
Objectives:

Explain why ecosystems require continuous energy from the Sun

Evaluate the efficiency of the flow of energy and matter through a food chain or pyramid

Catalyst:

Imagine that Mr. J wanders into the food web (shown at right) and eats all the mountain lions. What happens to the elk population?


Homework Review

Catalyst Review

Food Webs Need the Sun!

White boards

Trophic Levels and Vegetarianism

Draw your own FOOD WEB!!! GROUP WORK!

Closing

Exit Question


Imagine that a bear wanders into the food web
(shown at right) and eats all the mountain lions.
What happens to the elk population?

Elk population decreases in size

Remember, whenever a population loses its predators, it will increase in size.


Key Point #1: Ecosystems require continuous input of energy from the Sun

All of the energy in a food web ALWAYS begins with the Sun.

What if the energy from the Sun were removed?
 Without energy from the Sun, producers die.
 If producers die, primary consumers die.
 If primary consumers die, secondary consumers die.

The bottom line: ecosystems require energy from the Sun, or else everything dies!!!

What would happen to the producers in this ecosystem if the Sun stopped shining?

What would happen to the primary consumers in this ecosystem if the
Sun stopped shining?

What would happen to the secondary consumers in this ecosystem if the
Sun stopped shining?

Why does this food web require continuous input of energy from the
Sun?



Trophic level = step in a food chain
Key Point #2: Only 10% of the energy in a food web is passed from one trophic level to the next.

The rest is lost as heat.

Called the “10% rule.”

The higher up in the food chain you go, the more food an organism must eat to get the same amount of energy.
100%
1%
10% 10%

100%
1%
10%
10%



If you eat beef, you go through an extra trophic level (2 steps vs. 1)
Because of this extra step, it takes about the same amount of the Sun’s energy to make 1kg of beef as 10kg of grain
Think of how many people could be fed with that extra food…

What % of energy does each organism receive?
100%

The taiga is one of the coldest ecosystems on Earth: Winter lasts 5-6 months, and hardly any sunlight reaches it during the rest of the year. Fur trees and grass use this meager sunlight to grow. Mice feed on the grass and, though they are rare, a few owls feed upon the mice.
1%
10%

What % of energy does each organism receive?

In the tropical savanna, large amounts of sunlight allow for an enormous, unbroken layer of grass to grow. Because of the abundance of grass, there are many grazing animals, such as sheep, goats, and cattle. A few lions roam the grassland, eating these delicious mammals.
100%
10%
1%


Write your own description of a food web on the “Describe Your Own Food Web” worksheet.

Your food web should contain AT LEAST one producer, three primary consumers, two secondary consumers, one tertiary consumer.

It does not have to be realistic.

Can be about aliens, Lil’ Wayne, dragons…


In the first box of your “Drawing Time!” worksheet, draw the food web you just described.

Label the amount of the Sun’s energy that each organism in your food web receives.


Trade your “Describe Your Own Food Web” with someone else in your group.

In the second box of your “Drawing Time!” worksheet…

Draw a food chain from this food web

Label the amount of the Sun’s energy that each organism receives (Producer=100%)

Keep trading, until all four boxes are filled.

When you get your paper back, make sure that all the food chains are correct!


Ecosystems require continuous input of energy from the Sun

Sun provides energy for producers

Producers provide energy for consumers

No Sun  no producers  no consumers

Only 10% of the energy in a food web is passed from one trophic level to the next

100%  10%  1%  0.1%



A
Exit Questions: Choose One (Both for Extra Credit)
In your own words, explain WHY ecosystems require a continuous input of energy from the Sun.
Hint: Use the words
“producer,” “primary consumer,” “secondary consumer.”
B
Read the following passage to answer the questions below:
The ranches of the American Midwest are full of grass. The grass uses sunlight to grow. Cows and rabbits graze on the grass. However, the grass provides these animals little shelter from wolves, which eat the cows and rabbits.



Where does all the energy that enters this food web begin?
What percent of the food web’s energy does the grass receive?
What percent of the food web’s energy does the wolves receive?


GP went over poorly, students un-invested in it.
Think it would have gone over better as a review for unit test, or extra credit opportunity.

Not enough material for today. Think yesterday and today could be consolidated into one day, but be careful… could make for too much notes.

Add in the “energy flows” slide from when we taught P/CR to help explain why we need constant input of energy from the Sun!!! Great idea, DJ!!!