SA: V and gas exchange

Question 1

how does an organism’s size relate to their SA:V

Answer 1

larger organism = lower SA:V

Question 2

how does an organism’s SA:V relate to their metabolic rate

Answer 2

smaller the SA:V = higher metabolic rate

Question 3

how might a large organism adapt to compensate for its small SA:V

Answer 3

changes that increase SA
e.g. folding
body parts becoming larger (elephants ears)
elongating shape
developing a specialised gas exchange surface

Question 4

why do multicellular organisms require specialised gas exchange surfaces

Answer 4

their smaller SA:V means the distance that needs to be crossed is larger and substances can’t easily enter the cells as in a single-celled organism

Question 5

3 features of an efficient gas exchange surface

Answer 5

1) large SA e.g folded membranes in mitochondria
2) thin/short distance e.g capillary walls
3) steep conc gradient maintained by bloody supply/ventilation e.g. alveoli

Question 6

why can’t insects use their bodies as an exchange surface

Answer 6

waterproof chitin exoskeleton and a small SA:V in order to conserve water

Question 7

name+ describe 3 main features of an insect’s gas transport system

Answer 7

1) spiracles = holes on body’s surface which may be opened/closed by a valves for gas/water exchange
2) tracheae= large tubes extending through all body tissues , supported by rings to prevent collapse
3) tracheoles= smaller branches dividing off the tracheae

Question 8

process of gas exchange in insects

Answer 8

• gases move in/out tracheae through spiracles
  -a diffusion gradient allows oxygen to diffuse into the body tissue while waste co2 diffuses out
  -contraction of muscles in the tracheae allows mass movement of air in/out

Question 9

why can’t fish use their bodies as an exchange surface

Answer 9

waterproof, impermeable outer membrane and small SA:V

Question 10

name and describe the 2 main features of a fish’s gas transport system

Answer 10

gills = located within body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles

lamellae= at right angles to the gill filaments, increase the SA . blood and water flow across them in opposite directions (countercurrent flow)

Question 11

explain the process of gas exchange in fish

Answer 11

-the fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure
- water passes over the lamellae, and the o2 diffuses into the bloodstream
- waste co2 diffuses into the water and flows back out of the gills

Question 12

how does the countercurrent exchange system maximise o2 absorbed by the fish

Answer 12

maintains steep conc gradient, as water is always next to blood of a lower o2 conc. keeps rate of diffusion constant and enables 80% of available o2 to be absorbed

Question 13

name and describe 3 adaptations of a leaf that allow efficient gas exchange

Answer 13

1) thin and flat- short diffusion pathway and large SA:V
2) many stomata- in underside of leaf allow gases to easily enter
3) air spaces in mesophyll - allow gases to move around leaf, facilitating photosynthesis

Question 14

how do plants limit their water loss while still allowing gases to be exchanged

Answer 14

stomata regulated by guard cells which allows them to open and close as needed- most stay closed to prevent water loss while some open to let o2 in

Question 15

describe the pathway taken by air as it enters the mammalian gaseous exchange system

Answer 15

nasal cavity
trachea
bronchi
bronchioles
alveoli

Question 16

nasal cavity function

Answer 16

good blood supply warms and moistens the air entering the lungs. goblet cells in the membrane secrete mucus which traps dust and bacteria

Question 17

trachea and its function

Answer 17

• wide tube supported by C-shaped cartalige to keep the air passage open during pressure changes
  -lined by ciliated epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections
  -carries air to the bronchi

Question 18

bronchi and their function

Answer 18

-supported by rings of cartilage and lined by ciliated epithelium cells
-narrower and there are 2 of them, one for each lung
-allow passage of air into the bronchioles

Question 19

bronchioles and their fucntion

Answer 19

• narrower than bronchi
• don’t need to be kept open by cartilage, therfore mostly have only muscle and elastic fibres so they can contract and relax easily during ventilation
  -allow passage of air into alveoli

Question 20

alveoli and their function

Answer 20

• mini air sacs, lined with epithelium cells, site of gas exchange
• walls only 1 cell thick, covered with a network of cappilaries, 300 million in each lung, all of which facilitates gas diffusion

Question 21

process of inspiration and changes that occur throughout thorax

Answer 21

• external intercostal muscles contract (internal relax), pulling ribs up and out
  -diaphram contracts + flattens
  -vol of thorax increases
  -air pressure outside lungs is therefore higher than the air pressure inside, so air moves in to rebalance

Question 22

process of expiration and changes that occur throughout thorax

Answer 22

• external intercostal muscles relax (internal contract), bringing the ribs down and in
  -diaphram relaxes and domes upwards
  -vol of thorax decreases
  -air pressure inside lungs is therefore higher than the air pressure outside, so air moves out to rebalance

Question 23

tidal volume

Answer 23

vol of air we breathe in and out during each breath at rest

Question 24

breathing rate

Answer 24

number of breaths we take per minute