Transcript energy in faeces

PRODUCTI
VITY
AND ENERGY FLOW
Source: http//web3.ibo.org/
ENERGY ENTERS THE ECOSYSTEM AS
SUNLIGHT
• Only 2% of the light
energy falling on a
tree is captured and
turned into chemical
energy by
PHOTOSYNTHESIS
• The rest is reflected,
or just warms up the
tree as it is absorbed
Gross productivity is a measure of total
energy captured
• It is measured in
joules (J)
• It is the energy
captured or
assimilated by an
organism
• for a plant, it is the
sunlight actually fixed
by the leaves during
photosynthesis
Energy is
stored in leaf
as sugars
and
starches,
which later
are used to
form flowers,
fruits,
seeds,etc.
Net productivity
• Plants have to use some of the energy they capture
to keep themselves growing:
– they move water and stored chemicals around
– they make hormones and enzymes to control their
metabolism
– they make flowers, fruits, new leaves and stems
• the energy left over after they have used what they
need is called the net productivity
• the energy used by the plant for essential tasks is
called respiration energy, and eventually it is
released to the environment as heat
So how are gross and net
productivity related ?
Net productivity = Gross productivity
– Respiration Energy
or using symbols
NP = GP - R
This equation applies to animals too,
but more on that later…..
The productivity of a plant is called:
PRIMARY PRODUCTIVITY
So, what about animal productivity?
• Animals must eat other organisms to obtain energy, unlike
plants which photosynthesize
• Animals may eat plants or animals or both
• Not all the energy in food is absorbed (assimilated) into an
animal’s body
• Unassimilated food is ejected as faeces or droppings
So gross productivity = food assimilated
or gross productivity = food eaten – energy in
faeces
What about net productivity for an animal
(secondary consumer)?
• Gross secondary productivity =
Energy eaten - energy in faeces
• As well as keeping themselves alive, animals must use
energy to move and keep warm - plants need rather less
energy- but in the end it, as in plants, it all turns to heat
• Net secondary productivity (NSP ) =
food eaten - faeces - respiration energy
so NSP = GSP- R (just like plants)
?
Net and gross productivity in the
food web
• In a food web diagram, you can usually
assume that:
– the energy input into an organism represents the
GP
– the energy output from that organism to the
next trophic level represents the NP
– the difference between GP and NP = R
(respiration energy ) and/or loss to decomposers
?
Now check what you have
understood!
– Complete this energy flow diagram:
• label GPP, NPP and R for the primary producer
• add arrows to show missing energy pathways (3 in total)
• fill in the blank box to explain why some sunlight is not fixed
by plant
HERBIVORES
PLANT
SUN
RESPIRATION
………………
……..……….
DECOMPOSERS
The following data were collected in a study of secondary
productivity in a population of woodlice. Some of the
woodlice produced offspring during the experiment.
Source: IB Examination Paper 1 May01
Estimated Dry Mass at
start of experiment (g)
Estimated Dry Mass
at end of experiment (g)
Adult woodlice
1.53
1.59
Young woodlice
-
0.63
22
19.45
-
0.84
Food (dead leaves)
Fecal matter
ANSWER
1. What is the Gross Productivity (g) of this
population over the period of the experiment?
Answer: GP = Food Eaten – Fecal Loss
GP =
(22 - 19.45) – 0.84
GP = 1.71
2. What is the Net Productivity (g) of this
population over the period of the experiment?
Answer: NP = Biomass (dry mass)
NP = 1.59 – 1.53 + 0.63
NP = 0.69
ANSWER
1. What is the Gross Productivity (g) of this
population over the period of the
experiment?
2. What is the Net Productivity (g) of this
population over the period of the
experiment?