gas exchange in humans

Question 1

Features of Gas Exchange Surfaces

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 surface in humans is

Answer 2

The alveolus

Question 3

Answer 3

Question 4

Several of the features of alveoli that make them suited to their function are the same as those that make

because all of these structures are involved in

Answer 4

villi suited to their function; or root hair cells suited to their function.

-transporting substances across their surfaces – by diffusion, active transport, osmosis or a combination.

Question 5

Answer 5

Question 6

Answer 6

Question 7

The Intercostal Muscles

Answer 7

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 external intercostal muscles)

The other set is found on the inside of the rib cage (the internal intercostal muscles)

here are two sets of intercostal muscles: the external, on the outside of the rib cage, and the internal, on the inside of the rib cage

Question 8

Answer 8

Question 9

The Trachea

Answer 9

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 may collapse inwards when the air pressure inside the tubes drops

Question 10

The Function of Cilia & Mucus

Answer 10

he 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 11

The function of cilia and mucus

Answer 11

• The mucus is produced by goblet cells and traps bacteria, dust, particles
• The cilia beat

and push the mucus away from the lungs towards the throat

Question 12

inhalation

Answer 12

During inhalation the external set of intercostal muscles contract to pull the ribs up and out

The external and internal intercostal muscles work as antagonistic pairs

The external and internal intercostal muscles work as antagonistic pairs

Question 13

exhalation

Answer 13

Question 14

Inhalation & Exhalation basics

Answer 14

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

During exhalation the internal set of intercostal muscles contract to pull the ribs down and in

The point of this is to increase or decrease the volume of the chest cavity (thorax) so that the lungs can follow and increase or decrease in size

The muscle surrounding the diaphragm also helps to increase and decrease the volume of the thorax

This means that when we are doing ‘quiet breathing’ there may be no noticeable chest movement as the lungs are ventilated mainly by changes in the shape of the diaphragm

When we need to increase the rate of gas exchange (for example during strenuous activity) the intercostal muscles will also work to pull the ribs up and out and increase the volume of the thorax more

This is because we now require a greater volume of gases to be exchanged, so we need to inflate the lungs quicker and almost to their maximum

As the volume of the thorax increases, the pressure inside the lungs decreases

Once it drops below the air pressure outside the lungs, air will be forced in

During exhalation, the reverse occurs; volume decreases, pressure in the thorax increases and air is forced out

Question 15

be able to explain in detail what is happening when breathing in and out to:

Answer 15

the external and internal intercostal muscles

the rib cage

the diaphragm

the volume and the pressure of the lungs

Question 16

inhalation OR …(breathing in)

exhalation OR ..(breathing out)

Answer 16

• inspiration
• expiration

Question 17

Differences between Inhaled & Exhaled Air

Answer 17

Question 18

Reasons for Differences in Inhaled & Exhaled Air

Answer 18

Question 19

Using Limewater to Test for CO2 in Exhaled Air

Answer 19

We can use the apparatus below to investigate the difference between the amount of carbon dioxide in inhaled air and exhaled air

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 21

Investigating the Effect of Exercise on Breathing

Answer 21

Exercise increases the frequency and depth of breathing

This can be investigated by counting the breaths taken during one minute at rest and measuring average chest expansion over 5 breaths using a tape measure held around the chest

Exercise for a set time (at least 3 minutes)

Immediately after exercising, count the breaths taken in one minute and measure the average chest expansion over 5 breaths

Following exercise, the number of breaths per minute will have increased and the chest expansion will also have increased

Question 22

Explaining the Effect of Exercise on Breathing

Answer 22

Frequency and depth of breathing increase when exercising

This is because 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 23

Carbon Dioxide Concentration & the Brain

Answer 23

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