1. Topic 4: How Organisms Interact
Grade 7 Unit 1
Topic 4: How Organisms Interact

2. Objectives:
I can describe and give examples of interaction and interdependence in an ecosystem
I can analyze an ecosystem and identify producers, consumers and decomposers
I can describe how energy and matter are transferred in an ecosystem

3. An Overview
The natural environment or habitat of an organism is their physical environment  
There can be differences in the habitats due to biotic components.
For example, the quantity and type of other organisms that could live there.
There can also be differences in habitats due to abiotic or physical components.
For example: rain, temperature, humidity, chemical composition of the soil, longitude, latitude, variation in seasons, etc..

4. Niche Name three roles that you have in the school: - - - -
Each role is one of your niches and an organism normally occupies several niches. A niche is the role or characteristic activity that is undertaken by an organism in an ecosystem.

5. Niche cont.. When defining a niche, keep in mind all these things:
How an organism gets its food and energy.
How an organism eliminates its waste.
How an organism interacts with other organisms in its environment (including competition, predators and sharing resources)
How an organism moves in its habitat
How an organism reproduces
How an organism modifies its environment

6. The Roles of Organisms in an Ecosystem cont.
**Note: Niche is not the same thing as habitat
Knowing an organisms niche can help explain why organisms act and interact as they do.

7. Food chain
A food chain is a model of feeding relationships among living organisms that indicates how energy is transferred within an ecosystem.

8. Food chain cont..
Producer – makes its own food by utilizing energy from the sun (photosynthesis). Examples: flowers, bacteria

9. Food chain cont..
Consumer – depends on other organisms for its food. All organisms that are not producers occupy the niche of consumers.
Herbivore– an organism that eats only plant material Ex: rabbit
Omnivore– an organism that eats other animals and plant material Ex: humans
Carnivore– an organism that eats only other consumers (herbivore, omnivore, carnivore) Ex: tiger
Predator – an organism that catches and eats other organisms of a different species
prey – an organisms that is caught and eaten by another organism of a different species.

10. Food Chains cont..
As dead organisms are broken down, their stored nutrients are released back into the ecosystem. Two types:
Decomposer – an organism that breaks down the cells of dead or waste materials and absorbed their nutrients. Ex: mushrooms and bacteria
Scavenger – a type of consumer that eats dead or decaying plant or animal matter. Ex : vulture, a carrion beetle

13. Take action p 41

14. Food Web
A food web is made up of many food chains. Normally consumers do not have one source of food. A food web is the network of feeding relationships among organisms.
Draw a food web of your region

15. Food web

16. Transfer of energy Matter and energy are two different things.
Matter is anything that occupies space, has a mass and is made up of particles.
Energy is transferred from one organism to another.
It is constantly recycled.

17. Transfer of energy cont..
At each step along the food chain, energy is taken in by an organism and used as fuel.
Some of this energy is also released as heat
Some of this energy is stored in body tissues
Some of this energy, that cannot be used, is passed out of the animal as waste.

18. Transfer of energy cont..
Ex: Most of the energy in grass eaten by a cow is not passed along the food chain.
Only 4% goes to build/repair the cow’s body.
30% fuels the cow’s normal activities.
60% is passed out as waste.

19. Transfer of energy cont..
If the energy is used by the organism it is NOT available to be passed onto the next organism. Therefore the energy is always higher in the previous level. Approximately 10% of the energy available is transferred from one level of the food chain to the next. (See figure 1.31)

20. Pyramid of Numbers
The pyramid of numbers is a model of an ecosystem that represents the number of organisms consumed at each level. Each level is called a trophic level. The producers are always at the base of the pyramid, therefore the first level.

21. Pyramid of Numbers
A pyramid of numbers represents the relative population necessary for the health of an ecosystem This means that we need:
A big population of producers
A smaller population of herbivores
An even smaller population of omnivores
And again and even smaller population of carnivores

22. Pyramid of Numbers cont.
Biomass represents the total mass of all the organisms in an ecosystem.
Knowing this, which trophic level has the biggest biomass?
The least?

23. ***Remember****
The transfer of energy in a pyramid of numbers: there is more available energy in the first trophic level then the other levels because there is always a loss of energy: heat, waste, growths and reproduction

24. Interesting facts.
Whenever a caterpillar is eating a maple leaf, there is a loss of energy as heat and a small amount is stored in the tissues of the caterpillar. That is why the energy of caterpillars feed only six blackbirds (robins)!

25. ? Read « Did you know » on page 45 and answer the following ? questions
When could the Titanic completely disappear?