humans gas exchange 2.46, 2.47, 2.48, 2.50

Question 1

what happens when we breathe in air?

Answer 1

gas exchange is located in the thorax

• when we breathe in air passes down the trachea, which is surrounded by c-shaped rings of cartilage keeping the trachea open and making swallowing easier
• trachea splits to form two bronchi, that lead to the lungs (which are also surrounded by cartilage rings)
• the bronchi divide into smaller tubes called bronchioles
• at the end of the bronchioles are alveoli, which are the site of gas exchange

Question 2

how does pleural membrane/ fluid protect the gas exchange system?

Answer 2

the pleural membrane - a layer between the lungs and the thorax walls
a thin layer of pleural fluid - this is in between the membranes
= together forming an air-tight seal and preventing the lungs from sticking to the thorax wall as they inflate and deflate

Question 3

what occurs during inhalation?

Answer 3

• diaphragm contracts, moving down and flattening
• intercostal muscles contract moving the rib cage up and out
  -increasing volume of the thorax
• decreasing the air pressure
  pressure in the thorax
  = air pressure is less than the atmosphere so air moves into the lungs

Question 4

what occurs during exhalation?

Answer 4

• diagram relaxes, moving up and doming
• intercostal muscles relax, moving rib cage down and in
• the volume of the thorax decreases
• increases air pressure
  = air pressure in the thorax greater than atmosphere, causing air to move out of the lungs

Question 5

what happens with gas exchange in the alveoli?

Answer 5

• a large number of alveoli = large surface area increasing diffusion
• surrounded by capillaries which carry deoxygenated blood to the alveoli and oxygenated blood away from alveoli = high concentration gradient, increasing diffusion rate
• walls of alveoli only one cell thick and capillary are directly next to alveoli = small distance, increasing rate of diffusion

Question 6

what structures are involved in the gas exchange system?

Answer 6

thorax:
- trachea
- bronchus
- bronchiole
- alveoli
- rib
- intercostal muscle
- diaphragm
- pleural membrane

Question 7

how do the ribs and intercostal muscles protect the gas exchange system?

Answer 7

• ribs protect organs
• the intercostal muscles between the ribs connect the bones and they are an important part of moving air in and out of the lungs (the diaphragm also helps move air in and out of lungs)

Question 8

how does oxygen/carbon dioxide get into the gas exchange system?

Answer 8

• oxygen diffuses from the air into the red blood cells where it binds with hemoglobin for transport
• carbon dioxide dissolves in the plasma, diffuses from blood into alveoli

Question 9

practical, investigating the composition of inhaled and exhaled air:

Answer 9

• compares the content of inhaled and exhaled air using a t-tube arrangement going from a mouthpiece into two conical flasks or boiling tubes
• inhaled and exhaled air bubbles though the indicator as the student breathes in and out
• you could use limewater or hydrogen-carbonate indicator to compare the inhaled and exhaled air

Question 10

practical, investigating the composition of inhaled and exhaled air:
what colour would a limewater indicator turn for inhaled and exhaled air?

Answer 10

inhaled air = stays colourless
exhaled air = turns milky white/cloudy

Question 11

practical, investigating the composition of inhaled and exhaled air:
what colour would a hydrogen-carbonate indicator turn for inhaled and exhaled air?

Answer 11

inhaled air = stays red
exhaled air = turns yellow

Question 12

practical, investigating the effects of exercise on breathing rate:

Answer 12

watch and count the number of breaths someone takes in 1 minute at rest
then ask the subject to exercise and count how many breathes they take in 1 minute after exercising

Question 13

why does our breathing rate increase during exercise?

Answer 13

• during exercise, our breathing rate increases, as well as the depth of each breath = this is a response to an increased concentration of carbon dioxide in the blood
• since our breathing rate increases, we excrete carbon dioxide more rapidly
• oxygen can also diffuse into the blood at a faster rate (as there is a higher concentration gradient)
• increase in heart rate, supplies more oxygen to the muscles for aerobic respiration
• our muscles might also respire anaerobically during exercise, therefore our breathing rate will remain high even after exercise to supply the extra oxygen needed to oxidise the lactic acid