Sunday, 4 September y
Exchange of substances
Adaptions for gas exchange
Surface area : volume
Size of an organism
- the size of an organism is inversely proportional to its surface area to volume ratio
SA:V vs SA:mass
- more accurate when measuring mass (easier to find mass as some organisms have
an irregular shape
- Measuring mass causes less damage to the animal
- Measuring mass requires fewer measurements
Single cell organisms
Spherical - ideal shape for gas exchange by diffusion
- highest SA:VOL and allows for shortest diffusion pathway
- Surrounded by exchange medium on all sides
Limited to a size of around 100um
- larger cells have a smaller surface area : volume so the diffusion of oxygen etc will be
too slow to meet metabolic demands
Agar experiment
- cut agar cubes (with pH indicator in e.g. phenopheylein) of different sizes
- Measure out beakers with the same vol of HCL - enough to fully submerge the cube
- place each cube in a beaker and start the stopwatch
- Leave cubes in acid for 5 mins and use a ruler to measure how much of the cube has
changed colour/become colourless
- Repeat experiment twice for each cube size and calculate a mean for each
- Ensure temperature stays the same throughout the experiment
- Calculate SA:V and the rate of diffusion for each cube
Plot a graph
- Y axis (time for diffusion (s))
- X axis (surface area : volume)
1
, Sunday, 4 September y
BMI
Measuring BMI
- o2 consumption
- co2 produced
- heat generated
Why do plants have a lower BMI
- do not move
- Plants don't have to maintain a high body temp
- less energy is required so respiration and metabolism are slower
Why is a mouses heart rate faster than a humans
- mouse has a higher SA:VOL so loses heat faster
- Faster heart rate supplies cells with oxygen for respirate to generate heat
Plants
Xerophyte
- a plant that is evolved to live in areas with little water
Features
Rolled leaves - reduce the water potential gradient between leaf and the air - traps moist
air inside - reduces air movement across the stomata
Sunken stomata - reduce the water potential gradient between leaf and the air - traps
moist air inside the stomata - reduces air movement across the stomata
Thick cuticle - reduces evaporation from leaf surface / increases diffusion distance
Hairs - trap moist air - maintains high water potential outside leaf to reduce water loss
Densely packed cells in the leaf - reduces evaporation of water from the surface of the
cells
Cactus adaptations
- thick cuticle
- Widespread root network
Stomata
- guard cells cause stomata to open and close by…
2
, Sunday, 4 September y
- changing shape via osmosis - lose water and become flaccid
- Curved shape becomes straight and stomata closes
Why are stomata not on the top of leaves
- would be blocked by rain - would reduce gas exchange and uptake of co2
- Stomata would be in direct sunlight which would increase evaporation
Stomatal density and altitude
- as altitude increases, so does stomatal density and then it decreases
- as altitude increases there is more photosynthesis - more stomata needed for gas ex-
change
- at very high altitudes temps are lower and co2 concentration is lower so photosynthe-
sis decreases
Counting stomata
- measuring stomatal density (stomata/mm2)
- allows for comparison between leaves of different shapes and sizes
Insects
muscle tissue
- provides pressure changes required to change breathing rate
Exoskeleton
- chitin - waterproof - impermeable to gases
- do not use this surface for gas exchange as…
- it has a role in being water proof
- surface area isn't big enough
- water loss would be too great
- breathing system carries out gas exchange well so outer surface not needed
Why do insects need a specialised breathing system
- chitin exoskeleton - difficult for gases to diffuse through
- Insects are highly active - high metabolic rate and demand for oxygen to facilitate aer-
obic respiration
How oxygen enters muscle cells in insects
- air diffuses along the trachea and tracheoles
3
Exchange of substances
Adaptions for gas exchange
Surface area : volume
Size of an organism
- the size of an organism is inversely proportional to its surface area to volume ratio
SA:V vs SA:mass
- more accurate when measuring mass (easier to find mass as some organisms have
an irregular shape
- Measuring mass causes less damage to the animal
- Measuring mass requires fewer measurements
Single cell organisms
Spherical - ideal shape for gas exchange by diffusion
- highest SA:VOL and allows for shortest diffusion pathway
- Surrounded by exchange medium on all sides
Limited to a size of around 100um
- larger cells have a smaller surface area : volume so the diffusion of oxygen etc will be
too slow to meet metabolic demands
Agar experiment
- cut agar cubes (with pH indicator in e.g. phenopheylein) of different sizes
- Measure out beakers with the same vol of HCL - enough to fully submerge the cube
- place each cube in a beaker and start the stopwatch
- Leave cubes in acid for 5 mins and use a ruler to measure how much of the cube has
changed colour/become colourless
- Repeat experiment twice for each cube size and calculate a mean for each
- Ensure temperature stays the same throughout the experiment
- Calculate SA:V and the rate of diffusion for each cube
Plot a graph
- Y axis (time for diffusion (s))
- X axis (surface area : volume)
1
, Sunday, 4 September y
BMI
Measuring BMI
- o2 consumption
- co2 produced
- heat generated
Why do plants have a lower BMI
- do not move
- Plants don't have to maintain a high body temp
- less energy is required so respiration and metabolism are slower
Why is a mouses heart rate faster than a humans
- mouse has a higher SA:VOL so loses heat faster
- Faster heart rate supplies cells with oxygen for respirate to generate heat
Plants
Xerophyte
- a plant that is evolved to live in areas with little water
Features
Rolled leaves - reduce the water potential gradient between leaf and the air - traps moist
air inside - reduces air movement across the stomata
Sunken stomata - reduce the water potential gradient between leaf and the air - traps
moist air inside the stomata - reduces air movement across the stomata
Thick cuticle - reduces evaporation from leaf surface / increases diffusion distance
Hairs - trap moist air - maintains high water potential outside leaf to reduce water loss
Densely packed cells in the leaf - reduces evaporation of water from the surface of the
cells
Cactus adaptations
- thick cuticle
- Widespread root network
Stomata
- guard cells cause stomata to open and close by…
2
, Sunday, 4 September y
- changing shape via osmosis - lose water and become flaccid
- Curved shape becomes straight and stomata closes
Why are stomata not on the top of leaves
- would be blocked by rain - would reduce gas exchange and uptake of co2
- Stomata would be in direct sunlight which would increase evaporation
Stomatal density and altitude
- as altitude increases, so does stomatal density and then it decreases
- as altitude increases there is more photosynthesis - more stomata needed for gas ex-
change
- at very high altitudes temps are lower and co2 concentration is lower so photosynthe-
sis decreases
Counting stomata
- measuring stomatal density (stomata/mm2)
- allows for comparison between leaves of different shapes and sizes
Insects
muscle tissue
- provides pressure changes required to change breathing rate
Exoskeleton
- chitin - waterproof - impermeable to gases
- do not use this surface for gas exchange as…
- it has a role in being water proof
- surface area isn't big enough
- water loss would be too great
- breathing system carries out gas exchange well so outer surface not needed
Why do insects need a specialised breathing system
- chitin exoskeleton - difficult for gases to diffuse through
- Insects are highly active - high metabolic rate and demand for oxygen to facilitate aer-
obic respiration
How oxygen enters muscle cells in insects
- air diffuses along the trachea and tracheoles
3
