Energy flow, food chains and food webs
ENERGY FLOW IN ECOSYSTEMS FOOD CHAINS IN THE
The source of energy in ecosystems ECOSYSTEM
➢ The sun is the main source of energy in Food chains
ecosystems.
➢ During photosynthesis, the plant uses light Diagram shows the transfer of
energy from the sun to make glucose energy from one organism to the
molecules. next, beginning with a producer.
➢ The sun's light energy is transformed into
chemical energy in the synthesis of glucose.
➢ The glucose can then be broken down by
respiration to release the energy it contains.
➢ Animals cannot make their own food.
➢ They get their energy from the food they eat.
➢ They feed on plants that have captured the
sun's energy during photosynthesis, or they
feed on animals that have fed of plants.
➢ Therefore, animals get their energy indirectly
from the sun. Trophic levels
The flow of energy through living organisms
The flow of energy in an ecosystem is linked to
the way living organisms get their food.
When one living organism feeds on another The flow of energy between trophic
organism, the stored chemical energy in the levels
organism being eaten is transferred to the • Energy transfer between trophic
organism that eats it. levels in an ecosystem is insufficient
and wasteful.
Organisms are classified as producers, • As energy is passed along a food
consumers and decomposers. chain, a lot of the energy is lost at
each trophic level as heat energy.
Producer: an organism that makes its • In fact, on average only about 10%
own organic nutrients usually using of the chemical energy stored in the
energy from sunlight through the process
of photosynthesis. body of one organism is tranfered to
Consumer: an organism that gets its the next organism in the food chain.
energy by feeding on other organisms. • The other 90% of the energy is lost
Decomposer: an organism that gets its as heat energy, produced during the
energy from dead or waste organic
material. metabolic processes, such as
respiration, growth and repair and
egestion.
Only energy that is converted into stored
energy in the form of new or repaired
animal tissues can be passed on to the
next organism in the food chain, the rest
of the energy is lost to the environment.
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The effects of inefficient energy transfer ECOLOGICAL PYRAMIDS
along food chains Ecological pyramids
1. The length of food chains 1. Pyramid of numbers
• Food chains cannot be very due to the ➢ A pyramid of numbers is an
inefficient energy transfer between trophic ecological pyramid that indicates the
levels. total number of individuals in each
• The decreasing levels amount of energy trophic level in an ecosystem.
that is passed from one trophic level to the ➢ The problem with a pyramid of
next means that there is usually only numbers is that it does not take size
enough energy for a maximum of five of the organism into account.
trophic levels in a food chain.
• The number of organisms in subsequent
trophic levels usually decreases along the
food chain, because there is less and less
energy to support these organisms.
2. Human food production
• A farmer can determine the production the
most energy-efficient type of food to grow.
• It is more energy efficient to eat foods that
come from organisms nearer the beginning
of the food chain than food that comes from 2. Pyramid of biomass
organisms further along the food chain. ➢ A pyramid of biomass is an
• This avoids the loss of energy that occurs ecological pyramid that indicates the
between producers and consumers in the total weight of all the living
farming food chain. organisms in each trophic level in an
• This is why staple foods all around the world ecosystem.
are plant-based, including maize, millet, ➢ The pyramid of biomass is a
sorghum, wheat, etc. conventional pyramid shape, but the
• Animal-based foods, such as meat eggs pyramid of numbers for the same
and milk, come from animals further along forest ecosystem was not.
the food chain and, therefore, a lot of energy ➢ This demonstrates that a pyramid of
has been lost in their production. biomass is a more accurate
• It takes about 16 times more energy to representation of the energy in an
produce one kilogram of beef than it takes ecosystem than a pyramid of
to produce one kilogram of a cereal crop. numbers.
FOOD WEBS IN ECOSYSTEMS
Food webs
→ Food chains are networks of interconnected
food chains.
→ They only show how one organism feeds on
one other organism.
→ In real ecosystems, organisms feed on
many different types of organisms
throughout their lives.
→ As with food chains, the arrows in a food
web show the direction of energy flow.
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