Energy Cycle Notes 8th Grade Science

ENERGY!!! All living things need energy to live. Energy can be converted from one form to another. It can also be transferred from one organism to another. Consumers cannot make their own energy; they have to eat producers and other consumers to get energy.

When an organism eats another, the energy that is stored in one organism is transferred to the other. Suppose you ate a hamburger. When a cow eats a plant, the energy stored in the plant is transferred to the cow, which in turn is transferred to you when you eat a hamburger.

But where does all of this energy start? How do producers get their own energy?

Photosynthesis Photosynthesis is the process by which producers (plants) are able to capture energy from the sun and use that energy to make their own energy. It looks something like this: Energy from the sun + CO2 + water --> glucose (energy) + oxygen

Respiration All consumers need energy from plants in the form of sugars, we also need oxygen the plants make. The sugar and oxygen produced during photosynthesis are in turn used by consumers to produce CO2, water, and they release energy too. This process is known as respiration. Respiration looks something like this: O2 + glucose --> released energy + CO2 + water

Mechanical Energy

Respiration is almost the exact opposite reaction to photosynthesis. These two reactions work together to maintain a biological balance on earth.

So, everything needs energy to work; producers get energy from the sun and consumers get energy from the sugars in the producers either by eating the producers or eating a consumer that has eaten a producer. So in food chains the arrows tell us how the energy is passed on.

Sun’s energy -> Plants -> Mouse -> Snake -> Hawk (although we don’t really include the sun in food chains) The plants get energy from the sun, the mouse gets it’s energy from the plant, the snake gets its energy from the mouse, and the hawk gets its energy from the snake (remember, this is just one possibility).

Food chains usually have at least 3 links to them, but rarely more than 5. This limit exists because the amount of available energy is reduced as you move from one level to the next.

When a plant absorbs energy from the sun, the plant uses some of this energy to grow and produce seeds. When the mouse eats the grass, energy that was in the grass is transformed to the mouse.

However, most of the energy was already used by the plant to grow and produce seeds. Only 10% of the energy is actually passed on. Likewise, when the snake eats the mouse, most of the energy was already used by the mouse to grow, breath, move digest food, etc. Only 10% of the mouse’s energy was transferred to the snake and only 10% of the snake’s energy was transferred to the owl. So only part of the original sun’s energy is passed on throughout the community.

Rootbeer Demo... The sun has two liters or 2,000 mililiters of energy (rootbeer) to give Of that, the plant gets 10% of that or 200 milliliters The mouse gets 10% of the plants energy, which is 1% of the sun’s energy or 20 ml The snake gets 10% of the mouses energy, which is only 0.1% of the sun’s energy is 2 ml The hawk gets only 10% of the snake’s energy, which is only 0.01% of the sun’s energy or 0.2 ml!!!

Questions What did the rootbeer represent? ENERGY

Questions Which organism was most satisfied by the amount of “energy” it recieved? Which organism was least satisfied? Plant Hawk

Questions What happened to the 1,800 milliliters from the sun that the plant didn’t absorb? given off as heat

Questions How much “energy” did the mouse USE? 90%

Questions What organism in the food chain is going to eat the most food to meet their energy needs? HAWK

Questions Why couldn’t this food chain have any more links? No more energy to give

Therefore, as you move up the food chain, there is less energy available. What does this tell you about the animals located at the top of the food chain? They have to eat more!

Place picture here...

No matter how complex the food web or a food chain or a food pyramid a community always needs more producers than consumers. A food pyramid is also used to represent the energy levels of a food web. The producer level is the largest level, not only because it contains the most organisms, but also because it contains the most available energy.

For this reason, the pyramids are also known as energy pyramids as well as food pyramids. As you move up the pyramid, the transfer of energy is less efficient and so each level must become smaller, both in organism numbers and available energy. Therefore, only a few animals are found at the top of the energy pyramid.

The top of the food pyramid is the smallest, because there are less of those organisms and because there is less energy available.

These animals- the top consumers, such as lions, wolves, eagles, and bass - exsit in smaller populations because they have to eat more to stay alive, so the carrying capacity for these organisms is smaller. There must be more producers than primary consumers, more primary consumers than secondary consumers, and more secondary consumers than top consumers for the community to survive.

Make sure that the energy pyramid at the bottom of your paper has each level labeled and the arrows on each side drawn and labeled.