Factors Affecting Heart Rate and Respiratory Rate (VCE SSCE Biology): Revision Notes

Factors Affecting Heart Rate and Respiratory Rate

Introduction to homeostasis and exercise

For cells to work effectively, they need consistent conditions around them. However, our bodies constantly experience different environments and situations. To keep our internal environment as stable as possible, our bodies use various processes to maintain homeostasis.

Homeostasis is the maintenance of a stable internal environment despite external changes.

Exercise is one factor that significantly affects the environment of our cells. During physical activity, muscle cells carry out increased amounts of cellular respiration. This means they:

• Use more oxygen than usual
• Produce more carbon dioxide than when at rest

To maintain homeostasis during exercise and ensure cells function normally, our bodies must correct these changes as quickly as possible.

The role of body systems in homeostasis

Two internal systems are crucial for maintaining homeostasis during and after exercise:

The circulatory system:

• Transports oxygen and nutrients throughout the body to reach all cells
• Removes waste products that cells create
• Responds to increased demands during exercise by increasing heart rate

The respiratory system:

• Oxygenates the blood
• Removes carbon dioxide from the body
• Responds to exercise by increasing breathing rate

When exercise increases oxygen consumption by cells, both systems must work together to compensate for these increased demands and the increased production of waste products.

Investigating the effects of exercise

Aim

To observe and record how exercise affects heart rate and respiratory rate.

Materials

• 1 stopwatch
• Groups of 3-4 people
• One volunteer per group

Method

Part A: Measuring resting rates

Finding the pulse:

There are two main locations where you can measure pulse:

Radial pulse (wrist):

• Place two fingers on the groove in the wrist below the thumb
• Move your fingers around until you feel a slight pulsation
• This is the radial artery

Carotid pulse (neck):

• Place two fingers on the neck, roughly near the trachea (which can be found near the Adam's apple)
• Move your fingers around until you feel a slight pulsation
• This is the carotid artery

Taking measurements:

1. Have your volunteer sit quietly, breathing calmly
2. One group member should find and count the pulse for 15 seconds
3. Multiply this number by four to calculate heart rate in beats per minute
4. Simultaneously, another group member should count how many breaths the volunteer takes in the same 15 seconds
5. Multiply this by four to get respiratory rate in breaths per minute
6. Record both measurements in your results table

Part B: Low-intensity exercise (Exercise A)

1. Have the volunteer perform as many push-ups or sit-ups as they can in 20 seconds
2. Immediately after finishing, measure pulse and respiratory rate (using the same pulse location as before)
3. Record the results
4. Allow the volunteer to rest for one minute, then repeat measurements
5. Continue recording measurements at one-minute intervals for a total of five minutes
6. Allow the volunteer to rest for another five minutes before the next exercise

Part C: High-intensity exercise (Exercise B)

1. Once recovered, have the volunteer jog on the spot as fast as they can for two minutes
2. Immediately after finishing, measure pulse and respiratory rate
3. Record the results
4. Allow the volunteer to rest for one minute, then repeat measurements
5. Continue recording measurements at one-minute intervals for a total of five minutes
6. Give your volunteer a drink of water

Results

Record your data in a table like this:

Time point	Heart rate (beats per minute)	Respiratory rate (breaths per minute)
Resting
Immediately post-Exercise A
1-minute post-Exercise A
2-minute post-Exercise A
3-minute post-Exercise A
4-minute post-Exercise A
5-minute post-Exercise A
Immediately post-Exercise B
1-minute post-Exercise B
2-minute post-Exercise B
3-minute post-Exercise B
4-minute post-Exercise B
5-minute post-Exercise B

After collecting your data, create a line graph showing how heart rate and respiratory rate change over time for both exercises.

Understanding the results

The connection to cellular respiration

During exercise, cells need more energy, which they produce through aerobic cellular respiration. The chemical formula for this process is:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

This shows that:

• Glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) and oxygen ($\text{O}_2$) are needed as reactants
• Carbon dioxide ($\text{CO}_2$), water ($\text{H}_2\text{O}$), and energy (ATP) are produced

During exercise, cells use more oxygen and produce more carbon dioxide, which is why both heart rate and respiratory rate increase.

Homeostasis and negative feedback

The body maintains homeostasis largely through negative feedback loops. This means:

• When a change occurs (stimulus), the body detects it
• The body responds to counteract the change
• Once conditions return to normal, the response stops

In the context of exercise:

• Stimulus: Increased carbon dioxide and decreased oxygen in blood
• Response: Increased heart rate and respiratory rate
• Result: Oxygen levels increase and carbon dioxide levels decrease, returning to normal

Variables in this investigation

Independent variable: The type and intensity of exercise (Exercise A vs Exercise B)

Dependent variables:

• Heart rate (beats per minute)
• Respiratory rate (breaths per minute)

Control: The resting measurements provide a baseline for comparison

Expected observations

You should notice:

• Both heart rate and respiratory rate increase immediately after exercise
• High-intensity exercise (Exercise B) causes greater increases than low-intensity exercise (Exercise A)
• Both rates gradually return to resting levels during the recovery period
• The more intense the exercise, the longer it takes to return to resting levels

Other physiological changes

During exercise, you might also observe:

• Increased sweating (to regulate body temperature)
• Flushed skin (due to increased blood flow to the skin)
• Deeper breathing (to take in more oxygen per breath)
• Tiredness in muscles (due to accumulation of metabolic waste products)

Exam tips

Remember!