Part I: the Chain Vs. the Web

Part I: The Chain vs. the Web

Fundamental Question: How does energy flow in a food chain and food web?

The example on the right is a food chain. The arrows show how energy flows through the food chain by indicating what organism is eaten by another organism. The base of the food chain is the producer, grass. The grass obtained great energy from the sun using it for photosynthesis. Once the grasshopper eats the grass, some of the grass’s energy is transferred to the grasshopper. But the energy is not as great as it originally was in the grass. Once the frog eats the grasshopper, the grasshopper’s energy is transferred to the frog. The energy the frog obtains is not as great as it was in the grasshopper. Therefore, as you move up the food chain, energy decreases. So the hawk in the food chain would not obtain as much energy as the grass did, even though it is at the top of this particular food chain.

Food chains can be linked together to create a food web. A food web shows how all organisms in a particular ecosystem are related, andhow they depend upon each other in order to survive.

Part II: Producers, Consumers, Decomposers, Oh My!

Fundamental Question: How does energy flow in a food chain and food web?

Producers, or autotrophs, are organisms that produce their own food. We’re talking about plants! Any plant, tree, bush, etc. creates its own food through photosynthesis.

Consumers, or heterotrophs, are organisms that cannot make their own food. They have to eat other organisms to obtain energy and to live. Consumers are broken down into three categories: herbivores, carnivores, and omnivores.

Herbivores are organisms that eat only plants.

HINT: The prefix “herb” in the word herbivore means plant.

Carnivores are organisms that eat other animals, not plants.

HINT: The prefix “carn” in the word carnivore means meat.

Omnivores are organisms that eat both plants and animals.

HINT: The prefix “omni” in the word omnivore means all.

Decomposers are organisms that break down dead plants or animals.

Part III: Energy Pyramid

Fundamental Question: How does energy flow in an energy pyramid?

An Energy Pyramid places organisms into trophic levels. As you travel from the bottom of the pyramid on up, energy decreases. The bottom of the pyramid is where the primaryproducers or autotrophs are identified. Energy is the greatest at this level because of the sunsupplying energy to plants for photosynthesis to occur.The remaining levels up the pyramid are for the consumers or heterotrophs.

To break it downfurther, the first level of consumers are the primary consumers. Primary consumers areherbivores. The second level of consumers are the secondary consumers. Secondaryconsumers are either carnivores or omnivores. The third level of consumers are the tertiaryconsumers. Tertiary consumers are either carnivores or omnivores and are at the top of thefood web. But remember, just because these guys are at the top of the food web doesn’tmean they have the most energy. They have the least amount of energy.

Part IV: So Many Relationships!

Fundamental Question: Can you describe the predator/prey relationships and parasite/host relationships within a food web?

A predator is a carnivorous animal that hunts, kills, and eats other animals in order to survive.There are a variety of ways for predators to obtain their kill; it depends on the type of animal.Predators may hunt and attack actively for their prey, or they may hide and wait patiently astheir prey approaches closer to them before attacking. Once the prey is obtained, the predatormay slowly chew it or swallow it whole. Some predators may use venom to paralyze itsprey. Other predators may squeeze their victim to death. Some eat thousands of prey atonce, such as a whale eating plankton. Whatever method a predator uses, the goal is one inthe same: to kill and eat so to resolve hunger.

The prey is the underdog in the predator-prey relationship. The prey is the predator’s meal.The prey may try to run away or fight back against its predator and sometimes this might allowit an escape from being eaten. Life is tough when you’re at the bottom of the food chain. Preyare always having to be on the look out for their predators. It is not an easy life. They lack theagility and sometimes intelligence of their predator. The prey usually is the victim and cannotdefeat its predator.

Other types of relationships that exist between two organisms include commensalism,mutualism, and parasitism.In commensalism, one organism benefits from the relationship while the other organism doesnot benefit and is not harmed. An example of commensalism is a bird living in a tree. The birdbenefits by having its shelter in the tree. The tree does not benefit from the bird living in it andthe tree is not harmed from the bird living in it.

In mutualism, both organisms benefit from each other. An example is a bird that rides on theback of a rhino. The bird benefits by picking off the insects that are on the rhino and eatingthem as food. The rhino benefits by having the irritating insects removed off its back by thebird.

In parasitism, one organism (the parasite) benefits but the other organism (the host) does notbenefit. It is harmed. An example is a flea on a dog. The flea benefits by feeding off theblood of the dog. The dog is being harmed by the flea and can contract diseases from the fleathat could be life-threatening. The parasite-host relationship can be deadly. An example of aparasite-host relationship in a marine environment is a nematode inside a fish. Nematodescan live within the flesh of a fish. This infestation may cause health problems for the fish, andlead to death, but also nematodes can be transferred to and harm humans if consumed.