Unit 8 Lesson 2: Interactions

Obtaining Energy

● Living organisms need a constant supply of energy.

The energy that fuels most life on Earth comes from
the Sun.

● Some organisms use the Sun’s energy to create

energy-rich molecules through the process of
photosynthesis. The energy-rich molecules, usually
sugars, serve as food.

● When the molecules break apart⎯for example, during

digestion⎯the energy in the chemical bonds is
released to fuel life processes(give energy).

Producers

● Organisms that use an outside energy source like the Sun

to make energy-rich molecules are called producers.

● Most producers contain chlorophyll, a chemical that is

required for photosynthesis. Green plants are producers.
Some producers do not contain chlorophyll and do not use
energy from the Sun.

● They make energy-rich molecules through a process called

chemosynthesis. These organisms can be found near
volcanic vents on the ocean floor. Inorganic molecules in
the water provide the energy source for chemosynthesis.

●

⚫ Organisms that can make their own food are classified

as Autotrophs

Consumers

● Organisms that cannot make their own energy-rich

molecules are called consumers. Consumers obtain
energy by eating other organisms.

● Organisms that cannot make their own food are called

Heterotrophs

●

● Herbivores Herbivores are the vegetarians of the

world - eat only plants. They include rabbits, deer,
and other plant eaters.

● Carnivores Carnivores are animals that eat other

animals(meat). Frogs and spiders are carnivores that
eat insects.

○ Scavenger- feeds on the bodies of dead organisms

● Omnivores Omnivores, including pigs and humans,

eats both plants and animals

Decomposers

● Decomposers, including fungi, bacteria, and

earthworms, consume wastes and dead organisms,
breaks them down and returns the raw materials
back to the environments.

●

Food Chains

● Food Chains A food chain is a simple model of the

feeding relationships in an ecosystem. For example,
shrubs are food for deer, and deer are food for
mountain lions.

●
● More on food chains next unit!

Symbiotic
Relationships

● Many organisms live together and share resources in

other ways. Any close relationship between species
is called symbiosis.

○ Mutualism

Lichens are made up of an alga or a

cyanobacterium that lives within the tissues of a
fungus. Both organisms benefit from this
association. A symbiotic relationship in which both
species benefit is called mutualism,

○
○

Symbiotic
Relationships

○ Commensalism

Anemones use their tentacles to

capture shrimp, fish, and other small animals to eat.
Striped clown fish can swim among the tentacles without
being harmed. The anemone’s tentacles protect the
clown fish from predators. A symbiotic relationship in
which one organism benefits and the other is not
affected is called commensalisms.

○ Parasitism Roundworms, are common in puppies. The

roundworm attaches itself to the inside of the puppy’s
intestine and feeds on nutrients in the puppy’s blood.
The puppy may have abdominal pain, bloating, and
diarrhea. A symbiotic parasitism relationship in which
one organism benefits but the other is harmed is called.

○

Niche

● A rotting log in a forest can be home to many species

of insects, including termites that eat decaying wood
and ants that feed on the termites.

● Other species that live on or under the rotting log

include millipedes, centipedes, spiders, and worms.
Each species has different requirements for its survival.
As a result, each species has its own niche.

● An organism’s niche is its role in its

environment⎯how it obtains food and shelter, finds a
mate, cares for its young, and avoids danger.

●

Special Adaptations

● Special adaptations that improve survival are often

part of an organism’s niche.

● When the caterpillars eat milkweed, they become

slightly poisonous. Birds avoid eating monarchs
because they learn that the caterpillars and adults
butterflies have an awful taste and can make them sick.

●

Predator and Prey

● An organism’s niche includes how it avoids being

eaten and how it finds or captures its food.

● Predators are consumers that capture and eat other

consumers.

● The prey is the organism that is captured by the

predator.

● The presence of predators usually increases the

number of different species that can live in an
ecosystem. Predators limit the size of prey
populations.

●

Cooperation

● Individual organisms often cooperate in ways that

improve survival.

● For example, a white-tailed deer that detects the

presence of wolves or coyotes will alert the other deer
in the herd.

● These cooperative actions improve survival and are a

part of the specie’s niche.

●

Question?

● Fleas often live on dogs or cats and bite them for a

meal of blood. This can be harmful to the cat or dog
that is bitten. What type of symbiotic relationship is
this?

●

Question?

● This is an example of parasitism. In this type of

relationship, one organism is harmed, while the other
benefits.

●

Question?

● Which describes how predators affect an ecosystem?

○ A. decrease the number of niches in the ecosystem
○ B. decrease the number of species in the ecosystem
○ C. increase competition among species
○ D. limit the size of the prey population