Breathing, Respiration and Gas Exchange

1. Breathing the process of getting oxygen into the lungs and carbon dioxide out of the lungs

• Allows for gas exchange whereby oxygen is absorbed from an area of high concentration (alveoli in lungs) into an area of low concentration (red blood cells) and carbon dioxide is absorbed from an area of high concentration (blood plasma) into an area of low concentration (alveoli in lungs) by diffusion

Inhalation	Exhalation
Intercostal muscles contract	Intercostal muscles relax
…which moves ribcage up and out	….which moves ribcage down and in
Diaphragm contracts -> moves down	Diaphragm relaxes -> moves up
↑volume of thoracic cavity -> pressure -> air enters lungs to equalize pressure	volume of thoracic cavity ->↑ pressure -> air exits lungs to equalize  pressure

• Pleural membranes and pleural fluid are slippery to reduce friction during breathing movements

How are alveoli adapted for gas exchange?

Feature	Function
Thin (one cell thick)	Short diffusion distance
Large surface area	Large volumes of gas can diffuse at once
Moist	Keeps cells alive
Well ventilated (constant fresh supplies of air)	Maintains concentration gradients for oxygen and carbon dioxide
Close to a blood supply	Efficient transport of gases to/from cells

2. Respiration the process of releasing energy through the breakdown of glucose in all living cells

Aerobic respiration	Anaerobic respiration
Requires oxygen	Does not require oxygen
Glucose + oxygen -> carbon dioxide + water + energy C6H12O6 + 6O2 -> 6CO2 + 6H20 + 2900kJ/mol (kilojoules per mole of glucose)	(In plants) Glucose -> carbon dioxide + ethanol + energy (In animals) Glucose -> lactic acid + energy
Produces a lot of energy	Does not produce a lot of energy
Involves mitochondria	Does not involve mitochondria

Breathing and exercise

When we exercise…

• ↑rate of breathing
• ↑depth of breathing
• ↑heart rate

…to deliver more oxygen and glucose to the muscles faster and remove carbon dioxide 

• Before, during and after exercise, an unfit person usually has a higher pulse rate than a fit person
• After exercise, a fit person recovers much faster than an unfit person

Respiratory diseases

Chemical	What it is	Long term effect on the body
Nicotine	Highly addictive drug	Affects the CNS and brain Makes the heart beat faster Narrows blood vessels Causes heart disease Raises blood pressure Stomach ulcers Stomach cancer Lung disease
Tar	Brown substance that collects in the lungs Contains thousands of chemicals, some of which are carcinogens.	Mouth, lips, throat and lung cancer Smoker’s cough Bronchitis Pneumonia
Carbon monoxide	Poisonous gas Taken up by the blood instead of oxygen.	Reduces the body’s capacity to carry oxygen as carbon monoxide combines with haemoglobin more easily than oxygen, Deposits fats in arteries which can lead to a heart attack or stroke Poor circulation can lead to gangrene and limb amputation
Irritants and toxic substances	Chemicals	Effects the respiratory tract Causes bronchitis Poor health Reduced energy

Experiment proving that exhaled air contains more carbon dioxide than inhaled air

(A, B and C refer to the tubes unless specified)

Close end of B. Breathe in. Air from atmosphere enters through A, passes through limewater and enters your mouth (cannot enter through B because closed).

Open end of B and close end of A. Breathe out. Exhaled air passes through limewater in test tube B and exits through B.

Limewater in test tube B (which contained the air you exhaled) turns milky much faster than in test tube A (which contained the air you inhaled).