2 g) gas exchange

Question 1

2.32 Diffusion in gas exchange

Answer 1

the gases move by diffusion from an area of high concentration to an area of low concentration.

Question 2

2.33 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

Answer 2

CO2 diffuses in and O2 diffuses out of leaves through the stomata. CO2 is used in photosynthesis and produced by respiration, whereas O2 is used in respiration and produced in photosynthesis.

Question 3

2.41 explain how the structure of the leaf is adapted for gas exchange

Answer 3

Air Spaces
Increase the surface area inside the leaf to maximise gas exchange across the surface of the Spongy Mesophyll cells

Stomata
Allow exchange of CO2 and O2

Mesophyll cells
Have a large surface area and moist surfaces, which speeds gas exchange

Leaf shape
Leaves are thin, which increases diffusion speeds and leaves also have a very large surface area, which also increases diffusion speed.

Stomata distribution
Stomata are spread out over leaves, which means waste gases produced by the leaf can diffuse away quickly, this stops the build-up of excreted products, which would slow gas exchange

Question 4

2.35 describe the role of stomata in gas exchange

Answer 4

The stomata control gas exchange in the leaf. Each stomata can be opened or closed, depending on how turgid (enlarged and swollen with water) its guard cells are.

Question 5

Humans
2.36 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes

Answer 5

Once air is breathed in through the mouth or nose it travels down the trachea. The trachea splits into two- one going into the left lung and one going into the right lung- these pipes are called bronchi. Each bronchus will then divide further into many bronchioles: each ending in a sac called an alveoli.

The trachea and bronchi have walls of muscle that are supported by cartilage. The cartilage is in partial rings so that the tubes can be moved in any direction. Cilia on the walls move mucus out of the breathing system and into the stomach.

Question 6

2.37 understand the role of the intercostal muscles and the diaphragm in ventilation

Answer 6

Breathing in
The intercostal muscles contract
The ribs move up and out
The diaphragm contracts and moves down
The trachea carries air towards the lungs; it splits into two bronchi- one leading to the left lung, and one o the right- which then split into even smaller tubes, called bronchiles; these end in alveoli where gas exchange takes place.
The pleural membranes prevent friction.

Breathing out
The intercostal muscles relax
The ribs drop down
The diaphragm also relaxes and moves upward
These things reduce the space inside the lungs, pushing the air out.

Question 7

2.38 explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

Answer 7

• The alveoli are thin, which allows gases to diffuse through them easily.
• They are small and there are many of them meaning there is a large surface area through which much gas can diffuse at once. It also means that there is a lot of surface in contact with the blood stream for gassiest diffuse into.
• Alveoli have a moist lining for gases to dissolve into

Question 8

2.39 understand the biological consequences of smoking in relation to the lungs and the circulatory system, including coronary heart disease

Answer 8

Tar in the cigarettes blocks the lungs, which can then cause lung cancer as its a carcinogen and can also emphysema.

• Carbon monoxide provides less oxygen for the body, as they join onto the red blood cells, stopping the red blood cells from forming oxyhemoglobin, less oxygen then is able to reach the cells to be used in respiration.
• smoke removes the cilia (tiny hairs), which keep the lungs clean allowing them to be clogged up with mucus and doesn’t stop pathogens and bacteria. - bronchitis
• smoking hardens the batteries, which constricts blood flow and puts strain on the heart, which results in coronary heart disease.

Question 9

2.40 describe experiments to investigate the effect of exercise on breathing in humans.

Answer 9

During exercise cells respire more quickly (to provide more energy for movement) this means oxygen has to be delivered more quickly and carbon dioxide taken away more quickly. As a result of this the lung muscles contract and relax more rapidly and the heart beats faster.

Measure a persons breaths per 10 seconds when stationary.
Then after one minute after running at 5mph then at two minutes and so on.
You will find a linear relationship as described above between the two.