3.1.1 Exchange surfaces

Question 1

Explain the need for specialised exchange surfaces in multicellular organisms

Answer 1

Specialised exchanged surfaces are needed in multicellular organisms because:
* Metabolic activity is much higher than single celled organisms as organisms are larger
* Smaller Sa:V ratio as they are bigger organisms
* So less sa for diffusion of nutrients
* And a greater diffusion distance due to a greater volume

Demand is not being met through diffusion alone as it is too great

Question 2

Surface area of a sphere equation

Answer 2

Sa = 4 pi r^2

Question 3

Volume of a sphere equation

Answer 3

V= 4/3 pi r^3

Question 4

The bigger the organism……..

Answer 4

the smaller the sa:v ratio

Question 5

Name the features of a good exchange surface

Answer 5

1. Large surface area
2. Thin layers
3. Good Blood supply
4. Ventilation

Question 6

Why does a large surface area make for a good exchange surface?

Answer 6

• Provides area for exchange
• Overcomes Sa:V ratio of larger organisms
• Eg, root hair cells, villi

Question 7

Why do thin layes make for a good exchange surface?

Answer 7

• Shorter diffusion distance
• Increases the speed and efficiency
• Examples: alveoli, villi

(instead of saying efficiency in EQ state what the function of the surface is actually eg, alveoli= increasing the speed it moves O2 in and CO2 out etc)

Question 8

Why does a good blood supply make for a good exchange surface?

Answer 8

• Steeper concentration gradient
• Faster diffusion
• Substances are constantly delivered and removed from surface
• Examples: alveoli, gills, villi

Question 9

Why does good ventillation (gases) make for a good exchange surface?

Answer 9

• Maintains concentration gradient
• Makes process more efficient (specify the process)
• Example: Fish gills- ventillation means a constant flow of dissolved gases in water
• Example: Villi

Question 10

Why do mammals need a gaseous exchange system?

Answer 10

• They are relatively big with a small SA:V ratio and a large volume of cells
• High Metabolic rate
• Because they are active and maintain their body temp independent of the environment
• So, need lots of oxygen for cellular respiration
• And, produce CO2 which needs removed

Question 11

Important features of the nasal cavity

Answer 11

• Large SA with good blood supply which warms the air to body temperature
• Hairy lining which secretes mucus to trap dust and bacteria (protecting lung tissue from irritation and infection)
• Moist surfaces which increases humidity of incoming air, reducing evaporation from exchange surfaces

Question 12

Trachea function (summary)

Answer 12

Tube which carries air into lungs, branches into two bronchi

Question 13

Trachea tissues related to function

Answer 13

• Supported by C-shaped rings of cartillage preventing collapse during inhalation
• C-shaped to allow passage of food down oesophagus
• Lined with ciliated epthilium
• Mucus is released by goblet cells
• Mucus traps pathogens
• Cilia waft mucus to top of airway
• Contain smooth muscle and elastic fibres

Question 14

Bronchi function (summary)

Answer 14

Two tubes carry air into left and right lung which branches into bronchioles

Question 15

Bronchi structure related to function

Answer 15

• Narrower than trachea
• Full rings of cartillage to prevent collapse during inhalation
• Lined with ciliated epithelium calls
• Goblet cells release mucus
• Mucus is wafted by cilia away from bronchioles and alveoli
• Contains smooth muscle and elastic fibres

Question 16

Bronchioles function (summary)

Answer 16

Many tubules carrying air and the smallest tubules terminate into alveoli

Question 17

Bronchioles structure related to function

Answer 17

• Larger tubes contain cartillage but small tubes don’t
• Wall comprised (mainly) of smooth muscle and elastic fibres
• Smooth muscle contracts to constrict airways
• When muscle stops contracting, elastic fibres recoil to return bronchioles to original diameter (dilated)
• Also lined with ciliated epithelium and goblet cells

Question 18

Alveoli function (summarised)

Answer 18

Air sacs, site of gaseous exchange

Question 19

Alveoli structure related to function

Answer 19

• Composed of squamous epithelium which is one cell thick
• So, very short diffusion distamce
• Contain elastic fibres
• These stretch when inhaling and recoil to push air out when exhaling
• Also contains collagen

Question 20

Adaptations of alveoli for effective gas exchange

Answer 20

1. Large surface area
2. Thin layers- alveoli + capillaries are one squamous epithelial cell thick so diffusion distance between air in alveolus and blood in capillary are short
3. Good blood supply- constant flow of blood through capillaries brings carbon dioxide and carries off oxygen, maintaining a steep conc gradient
4. Good ventillation- breathing moves air in and out of alveoli mainting steep diffusion rate between blood and air

Question 21

Describe inspiration/inhalation in mammals

Answer 21

1. External intercostal muscles contract moving the ribcage upwards and outwardss
2. Diaphragm muscle contracts and moves downwards
3. Volume of the thorax is increased by these 2 actions
4. Pressure in the chest therefore decreases
5. Pressure in thorax is now lower than pressure outside so air is drawn into lungs

Question 22

Describe expiration/exhalation

Answer 22

1. External intercostal muscles relax so the rib cage falls under its own weight due to gravity
2. Diaphragm muscle relaxes and moves upwards
3. Volume inside the thorax/chest cavity decreases due to these 2 actions
4. Pressure inside chest therefore increases
5. So, air moves out of lungs as pressure inside thorax is greater than outside

Question 23

Explain how the lungs are specifically adapted to gas exchange

Answer 23

• Pulmonary vein continually removes oxygenated blood
• Pulmonary artery bring deoxygenated blood to the lungs
• Concentration gradient is maintained
• Squamous epithelium cells in alveoli are flattened so diffusion path is short
• RBC carry oxyegn in haemoglobin
• Oxygen moves into blood by diffusion down conc gradient
• Carbon dioxide moves out of alveoli by diffusion down conc gradient
• Frequent ventillation keeps oxygen high and carbon dioxide low

Question 24

Define tidal volume

Answer 24

Volume of air that moves in OR out in each resting breath

Question 25

Define vital capacity

Answer 25

The volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest breath in

Question 26

Define inspiratory reserve volume

Answer 26

Maximum volume breathed in over and above normal tidal

Question 27

Expiratory reserve volume

Answer 27

The extra air that can be forced out of the lungs over the normal tidal volume breathed out

Question 28

Residual volume

Answer 28

Volume of air left in the lungs when you have exhaled as hard as possible. Cannot be directly measured

Question 29

Breathing rate

Answer 29

Number of breaths per miniute

Question 30

Ventilation rate

Answer 30

Tidal volume x breathing rate (min^-1)

Question 31

Oxygen uptake

Answer 31

The volume of oxygen absorbed by the blood. It is assumed that this is equal to the volume of carbon dioxide absorbed by the soda lime in a spirometer

Question 32

Describe the relationship between tidal volume, breathing rate and oxygen uptake

Answer 32

As breathing rate increases, oxygen uptake increases because more oxygen is being breathed in. During excercise tidal volume increases as does the depth of breathing and the rate of breathing.
Ventillation rate = breathing rate x tidal volume

Question 34

What are tracheae + how are they adapted?

Answer 34

• Tracheae are air filled tubes branching throughout the body
• Reinforced with chitin to prevent collapse
• There are multiple throughout the body so the SA is higher

Question 35

What are tracheoles and how are they adapted?

Answer 35

• Tracheoles are fine branches of tracheae that deliver gases to cells
• Penetrate directly into tissues to reduce the diffusion distance of gases
• Have thin walls to reduce the diffusion distance of gases
• Highly branched to maximise SA
• Not reinforced with chitin to allow gas exchange to occur
• Fluid at ends of tracheoles (tracheal fluid) so all oxygen can dissolve and aid diffusion and reduce water loss

Question 36

Describe how gas exchange occurs in insects

Answer 36

1. Air enters the tracheal system through open spiracles.
2. Air moves into larger tracheae and diffuses into smaller tracheoles.
3. Tracheoles branch throughout the body, transporting air directly to cells.
4. Oxygen dissolves in water in tracheal fluid and diffuses down its concentration gradient from tracheoles into body cells.
5. Carbon dioxide diffuses down its concentration gradient out of body cells into the tracheoles.
6. Air is then carried back to the spiracles via the tracheae and released from the body.

Question 37

Ventilation mechanisms in insects

Answer 37

1.More spiracles open - This allows more oxygen to enter the tracheal system.
2. Mechanical active ventilation - This is when muscles around the tracheae contract and relax, changing the volume and pressure in the abdomen and squeezing the tracheae to pump air in and out of the spiracles.
3. Movement of tracheal fluid out into tissues - This increases the diffusion rate and surface area for gas exchange.
4. Enlarged collapsible tracheae, accessory sacs, and air reservoirs - These inflate or deflate to ventilate the tracheal system and can increase the volume of air moved through the system.
5. Movement of wing muscles connected to sacs - These pump air to ventilate the tracheal system.
6. Vibration of thoracic muscles - This pumps air to ventilate the tracheal system.

3, 4 + 6 are named in spec

Question 38

Challenges of bony fish gas exchange

Answer 38

1. Water is denser and more viscous than air, resulting in slower diffusion of oxygen.
2. Water has less oxygen than air.
3. Bony fish are very active so have high oxygen demands.

Question 39

Structure of the gills

Answer 39

1. Gills are covered by an operculum flap.
2. Gills consist of stacked filaments containing gill lamellae.
3. Gill lamellae are surrounded by extensive blood vessels.

Question 40

Adaptations of the gills for efficient gas exchange

Answer 40

1. The lamellae provide a large surface area.
2. The lamellae membranes are thin to minimise diffusion distance.
3. The gills have a rich blood supply to maintain steep diffusion gradients.
4. The countercurrent flow of blood and water creates even steeper concentration gradients.
5. Overlapping filament tips increase resistance, slowing water flow over gills and allowing more time for gas exchange.

Question 41

Explain how the countercurrent system works in bony fish

Answer 41

1. Blood and water flow over the lamellae in opposite directions.
2. This means that oxygen-rich blood meets water that is at its most oxygen rich when it first moves across the gills, maximising diffusion of oxygen into the blood.
3. Oxygen-poor blood returning from body tissues meets oxygen-reduced water that has had most of its oxygen removed, still allowing diffusion of oxygen into the blood.
4. This maintains a steep concentration gradient across the entire gill as oxygen conc in water is always higher than in blood of gill

Question 42

Explain ventillation in bony fish

Answer 42

1. Fish opens its mouth which lowers floor of buccal cavity and increases the volume of the buccal cavity
2. This lowers pressure inside the buccal cavity which forces pressure into it
3. Thee operculum is shut
4. The fish closes ita mouth, reducing the volume in the buccal cavity
5. Pressure inside the buccal cavity increases, forcing water across gill filaments
6. The operculum opens and water flows out of gills