Chapter 7- Exchange Surfaces+ Breathing

Question 1

Why can diffusion alone supply the needs of single celled organisms?

Answer 1

• the metabolic activity is relatively low, so oxygen demands and co2 production are low.
• sa:v ratio is large

Question 2

Why is diffusion not enough for larger organisms?

Answer 2

They have high metabolic activity.

• oxygen demands are high and lots of co2 is produced.
• diffusion is in effective as distance between cells is too far.
• the bigger the organism the smaller the sa:v ratio so gases can’t be exchanged fast enough to survive.

Question 3

What are the features of effective exchange surfaces?

Answer 3

1. Increased surface area- provides space needed for exchange and overcomes limitation of sa:v ratio in larger organisms.
2. Thin layers- distances for diffusion are short, so process is faster.
3. Good blood supply- maintains a steep concentration gradient by ensuring substances are continuously delivered to and removed from the exchange surface.
4. ventilation- also helps maintain steep concentration gradient, making process more efficient.

Question 4

What is the need for the human gaseous exchange system?

Answer 4

1. High metabolic rate due to being very active and having to maintain body temperature. There is therefore a greater demand for oxygen and the removal of co2.
2. Due to the small SA:V ratio and very large volume of cells.

Question 5

What are the 5 key structures of the human gaseous exchange system?

Answer 5

1. Nasal cavity.
2. Trachea.
3. Bronchus.
4. Bronchioles.
5. Alveoli.

Question 6

Nasal cavity.

Answer 6

1. large surface area with good blood supply- warms incoming air to body temperature.
2. Hairy lining- secretes mucus to trap dust/bacteria, protecting irritation and infection.
3. Moist surfaces- increase humidity of incoming air, reducing evaporation from exchange surfaces.

Question 7

Trachea.

Answer 7

The trachea is the main airway carrying clean, warm and moist air from the nose down into chest.

• wide tube supported by incomplete rings of strong, flexible cartilage which stop it from collapsing.
• rings are incomplete to allow space for oesophagus.
• lined with ciliated epithelium, with goblet cells between and below the epithelial cells.
• goblet cells secrete mucus onto its lining, cilia brush mucus away into the throat. It is then swallowed and digested.

Question 8

Bronchus.

Answer 8

In the chest cavity, the trachea divides to for, the left and right bronchus.
Have a similar structure to trachea:
- the same supporting rings of cartilage, however, they are much smaller.

Question 9

Bronchioles.

Answer 9

In the lungs, the bronchi divide to form many small bronchioles.
- they have no cartilage rings.
- walls contain smooth muscle.
- smooth muscle contract= bronchioles constrict.
smooth muscle relaxes= bronchioles dilate.
- this changes the amount of air entering the lungs.
- lined with thin layer of flattened epithelium, making some gaseous exchange possible.

Question 10

Alveoli.

Answer 10

The alveoli are tiny air sacs, which are the main gas exchange surfaces in the body.
- diameter of 200-300um.
- consists of layer of thin flattened epithelial cells, along with some collagen and elastic fibres( made from elastin).
- elastic tissues allow alveoli to stretch as air is drawn in. When they return to resting size, they help squeeze air out. = known as elastic recoil of the lungs.
(Textbook)

Question 11

What are the main adaptations of the alveoli for effective gas exchange?

Answer 11

1. Large SA- there are 300-500 million alveoli per adult lung. Provides space needed for oxygen to diffuse.
2. Thin layers- alveoli and the capillaries surrounding them are one cell thick. Short diffusion distance.
3. Good blood supply- constant flow of blood through capillaries maintains steep conc gradient = faster diffusion.
4. Good ventilation- breathing moves air in and out maintaining steep conc gradient.
5. Inner surface covered in thin layer of solution os salt, water and lung surfactant.

Question 12

What is the role of the solution on the inner surface of the alveoli?

Answer 12

• lung surfactant makes it possible for alveoli to remain inflated. It does this by reducing surface tension.
• oxygen dissolves in the water before diffusing as diffusion can only occur once the gases are dissolved.

Question 13

What features play a role in ventilating the lungs?

Answer 13

• air is moved in/out due to pressure changes in the thorax (chest cavity).
• thorax is lined by the pleural membranes which surround the lungs.
  space between them (pleural cavity) filled with thin layer of lubricating fluid so membranes easily slide over each other during breathing.
• rib cage provides semi-rigid case within which pressure can be lowered.
• diaphragm is a broad, domed sheet of muscle which forms the floor of the thorax.
• external/internal intercostal muscles are found between the ribs.

Question 14

Explain what happens during inspiration.

Answer 14

An energy using process.

• diaphragm contracts, flattens and lowers.
• external intercostal muscles contract, moving ribs upwards and outwards.
• volume of thorax increases so pressure in thorax is reduced.
• pressure is lower than pressure of atmospheric air, so air is drawn into the lungs to equalise the pressures.

Question 15

Explain what happens during expiration.

Answer 15

Passive process.

• diaphragm relaxes, moves up into resting dome shape.
• external intercostal muscles relax, ribs move down and inwards.
• elastic fibres in alveoli return to their normal length.
• pressure in thorax increases as volume has increased.
• pressure is greater than atmospheric pressure so air moves out until equilibrium is reached.

Question 16

What is a peak flow meter?

Answer 16

A simple device that measures the rate at which air can be expelled from the lungs. People with asthma often use this to measure how well their lungs are working.

Question 17

What are vitalographs?

Answer 17

More sophisticated version of peak flow meter.

• patient breathes out as fast as they can through mouthpiece.
• instrument produces graph of amount and speed of air breathed out.
• this volume= forced expiratory volume in 1 second.

Question 18

What is a spirometer?

Answer 18

Can be used to measure the volumes of gas breathed in and out under different conditions.

• commonly used to measure different aspects of the lung volume/ breathing patterns.
• many different forms of spirometer but all follow a common principle.

Question 19

What is tidal and residual volume?

Answer 19

Tidal volume= vol of air that moves into and out of the lungs with each resting breath.
Residual volume= vol of air left in the lungs after exhaling as hard as possible.

Question 20

What is vital capacity and total lung capacity?

Answer 20

Vital capacity = vol of air that can be exhaled when the deepest possible intake of breath is followed by the strongest possible exhalation.

Total lung capacity = sum of vital and residual volume.

Question 21

What is inspiratory and expiratory reserve volume?

Answer 21

Inspiratory reserve volume= maximum vol of air you can breath in over and above a normal inhalation.
Expiratory = extra vol of air you can force out of your lungs over and above the normal tidal volume of air you breathe out.

Question 22

What is breathing rate and ventilation rate?

Answer 22

Breathing rate= number of breaths taken per minute.
Ventilation rate= total volume of air inhaled in one minute.

Ventilation rate= tidal volume x breathing rate per min

Question 23

What happens when oxygen demands increase (mammals)?

Answer 23

When they increase, for example during exercise, the tidal volume can increase from 15% to as much as 50% of the vital capacity.

• breathing rate can also increase.
• this results in increased ventilation of the lungs and therefore increased oxygen uptake.

Question 24

Why is the insect gas exchange system the way that it is?

Answer 24

• insects are very active mainly land-dwelling animals with relatively high oxygen requirements.
• however they have a tough, impermeable exoskeleton through which little or no gaseous exchange can take place.
• they also don’t have blood pigments that can carry oxygen.
  Their gaseous exchange system has developed to deliver oxygen directly to the cells and remove carbon dioxide in the same way.

Question 25

When air is breathed in by mammals, what is the order of structures it passes through?

Answer 25

Nasal cavity - pharynx- larynx- trachea - bronchus - bronchioles- alveoli.

Question 26

What are spiracles and their role (insects)?

Answer 26

Small openings found along the thorax and abdomen of most insects.
- air enters and leaves the system through the spiracles, but water is also lost.

Question 27

How is water loss in insects from the spiracles minimised?

Answer 27

The spiracles can be open or closed by sphincters.
-when an insect is inactive and oxygen demands are low, the spiracles will all be closed most of the time.
- when oxygen demand is raised or carbon dioxide levels build up, more spiracles are opened.
This maximises the efficiency of exchange and minimises water loss.

Question 28

What are the tracheae and their role in insects?

Answer 28

The largest tubes of the insect respiratory system and lead away from the spiracles

• they run into and along the body of the insect, carrying air.
• the tubes are lined with spirals of chitin (a fibrous polysaccharide), which keeps them open if they are bent/pressed.
• chitin is relatively impermeable to gases so little gas exchange takes place in the trachea.

Question 29

What are the tracheoles and their role in insects?

Answer 29

The tracheae branch to form narrower tubes called the tracheoles.

• each tracheole is a single, greatly elongated cell (squamous epithelium) with no chitin lining so are permeable to gases.
• they spread throughout the tissues of the insect and this is where most gaseous exchange takes place.
• vast numbers of tracheoles provides large SA.
• oxygen dissolves in moisture on the walls and diffuses into surrounding cells.

Question 30

What is tracheal fluid and its role in insects?

Answer 30

A fluid towards the end of the tracheoles which limits the penetration of air for diffusion.

• however when oxygen demands rise (eg. During flight) a lactic acid build up in the tissues results in water moving out of the tracheoles by osmosis due to a water potential gradient.
• this exposes more SA for gaseous exchange.

Question 31

What alternative methods do insects with very high energy demands have to increase gaseous exchange?

Answer 31

1. Mechanical ventilation- air is actively pumped into the system by muscular pumping movements of the thorax and abdomen. These movements change the volume or the body which changes the pressure in the tracheae and tracheoles. (As volume decreases, pressure increases, vice versa).
2. Collapsible air sacs- act as air reservoirs. Usually inflated/deflated by the ventilating movements of the thorax and are used to increase the amount of air moved through the system.

Question 32

When air is breathed in by insects, what is the order of structures it passes through?

Answer 32

Spiracles- tracheae- tracheoles

Question 33

What are the difficulties bony fish need to overcome?

Answer 33

• water is alot more dense and viscous (thick) than air.
• water has a much lower oxygen content.
• it would use up far too much energy to move the dense, viscous water in and out of lung-like respiratory organs.
  Moving water in one direction is much better in energy and simplicity terms.

Question 34

Why do fish need an exchange system?

Answer 34

Bony fish such as trout and cod are relatively big, active animals.

• this means their cells have a high oxygen demand.
• their high SA:V ratio means diffusion alone is not enough to supply their cells with the oxygen needed.
• their scaly outer covering does not allow gaseous exchange.

Question 35

What are the gills and their function?

Answer 35

• the organs of gaseous exchange.
• fish maintain a flow of water in one direction over the gills.
• gills have a large SA, good blood supply and thin layers for effective gas exchange.
• in bony fish they are contained in a gill cavity.
• bony gill arch supports the structure of the gills.

Question 36

Operculum and its role?

Answer 36

• a protective bony flap that covers the gills.

- it is active in maintaining a flow of water over the gills and so opens and closes accordingly.

Question 37

Gill filaments.

Answer 37

• occur in large stacks called gill plates.
• need a flow of water to keep them apart, exposing the large SA needed for gaseous exchange.
• when in air they remain clumped together, with reduced SA but fan out once in water.

Question 38

Gill lamellae?

Answer 38

• folds that cover the gills.
• are the exact place gas exchange occurs.
• they have a rich blood supply with a maintained steep concentration gradient.
• large SA.
• thin layers.

Question 39

What is the role of the efferent and afferent blood vessel in fish?

Answer 39

• Efferent blood vessel carries the blood leaving the gills in the opposite direction to incoming water which maintains a steep concentration gradient.
• Afferent blood vessel brings blood into the system. Haemoglobin is used to carry oxygen.

Question 40

What is the difference between ventilation in cartilaginous and bony fish?

Answer 40

• cartilaginous fish (sharks/rays) rely on continual movement to ventilate the gills hence why they don’t stay still. This is ram ventilation: they just ram water past the gills.
• bony fish don’t rely on movement generated water flow over the gills. Their exchange system allows them to move water over the gills even when still due to the operculum. They constantly open and close their mouth.

Question 41

Explain how ventilation of the gills takes place.

Answer 41

1. mouth opened. Floor of buccal cavity lowered.
2. This increases volume of buccal cavity= decreased pressure so water moves into mouth to create equilibrium.
3. Opercular valve is shut, opercular cavity containing gills expands.
4. This lowers pressure in opercular cavity, floor of buccal cavity moves up increasing pressure so water moves from buccal c over the gills.
5. Mouth closes. Operculum opens. Sides of opercular cavity moves inwards.
6. This increases pressure in opercular cavity, forcing water over gills and out through operculum.
7. Floor of buccal cavity moves up, maintaining flow of water over gills.
   This is a continuous process.

Question 42

What are the 2 extra adaptions gills have for effective exchange?

Answer 42

1. Tips of adjacent gill filaments overlap. This increases resistance to flow of water over the gill surfaces and slows down water movement, allowing more time for gaseous exchange.
2. Countercurrent system: water and blood flow in different directions. This ensures that steep concentration gradients are maintained allowing more efficient gas exchange.

Question 43

Compare the countercurrent and parallel system.

Answer 43

1. Parallel:
   - blood and water flow in same direction, providing an initial steep conc gradient. Diffusion takes place until there is conc equilibrium. Then no net movement of oxygen into blood occurs.
   This allows cartilaginous fish to only extract 50% of oxygen from the water.
2. Countercurrent:
   - flow in opposite directions so steep gradient between water and blood is maintained along the gill. Oxygen continues to diffuse down the conc gradient so much higher levels of oxygen saturation in blood achieved.
   This allows bony fish to remove 80% of oxygen from the water flowing over them.