11. Gas Exchange

Question 1

Features to allow maximum amount of gas exchange

Answer 1

• Large surface area to allow faster diffusion of gases across the surface
• Thin walls to ensure diffusion distances remain short
• Good ventilation with air so that diffusion gradients can be maintained
• Good blood supply to maintain a high concentration gradient so diffusion occurs faster

Question 2

Gas Exchange in Humans (Picture)

Answer 2

The alveolus is the gas exchange surface in humans

Question 3

Structure of the Breathing System

Answer 3

Question 4

The Intercostal Muscles

Answer 4

• Muscles are only able to pull on bones, not push on them
• This means that there must be two sets of intercostal muscles; one to pull the rib cage up and another set to pull it down
• One set of intercostal muscles is found on the outside of the ribcage (the externalintercostal muscles)
• The other set is found on the inside of the rib cage (the internal intercostal muscles)

Question 5

The Trachea

Answer 5

• Rings of cartilage surround the trachea (and bronchi)
• The function of the cartilage is to support the airways and keep them open during breathing
• If they were not present then the sides could collapse inwards when the air pressure inside the tubes drops

Question 6

The Function of Cilia & Mucus

Answer 6

• The passages down to the lungs are lined with ciliated epithelial cells
• Cilia comes from the Latin for eyelash, so unsurprisingly these cells have tiny hairs on the end of them that beat and push mucus up the passages towards the nose and throat where it can be removed
• The mucus is made by special mucus-producing cells called goblet cells because they are shaped like a goblet, or cup
• The mucus traps particles, pathogens like bacteria or viruses, and dust and prevents them getting into the lungs and damaging the cells there

Question 7

Percentage of composition of Nitrogen, oxygen and carbon di oxide in inhaled air

Answer 7

Question 8

State amount of difference in the amount of water paper present in inhaled air and exhales air.

Answer 8

Exhaled air tends to have more water vapour than exhaled air

Question 9

Difference in the % of CO2 and O2 in inhaled and exhaled air?

Answer 9

Lower % of oxygen in exhaled air - since body has used it up.

More of CO2 - Since body sending out oxygen

Question 10

diaphragm

Answer 10

• The diaphragm is a thin sheet of muscle that separates the chest cavity from the abdomen; it is ultimately responsible for controlling ventilation in the lungs
• When the diaphragm contracts it flattens and this increases the volume of the chest cavity (thorax), which consequently leads to a decrease in air pressureinside the lungs relative to outside the body, drawing air in.
• When the diaphragm relaxes it moves upwards back into its domed shape and this decreases the volume of the chest cavity (thorax), which consequently leads to an increase in air pressure inside the lungs relative to outside the body, forcing air out

Question 11

Inhalation

Answer 11

• The external and internal intercostal muscles work as antagonistic pairs (meaning they work in different directions to each other)
• During inhalation the external set of intercostal muscles contract to pull the ribs up and out:
• This also increases the volume of the chest cavity (thorax), decreasing air pressure, drawing air in

Question 12

exhalation

Answer 12

During exhalation, the external set of intercostal muscles relax so the ribs drop down and in: This decreases the volume of the chest cavity (thorax) increasing air pressure, forcing air out

Question 13

forced exhalation

Answer 13

• When we need to increase the rate of gas exchange (for example during strenuous activity) the internal intercostal muscles will also work to pull the ribs down and in to decrease the volume of the thorax more, forcing air out more forcefully and quickly – this is called forced exhalation
• There is actually a greater need to rid the body of increased levels of carbon dioxide produced during strenuous activity!
• This allows a greater volume of gases to be exchanged

Question 14

INHALATION (Picture)

Answer 14

Question 15

Exhalation (Picture)

Answer 15

Question 16

Using Limewater to Test for CO2 in Exhaled Air

Answer 16

• When we breathe in, the air is drawn through boiling tube A
• When we breathe out, the air is blown into boiling tube B
• Lime water is clear but becomes cloudy (or milky) when carbon dioxide is bubbled through it
• The lime water in boiling tube A will remain clear, but the limewater in boiling tube B will become cloudy
• This shows us that the percentage of carbon dioxide in exhaled air is higher than in inhaled air

Question 17

Explaining the Effect of Exercise on Breathing

Answer 17

• Frequency and depth of breathing increase when exercising
• Muscles are working harder and aerobically respiring more and they need more oxygen to be delivered to them (and carbon dioxide removed) to keep up with the energy demand
• If they cannot meet the energy demand they will also respire anaerobically, producing lactic acid
• After exercise has finished, the lactic acid that has built up in muscles needs to be removed as it lowers the pH of cells and can denature enzymes catalysing cell reactions
• It can only be removed by combining it with oxygen – this is known as ‘repaying the oxygen debt’
• This can be tested by seeing how long it takes after exercise for the breathing rate and depth to return to normal – the longer it takes, the more lactic acid produced during exercise and the greater the oxygen debt that needs to be repaid

Question 18

Carbon Dioxide Concentration & the Brain

Answer 18

• As respiration rates increase, more carbon dioxide is produced and enters the blood
• Carbon dioxide is an acidic gas in solution and so it can affect the working of enzymes in the cells and needs to be removed as quickly as possible
• As blood flows through the brain, the increase in carbon dioxide concentration stimulates receptor cells
• These send impulses to the muscles of the lungs, causing them to contract faster and more strongly
• This causes the frequency and depth of breathing to increase until the carbon dioxide concentration of the blood has lowered sufficiently