Gas exchange

Question 1

Describe the structure of an insects gas exchange system?

Answer 1

Air moves into the tracheae through the spiracles. The tracheae then branches into tracheoles, which allows oxygen to diffuse directly into cells.

Question 2

What is a spiracle?

Answer 2

An opening in the exoskeleton of an insect that is permeable to gases, that has valves that allows for air to enter the insect and flow into the system of tracheae.

Question 3

How do insects overcome water lose during gas exchange?

Answer 3

If they are losing too much water they close their spiracles using muscles. They also have a waterproof, waxy cuticle layer and tiny hairs surrounding the spiracles that trap water to reduce the water potential gradient.

Question 4

How does the structure of an insects exchange system increase the rate of diffusion?

Answer 4

Thin tracheole walls, means there is a short diffusion distance.
The highly branched tracheoles increases the surface area for gas exchange.
Muscles can pump body and force air out in order to maintain a concentration gradient for gases.
Spiracles can open and close in order to prevent water loss.

Question 5

What are the adaptations of a leaf that improve gas exchange?

Answer 5

The air spaces within the spongy mesophyll layer increase the surface area to increase the rate of diffusion of carbon dioxide.
Thin tissue within the leaf and stomata means that there is a short diffusion pathway.
Carbon dioxide is used immediately by photosynthetic cells so a concentration gradient is made.

Question 6

How do plants control water loss?

Answer 6

Water enters the guard cells making them turgid, opening the stomata to allow gas exchange. If the plant loses too much water, then the guard cells lose water and become flaccid, which closes the pore.

Question 7

What are xerophytic plants?

Answer 7

They are plants that live in an environments that are warm, dry or windy, so water loss is a problem.

Question 8

Explain the adaptations of xerophytic plants?

Answer 8

Have sunken stomata that traps water vapour, reducing the concentration gradient between the leaf and the air.
Hairs on the epidermis that trap water vapour around the stomata.
Curled leaves have stomata on the inside that will protect them from the wind, which increases the rate of diffusion and evaporation.
Reduced number of stomata so that there are fewer places for water loss.
They have a thicker waxy cuticle that reduces water lose by evaporation.

Question 9

Describe the structure of fish gills?

Answer 9

Each gill is made of lots of thin plates called gill filaments and each filament is covered in lots of lamellae, which each are full of blood capillaries.

Question 10

Explain the adaptations of fish gill that allow for efficient gas exchange?

Answer 10

The many gill filaments that are all covered in lamellae gives them a large surface area.
The thin epithelium of the lamellae means that there is a short diffusion distance.
The countercurrent flow system helps maintain a concentration gradient.
The large number of capillaries in the lamellae means that there is a constant circulation to remove oxygenated blood.

Question 11

How does water reach the gills?

Answer 11

When a fish closes its mouth, the floor of the mouth rises. This decreases the volume of the mouth and increase pressure. The operculum is a flap covering the gills and when the mouth closes the volume of the opercular cavity increases and the pressure decreases. This ensures that water is forced over the gills.

Question 12

Explain inhalation?

Answer 12

The external intercostal muscles contact, so the ribcage moves upwards and outwards. The diaphragm contracts and flattens, which increases chest volume. The increase in volume causes the air pressure in the lungs to decrease. Air moves down the pressure gradient and flows into the lungs. It is an active process and requires energy.

Question 13

Explain exhalation?

Answer 13

External intercostal muscles relax, so the ribcage is pulled downwards and inwards. The diaphragm relaxes and becomes dome shaped. The volume of the chest decreases and the pressure increases. Air is forced down the pressure gradient and out of the lungs. It is a passive process and air is forced out of the lungs.

Question 14

How are alveoli adapted for gas exchange?

Answer 14

The lungs have a large number of alveoli, which means there is a large surface area available for oxygen and carbon dioxide to diffuse.
The alveoli walls are one, flattened cell thick walls, so there is a short diffusion distance.
The extensive capillary network means that there is a constant flow of blood that maintains a concentration gradient.

Question 15

Describe the structure of the trachea?

Answer 15

A flexible airway supported by rings of cartilage, that prevent it collapsing as the pressure falls when you breath in. The walls are made of muscle lined with ciliated epithelium and goblet cells.

Question 16

Describe the structure of the bronchi?

Answer 16

Two divisions of the trachea, and have a similar structure but the amount of cartilage reduces as the bronchi get smaller. They also produce mucus to trap dirt and have cilia to sweep the mucus towards the throat.

Question 17

Describe the structure of the bronchioles?

Answer 17

A series of branching subdivisions of the bronchi. The walls are made of muscle line with epithelial cells. The muscle allows them to constrict so they can control the flow of air in and out of the alveoli.

Question 18

Describe the structure of the alveoli?

Answer 18

Small air sacs with diameter, 100-300μm. Between each alveoli is collagen and elastic fibres lined with epithelium. The elastic fibres allow them to stretch as they fill with air. They spring back to expel the carbon dioxide rich air.

Question 19

What is the pulmonary ventilation rate?

Answer 19

The total volume of air moved into the lungs during a minute.

Question 20

What is tidal volume?

Answer 20

The volume of air normally taken in at each breath when the body is at rest.

Question 21

What is breathing rate?

Answer 21

The number of breaths taken in, in one minute.

Question 22

What equation links pulmonary ventilation rate, tidal volume and breathing rate?

Answer 22

Pulmonary ventilation rate (dm^3 min^-1) = tidal volume (dm^3) x breathing rate (min^-1)

Question 23

What is a restrictive lung disease?

Answer 23

One that makes it difficult to fully breath in, as it affects the elastic tissue. Severely reduces the forced expiratory capacity as breathing in is difficult but forced expiratory volume is less affected because breathing out is still normal.

Question 24

What is an obstructive lung disease?

Answer 24

They make it difficult to breath out as airways are blocked. Both the FVC and FEV are much lower than normal.

Question 25

Explain the lung disease tuberculosis?

Answer 25

Immune system builds walls around the bacteria forming tubercles. The infected tissue in the tubercles dies and the gaseous exchange surface becomes damaged, which decrease tidal volume. A reduced tidal volume means less air can be inhaled with each breath, so in order to take in enough air ventilation rate is increased. Symptoms include a persistent cough, coughing up blood and mucus, chest pains, shortness of breath and fatigue.

Question 26

Explain the lung disease fibrosis?

Answer 26

Caused by infections like TB or substances like asbestos or dust. The lung tissue is scarred, less elastic and thicker than normal. The lungs are less able to expand, so tidal volume is reduced and so is FVC. The rate of gas exchange is reduced due to slower diffusion across thick scarred tissue. There is a faster ventilation rate to get enough air into the lungs to oxygenate the blood. Symptoms include shortness of breath, a dry cough, chest pains, fatigue and weakness.

Question 27

Explain the lung disease asthma?

Answer 27

The cause is usually an allergic reaction to substances like pollen or dust. The smooth muscle lining contracts and a large amount of mucus is produced. The constriction of the airways makes it difficult to breath. Air flow in and out of the lungs is reduced, so less oxygen enters the alveoli and move into the blood. Symptoms include shortness of breath, wheezing and a tight chest. The symptoms can be relieved by a inhaler, which cause the muscles in the bronchioles to relax and open up the airways.

Question 28

Explain the lung disease enphysema?

Answer 28

Caused by smoking or long term exposure to air pollution. It causes inflammation, which attracts phagocytes to the area, which produce an enzyme which breaks down elastin. Elastin is elastic and helps the alveoli return to their original shape, so the loss of the elastin means the alveoli can’t recoil to expel air. It also leads to the destruction of the alveoli walls, which reduces the surface area, so rate of gas exchange decreases. It also causes an increased ventilation rate as thy try to increase the volume of air reaching the lungs. Symptoms include shortness of breath and wheezing.

Question 29

What are the effects of smoking on lung disease?

Answer 29

The chemicals in cigarettes include, tar, which is a carcinogen, nicotine, an addictive substance, which can narrow blood vessels and carbon monoxide, which reduces the oxygen-carrying capacity of the blood. Tar also destroys cilia, which carry the dust trapped in mucus away from the lungs, causing the build up of mucus and eventually bronchitis. Tar also affects the alveoli by breaking down the wall of the alveoli, causing them to merge. This reduces the SA:V ratio, which reduces the efficiency of gas exchange, which can lead to emphysema. Tar can also build up in the alveoli, which increase the diffusion distance.