Case Study:

During the annual Mumbai Marathon, thousands of runners participate in a 42 km race. Among them is Arjun, a 19-year-old student who has trained for months. As the race begins, his muscles start contracting repeatedly to maintain speed. These contractions require large amounts of energy in the form of ATP, which is produced during cellular respiration.

When Arjun runs, his breathing rate and heart rate increase significantly. This happens because his muscle cells need more oxygen and glucose to produce energy through aerobic respiration. During normal conditions, the body consumes about 250 mL of oxygen per minute, but during intense exercise like running, oxygen consumption can increase more than 10 times to meet the energy demand of muscles. 

The oxygen inhaled through the lungs is transported by red blood cells to the muscles. Inside the cells, glucose reacts with oxygen to release energy, carbon dioxide, and water. However, if the muscles require energy faster than oxygen can be supplied, they temporarily switch to anaerobic respiration, producing lactic acid as a by-product. The accumulation of lactic acid may cause muscle fatigue or cramps. 

After running several kilometers, Arjun begins breathing heavily. This increased breathing helps remove excess carbon dioxide and supply additional oxygen to the muscles. The body later uses extra oxygen to break down the accumulated lactic acid, a process known as repaying oxygen debt.

This real-life example shows how several life processes-respiration, transport of substances, and energy release from food-work together to maintain the body's functioning during intense physical activity like marathon running.

Questions

Section A - MCQs

1. During the marathon, Arjun’s breathing rate increases mainly because:

A. Muscles require more oxygen for energy production
B. The lungs become weaker during running
C. The body stops producing glucose
D. Oxygen is not needed during exercise

2. If oxygen supply to the muscles becomes insufficient during the race, the muscles will:

A. Stop producing energy
B. Switch to anaerobic respiration
C. Convert oxygen into glucose
D. Stop contracting immediately

3. The immediate cause of muscle fatigue during intense exercise is mainly due to:

A. Excess oxygen in muscles
B. Lack of glucose in blood
C. Accumulation of lactic acid
D. Formation of carbon dioxide

4. Which body system mainly transports oxygen from lungs to muscles during running?

A. Digestive system
B. Circulatory system
C. Nervous system
D. Excretory system

Section B - Short Answer Questions

1. Why does the heart rate increase when a person runs a marathon?

2. Explain why marathon runners breathe heavily even after finishing the race.

3. How does aerobic respiration help a runner maintain energy for long-distance running?

Section C - Long Answer Question

1.During a marathon, a runner suddenly feels muscle cramps after running continuously for a long time.

a) Explain the role of aerobic respiration in providing energy to muscles during running.
b) Why do muscle cells sometimes switch to anaerobic respiration?
c) Suggest two ways the body recovers after the race.

Answer Key

MCQ Answers

1. A - Muscles require more oxygen for aerobic respiration during exercise.
2. B - Muscles switch to anaerobic respiration when oxygen supply is insufficient.
3. C - Lactic acid accumulation causes muscle fatigue.
4. B - The circulatory system transports oxygen through the blood.

Short Answer Solutions

1.Heart rate increases to pump more oxygenated blood to working muscles and remove carbon dioxide produced during respiration.

2.After exercise, the body needs extra oxygen to break down accumulated lactic acid and restore normal conditions. This is known as oxygen debt.

3.In aerobic respiration, glucose reacts with oxygen to release a large amount of energy (ATP). This energy allows muscles to contract continuously during long-distance running.

Long Answer Solution

a) Role of aerobic respiration
Aerobic respiration occurs in muscle cells where glucose reacts with oxygen to produce ATP, carbon dioxide, and water. ATP provides energy for muscle contraction during running.

b) Switch to anaerobic respiration
When oxygen supply is insufficient during intense activity, muscles temporarily perform anaerobic respiration to produce energy quickly, resulting in lactic acid formation.

c) Recovery after race

• Increased breathing to supply extra oxygen
• Breakdown of lactic acid in muscles
• Rest and hydration to restore normal metabolic balance