D3.1.15 (HL)—Preventing polyspermy
Polyspermy is prevented after one sperm enters because the cortical reaction alters the zona pellucida and blocks further sperm binding.
- Syllabus
- First assessment 2025
- Objective
- D3.1.15
- Level
- HL
Exam analysis
Chance of appearing9%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper1
Typical marks1
Common command terms
- Identify
- Explain
Scoring notes
- Common mistake
- Mixing up the acrosome reaction that allows sperm entry with the cortical reaction that blocks other sperm.
Recent exam appearances
November 2023Paper1 ["HL"] · TZ240[ 1 ]D3.1.15 (HL)—Preventing polyspermy
May 2023Paper1 ["HL"] · TZ140[ 1 ]D3.1.15 (HL)—Preventing polyspermy
May 2022Paper1 ["HL"] · TZ137[ 1 ]D3.1.15 (HL)—Preventing polyspermy
November 2021Paper2 ["HL"] · TZ02(d)[ 2 ]D3.1.15 (HL)—Preventing polyspermy
May 2017Paper1 ["HL"] · TZ240[ 1 ]D3.1.15 (HL)—Preventing polyspermy
Practice this objective
Coverage 2012–2023 · Updated 16 Jul 2026
Concept essentials
- The acrosome reaction helps one sperm penetrate the zona pellucida.
- The cortical reaction follows sperm entry and blocks additional sperm.
- The zona pellucida is altered so further sperm cannot bind or enter.