TEKS 5.9B Describe how the flow of energy derived form the Sun, used by producers to create their own
food, is transferred through a food chain and food web to consumers and decomposers.
Background
In third grade, students learned to identify and describe the flow of energy in a food chain and predict how
changes in a food chain affect the ecosystem such as removal of frogs from a pond or bees from a field (TEKS
3.9B). In 4th grade, students were able to describe the flow of energy through food webs, beginning with the
Sun, and predict how changes in the ecosystem affect the food web such as a fire in a forest (TEKS 4.9B).
Understanding the transfer of energy in food chains and food webs provides a foundation for more advanced
topics in biology in high school and college.
Key Concept 1: All energy transferred through food chains and webs is derived from the Sun.
The source of all energy on Earth is the Sun. However sunlight is not
usable food for animals. It must first be changed to a usable form by
plants. Animals, not able to produce their own food, are required to eat
plants or other animals to gain energy. An example is grass which
absorbs sunlight and is eaten by a grasshopper, which is eaten by a toad,
which gets eaten by a snake, which finally gets eaten by a hawk. In time
the hawk dies, decays, and is broken down by the decomposers which
return the nutrients back to the soil which is used again by nearby
plants. A food chain shows the transfer of this energy.
Sometimes more than one animal will eat a mouse, for example,
and a complex set of energy transfers occur. The interconnected
food chains are called a food web. Regardless of how simple a food
chain may be, or how complicated a food web becomes, the Sun is
still the original source of energy for all living things.
Key Concept 2: Producers use the Sun’s energy to create their
own food through photosynthesis.
Plants use sunlight, water, and carbon dioxide to make glucose,
a type of sugar the plant uses for food. When animals eat plants,
the energy stored in the plant is transferred to the animal. Only
plants produce their own food, so they are called producers.
From the smallest green algae in a pond to the largest tree on
earth, all plants produce their own food through
photosynthesis.
Key Concept 3: Consumers and decomposers get their energy from producers or other consumers.
Some animal consumers get their energy by eating plant
producers. Other animal consumers get their energy by
eating other consumers (animals). Some animals eat both
plants and other animals to obtain energy. (Decomposers
such as bacteria and fungi, are organisms that break down
dead organisms and their wastes to get energy.)
Key Concept 4: The different parts of a food web are producers, consumers, and decomposers.
In order to ensure a successful interactive ecosystem, there must
be a proper balance in the populations of organisms within a
food web. Any change in the population of any organism in the
food web or food chain will affect other organisms. If all the grass
in an area was killed in a wildfire, there would be less grass for
the deer to eat and they could die off. If there were not enough
deer to eat, then the predators (coyotes) would die off. If any
population of organisms changes in some way, either increasing
or decreasing, it will affect other organisms in the food web.
Ultimately decomposers, through their chemical breakdown of
the remains of dead plants and animals, return the nutrients in those decaying bodies back to the soil. This
decaying material becomes soil “humus”, a rich organic material that supports plant growth and the food web
continues.
TEKS 5.9D Identify the significance of the carbon dioxide-oxygen cycle to the survival of plants and animals.
Explanation:
The interdependence of plants and animals is underscored when students study plant photosynthesis and
animal respiration.
Key Concept 1: People and animals exhale carbon dioxide during respiration.
Most students know that blood flows in an animal’s body. One job of those
thousands of blood vessels is to carry oxygen from the lungs to every cell,
and then carry the discarded carbon dioxide waste from every cell back to
the lungs where it is exhaled. Plants need this exhaled carbon dioxide for
survival.
Key Concept 2: Plants use carbon dioxide, water, and sunlight to produce their own food, releasing oxygen
as a waste product.
During photosynthesis, plants absorb sunlight and carbon dioxide
through their leaves. There, a special chemical process combines the
water absorbed by plant roots with the sunlight and carbon dioxide to
produce glucose, a sugar plants use as food for growth. Plant cells
release oxygen as a waste product into the air. This oxygen is needed by
animals for survival.
Key Concept 3: In order to survive, people and animals inhale the
oxygen released by plants.
Plants release oxygen into the air which animals inhale. During
respiration, this inhaled oxygen is carried from the lungs by blood
vessels to the heart which pumps the oxygen rich blood and other
nutrients to each body cell for energy and growth. Plants also consume
oxygen during respiration when they burn sugars to gain energy.
Nature has provided an environment so that animals and plants can
interact together to provide necessities that each need for survival.
During the process of photosynthesis plants use sunlight, water, and
carbon dioxide to produce food (glucose or sugar) and release
oxygen.
Animals breathe in that oxygen and use digested food to produce
energy and carbon dioxide. Animals release carbon dioxide into the
air, which plants use and the cycle starts again.
The process by which animals and plants exchange gases is called the carbon dioxide/oxygen cycle. When this
cycle is in balance, both plants and animals will be able to survive in an environment. The burning of fossil
fuels has added an excess of carbon dioxide into the air.