To read a flow diagram, go arrow by arrow. For each one, name the process, the input and the output. Each arrow then becomes one sentence of an explanation.
This lesson follows evaluating benefits and risks using evidence and draws on explaining biotechnology processes at syllabus level. It belongs to SPM Biology.
Worked example: an invented diagram in words
An original diagram has five boxes joined by four arrows. The table reads it one arrow at a time.
| Arrow | Input | Process | Output |
|---|---|---|---|
| 1 | Source DNA and plasmid | Cut with a restriction enzyme | Gene fragment and opened plasmid |
| 2 | Gene fragment and opened plasmid | Joined by DNA ligase | Recombinant plasmid |
| 3 | Recombinant plasmid and bacteria | Placed into the bacteria | Modified bacteria |
| 4 | Modified bacteria | Grown in culture | Many bacteria producing the protein |
Notice that each output becomes the input of the next arrow. Once you can follow the inputs and outputs, you can rebuild the whole diagram from memory.
How do I turn it into an answer?
Write one sentence for each arrow, naming the tool and the result.
“The restriction enzyme cuts the source DNA and the plasmid. DNA ligase joins the gene into the plasmid to form a recombinant plasmid. The recombinant plasmid is placed into bacteria, which are grown so that many cells make the protein.”
The mistake that costs marks
The common slip is to label the wrong structure. A student calls the recombinant plasmid “the gene” or writes that the plasmid is a bacterium.
| Claim | Why it fails |
|---|---|
| “The gene is inserted into the bacterium as it is” | The gene is first joined into a carrier, the plasmid |
| “The plasmid is the host cell” | The plasmid is a small circle of DNA inside the host |
| Correct: “The gene is joined into the plasmid, and the recombinant plasmid enters the bacterium” | Keeps the three terms apart |
On your own copy of the diagram, write a short label beside each box: gene, plasmid, recombinant plasmid or host.
Check yourself
In the diagram above, state what arrow 3 shows, and name its input and output.
Answer
Arrow 3 shows the recombinant plasmid being placed into bacteria.
The input is the recombinant plasmid and the bacteria. The output is the modified bacteria, which now carry the gene.
What to study next
Test all four lessons in the genetic technology practice set. The biological data interpretation trainer can help you write explanations of diagrams and data.
If you want a teacher to go through diagrams with you, see online one-to-one Biology tuition.