Energy transfer Flashcards
(18 cards)
Energy transfer
between trophic
levels
- Biomass and its stored energy
is transferred through trophic
levels very inefficiently - most energy is lost due to
respiration and excretion
Producers
- Green plants
produce their own - carbohydrates from carbon
dioxide (autotrophs) in
photosynthesis - start of a food web
Consumers
- Heterotrophs that cannot
synthesise their own energy - obtain chemical energy through
eating
Biomass
- Measured in terms of:
mass of carbon
dry mass of tissue per given
area
How is dry mass
of tissue
estimated
- Sample of organism dried in
oven below 100C (avoiding
combustion + loss of biomass) - sample reweighed at regular
intervals - all water removed when mass
constant
Why is dry mass a
representative
measure of biomass
Water content in tissues varies
heating until constant mass
allows standardisation of
measurements
for comparison
Calorimetry
Laboratory method used to
estimate chemical energy
stored in dry biomass
Calorimetry
method
Sample of dry biomass is burnt
energy released used to heat
known volume of water
change in temperature of water
used to calculate chemical
energy
Gross primary
production
Chemical energy stored in plant
biomass, in a given area / volume
total energy resulting from
photosynthesis
measured in kJ ha⁻¹ year⁻¹
(kilojoules per hectare per year)
Net primary
production
Chemical energy stored in plant
biomass after respiratory losses
available for plant growth and
reproduction - create biomass
available to other trophic levels
measured in kJ ha⁻¹ year⁻¹
(kilojoules per hectare per year
Calculating net
primary
production
NPP = GPP - R
R = respiratory losses to the
environment
Calculating net
production of
consumers (N)
N = I - (F + R)
I = chemical energy store in
ingested food
F = chemical energy store in
faeces / urine
R = respiratory losses
Units of
productivity
rates
measured as biomass in a given
area in a given time
kJ ha-1 year-1
kJ is the unit for energy
Why is
productivity
measured per area
Per hectare (for example) is
used because environments
vary in size
standardises results so
environments can be compared
Why is
productivity
measured per year
More representative of
productivity
takes into account effects of
seasonal variation
(temperature) on biomass
environments can be compared
with a standardised amount of
time
Why is energy
transfer
inefficient from
sun -> producer
Wrong wavelength of light - not
absorbed by chlorophyll
light strikes non-
photosynthetic region (bark)
light reflected by clouds / dust
lost as heat
Why is energy
transfer inefficient
after producers
Respiratory loss - energy used
for metabolism (active
transport)
lost as heat
not all plant / animal eaten
(bones)
some food undigested (faeces)
