PRELIMINARY STAGE, ROUND 2 SPEED RACE
2021
KNUST Senior High School: 44 points
Simms Senior High School: 43 points
Tuasi Senior High School: 31 points
QUESTION
For muscle contraction to occur, what molecules or ions must be readily available?
ANSWER: Calcium ions (Ca$^{2+}$), ATP, and the contractile proteins actin and myosin
SOLUTION
An action potential triggers release of Ca$^{2+}$ from the sarcoplasmic reticulum; Ca$^{2+}$ binds troponin, shifting tropomyosin to expose the myosin-binding sites on actin, and ATP powers the repeated myosin cross-bridge cycling that pulls the actin filaments inward (the sliding filament model).
PRACTICE QUESTIONS
1. Which ion triggers muscle contraction?
ANSWER: Calcium ions
2. Where are the calcium ions stored in muscle?
ANSWER: Sarcoplasmic reticulum
3. What is the role of ATP in muscle contraction?
ANSWER: Powers the myosin heads to pull on actin
4. Which protein forms the thin filaments?
ANSWER: Actin
5. Which protein forms the thick filaments?
ANSWER: Myosin
6. Which protein binds calcium?
ANSWER: Troponin
7. What does tropomyosin do at rest?
ANSWER: Covers the myosin-binding sites on actin
8. What is the sliding filament model?
ANSWER: Actin filaments slide over myosin so the sarcomere shortens
9. Which neurotransmitter starts contraction at the neuromuscular junction?
ANSWER: Acetylcholine
10. What kind of neurone stimulates skeletal muscle?
ANSWER: Motor neurone
11. Why does rigor mortis occur?
ANSWER: No ATP to detach the myosin heads
12. What builds up in tired muscles?
ANSWER: Lactic acid