Grade 9 · Ions and Our Health · Ionic Compounds and Health
Ions in the Human Body
Electrolytes, nerve signals and why sports drinks exist.
Learning objectives
- Name key electrolytes in the human body.
- Explain the role of ions in nerve and muscle function.
- Evaluate claims made about electrolyte drinks.
NGSS alignment
MS-LS1-3
Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.
MS-PS1-1
Develop models to describe the atomic composition of simple molecules and extended structures.
HS-LS1-3
Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
MYP criteria
- Criterion D — Reflecting on the Impacts of Science
ENGAGE
Why can a small electric signal move your muscles?
EXPLAIN
Electrolytes at work
Sodium (Na+), potassium (K+), calcium (Ca2+) and chloride (Cl-) ions are called electrolytes. Cells pump them across membranes to create tiny voltage differences.
- Nerve impulses: rapid movement of Na+ into a cell and K+ out of it.
- Muscle contraction: Ca2+ released inside muscle cells triggers contraction.
- Hydration: ion balance controls how water moves between cells and blood.
Criterion D thinking
Sports drinks replace ions lost in sweat, but most are also high in sugar. Evaluating them means weighing evidence, marketing claims and health impacts together.
Practice questions
0/1 correct
Level 1
Which pair of ions is most directly involved in transmitting nerve impulses?
MYP criterion tasks
Level 4 · Criterion D
A sports drink advertises that it "replaces vital electrolytes". Evaluate this claim for a student who has just walked home from school.
Reflect & track
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