Interactions Within

Ecosystems

Chapter 2

Grade 7 Science

Unit 1

Symbiosis

Interactions between the biotic parts of the environment.

There are 3 types:

1. Parasitism

2. Mutualism

3. Commensalism

1. Parasitism

One organism will benefit (the

parasite) and the other is harmed

(the host).

2. Mutualism

Both organism benefit.

Lichen = algae + fungus

3. Commensalism

One organism benefits while the

other neither gains or loses.

Roles of Organisms in the

Ecosystem

1. Producers

2. Consumers

3. Decomposers

4. Scavengers

1. Producers

Plants can produce their own

food from the abiotic

environment. (photosynthesis)

Water + carbon dioxide + Sunlight

Food (sugar) + oxygen

2. Consumers

Animals must consume, eat

other organisms. (the biotic

environment)

Can be classified as... herbivores,

carnivores, or omnivores.

Herbivore:

Animals that eat ONLY plants

(producers).

Omnivore:

Animals that eat both plants

AND animals.

Carnivore:

Animals that eat ONLY other

animals.

3. Decomposers

Organisms that break down dead and waste materials into their basic parts.

They release chemicals that break apart dead tissues and cells and absorb the nutrients for their own use.

Examples include bacteria and

other microorganisms, fungi and

worms.

4. Scavengers

Animals that eat decaying

animals and waste materials.

Examples include vultures, dung

beetle larvae, houseflies, crows

and some gulls.

Food Chains

The transfer of energy from organism to organism. Arrows show the direction of energy flow.

Green plants are the food (energy) source for all consumers and decomposers.

Producers Primary

Consumers

Secondary

Consumers

A

Sample

Food

Chain

Food Webs

Interconnecting food chains.

A

Marine

Food

Web

Energy Pyramids

Describes the gradual loss of

energy in food chains

About 10% is lost as you move

from one level to the next and

10% of the new energy is lost as

you move up and so on.

Energy in grass: 10 000 J

Energy in mice: 1000 J

Energy in weasel: 100 J

Energy in hawk: 10 J

Note: Energy pyramids are

not exact. Energy is

transferred to other types

(eg. heat) as it moves from

one level to the next. ie.

Not all of the 10% is

transferred.

Nutrient Cycles

Nutrients, such as nitrogen and carbon, are recycled in the environment.

All organisms are eventually recycled and their nutrients are returned to the soil by the action of decomposers.

Nutrient Cycles…

Herbivore

Carnivore

Omnivore

Producer

Decomposer