Respiratory System, Breathing and Respiration (CCEA)

Gas exchange occurs in the alveoli which are found in the lungs.

When air is inhaled, oxygen diffuses from the alveoli into the blood to be used for respiration by the body’s cells.

Carbon dioxide is a waste product made by the body’s cells during respiration.

It diffuses from the blood into the alveoli and is exhaled.

Adaptations of the alveoli:

• Large surface area - many alveoli are present in the lungs with a shape that further increases surface area.

• Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance.

• Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.

• Permeable walls - allow gases to pass through.

• Good blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.

• A large diffusion gradient - breathing ensures that the oxygen concentration in the alveoli is higher than in the capillaries so oxygen moves from the alveoli to the blood. Carbon dioxide diffuses in the opposite direction.

Gas exchange occurs in the spongy mesophyll cells that surround air spaces in the leaves.

Adaptations of the leaf:

• Large surface area - spongy mesophyll cells are in contact with the air spaces for gas exchange.
• Thin walls - gases have a short diffusion distance.
• Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface.
• Permeable walls - allow gases to pass through.
• A large diffusion gradient – allows efficient gas exchange as carbon dioxide diffuses from high concentration in the air space into the cells, while oxygen moves in the opposite direction.

A lung model can be used to demonstrate the process of breathing.

Inhalation:

• The diaphragm (rubber sheet) moves down
• The thorax (glass jar) volume increases, lowering pressure
• Air enters, inflating the lungs (balloons) until pressure inside equals outside

Exhalation:

• The diaphragm moves up
• The thorax volume decreases, raising pressure
• Air exits, deflating the lungs until pressures balance

There are a few differences between the model and real breathing:

• The model lacks ribs and intercostal muscles, which move during real breathing to change thorax volume
• The diaphragm is really dome-shaped and flattens during inhalation, while in the model, a flat rubber sheet is pulled down
• The space between the lungs and wall of the thorax is very small but the model shows a large space

During exercise, muscle contraction requires more energy. Energy is released during respiration.

Your body needs more oxygen and produces more carbon dioxide due to increased respiration.

To handle this:

1. breathing rate increases: you take more breaths per minute to bring in more oxygen and remove carbon dioxide.
2. breathing depth increases: allowing more air to enter and leave your lungs.

This helps supply your muscles with more oxygen and gets rid of the extra carbon dioxide.

The harder you exercise, the faster and deeper you breathe.

The time taken for the breathing rate to return to normal is known as the recovery time.

This can be used as a measure of fitness as fitter people have a shorter recovery time.

Respiration is an exothermic reactions that occur in the mitochondria of cells to release energy.

This energy can then be used for

• heat
• movement
• growth
• reproduction
• active uptake

There are two types of respiration - aerobic and anaerobic.

Aerobic respiration happens in the presence of oxygen and releases more energy than anaerobic respiration.

Anaerobic respiration happens in the absence of oxygen.

It occurs during strenuous exercise. The build up of lactic acid causes muscle cramps.

Anaerobic respiration word equation (in mammalian muscle cells):

glucose → lactic acid + energy

Anaerobic respiration word equation (in yeast cells):

glucose → alcohol + carbon dioxide + energy

The alcohol produced is the basis of wine and beer production.

Similarities - both:

• Release energy
• Occurs in both plants and animals
• Catalysed by enzymes

Differences -

Temperature - procedure

1. Mix yeast, glucose, and water; leave for 30 minutes at 20°C.
2. Place 20 ml of yeast solution in a boiling tube.
3. Attach a bung with a delivery tube into water.
4. Place the boiling tube in a water bath at 20°C.
5. After 5 minutes, count the bubbles produced for 1 minute.
6. Repeat steps 2-5 at different temperatures (e.g., 30°C, 40°C, 50°C, 60°C).
7. Record the results in a table.

Results

Conclusion:

The higher the temperature, the faster the rate of respiration due to increased kinetic energy.

The optimum temperature was 40°C, where the most bubbles of carbon dioxide were produced. Above 50°C, enzymes become denatured, or the yeast is killed.

Independent variable : temperature / °C

Dependent variable: number of bubbles (rate of respiration)

Controlled variables: volume and concentration of yeast solution, time

Further factors to investigate: different sugars

1. Follow steps 1-5 from the previous experiment, using different sugars (eg, sucrose, fructose, lactose, maltose) or varying amounts (1g, 2g, 3g, 4g, 5g).

Ensuring anaerobic respiration

1. Boil the glucose solution to sterilise and remove oxygen.
2. Cool it before adding the yeast (high temperatures will kill it).
3. Add a layer of oil on top to prevent oxygen entry.