Indiana Science HS-AP10-4

ScienceGrades 9–12Absorption and Excretion, the Digestive System

The Standard

Differentiate between metabolic and respiratory acidosis and alkalosis.

Indiana Academic Standards for Science (2023) · Absorption and Excretion, the Digestive System

Teacher's field guide

What Students Need to Do: Students decide whether a blood pH is too low or too high. They use CO2 and bicarbonate readings to tell whether the cause is respiratory or metabolic.
What Mastery Looks Like: Given pH, CO2, and bicarbonate readings, students can name all four disorders and point to the reading that explains each one. They can explain why retained CO2 lowers pH and why repeated vomiting can raise it.
Common Misconceptions: Students may label every low pH reading as metabolic acidosis, even when high CO2 is the cause. They may think fast breathing traps CO2 or that vomiting causes acidosis because stomach acid is involved.
How to Assess It: Give students normal ranges: pH 7.35 to 7.45, CO2 35 to 45, and bicarbonate 22 to 26. Ask them to label and justify four cases with (pH, CO2, bicarbonate) readings: (7.30, 55, 24), (7.30, 40, 18), (7.50, 28, 24), and (7.50, 40, 32).

Lesson moves

Give each pair a straw and cup of bromothymol blue solution; have them bubble exhaled air through it and record the color change.
Ask students to write why rapid breathing during a panic attack can raise blood pH.
Play four-corner diagnosis: read pH, CO2, and bicarbonate values; students move to labeled corners and defend their choice with one reading.
Post two clinic notes, repeated vomiting and shallow breathing after opioid use; have students identify the likely pH disorder in each.

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