Friday Aug 30/Monday Sept 3
Turning in supplies? Place
AGENDA
• Grade Homework
• Notes: Energy Flow in Ecosystems
• Lab Safety Review
• QUIZ: Lab Safety
• Desert Food Web Activity (Homework if not finished)
HOMEWORK
• Food Chains and Food Webs
• Pyramids of Ecology
What would we do without energy?
Energy = The ability to do work
The Laws of Thermodynamics:
1. Conservation of energy- energy can change
type, but the total amount of energy present
remains constant.
2. Energy is transformed from one
form to another but remains constant
in ecosystems.
What is the main energy
source for life on earth?
•The sun
• Sometimes called autotrophs (self
feeders).
• Producers can make the nutrients they
need to survive from the compounds in
their environment.
• In land ecosystems most producers are
green plants.
• In aquatic ecosystems most producers
are algae or phytoplankton.
• Most producers use sunlight to make food
by photosynthesis.
6CO2 + 6H2O + energy -- C6H12O6 + O2
Though plants do most
of the planet’s
photosynthesis, bacteria
invented the process.
Photosynthetic bacteria still
exist.
• A few producers – mainly specialized
bacteria- produce nutrients without
using sunlight.
• Chemosynthesis – heat is used to
convert inorganic compounds into
nutrients.
– Ex. Bacteria that live near hot vents
on the ocean floor.
Producers… Yeah, Yeah,Yeah !
• Consumers or
heterotrophs get
their nutrients from
feeding on the other
organisms.
• There are several classes of consumers
depending on their food source.
• Herbivores- plant eaters, called
primary consumers because they feed
directly on other producers.
• Carnivores –
meat eaters, feed
on other
consumers
• Omnivores – eat
both plants and
animals
• Decomposers –
break down
organic matter.
Example – bacteria
and fungi.
• Detrivores –
organisms that
feed on dead
matter or detritus.
Example- snails,
earthworms.
• All organisms dead or alive
are potential sources of food
(energy) for other organisms
– The sequence of who
eats or decomposes
whom in an
ecosystem is called a
food chain. It
illustrates how
energy moves from
one organism to
another through the
ecosystem.
Ecologists assign every organism in an
ecosystem a feeding level or trophic
level (from the Greek word trophos,
“nourishment”)
• producers belong to the first trophic
level
• primary consumers belong to the
second trophic level
• secondary consumers belong to the
third trophic level.
Trophic Levels
In most ecosystems, organisms form a
complex network of feeding
relationships called a food web.
Ecosystems are very complicated,
food chains and food webs are
only simplistic representations
of existing relationships.
• There are three ways to show the
relative amounts of energy or
matter contained within each
trophic level.
1. Pyramid of numbers
2. Energy Flow pyramid
3. Biomass pyramid
1. Pyramid of Numbers – by
counting the organisms at each
trophic level, ecologists can
graph this information to yield a
pyramid of numbers.
• Since the typical ecological
structure is many producers,
not as many primary
consumers, and just a few
secondary consumers, the
graph usually looks like a
pyramid.
Pyramid of Numbers
2. The energy flow
pyramid explains why the
earth can support more
people if they eat at
lower trophic levels.
• This also explains why
top carnivores (sharks,
eagles, tigers) are the
first to suffer when the
ecosystems that support
them are disrupted.
Pyramid of energy flow:
• The percentage of useable energy transferred from
one trophic level to the next is about 10%.
• Organisms use the energy they consume for
respiration, reproduction and movement.
• The pyramid of energy flow shows that the more
trophic levels in a food chain or web, the greater the
loss of useable energy.
• Energy is lost to the
atmosphere as heat.
•10% of the available energy is transferred to the next
trophic level.
•Energy flows in one direction only. It is not recycled!!
3. Biomass Pyramid- Represents the amount of
potential food available for each level in an
ecosystem. Biomass is usually expressed in terms of
grams of living organic matter per unit area.
Not all pyramids are shaped
like pyramids!!!
Biological Magnification
• The process where pollutants
such as pesticides or heavy
metals move up the food chain.
• Pollutants can be non-biodegradable which means they
cannot be broken down by the
metabolism of the organism.
• The substances or pollutants
become concentrated in their
toxic form in the tissues or
internal organs of the
organisms as they move up the
food chain.
• This happens because
when larger animals
eat smaller animals or
prey, they don't just
eat one or two of these
animals during their
lifetime, sometimes
they eat thousands or
millions. Not only are
these animals ingesting
their prey, they're also
ingesting all of their
prey's toxins!