surface area to volume ratio and gas exchange

Question 1

how does an organisms size relate to sa:v

Answer 1

larger organism means lower sa:v

Question 2

how does an organisms sa:v relate to metabolic rate

Answer 2

smaller sa:v, higher metabolic rate

Question 3

how might large organism adapt to compensate for its small sa:v

Answer 3

changes that increase surface area
larger body parts
elongating shape
developing specialised gas exchange surface

Question 4

why do multicellular organisms require specialised gas exchange surfaces

Answer 4

their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single-celled organism

Question 5

name three features of an efficient gas exchange surface

Answer 5

1. large surface area
2. short diffusion distance
3. steep concentration gradient

Question 6

why cant insects use their bodies as an exchange surface

Answer 6

they have a waterproof chitin exoskeleton and a small sa:v ratio in order to conserve water

Question 7

name and describe the three main features of an insect’s gas transport system

Answer 7

• spiracles = holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
• tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
• tracheoles = smaller branches diving off the tracheae

Question 8

explain the process of gas exchange in insects

Answer 8

• gases move in and out of the tracheae through the spiracles
• 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 and out

Question 9

explain the process of gas exchange in insects

Answer 9

• gases move in and out of tracheae through spiracles
• a diffusion gradient allows oxygen to diffuse into body tissue while waste CO2 diffuses out
• contraction of muscles in the tracheae allows mass movement of air in and out

Question 10

why cant fish use their bodies as an exchange surface

Answer 10

they have a waterproof, impermeable outer membrane and a small sa:v

Question 11

two main features of fish gas transport

Answer 11

gills and lamellae

Question 12

describe the gill

Answer 12

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

Question 13

describe lamellae

Answer 13

at right angles to the gill filaments, give an increased surface area
blood and water flow across them in opposite directions
(COUNTERCURRENT SYSTEM)

Question 14

explain the process of gas exchange in fish

Answer 14

• fish opens mouth to enable water to flow in, then closes mouth to increase pressure
• water passes over the lamellae, and the oxygen diffuses into the bloodstream
• waste CO2 diffuses into the water and flows back out of the gills

Question 15

how does the countercurrent exchange system maximise oxygen absorbed by fish

Answer 15

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

Question 16

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

Answer 16

1. thin and flat to provide short diffusion pathway and large sa:v
2. many stomata allow gases easily enter
3. air spaces in the mesophyll allow gases to move around leaf, facilitating photosynthesis

Question 17

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

Answer 17

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 oxygen in

Question 18

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

Answer 18

nasal cavity
trachea
bronchi
bronchioles
alveoli

Question 19

describe the function of the nasal cavity in the mammalian gaseous exchange system

Answer 19

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

Question 20

describe the trachea and its function in the mammalian gaseous exchange system

Answer 20

• wide tube supported by C-shaped cartilage 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 21

describe the bronchi and their function in the mammalian gaseous exchange system

Answer 21

• like the tracheae they are supported by rings of cartilage and are lined by ciliated epithelium cells
• however they are narrower and there are two of them, one for each lung
• allow passages of air into the bronchioles

Question 22

describe the bronchioles and their function in the mammalian gas exchange system

Answer 22

• narrower than bronchi
• do not need to be kept open by cartilage, therefore have only muscle and elastic fibres so that they can contract and relax easily during ventilation
• allow passage of air into alveoli

Question 23

describe alveoli and their function in mammalian gas exchange system

Answer 23

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

Question 24

explain the process of inspiration and the changes that occur throughout the thorax

Answer 24

• external intercostal muscles contract
• ribs up and out
• volume of thorax increases
• air pressure outside lungs is therefore higher than the air pressure inside, so air moves in to rebalance

Question 25

explain the process of expiration and changes in thorax

Answer 25

• external intercostal relax
• ribs down and in
• diaphragm relaxes and domes upwards
• volume of thorax decreases
• air pressure inside lungs therefore higher than the air pressure outside, so air moves out to rebalance

Question 26

what is tidal volume

Answer 26

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

Question 27

what is breathing rate

Answer 27

number of breaths per minute