Precision (AQA A Level Biology): Revision Note
Exam code: 7402
The importance of precision
Students often lose marks in exams because their answers are not precise enough
Precision is not about writing more; it is about:
choosing exact scientific language
making clear causal links between ideas
choosing the correct level of detail
making your meaning unambiguous
Using precise scientific terminology
Failing to use the correct biological terms will cause you to lose marks, even if your overall grasp of the content is correct
At A level, examiners expect you to move beyond GCSE-level language
Improve your use of precise biological language as follows:
use the specific scientific term, not a vague substitute, e.g.:
nerve impulses rather than “messages” or “signals”
hydrolysis rather than “break down” when water is used to split a molecule
volume or concentration rather than "amount" when describing measurements
choose the exact scientific term, not a related but different one, e.g. students often confuse:
gene and allele
capsule and capsid
chromosome and chromatid
name ions and atoms accurately, e.g.:
saying “sodium” or “ions” is too imprecise when you mean sodium ions
"hydrogen" is incorrect when describing protons, which can also be correctly termed H+ or hydrogen ions
Worked Example
When pathogens enter the body, phagocytes carry out a process called phagocytosis.
Describe the sequence of events that take place during phagocytosis.
[3]
Mark scheme
The neutrophil/phagocyte cell membrane surrounds the pathogen OR the pathogen is engulfed / ingested [1 mark]
The phagosome/vesicle/vacuole fuses with a lysosome [1 mark]
Lysozymes / hydrolytic enzymes are released AND digest the pathogen [1 mark]
The digested parts of the pathogen are displayed on the cell surface membrane [1 mark]
Student answers
0/3 marks | 3/3 marks |
|---|---|
The phagocyte moves towards the pathogen and then it surrounds it. Enzymes called lysosomes are released by the phagocyte and they break down the pathogen. Mark: 0/3 Reason for mark: this answer, while it is essentially correct, is imprecise. It does not mention the role of the cell surface membrane in surrounding the pathogen, lacks important key terminology, and it uses the term lysosome incorrectly. | The phagocyte’s cell surface membrane surrounds and engulfs the pathogen [1], forming a phagosome within the cytoplasm. Lysosomes fuse with the phagosome [1] and release lysozymes, hydrolytic enzymes which then digest the pathogen [1]. Mark: 3/3 Reason for mark: this answer describes the process correctly using essential key terms such as "receptors", "phagosome", "lysosome" and "hydrolytic enzymes" |
Making clear causal links
Many students lose marks on “explain” and “suggest” questions, not because they do not know the facts, but because they do not spell out the logical chain of events from cause to effect
To avoid losing marks for this reason, consider the following:
avoid gaps in chains of events
Ensure that sequences of events progress from cause all the way to consequence with no missing steps
link structure and function clearly where relevant, e.g.:
tracheoles have thin walls, resulting in a short diffusion distance to cells
the aorta wall contains elastic tissue that stretches and recoils to maintain blood pressure
use linkage words
Words like “so” and “therefore” make the cause-and-effect relationship clear, e.g. a membrane is folded so there is an increased surface area
Worked Example
A banned performance enhancing drug increases the number of red blood cells in an individual's blood.
Suggest why this would be beneficial for endurance athletes.
[4]
Mark scheme
Any four from:
More red blood cells can contain more haemoglobin [1 mark]
More oxygen can be delivered to muscle cells (by the blood) [1 mark]
Higher rate of aerobic respiration [1 mark]
More ATP can be produced for muscle contraction [1 mark]
Reduced reliance on anaerobic respiration / less lactate produced SO fatigue is delayed [1 mark]
Student answers
1/4 marks | 4/4 marks |
|---|---|
The drug increases the number of red blood cells which increases the amount of oxygen in the blood. Mark: 1/4 Reason for mark: this answer makes the connection between red blood cells and oxygen being transported to the muscles (MP2), but it fails to mention haemoglobin, and it also fails to clearly link the cause (more red blood cells) to the effect (longer endurance). | More red blood cell mean that there is more haemoglobin [1] in the blood. Mark: 4/4 Reason for mark: this answer contains all the important biological ideas, and makes a clear link from cause to effect: red blood cells → haemoglobin → oxygen transport → aerobic respiration → ATP → muscle endurance |
Choosing the correct level of detail
Being precise is not just about using the right word; it is also about giving enough A-level detail without waffling
Consider the following:
is your answer an A-level response or are you working at GCSE level?
If you could have written the same answer in a GCSE exam, then it probably doesn't include enough detail, so consider what else you should include
This is also related to correct use of A Level terminology (see above)
be aware of the number of marks available
The number of marks available usually needs to match with the number of creditworthy points that you make, e.g. if you have only written one sentence, then you are unlikely to have included enough detail to gain three marks
The exception to this is the essay question, which is marked differently
Worked Example
Describe the role that enzymes play in the digestion and complete breakdown of starch.
[4]
Mark scheme
Any four from:
The enzyme amylase [1 mark]
Breaks starch down into maltose [1 mark]
The enzyme maltase [1 mark]
Breaks maltose down into glucose [1 mark]
(Both enzymes) break the glycosidic bonds [1 mark]
(The reaction is) hydrolysis [1 mark]
Student answers
1/4 marks | 4/4 marks |
|---|---|
Starch is broken down by the enzyme amylase [1]. It is broken down into glucose by breaking down the bonds between individual sugar molecules. Mark: 1/4 Reason for mark: this answer covers starch digestion at GCSE level. It does not use A Level language, e.g. it refers to "bonds" and "sugar molecules", and it is too short to be worth four marks. | Starch is first broken down by the enzyme amylase [1] into the disaccharide maltose [1]. Maltose is broken down again by another enzyme, maltase [1] into glucose [1]. The enzymes hydrolyse the glycosidic bonds between monosaccharides. Mark: 4/4 Reason for mark: this answer uses A Level language, e.g. "hydrolyse" and "glycosidic" and it contains additional detail about the two-stage breakdown of starch. This means that it contains enough creditworthy content to gain full marks. |
Being unambiguous
Examiners will not infer meaning from vague statements, so it is essential that your meaning is always clear; statements that can be interpreted in more than one way will not be given credit
Overusing words like “it”, “this” or “they” can make answers unclear; if there is any chance of confusion, repeat the key noun, e.g. “the enzyme”, “the sodium ion channel”, “the membrane”, so there is no room for ambiguity
Worked Example
Describe the role of a ribosome in translation.
[3]
Mark scheme
Any three from:
mRNA binds to the ribosome [1 mark]
The ribosome has two codons / binding sites [1 mark]
tRNA with anticodons bind / associate (with the ribosome) [1 mark]
The ribosome catalyses formation of peptide bond between amino acids (held by tRNA molecules) [1 mark]
The ribosome moves along the mRNA / to the next codon [1 mark]
Student answers
1/3 marks | 3/3 marks |
|---|---|
It binds to mRNA [1], allowing complementary tRNA anticodons, with their amino acids, to bind to it. It then catalyses the formation of peptide bonds between them. Mark: 1/3 Reason for mark: this answer shows some understanding of the role of ribosomes, but it uses "it" and "them" in ambiguous ways. The initial "it" can be assumed to be a ribosome, so credit can be given here. but the term "it" is then used twice more, in ways that correctly apply to different structures. It is also not clear where the peptide bonds are forming because the answer uses "them" rather than referring directly to the amino acids. | mRNA binds to the ribosome [1]. tRNA molecules with complementary anticodons bind to the codons on the mRNA at the ribosome [1], each bringing a specific amino acid. The ribosome holds the tRNA molecules in place and catalyses the formation of peptide bonds between two adjacent amino acids [1]. It then moves to the next codon so that more amino acids are added in sequence, forming a polypeptide chain. Mark: 3/3 Reason for mark: this answer uses clear biological terminology throughout, so there is no ambiguity around which structure is doing what. |
Examiner Tips and Tricks
When you check an answer, ask yourself four questions:
have I chosen the exact term?
have I shown how one step leads to the next?
have I given enough A-level detail?
could any sentence be misunderstood?
Students will often say 'but that's what I meant!' when they are marked down for being imprecise. Remember that examiners will not extrapolate from your inferred answers; assume that the examiner knows nothing, and always say exactly what you mean.
Unlock more, it's free!
Did this page help you?