Developmental Biology: How One Cell Builds a Body
From fertilization to regeneration, how a single cell turns into an animal and what that reveals about evolution.
Developmental Biology · 50 questions
Try 3 questions
1. Why does only one sperm normally fertilize a human egg?
- The egg blocks others after the first
- Sperm attack and disable their rivals
- Only one sperm is released each time
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Answer: The egg blocks others after the first
After fusion, the egg changes its membrane and releases enzymes that harden its coat, preventing extra sperm from entering.
2. Of the hundreds of millions of sperm released, roughly how many get near the egg?
- Tens of millions
- A few hundred at most
- About half of them
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Answer: A few hundred at most
Acidity, mucus, immune cells and wrong turns eliminate almost all sperm long before the fallopian tube.
3. Besides its DNA, what key structure does a human sperm contribute to the embryo?
- Most of the embryo's mitochondria
- A centriole that organizes division
- The yolk that feeds the embryo
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Answer: A centriole that organizes division
In humans the sperm's centriole builds the first spindle; the egg supplies the mitochondria and nutrients.
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