gas exchange
1) Key Structures of the Human Respiratory System
- Lungs: Are the main organs in the respiratory system, containing the surfaces where gas exchange takes place
- Ribs and intercostal muscles: intercostal muscles are found between the ribs. Internal and external intercostal muscles work antagonistically in pairs to expand and contract the rib cage during breathing. The ribs also protect the lungs and heart from physical damage.
- Larynx: contains the vocal cords.
- Trachea: connects the throat to the bronchi. C-shaped cartilage rings are present to provide structural strength, keeping the trachea open so that air can pass through it.
- Bronchi: hollow tubes composed of cartilage rings that carry air from the trachea to the lungs. The bronchi splits into two tubes to enter the left and right lung, before branching further inside the lungs.
- Bronchioles: smaller tubes which branch off from the bronchi in the lungs, leading to the alveoli.
- Alveoli: where gas exchange occurs; comprised of tiny air sacs with a capillary network. Oxygen from the air diffuses into the capillaries, whilst waste carbon dioxide diffuses out. Waste gases are then breathed out.
2) List the features of Gas Exchange Surfaces in Humans
Property of surface |
Reason |
Thin (one cell thick) |
Short distance to diffuse, exchange more rapidly. |
Large surface area |
Many molecules can diffuse at once |
Moist |
Allow gases to dissolve before diffusing across the membrane. |
Well ventilated |
Regular fresh supplies of air maintains concentration gradient. |
Good blood supply |
Maintains concentration gradient by carrying away substances which have diffused already. |
3) State the differences in composition between Inspired and Expired Air
Inspired air |
Expired air |
21% oxygen 0.04% carbon dioxide 78% nitrogen water vapour varies to climate |
18% oxygen 3% carbon dioxide 78% nitrogen saturated water vapour |
- Oxygen: more in inspired air because it is needed be cells for respiration
- Carbon dioxide: more in expired air because it is made inside respiring cells and diffuses out from the gas exchange surface
- Water: more in expired air because gas exchange surfaces are kept moist, some of these moisture evaporates out.
Test for CO2: blow CO2 through limewater. CO2 will turn limewater cloudy.
4) Explain the Effects of Physical Activity on Rate and Depth of Breathing
- When exercise is carried out, muscles increase the rate of respiration to produce energy for muscle contraction.
- Aerobic respiration requires oxygen; thus, a greater amount of oxygen is demanded. In addition, a greater amount of carbon dioxide is produced as a waste substance, which diffuses into the blood.
- This increase in carbon dioxide in the blood is detected by the brain, which causes the rate of breathing to speed up, allowing gas exchange to happen more rapidly, expelling the carbon dioxide whilst taking in more oxygen.
- The heart rate is also increased to pump substances around the body more quickly in the blood.
* 5) Explain the Role of Ribs, Internal and External Intercostal Muscles and Diaphragm
- Ventilation is the act of moving air into and out of the lungs to allow gas exchange to occur.
- Breathing in: internal intercostal muscles relax whilst the external intercostal muscles contract, pulling the ribs up and out while the diaphragm flattens, pushing the abdominal muscles downwards. The volume in the thorax (chest cavity) increases, so air enters the lungs. Air diffuses into the lungs, rather than being ‘sucked’ in. This is because when the volume of the chest increases, there is a lower concentration of air inside the lungs compared to outside, thus air diffuses in.
- Breathing out: volume of thorax decreases, increasing pressure so that air is forced out. This is passive (does not require muscle contraction) except when forcibly breathing out, where the internal intercostal muscles contract.
* 6) Explain the Differences in composition between Inspired and Expired Air
- Inspired air: 21% oxygen, 0.04% carbon dioxide, lesser water vapour.
- Expired air: 16% oxygen, 4%carbon dioxide, more water vapour.
* 7) Investigate and Describe the Link between Physical Activity and Rate and Depth of Breathing
- When exercise is carried out, muscles increase the rate of respiration to produce energy for muscle contraction.
- Aerobic respiration requires oxygen; thus, a greater amount of oxygen is demanded. A greater amount of carbon dioxide is also produced as a waste substance, which diffuses into the blood.
- This increase in carbon dioxide in the blood is detected by the brain, which causes the rate of breathing to speed up, allowing gas exchange to happen more rapidly, expelling the carbon dioxide whilst taking in more oxygen.
- The heart rate is also increased to pump substances around the body more quickly in the blood.
- The rate of breathing can be measured by counting the number of breaths in one minute. The depth of breathing can be measured using a spirometer (a device that measures the volume of air inhaled and exhaled).
- To investigate the effects of exercise on breathing, record the rate of breathing for a few minutes when the person is at rest. After they do some exercise, record their rate of breathing every minute until it returns to the normal resting value.
8) Explain Role of Goblet Cells, Mucus and Ciliated Cells
- The lungs are also adapted to protect from foreign pathogens and particles.
- Goblet cells, found in the trachea and bronchi, are adapted to secrete mucus into the respiratory tract. Foreign pathogens and particles stick to this mucus.
- These are then moved upwards towards the throat by cilia (hair-like projections from some cells).
- Some mucus is swallowed, and pathogens are destroyed in the acidic conditions in the stomach.
9) Describe the Effects of Tobacco smoke on the Gas Exchange System
Smoking causes lung disease, heart disease and increased risks of several different types of cancer. Chemicals in cigarettes include:
Tar:
Nicotine:
Carbon monoxide:
Smoke Particles:
Tar:
- A carcinogen (a substance that causes cancer).
- Destroys the cilia: dust and microbes trapped by mucus cannot be carried away. This buildup of mucus and constant irritation on the lining of the bronchi can lead to bronchitis.
- Break down of the walls of the alveoli: causing them to merge together, creates an insufficient surface area to volume ratio, allowing less gas exchange, can lead to emphysema where less oxygen is carried in blood (making exercise difficult).
Nicotine:
- An addictive substance which also narrows blood vessels.
Carbon monoxide:
- Reduces the oxygen carrying capacity of the blood.
Smoke Particles:
- Irritate air passages, can cause inflammation and increase mucus production, leading to chronic bronchitis.
respiration
10) State the Uses of Energy in the body of Humans
- Uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature.
- Involves the action of enzymes in cells.
11) State the Word and Balanced Chemical Equation for Aerobic Respiration
- Chemical reactions that break down nutrient molecules in living cells to release energy.
- Catalyzed by enzymes.
- Takes place in mitochondria.
- The rate of respiration can be influenced by temperature and pH.
Release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen
Glucose + oxygen → carbon dioxide + water
\[C_{6}H_{12}O_{6}+6O_{2}\rightarrow 6CO_{2}+6H_{2}O\]
10) State the Word and Balanced Chemical Equation for Anaerobic Respiration
- Chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
- Catalyzed by enzymes.
- Takes place in cytoplasm.
Disadvantages of anaerobic respiration:
- Release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen.
- Produces poisonous lactic acid.
In muscles:
- Animal cells undergo anaerobic respiration during vigorous exercise as not enough oxygen is delivered to muscles.
- In this reaction, glucose is broken down to produce lactic acid, as well as releasing energy.
- This lactic acid builds up in muscles and causes muscle fatigue.
- Anaerobic respiration also produces an ‘oxygen debt’.
- To repay this, the lactic acid must be transported to the liver where it is broken down into carbon dioxide and water using oxygen.
- This is the reason why the breathing and heart rates remain high after exercise.
Glucose → lactic acid
In yeast (single-cell fungi):
- Microorganisms, such as yeast, also undergo anaerobic respiration. Yeast breaks down anaerobically to form alcohol and carbon dioxide instead of lactic acid.
Glucose → alcohol + carbon dioxide
\[C_{6}H_{12}O_{6}\rightarrow 2C_{2}H_{5}OH+2CO_{2}\]
