Download Biology I Chapter 2, Section 2 Nutrition and Energy Flow Ecologists

Biology I
Chapter 2, Section 2
Nutrition and Energy Flow
Ecologists trace the flow of energy through communities to discover
nutritional relationships between organisms.
Producers – Autotrophs
The ultimate source of energy of life is the sun. An organism that
uses light energy or energy stored in chemical compounds to make
energy-rich compounds is an autotroph. Plants are the most familiar
of autotrophs but some organisms such as green algae also make
their own nutrients. Other organisms in the biosphere depend on
autotrophs for nutrients and energy. These dependent organisms
are called consumers.
Consumers – Heterotrophs
An organism that cannot make its own food and feeds on other
organism is called a heterotroph. Heterotrophs display a variety of
feeding relationships.
1. Feeds only on plants is a herbivore (rabbits, grasshoppers,
squirrels, bees)
2. Eat other heterotrophs (lions kill and eat only other animals
carnivores).
3. Scavengers do not kill for food but scavenge and eat animals
that have already died (vultures). What would our ecosystems
be like without scavengers?
4. Omnivores: Humans are an example of a third type of
heterotroph. Most people eat a variety of foods that include
both animal and plant materials.
5. Decomposers (such as bacteria and fungi) break down the
complex compounds of dead and decaying plants and animals
into simpler molecules that can be more easily absorbed.
A food chain is a simple model that scientists use to show how
matter and energy moves through the ecosystem. In a food chain,
nutrients and energy move from autotrophs to heterotrophs and
eventually to decompose.
First order – heterotrophs - herbivores such as the deer, cardinal
turtle and fish obtain food from photosynthetic organisms.
Second order – heterotrophs – some carnivores feed on first-order
heterotrophs. Owls feed on fishes or mice, worms or small insects.
Third order - heterotrophs – Carnivores are animals that feed on
second-order heterotrophs (bears attack other animals such as the
deer and bears also rely on a large diet of berries and so are termed
omnivores.
Decomposers – at every level in a food chain, bacteria and fungi
break down living matter and help release nutrients.
Tropic levels represent links in the chain. Tropic level is the
passage of energy and materials. First level of heterotroph is an
organism that feeds on plants. A second order heterotroph is an
organism that feeds on a first order heterotroph. A food chain
represents only one possible route for the transfer of matter and
energy through an ecosystem.
Food web shows all the possible feeding relationships at each tropic
level in a community. A food web is a more realistic model than a
food chain because most organisms depend on more than one other
species for food.