Aerobic Respiration and Breathing System

Respiration is the release of energy from digested food by the living cells of organisms.

Aerobic respiration is respiration that uses oxygen to release the energy from food for cell work and the rest is released as heat.

We need energy from food for movement, blood flow, growth, repair, protection, the action of the nervous system, reproduction and to keep our body temperature at 37°C. The products of aerobic respiration are carbon dioxide, water and energy.

Respiration Equation

Glucose + Oxygen

Carbon Dioxide + Water + Energy

ManPractivity 4

Demonstrate that Carbon Dioxide is Produced by Aerobic Respiration

1. Place equal volumes of limewater in two jars – carbon dioxide turns limewater milky.

2. Each jar has a two hole stopper with plastic tubing through each hole.

3. Draw ordinary air through one and pass exhaled air through the other again and again.

Results: ordinary air causes milkiness after many breaths; exhaled air causes milkiness after a few breaths.

Conclusion: we exhale much more carbon dioxide than we inhale therefore we make carbon dioxide.

To Demonstrate that Water is Produced by Aerobic Respiration.

all that can be demonstrated is that exhaled air contains more water vapour than ordinary air

1. Two clear jar are needed.

2. Each jar has a two hole stopper with plastic tubing through each hole.

3. Measure the mass of each jar with a top pan balance.

4. Place each jar in a container of crushed ice.

5. Draw ordinary air through one and pass breathed out air through the other again and again and again.

6. Note any changes in the jars and then measure the mass of each jar again.

Results: condensed water is present in both jars but more in the one through which breather out air passed through and this jar also showed a greater increase in mass.

(The liquid is water because it will turn dry white copper sulphate a blue colour.)

Conclusion: we exhale much more water vapour than we inhale therefore we make water.

To Demonstrate that Heat is Produced by Aerobic Respiration

1. Set up a vacuum flask with live water-soaked germinating pea seeds.

2. Set up another flask with dead water-soaked pea seeds.

3. Measure the temperature each day with a thermometer each day.

Results: the flask with dead seeds remained at room temperature (20° C), the flask with live seeds shows an increase in temperature.

Conclusion: respiration by living organisms produces heat.

The breathing system brings about gas exchange between air and blood. The gas exchange at the alveoli of the lungs involves the uptake of oxygen from the air into the blood and the excretion of carbon dioxide from the blood into the air. The air is rich in oxygen at about 21% oxygen but the air is very low in carbon dioxide at about 0.04%.

One in five molecules in air is oxygen but only one in two thousand five hundred is carbon dioxide.

The Structure of the Breathing System

Nasal cavity: warms, cleans and moistens the air. `

Trachea / windpipe: for the passage of air to and from the bronchi.

Cartilage rings: keep the trachea and bronchi permanently open.

Bronchi: for the passage of air to and from the lungs.

Bronchioles: for the passage of air to and from the alveoli.

Alveoli: gas exchange sites - have large surface area, 90 m2 .

Capillaries: gas exchange sites – large surface area in contact with the alveoli.

Diaphragm muscle: responsible for three quarters of the air drawn into the lungs.

Intercostal muscles: responsible for a quarter of the air drawn into the lungs.

Ribs and rib cage: protect heart and lungs plus play a role in breathing.

Air passage lining: The air passages are covered with a layer of mucus-producing cells.

Mucus: a sticky material used to trap dirt and germs in air.

Cilia (tiny beating hair-like cell structures) move the mucus to back of throat for swallowing.

Breathing Mechanism

Inhalation: active process

The diaphragm and intercostal muscles contract expanding the elastic lungs drawing air into the lungs.

Exhalation: passive process

The diaphragm and intercostal muscles relax and so the stretched elastic lungs recoil to a smaller size driving the air out.

The purpose of the breathing process is to maintain a high rate of gas exchange at the alveoli. By frequently bringing in fresh air to the alveoli, the difference in gas concentration between air and blood is kept high. The greater the difference in concentration, the faster the diffusion of the gases.

Gas exchange/transport of gases

Oxygen diffuses into blood from the air in the alveoli. The oxygen then enters the red blood corpuscles where it combines with haemoglobin. If there is lots of oxygen, haemoglobin will take it on becoming oxyhaemoglobin. Where there is a lack of oxygen, oxyhaemoglobin will let the oxygen go.

As the blood flows through the capillaries in the other organs of the body, the oxyhaemoglobin breaks down, releases oxygen. The oxygen then diffuses out of the capillaries to the respiring cells.

Carbon dioxide produced by the respiring cells diffuses into the blood capillaries. Most of the CO2 is carried in the plasma and some in red blood corpuscles. The CO2 is excreted from the blood at the alveoli of the lungs.

Alveoli adaptations for gas exchange

Large surface area: the greater the surface, the greater the exchange of gases.

Moist lining: so oxygen dissolves first, speeding up diffusion.

Walls one cell thick: the shorter the distance, the faster the diffusion.

Good blood supply: for fast transport of gases to and from lungs.

Protecting your lungs and health — don’t smoke

Tobacco smoke contains hundreds of harmful chemicals:

a) Nicotine: an addictive drug which damages heart, blood vessels and nerves.

b) Tar: can cause lung cancer.

c) Carbon monoxide: poisonous gas which reduces the amount of oxygen that can be carried in blood by blocking haemoglobin from taking on the oxygen.

Heart disease and lung infections are much more common in smokers.

90% of the people who die from lung cancer are smokers.

50% of smokers have a much-reduced life expectancy.

Smoking whilst pregnant can result in low birth weight or premature birth.

Bronchitis and ‘smoker’s cough’ is much more common in smokers as the cleaning beating hairs are destroyed by cigarette smoke and so the dirty mucus is not moved away efficiently. This much often become heavily colonized by bacteria.

The Human Breathing Rate

The physically and mentally relaxed human breathing rate is about 16 breaths a minute. Each inhalation brings in about half of litre of air. A similar volume of air is exhaled. Physical exercise greatly increases the breathing rate (it also increases the depth of breathing increasing from half a litre to four litres.

During physical exercise more energy is needed and so respiration must increase. More oxygen is needed to increase respiration and so rate and debt of breathing increases to supply the extra oxygen. The rate may increased beyond 80 a minute. Also, increased respiration means more carbon dioxide waste is produced and so increased rate and depth of breathing is essential to get rid of this extra carbon dioxide.

Blood and the Circulatory system

The circulatory system is composed of blood + blood vessels + the heart.

Blood: plasma + suspended solids (red blood corpuscles, white blood cells, platelets)

Blood vessels: arteries, capillaries, veins.

Heart: double pump keeping the blood flowing without stop

Functions of the blood circulatory system

1. Transport: O2 and food nutrients to all cells plus transport of wastes (CO2 , urea) to the excretory organs (lungs, kidneys).

2. Defence: protection against disease-causing organisms and cancer.

3. Temperature control: by altering blood flow through the skin.

4. Communication: transport of hormones to their target tissues.