Week 8: Energy and Food Webs

All of the characteristics of living things require ENERGY, therefore EVERY organism needs to get energy from somewhere.

Energy Transfer

In order for all organisms to survive, they need to consume energy to do every action that is a part of life. This includes:

Movement
Digestion
Respiration (Breathing)
Pumping Blood (or other fluids and nutrients) Around
Replicating Cells
Even Brain Activity

This means that even while sleeping, you are consuming energy to survive.

BUT WHERE DOES THIS ENERGY COME FROM?

For all animals this comes from organisms we eat. This is why we call them CONSUMERS.

Producers: Photosynthesis

Most plants and microorganisms cannot 'eat' other organisms. Instead they get their energy from THE SUN, and turn it into useful units of energy in the form of GLUCOSE (sugar). Because these plants turn sunlight into sugar, providing a food source for herbivores and omnivores, they are called PRODUCERS as they are the entry point for energy into the ecosystem.

This process of turning sunlight into sugar is called PHOTOSYNTHESIS. This process consumes carbon dioxide and water, and produces oxygen which is why trees are good for managing the environment.

Every ecosystem MUST have one or more PRODUCERS in order to act as a starting point for energy in the ecosystem. Because of this the sun is considered the source of all energy on Earth.

The Food Chain

This is a simple example of the food chain. The arrow indicates the direction of ENERGY TRANSFER and can be read as "is eaten by". In this example the acorns (or more likely the oak tree that dropped the acorns) is the PRODUCER in the chain and every animal is a CONSUMER. We can break the consumers into three groups:

PRIMARY CONSUMERS are the first consumers in the chain and consumer the PRODUCERS.
SECONDARY CONSUMERS are the consumers who eat PRIMARY CONSUMERS.
TERTIARY CONSUMERS are the consumers who eat SECONDARY CONSUMERS. They are rarely eaten by other species.

Food Webs

Food chains are useful for identifying one particular flow of energy, but they don't provide a clear picture of the interactions of the entire ecosystem. Instead, species will often consume and be consumed by several different species in their ecosystem.

To more accurately describe the ecosystem, we can use a FOOD WEB to show the network of energy transfer as different species consume each other. For example, the Rabbit consumes Grasses, but is consumed by Foxes and Hawks.

With a food web we can show how changes in the POPULATIONS of different species will cause larger disruptions in the ecosystem.

QUESTIONS TO THINK ABOUT:

What would happen if the rabbit population were to grow quickly?
What would happen if the rabbit population were to suddenly shrink?
What species in this food web is the most important? Why?

Food Webs - Education Perfect

Head to Education Perfect and complete the Food Webs modules assigned to you.

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