FreeScienceLessons · AQA BiologyRespiration — aerobic and anaerobic
Key facts
Effects of exercise on the body
Breathing rate increases — more oxygen taken in, more CO₂ removed
Heart rate increases — more blood delivered to muscles per minute
Blood vessels dilate in muscles — more blood flow
More glucose and oxygen delivered to muscle cells → more aerobic respiration → more energy for movement
Glycogen stores in muscles are broken down to glucose
Oxygen debt and recovery
During intense exercise, anaerobic respiration produces lactic acid
Lactic acid builds up → muscle fatigue, pain, cramps
After exercise: breathing stays elevated to take in extra oxygen
Extra oxygen oxidises lactic acid (converts it to CO₂ and water in the liver)
The extra oxygen needed = the oxygen debt
Exam questions — 3 questions · 8 marks total
⚡ This module includes extended questions (4–6 marks). These are where most marks are lost. Read the hint carefully. Write in linked sentences. The AI will identify exactly which mark scheme points you missed.
1 markExercise responseAQA 8461 style
Why does heart rate increase during exercise?
A To cool the body down
B To deliver more oxygen and glucose to muscles and remove CO₂ faster
C To increase blood pressure permanently
D To produce more lactic acid
6 marksDescribe an investigationAQA Jun 2023 P2 style
A student wants to investigate how different types of exercise affect reaction time. Describe a method the student could use. Include control variables and how reliability would be ensured. (6 marks)
Hint: Cover: method for measuring reaction time, what exercise conditions you test, repeating, control variables. For Level 3 you must explain how you make results valid AND reliable.
+60 XP
1 markOxygen debtAQA 8461 style
What is the oxygen debt?
A The amount of oxygen used during exercise
B The deficit of oxygen in the blood during exercise
C The extra oxygen needed after exercise to break down lactic acid that built up during anaerobic respiration
D The amount of CO₂ produced during anaerobic respiration