1.6.10Inquiry Process
Environmental DNA and Barcodes — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 24 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Environmental DNA
eDNA allows scientists to survey an ecosystem without seeing any organism.
What it is
- What it is DNA released into water, soil or air from skin, mucus, faeces and gametes of organisms living there.
Collection
- Collection Water or soil is sampled and filtered, and DNA is extracted without needing to catch any animal.
Amplification
- Amplification PCR copies target gene regions so even tiny traces of DNA can be detected and sequenced.
Identification
- Identification Sequences are compared with a reference database to reveal which species left the DNA.
Advantages
- Advantages It is non-invasive, can detect rare or hidden species, and covers many species from one sample.
Section 2 of 5DNA Barcodes
DNA Barcodes
Definition
- Definition A short standard region of DNA that differs enough between species to act as a label.
Animals
- Animals The mitochondrial gene COI, coding for cytochrome c oxidase subunit I, is the usual barcode.
Plants
- Plants Chloroplast genes such as rbcL and matK are commonly used as barcodes.
Reference library
- Reference library A barcode is only useful if the correct sequences for known species have been recorded.
Section 3 of 5Applications and Limits
1
Biodiversity surveys of lakes, rivers and soils can list species present without capturing them.
2
Conservationists can detect rare, endangered or invasive species early.
3
Barcodes can identify species from fragments, larvae or processed food, helping to detect illegal trade or fraud.
4
Limitations include incomplete reference databases, contamination, and DNA that drifts or persists after animals leave.
5
Results usually show presence, not reliable numbers of individuals.
| Method | Advantage | Disadvantage |
|---|---|---|
| Traditional survey | Counts individuals | Time consuming, can miss rare species |
| eDNA | Detects hidden species | Less reliable for abundance |
Section 4 of 5Worked Example
Question
- A water sample from a pond is filtered, DNA is extracted and the COI gene is amplified and sequenced.
- Sequences match the great crested newt.
- Explain what this shows and one limitation.
- The newt shed cells into the water, so its DNA is present as environmental DNA.
- The COI barcode sequence is compared to a database of known species sequences.
- A match shows that the newt is present in or near the pond, even if no animal was seen.
- A limitation is that DNA may travel or persist after the animal has gone, and it cannot give reliable numbers.
Answer
- The newt is probably present in the pond;
- the result confirms presence but not abundance.
Section 5 of 5Exam Checklist & Tips
1.6.10 – Key Points for the Exam
- eDNA DNA collected from the environment rather than from an organism directly.
- DNA barcode A short standard DNA sequence used to identify species.
- PCR A technique that copies a specific section of DNA.
- COI A mitochondrial gene used as an animal barcode.
Common Mistakes
- Saying eDNA proves the number of individuals in an area.
- Thinking barcodes involve sequencing the entire genome.
- Forgetting that a reference database is required.
- Assuming eDNA is never affected by contamination.
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