Energy Flow in Ecosystems – 4th Grade Garden Curriculum

Lecture:

The source of energy: Explain how all of our energy comes from the sun. This lecture will cover food chains, energy flow, and how everything is connected in a constant flow.

Photosynthesis: A process that plants use to create food. Plants use their own leaves to take in carbon dioxide from the air, they use their roots to draw in water and nutrients from the ground

Chloroplasts: Little organelles in the leaves that absorb energy (sunlight) to convert water and sunlight into glucose (sugar)

Chlorophyll: Fills the chloroplasts and absorbs the sunlight, this also gives the plant it’s green color. Chlorophyll absorbs every color except green. As plants convert the carbon dioxide into sugar all they need is the carbon, so in turn the oxygen is released into the atmosphere for us to breathe

Ecosystem services: processes and resources that are provided by healthy natural ecosystems and benefit humans. 

Humans and animals are unable to create their own food, they must eat plants or other animals for energy. By doing this, their energy actually comes from the sun. Since plants use the sun to create food, and we eat the plants for food, our energy starts at the sun.

Producers: Plants, because they create their own food from the sun

Consumers: Any animal or organism who consumes another organism for energy

Food Chain: A series of organisms that depend on the next as a food source

Herbivore: Animals who only eat plants, these are also Primary Consumers because they eat the first level on the food chain; the plants

Carnivore: Animals that eat other animals for food. These are Secondary Consumers because they eat the carnivores, they can also be Tertiary Consumers, animals that eat other carnivores

Omnivores: Animals that can eat plants or animals, these can occupy more than one level of the food web. An example would be humans, bears, foxes… It all depends on what they are eating.

Decomposers: Organisms such as bacteria and fungi, which feed on dead and rotting matter and return the nutrients back into the soil. “In nature there is no waste, only decomposers”

When an herbivore eats, part of the energy from the plant is used to build body mass, and the rest of the energy helps the animal move and function or is lost as heat energy. Therefore, only a small percentage of the energy the animal got from the plant, about ten percent, is passed on to the next animal that eats it. The higher on the food chain, the less remaining energy there is, so there are far fewer individual animals higher up on the food chain than at the bottom.

Activity:

The classes will break up into the usual groups and will be given an “ecosystem” of flashcards. These will represent a food chain and each group must arrange each level of the chain. Sun, grass, cow, human, etc.

Teachers and docents will prompt a discussion about what the students had for dinner the previous night. If there is enough time then each student can share, otherwise volunteers will be taken. Ask what was eaten and what part of that meal contained the most energy, the least. 

Each group will present to the class their food chain; one volunteer will present the meal and which part contained more/less energy. 

Author:
Alrie Middlebrook
San Jose, CA
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