1.1.6Structure and Functions in Living Organisms: Part 2
Heart Rate and Exercise — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 7 parts Lesson 7 of 24
Part 1 of 5Controlling the heart rate
Measuring heart rate
- Measuring heart rate Heart rate is the number of beats per minute (bpm), found by counting the pulse.
The pacemaker
- The pacemaker A group of cells in the right atrium wall, the pacemaker, sets the resting rate.
- It sends out electrical impulses that make the cardiac muscle contract in a coordinated way.
Factors that change the rate
- Factors that change the rate Exercise and the hormone adrenaline both increase heart rate.
Part 2 of 5Why heart rate rises during exercise
1Muscles work harder
- Muscles work harder Muscle cells respire faster to release more energy for contraction.
2Greater demand
- Greater demand The muscles need more oxygen and glucose, and produce more carbon dioxide to be removed.
3Nervous response
- Nervous response The nervous system signals the heart to beat faster and to pump more blood with each beat.
4Faster delivery
- Faster delivery More blood reaches the muscles per minute, supplying oxygen and glucose and carrying away carbon dioxide.
Part 3 of 5Anaerobic respiration and oxygen debt
1
During intense exercise, the oxygen supply may not meet the demand of the muscle cells.
2
The muscles then also respire anaerobically, producing lactic acid, while aerobic respiration carries on at the same time.
3
Lactic acid builds up and causes muscle fatigue.
4
After exercise, breathing and heart rate stay high for a while to supply oxygen.
5
The oxygen is used to break down the lactic acid, which is called repaying the oxygen debt.
Part 4 of 5Adrenaline and the fight or flight response
Adrenaline
Where from
- Where from It is a hormone released into the blood by the adrenal glands in times of stress or danger.
Effect on the heart
- Effect on the heart It increases heart rate, so more oxygen and glucose reach the muscles.
Purpose
- Purpose It prepares the body for action, either to fight or to flee.
Part 5 of 5Typical pattern of heart rate
| Stage | Heart rate | Reason |
|---|---|---|
| Resting | Low (about 60 to 80 bpm) | Pacemaker sets a steady rate; demand for oxygen is low |
| During exercise | Rises | Muscles need more oxygen and glucose and produce more carbon dioxide |
| Just after exercise | Remains high, then falls slowly | Oxygen is needed to remove lactic acid and repay the oxygen debt |
Key terms
| Term | Meaning |
|---|---|
| Heart rate | The number of times the heart beats in one minute. |
| Pacemaker | A group of cells in the right atrium that initiate the heartbeat. |
| Adrenaline | A hormone that increases heart rate and prepares the body for action. |
| Lactic acid | A product of anaerobic respiration in muscle cells. |
| Oxygen debt | The extra oxygen needed after exercise to break down lactic acid. |
Avoid these mistakes
1
Saying the heart beats faster to give muscles more energy. It delivers more oxygen and glucose, which cells use to release energy.
2
Forgetting that carbon dioxide removal is also a reason for the increased rate.
3
Stating that anaerobic respiration replaces aerobic respiration during exercise. Both can happen at once.
4
Thinking heart rate returns to normal the moment exercise stops; it stays high to repay the oxygen debt.
Last updated: