maximum rate than without inhibitor) [1 mark]
Student answer
0/2 marks | 2/2 marks |
|---|---|
When a competitive inhibitor is added the rate of reaction is initially slower than the reaction without the inhibitor, but increasing the substrate concentration increases the rate until it reaches Vmax. When a non-competitive inhibitor is added the rate of reaction is slower than the reaction without the inhibitor and does not increase to Vmax when the substrate concentration increases. Mark: 0/2 Reason for mark: this answer describes how changing variables affects reaction rate. It does not offer any biological explanation for the patterns observed, so even though the description is correct, no credit can be awarded. | With the competitive inhibitor, increasing substrate concentration can overcome the effect of inhibition [1]. The non-competitive inhibitor changes the shape of the active site so the substrate's ability to bind is reduced [1] at all substrate concentrations. Mark: 2/2 Reason for mark: this answer gives a biological reason for the shapes of the two graphs. It explains how increasing the substrate concentration can overcome the effect of competitive inhibition, but not the effect of non-competitive inhibition. |
Evaluate
“Evaluate” questions assess analytical skills; they usually require arguments and/or evidence for and against a conclusion
Common reasons for lost marks in "evaluate" questions include:
one-sided answers
Students argue either in support of or against a conclusion, but fail to give a balance of both arguments
describing data
Students may just describe patterns in the data without clearly linking this to supporting or refuting arguments
incorrect use of statistics
A common error is to conclude that “the results are significant” or “the results are due to chance”, when what should be stated is that the difference between groups, or the difference between means, is significant or due to chance
failing to consider experimental design
Students often overlook constraints of investigation design, e.g. "the study only used one species", "it only shows results for a short time period" or "the sample size is too small to represent the entire population"
Worked Example
Changes in land use can affect the extent to which ecosystems store carbon in organic matter. Scientists investigated whether plant species richness in restored North American grasslands affects the rate of soil carbon accumulation.
They set up an experiment on former farmland that had been cleared, exposed to herbicides, and then abandoned. Across 168 plots, they sowed 1, 2, 4, 8 or 16 species of native perennial grassland plants. The same total number of seeds was sown in each plot, and all plots were weeded annually throughout the study to remove additional species.
Soil carbon storage in the top 20 cm of soil was measured at regular intervals for 22 years; the results are shown in Table 1 below.
Table 1
Number of species originally planted on the plot | Carbon storage rate during years 1-13 / Mg ha-1 yr-1 | Carbon storage rate during years 14-22 / Mg ha-1 yr-1 |
|---|---|---|
1 | 0.09 (± 0.06) | 0.28 (± 0.08) |
2 | 0.14 (± 0.06) | 0.31 (± 0.08) |
4 | 0.15 (± 0.07) | 0.36 (± 0.07) |
8 | 0.11 (± 0.07) | 0.45 (± 0.07) |
16 | 0.19 (± 0.06) | 0.51 (± 0.06) |
The scientists concluded that, when compared with natural succession, high-diversity planting of late-successional plants may increase the ability of abandoned agricultural land to store carbon.
Evaluate this conclusion.
[4]
Mark scheme
In support of the conclusion
A maximum of three from:
Carbon storage rate is significantly higher when there are 16 species than when there is 1 [1 mark]
Carbon storage rate is significantly higher in a diverse planted plot than during natural succession [1 mark]
Carbon storage rate is significantly higher during the later stages of succession / during years 14-22 / once plants are more established than during the early stage / years 1-13 / while plants are immature [1 mark]
168 plots is a large sample size [1 mark]
Against the conclusion
A maximum of three from:
Carbon storage rate decreases slightly between 4 and 8 species during years 1-13 [1 mark]
It may not be realistic to maintain a weeding schedule on all abandoned agricultural land [1 mark]
The experiment only measures carbon storage in the top 20 cm of soil, so this may not be truly representative of all soil [1 mark]
There may be unknown pollutants / heavy metals / severe nutrient depletion on other agricultural sites so the results may not be achieved everywhere [1 mark]
The results achieved with native North American plants may not be the same elsewhere in the world [1 mark]
The study needs to be replicated to back up the findings [1 mark]
Student answers
0/4 marks | 4/4 marks |
|---|---|
The table shows that as you add more plant species the carbon storage rate goes up, especially in the later years. The results are significant and prove that planting more species will allow land to store more carbon. However, we can’t really trust it because correlation does not mean causation and the sample size might be too small. There could be other factors affecting the results as well, so you can’t really say anything definite. Mark: 0/4 Reason for mark: this answer describes the pattern, but does not link this clearly to a supportive argument. It also misuses statistics, saying that “the results are significant", as well as saying that the results "prove that planting more species will allow land to store more carbon" which they then go on to contradict. While it does give a balance of arguments, it relies on generic stock phrases like “correlation does not mean causation, “sample size might be too small” and "there could be other factors" without linking them to the actual design. | There is some evidence in support of the scientists’ conclusion. Between years 1–13 and years 14-22 the mean carbon storage rate increases with species richness [1], and the standard deviations for 1 species plots do not overlap with the standard deviation for 16 species plots, indicating that the difference between these two data sets is significant [1]. The study also used 168 plots, which is a large sample size [1], making the averages reliable. However, there is also some evidence that does not support the conclusion. Between 4 and 8 species in years 1–13 the mean carbon storage rate actually decreases slightly [1], so the relationship between diversity and carbon storage is not consistently increasing at all richness levels. The experiment only measured carbon in the top 20 cm of soil, so it may not represent total soil carbon storage at greater depths. In addition, the work was done on former farmland using native North American grassland plants, so results from these sites may not apply to other regions. Mark: 4/4 Reason for mark: this answer describes data within the context of supporting the argument, and correctly uses the non-overlapping standard deviations as evidence that the two sets of data are significantly different to each other. It gives a balance of arguments, and also clearly links the arguments to specific elements of the investigation design, e.g. the source of the soil samples and the location of the study. While it contains more than four creditworthy points, the maximum number of marks is four marks. |
Suggest
"Suggest" and "suggest and explain" command words require the application of biological knowledge to unfamiliar situations
Common reasons for lost marks in "suggest" questions include:
not relating answers directly to the context
Students often rely on rote-learned facts instead of tailoring ideas to the specific scenario or data provided
incomplete explanations
Many “suggest” questions, especially those phrased as “suggest and explain…”, require a full causal chain of ideas, so students lose marks by failing to make clear links between suggestions and explanations
Worked Example
Rituximab is an antibody used in the treatment of some B cell cancers.
Suggest how rituximab might work to destroy cancerous B cells.
[3]
Mark scheme
Rituximab is complementary to receptors/antigens found on the surface of (cancerous) B cells [1 mark]
Rituximab binds to (cancerous) B cells, forming an antigen-antibody complex [1 mark]
Antibodies cause agglutination AND increase phagocytosis of (cancerous) B cells [1 mark]
Student answers
1/3 marks | 3/3 marks |
|---|---|
Rituximab might work to destroy cancerous B cells by being complementary to antigens. It could bind to antigens and form an antigen-antibody complex [1]. Mark: 1/3 Reason for mark: this answer shows that the student understands how antibodies and antigens interact, but it is very generalised and does not relate directly to the context, i.e. it does not state which antigens rituximab is complementary to. In addition to this, the chain of reasoning is incomplete, as the answer does not explain how the formation of an antigen-antibody complex aids in the destruction of B cells. | Rituximab might be complementary to the antigens on cancerous B cells [1], allowing it to bind and form an antigen-antibody complex [1]. This could cause agglutination and increase phagocytosis [1]. Mark: 3/3 Reason for mark: this answer directly applies understanding of antibodies to the context presented, i.e. it states that the antibodies are complementary to cancerous B cell antigens. It then gives a clear chain of reasoning that links the binding of antigens and antibodies to the agglutination of pathogens. |
Examiner Tips and Tricks
Notice that the 1/3 and 3/3 answers in the example above are very similar in length, and yet the second answer gains full marks while the first answer doesn't.
The reason for this is that the first answer spends most of the first sentence just repeating the question stem. While repeating the question in this way will not lose you marks, be careful that it doesn't trick you into thinking that you've written more creditworthy content than you actually have!
Compare and contrast
Questions that contain "compare" or "compare and contrast" require students to identify similarities and differences, and to describe them using comparative language
Common reasons for lost marks in "compare and contrast" questions include:
failing to use directly comparative statements
"Compare" statements must state how two items are similar, e.g.:
both animal and plant cells have a partially permeable membrane
both photosynthesis and respiration involve the enzyme ATP synthase
"Contrast" statements must state how two items are different, e.g.:
xylem cell walls are strengthened with lignin while phloem cell walls are not
prokaryotic cells are smaller than eukaryotic cells
cellulose contains beta glucose whereas starch contains alpha glucose
failing to both compare and contrast
In order to gain full marks a "compare and contrast" answer must contain both similarities and differences
Worked Example
Compare and contrast prokaryotic and eukaryotic chromosomes.
[3]
Mark scheme
Similarities
Both contain DNA in a double helix structure [1 mark]
Prokaryotic chromosomes and eukaryotic mitochondrial/chloroplast chromosomes are both short / circular / not associated with proteins [1 mark]
Differences
A maximum of three from:
Prokaryotic chromosomes are circular WHILE eukaryotic chromosomes are linear [1 mark]
Prokaryotic chromosomes are do not (often) contain histones WHILE eukaryotic chromosomes do contain histones [1 mark]
Prokaryotic chromosomes do not contain introns / noncoding regions WHILE eukaryotic chromosomes do [1 mark]
Prokaryotic chromosomes are smaller than eukaryotic chromosomes [1 mark]
Student answers
0/3 marks | 3/3 marks |
|---|---|
Prokaryotes have circular chromosomes that do not contain histones. Prokaryotic chromosomes are made of a DNA double helix and have no introns. Eukaryote chromosomes are linear and are often associated with histones. They contain non-coding regions called introns and are also made of a DNA double helix. Mark: 0/3 Reason for mark: this answer contains plenty of accurate and relevant ideas, but the structure of the answer (i.e. a separate paragraph on each type of chromosome) does not allow for direct comparison. Examiners will not comb through your answer to pick out inferred comparisons, so no credit can be awarded. | Both prokaryotic and eukaryotic chromosomes are made of DNA in a double helix structure [1]. However, prokaryotic chromosomes are circular whereas eukaryotic chromosomes are linear [1]. Prokaryotic chromosomes are not associated with histone proteins, whereas eukaryotic chromosomes are [1] associated with histones. Mark: 3/3 Reason for mark: this answer contains three directly comparative statements, and it gives a similarity as well as two differences, so full marks can be awarded. |
Examiner Tips and Tricks
The best way to ensure that a statement is directly comparative is to check whether it contains comparative language, e.g.:
Both...
... while...
...whereas...
...is smaller than...
...is faster than...
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