Exchange surfaces

Question 1

reasons for exchange systems in large multicellular organisms

Answer 1

• large multicellular organisms have a small surface area to volume ratio
• cells in the centre of organisms wouldn’t receive any materials if they relied on diffusion alone - diffusion distance too far
• multicellular organisms have a higher metabolic rate so oxygen demands are higher and more CO2 is produced - they need to exchange lots of materials fast

Question 2

features of efficient gas exchange surfaces

Answer 2

• large surface area eg. root hair cells
• thin layers eg. alveoli
• good blood supply - maintains conc. gradient so diffusion can take place faster eg. gills, alveoli
• ventilation - maintains diffusion gradient eg. gills, alveoli

Question 3

features of nasal cavity

Answer 3

• larger surface area and good blood supply - warms the air as it passes into the body
• hairy lining which secretes mucus - traps dust and bacteria to prevent them reaching lungs
• moist surfaces - increases humidity of incoming air - reduces evaporation from exchange surfaces

Question 4

trachea features in gas exchange

Answer 4

• supported by layer of cartilage holding it open and preventing it collapsing
• rings of cartilage are incomplete to allow it to bend when food is swallowed in the oesophagus behind
• lined with ciliated epithelial cells (beat regularly moving mucus with bacteria along) and goblet cells (secrete mucus) that prevent dust and bacteria entering

Question 5

bronchus

Answer 5

• trachea splits into 2, 1 for each lung
• similar structure to trachea
• smaller cartilage rings hold pipe open

Question 6

bronchioles

Answer 6

• bronchus split into much smaller tubes - 1mm or less diameter
• no cartilage - held open by smooth muscle
• muscle contracts and bronchioles constrict, muscle relaxes, bronchioles dilate - changes amount of air reaching lungs
• lined with thin layer of epithelium making some gas exchange possible

Question 7

alveoli

Answer 7

• little air sacs
• made of thin layer squamous epithelial cells and some collagen and elastic fibres
• epithelium is one cell thick - short diffusion distance
• elastic fibres allow recoil helping air move in and out of alveoli - (elastic recoil) - helps with ventilation
• they secrete lung surfactant coat inner surface of alveoli preventing them from collapsing from the surface tension
• large number of alveoli provide large SA
• good blood supply, good ventilation - maintains steep conc grad for oxygen to diffuse from the lung surface to the blood and for CO2 to diffuse from the blood to the lungs and leave the body

Question 8

inspiration

Answer 8

• diaphragm contracts, flattens, lowers
• external intercostal muscles contract causing ribs to move up and out
• thorax volume increases
• air pressure decreases
• pressure in lungs lower than atmospehere so air flows into lungs
• alveoli stretch
• active - involves muscle contraction

Question 9

expiration

Answer 9

• diaphragm relaxes, moves up
• external intercostal muscles relax so ribs move down and in
• thorax volume decreases
• lung pressure increases
• pressure in lungs greater than atmosphere so air pushed out of lungs
• alveoli recoil
• passive

Question 10

exhaling strongly

Answer 10

• internal intercostal muscles contract
• external intercostal muscles relax
• air is pushed out the lungs

Question 11

how do you use a spirometer?

Answer 11

• lower half of tank filled with water
• upper half full of oxygen
• breathe out into tank and upper half will rise
• breathe in from the tank and upper half will fall
• trace marker attached to mobile upper half

Question 12

why does the overall volume of the tank decline over time?

Answer 12

• sod lime absorbs carbon dioxide
• when breathing we use up oxygen from tank while carbon dioxide we breathe out is absorbed by soda lime
• gas volume of tank decreases because oxygen is used up by ppt

Question 13

precautions when using spirometer

Answer 13

• patient free from asthma and healthy
• soda lime fresh and functioning
• check for air leaks in apparatus
• sterilise mouthpiece
• don’t overfill water chamber

Question 14

tidal volume

Answer 14

• amount of air moving in and out of lungs during breathing at rest (smallest wave)
• ventilation rate/breathing rate

Question 15

inspiratory reserve volume

Answer 15

• how much extra air breathed in during forced inspiration (large wave going down)
• measure inspiratory capacity above tidal volume
• uses extra muscles

Question 16

expiratory reserve volume

Answer 16

• how much extra air is breathed out during forced expiration (smaller wave than inspiratory, going upwards)
• measures expiratory capacity beyond tidal volume
• uses different muscles

Question 17

residual volume

Answer 17

• volume remaining in lungs after maximum expiration (section below inspiratory residual volume)

Question 18

vital capacity

Answer 18

• largest possible volume change in lungs
• from max inspiration to max expiration

Question 19

total lung capacity

Answer 19

• vital capacity and residual volume
• everything

Question 20

breathing rate from spirometer

Answer 20

count number of breaths (peaks) in a minute

Question 21

rate of oxygen consumption from spirometer

Answer 21

• difference between inspiratory volume at start and end (how much has it gone down)
• divide by duration of experiment

Question 22

gas exchange in insects

Answer 22

• each segment of insect has pair of spiracles (openings)
• tracheae - connected to spiracles, lined with chitin to keep them open
• branch into tracheoles - divide until numerous microscopic ends penetrate into body cells, no chitin lining
• oxygen moves down conc. gradient into tracheoles and dissolves in moisture on walls
• tracheal fluid at the end of tracheoles limits diffusion, but when oxygen demand is high lactic acid builds up and water moves out tracheoles increasing SA for oxygen
• carbon dioxide moves down conc gradient into air

Question 23

ventilation in insects

Answer 23

• rhythmic muscular movements of abdomin/thorax
• changes volume and pressure in tracheoles
• generates mass movements of air in and out of tracheal tubes
• ventilation movements also inflate the collapsible tracheae, increasing air moving in and out

Question 24

structure of gas exchange in fish

Answer 24

• gills contained in gill cavity and covered by bony flap called operculum
• each gill consists of rows of gill filaments attached to bony arch
• gill filaments occur in stacks (gill plates) - provides large surface area and require water flow to keep them apart
• capillaries carry oxygenated blood to surface of gill lamellae where gas exchange takes place

Question 25

countercurrent flow in fish

Answer 25

- water and blood move in opposite directions - this maximises amount of oxygen absorbed from water - maintains high conc. gradient

Question 26

ventilation in bony fish

Answer 26

so fish don't have to keep moving for water to flow over gills - floor of buccal cavity (mouth) moves downwards, increasing volume, lowering pressure and drawing water in - meanwhile, the opercular valve is shut - mouth closes and floor is raised, increases pressure, starts pushing water through gills - operculum opens - opercular cavity walls move inwards, increasing pressure, helping water flow through gills