John Hay
John Hay Biomedical
Student Hub · Go Hornets 🐝
My ClassGlossaryAboutFeedback
Genetics of Disease (Medical Interventions)
Unit 1: Unit 1.1 Diagnostic Testing (ELISA prep)MI 1.1Biotechnology Research and Experiments

Build A Standard Curve

Use molecular-test evidence to build a standard curve accurately.

Builds on (2 levels back)inferred · high confidence
  • Control logic: Molecular results need positive and negative controls.
  • Signal interpretation: Bands, colors, curves, and E-values must be compared to a rule.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Use molecular-test evidence to build a standard curve accurately.

Step 1: Learn the key
Read the control [blank], compare the sample signal to the [blank], and report the result with one [blank].
Standard curve with dashed guides from absorbance to concentration
Step 2: Use the model
Read the figure, table, control, range, or protocol before choosing an answer.
Step 3: Name the limit
Say what the evidence can support and what it cannot prove yet.
Practice

An unknown sample reads an absorbance of 0.50. This value falls between two standards on the curve. Using the table, what concentration does the unknown have?

Reviewed
Standard concentration (ng/mL)Absorbance
00.00
10.20
20.40
30.60
40.80
Standard curve table of known concentrations and their absorbance readings
  1. A.2.5 ng/mL
  2. B.5 ng/mL
  3. C.2 ng/mL
  4. D.3 ng/mL
Show the worked solution ▾

Answer: A. 2.5 ng/mL

  1. Step 1: Bracket the reading: 0.50 is between absorbance 0.40 (2 ng/mL) and 0.60 (3 ng/mL).
  2. Step 2: Find the midpoint: 0.50 is exactly halfway between 0.40 and 0.60.
  3. Step 3: Read the concentration: Halfway between 2 and 3 ng/mL is 2.5 ng/mL.

Why it's right: 0.50 is midway between the 2 ng/mL and 3 ng/mL standards, so the unknown is 2.5 ng/mL.

Why the others miss:
  • B: Absorbance is not multiplied by 10; you read it off the curve.
  • C: 2 ng/mL would give 0.40, lower than the unknown's 0.50.
  • D: 3 ng/mL would give 0.60, higher than the unknown's 0.50.

Aligned to Biotechnology Research and Experiments · reading level ~grade 9

Where you'd see this
  • In Unit 1.1 Diagnostic Testing (ELISA prep), this skill turns class evidence into a result another person can check.
Careers that use this
Molecular Technologist: Uses build a standard curve to make a decision from evidence without overclaiming.
Video library
Watch: Build A Standard Curve
What is a Standard Curve?
ThePenguinProf
Guided notes

Fill these in as you work through the lesson.

Big idea: A standard curve plots known concentrations against the signal they produce, so you can read an unknown's concentration from its signal.
Key terms: write the meaning
  • Standard (a sample of known concentration):  
  • Standard curve (graph or table of known concentration vs signal):  
  • Interpolate (read a value that falls between two known points):  
  • Out of range (a reading higher or lower than all the standards):  
The rule

Find the unknown's   on the curve, then read across to the matching  ; if the reading is above the top standard,   and rerun.

Check yourself
  1. What concentration matches an absorbance of 0.40 on this curve? 
  2. How do you find a concentration when the reading falls between two standards? 
  3. Why can't you trust a reading that is higher than every standard? 
Work one example

Unknown absorbance = 0.50. It sits between the 2 ng/mL (0.40) and 3 ng/mL (0.60) standards, exactly halfway, so the unknown is 2.5 ng/mL.