If you are a runner, you want to follow the 10% rule. You should never increase your weekly mileage by more than 10% from week to week.

Some people believe that we only use 10% of our brains. Actually this is a misconception. We use all of our brain.

In some states, you must pay a 10% income tax.

On many TV show competitions, only the top 10% of the contestants move to the next level.

So what exactly is 10%, and what does it represent?

You can think of 10% as one part of ten parts.

For example, if you had 10 glasses of water, one glass of water would represent 10 percent, or one-tenth.

You can also write it as a decimal.

$\mathbf{\text{10\% = .1}}$

 Do you need a visual of 10%? It would look like this!

What would it look like if you transferred 10% of the liquid into another container?
It would look like this!

And what would it look like if you transferred 10% of the liquid in the second container?

What would 10% of 10%  look like?
Here is an example :

In an ecosystem, approximately 10% of an organism's energy is transferred to another organism when it is eaten.

The flow of energy from one organism to another is visualized in a food chain.

Go on an adventure, and explore the organisms that live in Antarctica.
Build a food web that shows how food chains are connected in an ecosystem.
Click on the picture below to begin the adventure!

*Note*The activity will open in a new window. Upon completion, close the window to return to this page.

An important abiotic factor within an community is energy. Energy is transferred when one organism is eaten by another organism. A food chain is an easy way to diagram the flow of energy in a community.



Click on the picture to watch the video to learn about food chains.

The video will open in a new window. After the video plays, close the window to return to this page.
Record notes from the video in your science notebook or use the Cornell notes located in the “Related Items” section below.

• How does energy flow in a food chain?
• What is the ultimate source of energy in a food chain or food web?
• What two things do all organisms need to grow and survive?
• Why is only 10% of the energy consumed by an organism passed to the next level?

All the food chains in an ecosystem are interconnected and are represented by a food web. Food webs show the interdependence among organisms. A food web for an ecosystem is very complex.

Some food webs include decomposers. Decomposers include organisms such as bacteria and fungi. Decomposers breakdown dead and decaying organic matter.

Watch the following video to learn about food webs.
Click on the picture to watch the video.

The video will open in a new window. After the video plays, close the window to return to this page. Record notes from the video in your science notebook or use the Cornell notes located in the “Related Items” section below.

As you watch the video, consider the following questions:

• How are food chains related to a food web?
• Why are food webs so complex?
• What is the importance of understanding the flow of energy within an ecosystem?

Arrows on a food chain, or food web, represent the flow of energy. The placement of the arrows in a food chain or food web is very important. The arrows always show the direction of the energy as it is transferred from one organism to another.

The flow of energy can also be represented within an energy pyramid.
Notice how the food chain can be modeled in an energy pyramid.

All organisms, directly or indirectly, get their energy from the Sun.
Energy flows from the bottom to the top layer of the pyramid.
Approximately 10% of an organism’s energy is transferred to another organism.
Some call it the 10% Rule.

Recall the beakers of water found in the Engage reading.  If the water in the beakers represented the energy being transferred from one trophic or feeding level to the next, how would the energy pyramid look?

Do You Need More Help?
The following video provides additional help with the correct placement of the arrows in a food web.