unit 3

Question 1

do smaller organisms have a larger or smaller SA:V and what does this mean

Answer 1

larger
-large SA provide good exchange surfaces; a small volume means more molecules can diffuse, removing the need for complex organ systems

Question 2

how to calculate SA:vol

Answer 2

SA= work out the area of one of the sides, then multiply the area by how many sides there are
V= L X W X H
SA:V= divide the SA by the V and express it against the ratio

Question 3

what is metabolic rate and how is it measured?

Answer 3

amount of energy used by an organism within a given period of time
- often measured by oxygen uptake: as used in aerobic respiration to make ATP for energy release

Question 4

explain the relationship between SA:V and metabolic rate

Answer 4

as SA:V increases, metabolic rate increases because:
-rate of heat loss per unit body mass increases
-so organisms need a higher rate of respiration
-to release enough heat to maintain a constant body temperature

Question 5

explain the adaptations that facilitate exchange as SA:V reduces in larger organisms

Answer 5

1.changes to body shape (e.g long/thin)
- increases SA:V ratio and overcomes long diffusion distance
2. development of systems, such as a specialised surface for gaseous exchange
- increases SA:V and overcomes long diffusion distance
- maintain a concentration gradient for diffusion e.g. by ventilation

Question 6

explain how the body surface of a single called organism is adapted for gas exchange

Answer 6

-thin, flat shape and large SA:V
-short diffusion distance to all parts of cells: e.g rapid diffusion of o2 and co2

Question 7

describe the tracheal system of an insect

Answer 7

1. spiracles= pores on surface that can open to allow for diffusion
2. trachea= large tubes full of air that allow for diffusion
3. tracheoles= smaller branches coming off the trachea, permeable to allow gas exchange within cells

Question 8

explain how an insects tracheal system is adapted for gas exchange

Answer 8

1. tracheoles have thin walls, so short diffusion distance to cells
2. high numbers of highly branched tracheoles, so short diffusion distance to cells, so large surface area
3. tracheae provides tubes full of air, so fast diffusion
4. contraction of abdominal muscles changes in pressure in body causing air to move in and out, maintains concentration gradient for diffusion
5. fluid in end of tracheoles drawn into tissues by osmosis during excercise, diffusion is faster through air to gas exchange surface

Question 9

explain structural and functional compromises in terrestrial insects that allow for efficient gas exchange while limiting water loss

Answer 9

-thick waxy cuticle/exoskeleton- increases diffusion distance to less water loss
-spiracles can open to allow gas exchange and close to reduce water loss
-hairs around spiracles- trap moist air reducing water potential gradient so less water loss

Question 10

explain how the gills of the fish are adapted for gas exchange

Answer 10

1. gills made of many filaments covered with many lamella which increases the surface area for diffusion
2. thin lamella wall so short diffusion distance between water/blood
3. lamella have a large number of capillaries which remove o2 and bring co2 quickly so maintains concentration gradient
4. counter current flow

Question 11

what is the counter current flow

Answer 11

-blood and water flow in opposite directions over the lamella
-so oxygen concentration always higher in water
-so maintains a concentration gradient of o2 between water and blood
-for diffusion along whole length of lamellae

Question 12

explain how the leaves of dicotyledonous plants are adapted for gas exchange

Answer 12

1. many stomata (high density)- large SA for gas exchange
2. spongy mesophyll contains air spaces- large surface area for gases to diffuse through
3. thin- short diffusion pathway

Question 13

explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

Answer 13

xerophyte=plant adapted to living in very dry conditions
1. thicker waxy cuticle- increases diffusion distance so less evaporation
2. sunken stomata in pits/hairs- trap water vapour, so reduced water potential gradient between leaf/air
3. spines/ needles reduces SA:V

Question 14

what is the pathway of air in the human gas exchange system

Answer 14

1. trachea
2. bronchi
3. bronchioles
4. alveoli