All ecosystems depend on energy from the sun which is converted to chemical energy by producers like plants through photosynthesis. This energy is transferred between trophic levels in a food chain or food web, but around 90% is lost at each level. The inefficiency of energy transfer means longer food chains are less viable as more energy is lost, limiting the productivity of the ecosystem.

1. Food Chains, Food Webs, Trophic
Levels, Energy Loss

2.  All ecosystems
depend on the input
of energy.
 This energy is in
most cases from the
sun. Living things are
needed to convert
solar energy from the
sun into chemical
energy for use by All energy originally comes from the
sun
living organisms.

3.  Energy is used in a variety of ways. It is
released from glucose in the process of
respiration.
 Energy is used by organisms for:
◦ movement of muscles
◦ to keep warm
◦ To create proteins, enzymes, fats and hormones
◦ Growth and repair
◦ Chemical reactions in organs.
◦ Movement of chemical in and out of cells
 Where the energy is used most will depend on
the organism and the stage of its life cycle.

4. Another way of saying producer

5.  Living things that convert solar
energy to chemical energy
include plants, algae and
cyanobacteria.
 They use chlorophyll found
within their cells to trap visible
light (red and blue light) and
use it to produce organic
compounds from inorganic
compounds taken from their
environment.
 These organisms supply all the
organic material on which
other organisms in an
ecosystem rely. These
organisms are known as
producers.
Cyanobacteria

6.  Photosynthesis can be
represented by the word
equation:
carbon dioxide + water + sunlight →
glucose + oxygen
 or as the balanced chemical
equation:
6CO2 + 6H2O → C6H12O6 + 6O2

7. 6CO2 + 6H2O → C6H12O6 + 6O2
+ +
6x Carbon Dioxide 6x Water Glucose 6x Oxygen
Carbon Dioxide Oxygen
Light
Water Chlorophyll Glucose

8.  Not all of the sunlight energy (ie. the sunlight
that falls on the plant) is successfully
trapped:
◦ Some is reflected off the waxy surface of the leaf
◦ It can be transferred to the water in the leaf
◦ Or it may be the wrong wavelength of light and
can’t be absorbed by the chlorophyll in each plant
cell.
 Overall a plant traps only about 2% of the
sunlight that falls on it.
 The amount of energy that does get trapped
(in glucose molecules) is called the gross
primary productivity of the plant .

9.  Gross primary productivity (GPP) represents the
rate that producers capture and store energy in
an ecosystem. It is a way of measuring the
photosynthesis process.
 The rate of GPP is affected by how efficient
photosynthesis is in a given ecosystem.
◦ Tropical rainforests for example have a very high GPP as
the rainforest has everything plants need to
photosynthesize.
 Not all GPP produced in a system is available to
the organisms that depend on it (consumers).
 The amount of biomass available if referred to as
net primary productivity (NPP).

11. Another way of saying consumer

12.  Organisms such as ourselves cannot create
organic compounds from inorganic materials
and we are known as heterotrophs.
 Heterotrophs consume other organisms to
obtain their organic material. They are known
as consumers.
 They may obtain these materials by
consuming the producer directly or by
consuming an organism that has consumed a
producer. These consumers include
animals, fungi and many kinds of bacteria.

13.  From the simple compounds and mineral
nutrients they consume, consumers create the
complex compounds they rely on for growth and
repair of damaged tissue.
 The energy need to do this is supplied by the
breakdown of some of the carbohydrates made
in photosynthesis.
 The process is called respiration- the release of
energy in the bonds of glucose. This process also
produces heat which is lost to the surroundings.


15.  As one organism feeds on another a food
chain is formed.
 Each link in the chain is known as a trophic
level.
 Each animal in the chain feeds on and
therefore gains its energy from the organism
preceding it in the food chain. In this way
matter and energy are passed from one
organism to the next.

18.  Animals that feed directly on producers are known as
herbivores (or omnivores) or first order consumers.
 Those carnivores (or omnivores) that depend on first
order consumers are called second order consumers
and so on.
 The top consumers are not usually preyed upon and
die of old age, disease or injury.
 Animals that feed on the remains of dead animals are
known as scavengers.
 Organisms that feed on dead or decaying remains
and waste (detritus) are known as detritivores.
 Organisms that live on complex molecules by
breaking organic material down are known as
decomposers.

19.  A simple food chain in reality is rare. Think about
what would happen if just one of the species in
the food chain ran out- the whole system would
collapse.
 Instead a herbivore will feed on a large number
of plants and in turn will be eaten by a range of
consumers and so on. These networks of food
chains form a food web.
 An organism in one food chain may have a
different trophic level in another food chain so it
can be hard to assign an organism to one trophic
level. Food webs are dynamic as ecosystems are
open and organisms can move in and out
bringing and taking matter and energy with
them.

22. How efficient is it?

23.  The food chain represents the transfer of energy
from one organism to the organism that eats it
and so on.
 However at each trophic level not all of the
energy is transferred. Some is lost from the food
chain as heat energy released during cell
respiration and some as chemical energy in
wastes and any left-over dead animal or plant
matter (detritus).
 This loss of energy means that as you move
along the food chain less energy is available to
pass on to the next level. Fortunately energy
continually flows into the system as producers
continue to trap the energy of sunlight.

24.  Three hundred trout are needed to support
one man for a year. The trout, in turn, must
consume 90,000 frogs, that must consume
27 million grasshoppers that live off of
1,000 tons of grass.

-- G. Tyler Miller, Jr., American Chemist
(1971)

25.  The percentage of energy at one trophic level
that ends up in the next trophic level is
referred to as trophic efficiency.


26.  As energy is lost at each trophic level, the
more trophic levels in a food chain the more
energy is lost and the more lower order
organisms must be consumed by the higher
order organism for it to obtain its energy
requirements. This also makes it more likely
that interruptions to the lower order
organisms will affect higher order organisms.
 The loss of energy also limits a food chain as
eventually much of the energy will be lost.

27.  The amount of energy that is available to be passed
from one organism to the next varies with the
organism. Insects for example pass on more energy
as they are ectothermic and do not use energy trying
to maintain a constant body temperature. A useful
rule is the 10% rule which states that about 10% of
the energy at one trophic level is passed on to the
next. The remaining 90% is lost as heat energy and
chemical energy in wastes.
 Measuring trophic efficiency has high relevancy to
agriculture. Refer to Figure 11.14 on page 353. Some
of the highest trophic efficiencies are found in the
ocean. It has been observed that zooplankton feeding
on phytoplankton (producer) receive up to 40% of the
energy found in the phytoplankton.

29.  The total mass of the organic matter at
each trophic level is called biomass
 Biomass is just another term for potential
energy – energy that is to be eaten and
used.
 The transfer of energy from one level to
another is very inefficient (10% Law)

30.  An ecological pyramid
shows the relationship
between consumers and
producers at different
trophic levels in an
ecosystem
 Shows the relative
amounts of energy or
matter contained at each
trophic level
 The Pyramid shows
which level has the most
energy and the highest
number of organisms