7 - Exchange surfaces and breathing

Question 1

two min reasons why diffusion alone is enough to supply a single-celled organisms

Answer 1

• metabolic activity of a single-celled organism is usually low, so O2 and CO2 production are relatively low
• surface area to volume ratio is large

Question 2

why isn’t diffusion enough for larger organisms

Answer 2

• as they get larger, metabolic activity increases
• oxygen demands are very high and will produce a lot of CO2
• the distance between the cells and oxygen is too large for diffusion
• SA:V ratio also is larger so gases cant be exchanged fast enough

Question 3

specialised exchange surfaces characters

Answer 3

• increased surface area
• thin layers
• good blood supply
• ventilation to maintain diffusion gradient

Question 4

increased surface area -specialised exchange surfaces character

Answer 4

provides the area needed for exchange and overcomes the limitations of the small SA:V in animals

• root hair cells and villi

Question 5

thin layers - specialised exchange surfaces character

Answer 5

the diffusion distances are short making the diffusion process fast and efficient
- eg alveoli in lungs

Question 6

good blood supply - specialised exchange surfaces character

Answer 6

the steeper the conc gradient the faster diffusion is
- having a good blood supply ensures substances are constantly delivered and removed to maintain a steep conc gradient

Question 7

ventilation to maintain diffusion gradient - specialised exchange surfaces character

Answer 7

helps to maintain conc gradients and makes the process more efficient

Question 8

key structures of mammalian gaseous exchange

Answer 8

Nasal cavity
Trachea
Bronchus
Bronchioles
Alveoli

Question 9

Nasal cavity

Answer 9

• a large surface area with a good blood supply, warming the air to body temp
• a hairy lining, secretes mucus to help trap dust and bacteria protecting the delicate lung tissue
• moist surfaces to increase the humidity of the air and reducing evaporation frim exchange surfaces

Question 10

Trachea

Answer 10

• main airway carrying air into the chest
• tube with incomplete rings of strong flexible cartilage (stops trachea from collapsing) incomplete to allow food down oesophagus
• lined with ciliated epithelium with goblet cells, between and bellow cells.
• goblet cells secrete mucus onto lining of trachea to trap dust and microorganisms
• cillia beat the mucus away from the longs into the throat

Question 11

bronchus

Answer 11

trachea divides into two bronchus
- smaller than the trachea with same rings of cartilage

Question 12

bronchioles

Answer 12

bronchi divide into many bronchioles
- the have no cartilage
- walls contain smooth muscle so they can constrict and dilate
- lined with thin layer of flattened epithelium (some gas exchange can happen)

Question 13

alveoli

Answer 13

tiny air sacs where gas exchange takes place
- only in mammalian lung
thin layer of epithelial cells, collagen and elastic fibres
- elastic tissue allows alveoli to stretch as air is drawn in and return to normal size (squeezing out air) the elastic recoil of the lungs

Question 14

main adaptions of the alveoli

Answer 14

• large surface area
• thin layer - alveoli and capillaries that surround have thin walls - short diffusion distance
• good blood supply- each surrounded by a network of capillaries. the constant flow of blood brings CO2 off and O2 in. maintain a steep conc grad
• good ventilation - breathing moves air in and out helping maintain a steep conc gradient

inner layer is also covered in a thin layer called ung surfactant

Question 15

what is lung surfactant

Answer 15

• inner surface is covered in it
• it allows the alveoli to be inflated
• oxygen dissolves in the water before diffusion into the blood. but water can only evaporate into the air of the alveoli

Question 16

structure of the thorax

Answer 16

• rib-cag provides a semi rigid case where pressure ca be changed compared to air pressure outside
• diaphragm is broad, domed sheet at bottom of thorax
• external and internal intercostal muscles are found between the ribs
• thorax is lined by pleural membranes

Question 17

inspiration

Answer 17

• taking air in requires energy
• dome shape diaphragm contracts, flattening and lowering.
• external intercostal muscles contract, so ribs move upwards and outwards
• volume of thorax increases
• pressure decreases
• air is drawn inwards through nasal passage

Question 18

Expiration

Answer 18

• breathing air out is passive
• flat shape diaphragm relaxes, goinginto dome shape
• external intercostal muscles contract, so ribs move upwards and outwards
• volume of thorax decreases
• pressure increases
• air is pushed outwards
• through nasal passage

Question 19

forced expiration

Answer 19

• this uses energy
• internal intercostal muscles contract
• pulling the ribs down hard and fast
• abdominal muscles contract forcing the diaphragm up to increase the pressure on the lungs

Question 20

ways to measure capacity of the lungs

Answer 20

• a peak flow
• vitalographs
• spirometer

Question 21

peak flow meter

Answer 21

• measures the rate that air can be expelled by the lungs

Question 22

vitalographs

Answer 22

• a sophisticated peak flow
• patient breathes as fast through the instrument and a graph is produced

Question 23

spirometer

Answer 23

measures different aspects of the lungs volume or breathing patterns

Question 24

components of lung volume

Answer 24

• tidal volume
• vital capacity
• inspiratory reserve volume
• expiratory reserve volume
• residual volume
• total lung capacity

Question 25

tidal volume

Answer 25

volume of air that moves into and out of the lungs with each resting breath
- it is around 500cm3
-uses 15% of the vital capacity of the lungs

Question 26

vital capacity

Answer 26

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

Question 27

inspiratory reserve volume

Answer 27

the maximum volume of air you can breathe in over and above the normal inhalation

Question 28

expiratory reserve volume

Answer 28

is the extra amount of air you can force out of your lungs over and above the normal tidal volume of air you breathe out

Question 29

residual volume

Answer 29

the volume of air that is left in your lungs when you have exhaled as hard as possible - cannot be directly measured

Question 30

total lung capacity

Answer 30

sum of the vital capacity and residual volume

Question 31

breathing rate

Answer 31

number of breaths taken per minute

Question 32

ventilation rate

Answer 32

the total volume if air inhaled in on minute
Tidal volume x breathing rate/min

Question 33

what are spiracles

Answer 33

along the thorax and abdomen is small openings called spiracles
- air enters and leaves here, as well as water
- spiracles can be opened or closed by sphincters
- wen O2 demand is low spiracles are mostly closed to reduce water loss
- they lead into the tracheae

Question 34

what is tracheae

Answer 34

• tubes that carry air into the body
• lined with chitin which keeps them open if they are bent or pressed
• it is impermeable to gas so no exchange takes place here
• branch to form narrower tubes until they divide into tracheole

Question 35

what are tracheoles

Answer 35

a single, elongated cell that has no chitin so is permeable to gas
- so exchange take place here
- they run between cells

Question 36

how does gas diffuse from tracheoles to cells

Answer 36

oxygen dissolves into the moisture on the walls of the tracheoles and diffuse into the surrounding cells
- this is limited by tracheal fluid

Question 37

what is tracheal fluid

Answer 37

• it is at the end of the tracheoles
• limits the penetration of air diffusion
• as O2 demand increases lactic acid builds up in the tissue and water moves out of tracheoles by osmosis - exposing more surface area for diffusion

Question 38

alternative was insects increase the level of gaseous exchange

Answer 38

• mechanical ventilation of the tracheal system - air is actively pumped into the system by muscular movements of thorax- changing the volume and pressure of the body
• collapsible enlarged tracheae which act as reservoirs. increases the amount of air moved through the gas exchange system. Usually inflated by the ventilating movements of the thorax

Question 39

gills

Answer 39

the gaseous exchange organ of fish, made of gill plates, gill filaments and gill lamellae

Question 40

water flow over the gills

Answer 40

• mouth opens and the floor of the buccal cavity is lowered. this increases the volume of the buccal cavity. SO the pressure drops and water moves into the buccal cavity. At the same time the opercular valve is shut and the opercular cavity expands (containing the gills). , this lowers pressure in oppercular cavity. the floor of the buccal cavity moves up, increasing the pressure, so water moves over the gills

Question 41

effective gas exchange in water

Answer 41

• the tips of adjacent gill filaments overlap. This increases the resistance to flow of water the gill surfaces and slows down the movement of the water. As a result there is more time for gaseous exchange
• water moving over the gills and the blood in the gill filaments in different directions. A steep concentration gradient is maintained.

Question 42

parallel system

Answer 42

• blood in gills and water flowing over the gills travel in the same direction

Question 43

counter current system

Answer 43

• 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.