Comprehensive Notes on Breathing, Gas Exchange, and the Effects of Smoking

Organisms and Life Processes

A piece of meat is a tissue composed of muscle fibres.
Muscle fibres use ATP when they contract.
Investigation to find out if a solution of ATP will cause the contraction of muscle fibres.

Animal Physiology: Breathing and Gas Exchange

Learning Objectives

Describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli, and pleural membranes.
Understand the role of the intercostal muscles and the diaphragm in ventilation.
Explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries.
Investigate breathing in humans, including the release of carbon dioxide and the effect of exercise.
Understand the biological consequences of smoking in relation to the lungs and circulatory system, including coronary heart disease.

Respiration and Breathing

Cells get their energy by oxidising foods such as glucose during respiration.
Aerobic respiration requires a continuous supply of oxygen from the blood.
Carbon dioxide from respiration needs to be removed from the body.
In humans, gases are exchanged between the blood and the air in the lungs.
Respiration is the oxidation reaction that releases energy from foods such as glucose.
Breathing is the mechanism that moves air into and out of the lungs, allowing gas exchange to take place.
The lungs and associated structures are called the 'gas exchange system'.

The Structure of the Gas Exchange System

The lungs are enclosed in the chest or thorax by the ribcage and diaphragm.
The ribcage and diaphragm facilitate the movement of air into and out of the lungs.
Intercostal muscles connect each rib to the next.
The diaphragm separates the thorax from the abdomen and has a dome shape with a fibrous middle part and muscular edges.
Air is moved in and out of the lungs for gas exchange between the air and the blood.
The air passages of the lungs form a branching network called the bronchial tree.
Air enters through the nose or mouth, passes down the trachea (windpipe).
The trachea splits into two bronchi, one leading to each lung.
Each bronchus divides into smaller bronchioles, ending at microscopic air sacs called alveoli, where gas exchange occurs.
The walls of the trachea and bronchi contain cartilage rings that support the airways and keep them open during breathing.
The thorax is separated from the lungs by two thin, moist pleural membranes, forming an airtight seal.
The pleural cavity, filled with pleural fluid, lies between the pleural membranes and acts as lubrication to prevent the lungs from sticking to the chest wall during breathing.

Keeping the Airways Clean

The trachea and larger airways are lined with cells that secrete mucus, which traps dirt and bacteria.
Other cells are covered with cilia, which sweep the mucus and trapped particles out towards the mouth.
Smoking destroys the cilia, impairing this protection mechanism.

Ventilation of the Lungs

Ventilation means moving air in and out of the lungs.
This requires a difference in air pressure, moving from high to low pressure.
Ventilation depends on the thorax being an airtight cavity.
Breathing changes the volume of the thorax, altering the pressure inside.
Movements of the ribs and the diaphragm bring about ventilation.
Inhalation: External intercostals contract, pulling the ribs up and out. Diaphragm muscles contract, pulling the diaphragm down, increasing the volume of the chest, and lowering the pressure inside the thorax, causing air to enter the lungs.
Exhalation: External intercostals relax, and internal intercostals contract, pulling the ribs down and in. Diaphragm muscles relax, returning to a dome shape. The volume of the thorax decreases, and the pressure in the thorax is raised slightly above atmospheric pressure, forcing air out of the lungs.
Lungs are elastic, aiding exhalation by collapsing and emptying like a balloon.
During normal (shallow) breathing, the elasticity of the lungs and the weight of the ribs acting downwards is enough to cause exhalation.
Internal intercostals are only really used for deep (forced) breathing out, for instance when we are exercising.
Changes in volume and pressure during ventilation are key.
Analogy: A bicycle pump illustrates the relationship between volume and pressure.
It's important to avoid the common mistake of saying that the lungs force air in and out - pressure differences do.

Gas Exchange in the Alveoli

Atmospheric air vs. exhaled air:
- Nitrogen: Atmospheric air 78%, Exhaled air 79%
- Oxygen: Atmospheric air 21%, Exhaled air 16%
- Carbon dioxide: Atmospheric air 0.04%, Exhaled air 4%
- Other gases (mainly argon): Atmospheric air 1%, Exhaled air 1%
Exhaled air is warmer and saturated with water vapour.
Lungs absorb oxygen into the blood and remove carbon dioxide from it; this happens in the alveoli.
About 700,000,000 alveoli in the two lungs, giving a total surface area of $60m^2$ .
Alveoli, viewed under a microscope, look like bunches of grapes and are covered with tiny blood capillaries.
The percentage of a gas in a mixture can vary, even if the actual amount of the gas stays the same. Imagine you have a bottle containing a mixture of 20% oxygen and 80% nitrogen. If you used a chemical to absorb all the oxygen in the bottle, the nitrogen left would now be 100% of the gas in the bottle, despite the fact that the amount of nitrogen would still be the same. That is why the percentage of nitrogen in inhaled and exhaled air is slightly different.
Deoxygenated blood from the heart passes through capillaries surrounding the alveoli.
Blood is separated from the air inside each alveolus by only two cell layers.
Distance is less than a thousandth of a millimetre.
A thin layer of fluid lines the inside of the alveoli, originating from the blood.
Oxygen dissolves in this moist surface before passing into the blood.
Oxygen concentration is higher in the alveolus than in the blood, so oxygen diffuses into the blood.
Carbon dioxide concentration is higher in the blood than in the alveolus, so carbon dioxide diffuses out of the blood.
The blood leaving the capillaries has gained oxygen and lost carbon dioxide.
The heart pumps the oxygenated blood around the body, to supply the respiring cells.
Remember: ‘The alveolus has a wall made of cells’.

Activity 1: Practical - Comparing the Carbon Dioxide Content of Inhaled and Exhaled Air

Apparatus is used to compare carbon dioxide in inhaled and exhaled air.
A person breathes gently in and out through the middle tube.
Exhaled air passes out through one tube of indicator solution and inhaled air is drawn in through the other tube.
Limewater will turn cloudy faster in the 'exhaled' tube.
Hydrogen carbonate indicator changes from red to yellow.
Safety Note: Wear eye protection and breathe gently; do not blow. A clean mouthpiece must be used for each person.

Activity 2: Practical - An Investigation into the Effect of Exercise on Breathing Rate

Measure a person's breathing rate before and after exercise.
Sit quietly for five minutes, then count breaths per minute to find a steady resting rate.
Carry out vigorous exercise, like running on the spot, for three minutes.
Record breathing rate immediately after exercise and every minute until it returns to normal.
Safety Note: Wear suitable footwear for exercising and if doing step-ups use a sturdy secure low box or a PE bench.
Breathing rate rises during exercise because the body requires more oxygen and needs to remove carbon dioxide more quickly
The rate does not immediately return to normal due to oxygen debt (see Chapter 1).

The Effects of Smoking

Smoking upsets conditions needed for gas exchange.
Smoking is associated with lung cancer, bronchitis, and emphysema.
Smoking is a major contributing factor to coronary heart disease and ulcers.
Pregnant women who smoke are more likely to give birth to underweight babies.

Effects of Smoke on the Lining of the Air Passages

Cilia are destroyed by chemicals in cigarette smoke.
Reduced cilia numbers cause mucus to block air passages.
Smoke irritates the lining of the airways, stimulating more mucus secretion.
Sticky mucus blocking the airways is the source of ‘smoker’s cough’.
Irritation and infections from bacteria in the mucus can cause bronchitis.
Bronchitis blocks normal airflow, causing breathing difficulties.

Emphysema

Emphysema is a lung disease that kills about 20,000 people in Britain every year.
Smoking is the cause of one type of emphysema.
Smoke damages the walls of the alveoli, which break down and fuse together again.
This greatly reduces the surface area for gas exchange, which becomes very inefficient.
The blood of a person with emphysema carries less oxygen.
In serious cases, the sufferer is unable to carry out even mild exercise.
Emphysema patients often have to have a supply of oxygen nearby at all times.
There is no cure for emphysema, and usually, the sufferer dies after a long and distressing illness.

Lung Cancer

Links between smoking and lung cancer appeared in the 1950s.
A study compared lung cancer patients and a control group regarding their smoking habits.
A greater proportion of the lung cancer patients were smokers than in the Control patients.
Lung cancer patient non-smokers was 0.5%, patients who smoked more than 15 cigarettes a day was 25%.
Control group patient non-smokers was 4.5%, patients who smoked more than 15 cigarettes a day was 13%.
There seemed to be a connection between smoking and getting lung cancer.
Over 20 similar investigations in nine countries have revealed the same findings.
Nicotine is a strongly addictive drug.
Smoke contains over 7,000 chemicals, including carbon monoxide, arsenic, ammonia, formaldehyde, cyanide, benzene, and toluene.
More than 60 of the chemicals are known to cause cancer and are called carcinogens, contained in the tar.
Cancer happens when cells mutate and start to divide uncontrollably, forming a tumour.
The more cigarettes you smoke, the more the risk increases. For example, smoking 20 cigarettes a day increases the risk by about 15 times.
Giving up smoking improves your chance of survival.

Carbon Monoxide in Smoke

Carbon monoxide is a poisonous gas found in cigarette smoke.
It interferes with the blood's ability to carry oxygen.
Carbon monoxide combines with haemoglobin more tightly than oxygen, forming carboxyhaemoglobin.
This reduces the amount of oxygen carried around the body.
Smoking is also a major cause of heart disease
If a pregnant woman smokes, she will be depriving her unborn fetus of oxygen which has an effect on its growth and development and leads to the mass of the baby at birth being lower, on average, than the mass of babies born to non-smokers.

Some Smoking Statistics

It is estimated that there are over 1 billion smokers worldwide. In 2014 they consumed 5.8 trillion cigarettes.
Every year nearly 6 million people are killed by tobacco-related illnesses. If the current trend continues, by 2030 this will rise to 8 million deaths per year and 80% of these premature deaths will be in developing countries.
Smoking causes almost 80% of deaths from lung cancer, 80% of deaths from bronchitis and emphysema, and 14% of deaths from heart disease.
More than a quarter of all cancer deaths are attributable to smoking.
While demand for tobacco has steadily fallen in developed countries like the UK, cigarette consumption is being increasingly concentrated in the developing world.
9.6 million adults in the UK smoke cigarettes, 20% of men and 17% of women. However, 22% of women and 30% of men in the UK are now ex-smokers.
It is estimated that worldwide, 31% of men and 8% of women are smokers.
In China alone there are about 350 million smokers, who consume about one-third of all cigarettes smoked worldwide.
In China there are over a million deaths a year from smoking-related diseases. This figure is expected to double by 2025.
Tobacco farming uses up land that could be used for growing food crops. In 2012, 7.5 million tonnes of tobacco leaf were grown on almost 4.3 million hectares of land (an area larger than Switzerland).

Giving Up Smoking

The nicotine in tobacco is a very addictive drug, and causes withdrawal symptoms when people stop smoking.
There are various ways that smokers can be helped to give up their habit. One method is ‘vaping’, which involves inhaling a vapour containing nicotine from an electronic cigarette or e-cigarette.
Other methods use nicotine patches or nicotine chewing gum.

Activity 3: Practical: Test for Starch

A little starch is placed on a spotting tile.
A drop of yellow-brown iodine solution is added to the starch.
The iodine reacts with the starch, forming a very dark blue, or ‘blue-black’ colour.
Starch is insoluble, but this test will work on a solid sample of food, such as potato, or a suspension of starch in water.

Practical: Test for Glucose

Glucose is called a reducing sugar. This is because the test for glucose involves reducing an alkaline solution of copper (II) sulfate to copper (I) oxide.
A small spatula measure of glucose is placed in a test tube and a little water added (about 2 cm deep).
The tube is shaken to dissolve the glucose.
Several drops of Benedict’s solution are added to the tube, enough to colour the mixture blue.
A water bath is prepared by half-filling a beaker with water and heating it on a tripod and gauze.
The test tube is placed in the beaker and the water allowed to boil (using a water bath is safer than heating the tube directly in the Bunsen burner).
After a few seconds the clear blue solution gradually changes colour, forming a cloudy orange or ‘brick red’ precipitate of copper (I) oxide.
All other ‘single’ sugars (monosaccharides), such as fructose, are reducing sugars, as well as some ‘double’ sugars (disaccharides), such as the milk sugar, lactose.
However, ordinary table sugar (sucrose) is not. If sucrose is boiled with Benedict’s solution it will stay a clear blue colour.

Practical: Test for Protein

The test for protein is sometimes called the ‘biuret’ test, after the coloured compound that is formed.
A little protein, such as powdered egg white (albumen), is placed in a test tube and about 2 cm depth of water added.
The tube is shaken to mix the powder with the water.
An equal volume of dilute (5%) potassium hydroxide solution is added and the tube shaken again.
Finally two drops of 1% copper sulfate solution are added.
A purple colour develops. (Sometimes these two solutions are supplied already mixed together as ‘biuret solution’.)

Practical: Test for Lipid

Fats and oils are insoluble in water, but will dissolve in ethanol (alcohol).
The test for lipid uses this fact.
A pipette is used to place one drop of olive oil in the bottom of a test tube.
About 2cm depth of ethanol is added, and the tube is shaken to dissolve the oil.
The solution is poured into a test tube that is about three-quarters full with cold water.
A white cloudy layer forms on the top of the water.
The white layer is caused by the ethanol dissolving in the water and leaving the lipid behind as a suspension of tiny droplets, called an emulsion.