SME
Grade 7 Science · Life Science
Energy flow and matter cycling in ecosystems
Use this for “Producers store 10,000 kcal. About how much reaches the top consumers, three levels up?”
Diagram
10% of 10,000 kcal = 1,000 kcal
10% of 1,000 kcal = 100 kcal
10% of 100 kcal = 10 kcal
This is an example. Type your own values to start a new problem.
E₁
Energy in the producers
example · kcal
p
Percent passed up
example · %
E₂
Energy in the first consumers
calculated · kcal
E₃
Energy in the second consumers
calculated · kcal
E₄
Energy in the top consumers
calculated · kcal
Formulas
E₂
=
E₁
×
p
÷
100
(energy
in
the
first
consumers
=
energy
in
the
producers
×
percent
passed
up
÷
100)
1,000 = 10,000 × 10 ÷ 100
E₃
=
E₂
×
p
÷
100
(energy
in
the
second
consumers
=
energy
in
the
first
consumers
×
percent
passed
up
÷
100)
100 = 1,000 × 10 ÷ 100
E₄
=
E₃
×
p
÷
100
(energy
in
the
top
consumers
=
energy
in
the
second
consumers
×
percent
passed
up
÷
100)
10 = 100 × 10 ÷ 100
Assumptions
•
Producers store the sun’s energy as sugar. Each level above eats the level below.
•
About 10% of the energy at one level is stored in the next; the rest is used for moving, growing and staying warm, or lost as heat.
•
That is why a pond has far more algae than fish, and few top predators.
•
Energy flows one way, up and out as heat. Matter cycles round and round (see the carbon cycle).
Step-by-step
WE KNOW
E₁ = 10,000 kcal (energy in the producers), p = 10% (percent passed up)
FIND
energy in the first consumers (E₂), energy in the second consumers (E₃), energy in the top consumers (E₄)
Step 1 · Find energy in the first consumers (E₂)
Use E₂ = E₁ × p ÷ 100 (energy in the first consumers = energy in the producers × percent passed up ÷ 100)
Only
p
percent
of
the
energy
in
the
producers
is
stored
in
the
level
above;
the
rest
is
used
for
living
or
lost
as
heat.
E₂
=
10,000
×
10
100
E₂
=
100,000
100
E₂
=
1,000
kcal
Step 2 · Find energy in the second consumers (E₃)
Use E₃ = E₂ × p ÷ 100 (energy in the second consumers = energy in the first consumers × percent passed up ÷ 100)
Only
p
percent
of
the
energy
in
the
first
consumers
is
stored
in
the
level
above;
the
rest
is
used
for
living
or
lost
as
heat.
E₃
=
1,000
×
10
100
E₃
=
10,000
100
E₃
=
100
kcal
Step 3 · Find energy in the top consumers (E₄)
Use E₄ = E₃ × p ÷ 100 (energy in the top consumers = energy in the second consumers × percent passed up ÷ 100)
Only
p
percent
of
the
energy
in
the
second
consumers
is
stored
in
the
level
above;
the
rest
is
used
for
living
or
lost
as
heat.
E₄
=
100
×
10
100
E₄
=
1,000
100
E₄
=
10
kcal
Check
Put the numbers back in. Both sides should match.
1,000 = 10,000 × 10 ÷ 100 ✓
100 = 1,000 × 10 ÷ 100 ✓
10 = 100 × 10 ÷ 100 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
Refresh
More problem types
The carbon cycle
Use this for “How does carbon get from the air into an animal, and back?”
Producer, consumer or decomposer?
Use this for “Which organisms in the food web are primary consumers?”
Take one out of the food web
Use this for “What happens to the fox population if the rabbits disappear?”
A pesticide up the food chain
Use this for “Which animal ends up with the most pesticide in its body?”
Will the population grow or shrink?
Use this for “How would planting fruit trees affect the orangutan population?”