Chapter 7 Exchange Surfaces & Breathing

Question 1

Why is diffusion alone enough to supply the needs of single-called organisms?

Answer 1

(1) The METABOLIC ACTIVITY of a single-called organism is usually LOW, therefore the oxygen demands and carbon dioxide production is usually low.

(2) The SA : V ratio of the organism is LARGE.

Question 2

What happens are organisms get larger?

Answer 2

Their METABOLIC ACTIVITY is usually much higher than most single-celled organisms.

The amount of energy required (used) means the OXYGEN DEMANDS and CO2 PRODUCTION is HIGHER.

The distance between the cells where the oxygen is needed and the supply of oxygen is becomes TOO LARGE for EFFECTIVE DIFFUSION to take place.

SMALLER SA : V ratio and therefore gases can’t be exchanged fast enough or in large amounts for the organism to survive.

Question 3

How have large, multicellular organisms evolved?

Answer 3

They have evolved specialised systems for the exchange of substances they NEED and substances they must REMOVE.

Question 4

What are 4 (effective) exchange surface features?

Answer 4

(1) INCREASED surface area

(2) Thin layers

(3) Good blood supply

(4) Ventilation to MAINTAIN diffusion gradient

Question 5

Increased surface area? AND what are some examples?

Answer 5

Provides :
- area needed for exchange
- overcomes the limitations of the (small) SA : V ratio of larger organisms.

E.g.
- root hair cells in plants
- villi in the small intestine (mammals)

Question 6

Thin layers? AND what are some examples?

Answer 6

DECREASES the diffusion distance that substances have to travel, making the process fast and efficient.

E.g.
- alveoli in the lungs
- villli in the small intestine (mammals)

Question 7

Good blood supply? AND what are some examples?

Answer 7

ENSURES that substances are constantly delivered to and removed from the exchange surface. THEREFORE, maintaining a STEEP CONCENTRATION GRADIENT for faster diffusion.

E.g.
- alveoli in the lungs
- gills of a fish
- villi in the small intestine (mammals)

Question 8

Ventilation to maintain a diffusion gradient? AND what are some examples?

Answer 8

FOR GASES, a ventilation system helps MAINTAIN a steep concentration gradient = INCREASES EFFICIENCY

E.g.
- alveoli in the lungs
- gills of a fish (ventilation means a flow of water carrying DISSOLVED gases)

Question 9

What is the conflict between the need for gaseous exchange and the need for water?
(In animals that live on land)

Answer 9

Gaseous exchange surfaces are moist, so oxygen dissolves in the water before diffusing into body tissues.
THEREFORE, the conditions needed to take in oxygen successfully are also ideal for the EVAPORATION OF WATER.

Mammals have evolved complex systems that allow them to exchange gases efficiently but MINIMISE the amount of water lost from the body.

Question 10

Characteristics of mammals?

Answer 10

• relatively big
• small SA : V ratio
• very large volume of cells
• HIGH metabolic rate
• active
• maintain their body temp. INDEPENDENT of the environment
• need lots of oxygen for CELLULAR RESPIRATION
• they produce carbon dioxide which must be removed
• gas exchange takes place in the LUNGS

Question 11

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

Answer 11

(1) Nasal cavity

(2) Trachea

(3) Bronchus

(4) Bronchioles

(5) Alveoli

Question 12

What are the important features of the NASAL CAVITY?

Answer 12

• a LARGE SA : V ratio with a GOOD BLOOD SUPPLY (warms the air to body temperature)
• a HAIRY LINING, which SECRETES MUCUS to trap dust and bacteria, protecting delicate lung tissue from irritation and infection.
• MOIST SURFACES, which increase the humidity of the incoming air, reducing evaporation from the exchange surfaces

Question 13

What is the result of the NASAL CAVITY FEATURES?

Answer 13

The air which enters the lungs is a SIMILAR TEMPERATURE and HUMIDITY to the air already there.

Question 14

What are the important features of the TRACHEA?

Answer 14

Trachea = the main airway carrying clean, warm, moist air from NOSE to CHEST.

WIDE TUBE supported by INCOMPLETE RINGS of strong, flexible CARTILAGE tissue.

The trachea (and branches) are lined with a CILIATED EPITHELIUM with GOBLET CELLS between the below epithelial cells

Question 15

Why are the rings of the trachea INCOMPLETE (rings of CARTILAGE)?

Answer 15

Rings are incomplete to so that food can move easily down the oesophagus behind the trachea.

These STOP the trachea from collapsing.

Question 16

Explain how the goblet cells and cilia work (trachea)?

Answer 16

Goblet cells secrete mucus onto the lining of the trachea, to trap dust and microorganisms that have escaped the nose lining.

The cilia beat and move the mucus, along with any trapped dirt/microorganisms, away from the lungs.
- most of it goes into the throat and is swallowed and digested.
- one effect of smoking is that it stops the cilia beating.

Question 17

What are the important features of the BRONCHUS?

Answer 17

In the chest cavity the trachea divides to form the LEFT BRONCHUS, leading to the LEFT LUNG and then the RIGHT BRONCHUS leading to RIGHT LUNG.

Similar in structure to the trachea, with the same supporting rings of cartilage, but they are SMALLER.

Question 18

What are the important features of the BRONCHIOLES?

Answer 18

In the lungs the bronchi divide to form many small bronchioles.

Diameter of 1mm or less.

Have NO CARTILAGE RINGS.

The WALLS of bronchioles contain smooth muscle.
- when the smooth muscle contracts, the bronchioles CONSTRICT (close up).
- when it relaxes the bronchioles DILATE (open up).
This changes the amount of air reaching the lungs.

Lined with a THIN LAYER OF FLATTENED EPITHELIUM making some gaseous exchange possible.

Question 19

What are the important features of the ALVEOLI?

Answer 19

The alveoli are TINY AIR SACS, which are the main gas exchange surfaces of the body.

Unique ONLY to mammalian lungs.

Each alveolus has a diameter of 200-300um.

Consists of a layer of THIN, FLATTENED EPITHELIAL CELLS, along with some COLLAGEN and ELASTIC FIBRES (composed of elastin).
- elastic tissues allow the alveoli to stretch as air is drawn in.

When they return to their restring size, they help squeeze the air out = ELASTIC RECOIL of the lungs.

Question 20

Adaptations of the ALVEOLI?

Answer 20

(1) Large SURFACE AREA
- there are 300-500 million alveoli per adult lung.
- alveolar surface area for gaseous exchange in the two lungs combined is around 50-75m^2

(2) Thin layers
- only a single epithelial cell thick
- diffusion distances between the air in the alveolus and the blood in the capillaries is very short

(3) Good blood supply
- supplied by a network of around 280 million capillaries
- brings carbon dioxide and carries off oxygen : maintaining a steep concentration gradient between the air in the alveoli and the blood in the capillaries

(4) Good ventilation
- breathing moves air in and out of the alveoli
- maintains a STEEP DIFFUSION GRADIENT between the blood and the air in the lungs

Question 21

Inner surface of the alveoli?

Answer 21

Covered in this layer of a solution of water, salts, and LUNG SURFACTANT.

SURFACTANT makes it possible for the alveoli to remain inflated.

Oxygen dissolves in the water before diffusing into the blood, but water can also evaporate into the air in the alveoli.

Question 22

What is ventilation? ,

Answer 22

Air is moved in and out of the lungs as a result to PRESSURE CHANGES in the THORAX (chest cavity), brought about by breathing movements.
Ventilation is this movement of air.

Question 23

Inspiration??

Answer 23

Taking air IN (inhalation)
- energy using process

1) broad, dome-shaped diaphragm contracts, flattening, and lowering

2) external intercostal muscles contract, moving ribs up and out

3) volume of thorax (chest cavity) increases, PRESSURE REDUCES in thorax

4) pressure of thorax < pressure of atmospheric air (air is drawn through nasal passages, trachea, bronchi, bronchioles, alveoli —> lungs)
- EQUALISES pressure inside and outside the chest

Question 24

Expiration?

Answer 24

Breathing air OUT (exhalation)
- PASSIVE process

1) muscles in diaphragm relax —> returns to resting dome shape

2) external intercostal muscles relax so the ribs move down and in (under the force of gravity)

3) elastic fibres in the alveoli of the lungs return to normal length (elastic recoil)

4) volume of thorax decreases

5) pressure in thorax > pressure of the atmospheric air, so air moves out of the lungs until pressure in and out is equal again

EXHALE FORCIBLY = requires energy

1) internal internalcostal muscles contract

2) pulls ribs down and in (hard and fast)

3) abdominal muscles contract forcing the diaphragm up to increase pressure in the lungs rapidly

Question 25

What ways can you measure the volume of air drawn IN and OUT of the lungs?

Answer 25

(1) PEAK FLOW METER
- simple device
- measures the rate at which air can be expelled from the lungs
- used often by asthmatic people

(2) VITALOGRAPHS
- sophisticated version of peak flow meter
- patient breathes out as quick as they can through mouthpiece
- instrument produces a graph of the amount of air they breathe out and how quickly it is breathed out
- THIS volume of air = FORCED EXPIRATORY VOLUME in 1 SEC

(3) SPIROMETER
- commonly used to measure different aspects of lung volume (investigate breathing patterns)

Question 26

Tidal volume??

Answer 26

Volume of air that moves in and out with each resting breath

Around 500 cm^3 in adults at rest

Uses about 15% of vital capacity of lungs

Question 27

Vital capacity??

Answer 27

Volume of air that can be breathed in when the strongest possible exhalation is followed by the deepest possible inhalation of breath.

Question 28

Inspiratory reserve volume?

Answer 28

Maximum volume of air you can breathe in over and above normal inhalation.

Question 29

Expiratory reserve volume??

Answer 29

Extra amount of air you can breathe out of your lungs over normal tidal volume of air you breathe out.

Question 30

Residual volume??

Answer 30

Volume of air left in your lungs when you have exhaled as hard as possible (CANNOT be measured directly)

Question 31

Total lung capacity??

Answer 31

= vital capacity + residual volume

Question 32

What is ventilation rate?

Answer 32

Ventilation rate is the total volume of air inhaled in one minute.

Ventilation rate = tidal volume x breathing rate (per minute)

Question 33

How and WHY has the gaseous exchange system of insects evolved?

Answer 33

Insects have a tough EXOSKELETON through which little or no gaseous exchange can take place.

Don’t usually have BLOOD PIGMENTS that can carry oxygen.

The gaseous exchange system has evolved to deliver the oxygen directly to the cells and to remove the carbon dioxide in the same way.

Question 34

How does gas exchange take place in insects? (Everything)

Answer 34

Along the thorax and abdomen of most insects, there are small openings = SPIRACLES.

Air enters and leaves the system through the spiracles, but water is also lost.
- just like mammals insects need to minimise the loss of water and maximise the efficiency of gas exchange.

In most insects the spiracles can be opened or closed by SPHINCTERS. The SPIRACLE SPHINCTERS are kept closed as much as possible to minimise water loss.

When an insect in inactive and oxygen demands are very low, the SPIRACLES will all be closed most of the time. When the oxygen demand is raised or the carbon dioxide levels build up, more of the spiracle will open.

Leading away from the spiracles are the TRACHEAE = the largest tubes of the insect respiratory system (1mm diameter). They carry air into the body. Run both into along the body of the insect.
The tubes are lined by SPIRALS OF CHITIN, which keeps them open if they are bent/pressed.

CHITIN = material that makes up the cuticle (relatively impermeable to gases and so little gaseous exchange takes place in the trachea)

Tracheae branch to form narrower tubes until they divide into the tracheoles. TRACHEOLE is a single elongated cell with NO CHITIN lining (freely permeable to gases).
- they are spread throughout the tissues of the insect, running between individual cells.

MOST of the gaseous exchange takes place between the air and respiring cells.

Vast numbers of tracheoles = large SA for gaseous exchange

Oxygen dissolves in moisture on the walls of the tracheoles and diffuses into surrounding cells.

Towards the end of the tracheoles there is TRACHEAL FLUID, which limits the penetration of air for diffusion. However when oxygen demands build up, lactic acid builds up in the tissues resulting in water moving in/out of tracheoles by osmosis.
- exposes more SA for gaseous exchange

All the oxygen needed by cells of an insect are supplied through tracheal system.

The extent of gas exchange in most insects is controlled by the opening and closing of the spiracles.

Question 35

Mechanical ventilation of tracheal system??

Answer 35

Air is actively pumped into the system by muscular pumping movements of the thorax and/or the abdomen.

These movements change the volume of the body and this changes the pressure in the trachea and tracheoles.

Air is drawn into the trachea and tracheoles, or forced out, as the pressure changes.

Question 36

Collapsible enlarged tracheae or air sacs??

Answer 36

Collapsible enlarged tracheae or air sacs, which act as air reservoirs - these are used to increase the amount of air moved through the gas exchange system.

They are usually inflated and deflated by the ventilating movements of the thorax and abdomen.

Question 37

How have fish evolved their respiratory systems?

Answer 37

Water is 1000 times denser than air.

Water is 100 times more viscous (thicker) than air and has a much lower oxygen content.

It would use up far TOO MUCH energy to move dense, viscous water in and out of lung like respiratory organs.

Moving water in ONE DIRECTION only is much simpler and more economical in energy terms.

Question 38

What is the issue with large, bony fish?

Answer 38

Bony fish are relatively big, ACTIVE animals that love almost exclusively in water.

= HIGH OXYGEN DEMAND

= LOW SA:V ratio (diffusion is NOT enough to supply their cells with enough oxygen)

= SCALY OUTER covering - doesn’t allow gaseous exchange

Question 39

How have bony, large fish evolved?

Answer 39

A ventilator system adapted to take oxygen from the water and get rid of carbon dioxide into the water.

They maintain a flow of water in ONE DIRECTION over the gills (which are the organs of gaseous exchange).

Question 40

What are the main features of the gills?

Answer 40

• Large SA
• Good blood supply
• Thin layers

Contained in a gill cavity and covered by a protective OPERCULUM (a bony flap), which is also active in maintaining a flow of water over the gills.

Question 41

Water flow over gills??

Answer 41

When fish are swimming they can keep a current of water flowing over their gills simply by opening their mouth and operculum.

Question 42

What is RAM ventilation?

Answer 42

More primitive cartilaginous fish (sharks, rays) often rely on continual movement to ventilate the gills.

They just ‘ram’ the water past their gills.

Question 43

How have bony fish evolved to allow them to move water over their gills at all times? (Mouth OPEN)

Answer 43

DO NOT rely on movement-generated water-flow over gills.

1) mouth opens

2) floor of buccal cavity (mouth) is lowered - INCREASES the volume of the buccal cavity

3) pressure in the buccal cavity DECREASES and water moves into the cavity

4) operculum valve is shut and the operculum cavity contains gills EXPANDS

5) pressure in the operculum cavity decreases

6) floor of buccal cavity moves up, increasing pressure there so water moves from the buccal cavity over the gills

Question 44

How have bony fish evolved to allow them to move water over their gills at all times? (Mouth CLOSE)

Answer 44

1) mouth closes

2) operculum opens and the sides of the opercular cavity move inwards

3) pressure in the operculum cavity INCREASES and forces water over the gills out of the operculum

4) floor of the buccal cavity is steadily moved up, maintaining a flow of water over the gills

Question 45

What are the 2 adaptations gills have to ensure most effective gaseous exchange?

Answer 45

(1) OVERLAPPING (adjacent) GILL FILAMENTS
- increases resistance to the flow of water over the gill surfaces and slows down the movement of water
- allows more time for gaseous exchange

(2) water/blood flow in different directions
- COUNTER-CURRENT exchange system is set up
- ensures that steeper concentration gradients are maintained
(Cartilaginous fish DO NOT have this = parallel system)

Question 46

Explain parallel system?

Answer 46

Blood in the gills and water flowing over the gills travel in the SAME direction, which gives an initial steep oxygen concentration gradient between blood and water.

Diffusion takes place until the oxygen concentration of the blood and water are in equilibrium, then no net movement of oxygen into the blood occurs.

Question 47

Explain counter-current system?

Answer 47

Blood and water flow in OPPOSITE directions so an oxygen concentration gradient between the water and the blood is maintained all along the gill.

Oxygen continues to diffuse down the concentration gradient so a much higher level of oxygen saturation of the blood is achieved.