AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Students should be able to appreciate that advances in immunology and…
Full specification wording
Species and taxonomy: Students should be able to appreciate that advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms.
Classification used to depend on what could be seen.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 9 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Classification used to depend on what could be seen. Bacteria, for example, were once grouped by the number, position and shape of their flagella viewed with an optical microscope, a method that was unreliable because flagella are fragile, hard to stain and can project from the cell at any angle, and because unrelated species can share a cell shape. Two kinds of evidence have replaced it. Genome sequencing reads the base sequence of DNA directly, and sequences can be compared base by base: the more similar the sequences of two organisms, the more recently they shared a common ancestor. Amino acid sequences of the same protein can be compared in the same way, since the base sequence determines the amino acid sequence. Immunology provides a third line of evidence: antibodies bind to similar proteins from another species, and the more precipitate formed, the closer the relationship.
What earns the marks
- Naming DNA or genome base sequencing as the evidence used to clarify evolutionary relationships.
- Naming amino acid sequencing of proteins as an alternative line of evidence.
- Stating that the more similar the sequences, the more closely related the species or the more recent the common ancestor.
- An immunological comparison in which antibodies bind to similar proteins from another species, with more precipitate indicating a closer relationship.
- Explaining that new evidence contradicted a grouping based on observable features, so species were renamed or moved.
Common mistakes and how to put them right
Writing that improved microscopes gave greater magnification when the mark scheme requires greater resolution.
Saying that DNA is compared without saying that it is the base sequence being compared.
Claiming similar DNA proves organisms are the same species, rather than indicating how closely related they are.
Describing the immunological method as a test for disease rather than as a comparison of proteins between species.
Presenting renaming as a change of opinion rather than as a response to new sequence evidence.
Exam tips
- When asked why species have been renamed, name a technique such as base sequencing or amino acid sequencing and link it to the evidence it provides.
- Use the word resolution, not magnification, whenever you explain what a better microscope provided.
- Say what is being compared in full: the base sequence of DNA, or the amino acid sequence of a named protein.
Try the lesson
The start of the Species and taxonomy: Students should be able to appreciate that advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms. lesson, made from checked teaching notes for this specification point.
Have a go first
Which advance allows biologists to compare the DNA base sequences of different species directly?
Listen
Classification used to depend on what could be seen. Bacteria, for example, were once grouped by the number, position and shape of their flagella viewed with an optical microscope, a method that was unreliable because flagella are fragile, hard to stain and can project from the cell at any angle, and because unrelated species can share a cell shape. Two kinds of evidence have replaced it. Genome sequencing reads the base sequence of DNA directly, and sequences can be compared base by base: the more similar the sequences of two organisms, the more recently they shared a common ancestor. Amino acid sequences of the same protein can be compared in the same way, since the base sequence determines the amino acid sequence. Immunology provides a third line of evidence: antibodies bind to similar proteins from another species, and the more precipitate formed, the closer the relationship. A strong answer earns marks for these points. naming DNA or genome base sequencing as the evidence used to clarify evolutionary relationships. naming amino acid sequencing of proteins as an alternative line of evidence. stating that the more similar the sequences, the more closely related the species or the more recent the common ancestor. an immunological comparison in which antibodies bind to similar proteins from another species, with more precipitate indicating a closer relationship. Exam tip: When asked why species have been renamed, name a technique such as base sequencing or amino acid sequencing and link it to the evidence it provides.
Key words
Say what each word means before you turn the card.
genome sequencing
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amino acid sequence comparison
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immunological evidence
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reclassification
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See every definition
- genome sequencing
- Reads the base sequence of DNA directly, and sequences can be compared base by base.
- amino acid sequence comparison
- Compares the amino acid sequences of the same protein in the same way, since the base sequence determines the amino acid sequence.
- immunological evidence
- Antibodies bind to similar proteins from another species, and the more precipitate formed, the closer the relationship.
- reclassification
- New evidence contradicted a grouping based on observable features, so species were renamed or moved.
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