12.2 · From Chains to Webs

From Ohio 5th Grade Science Power Workbook · Chapter 12 · Lesson 12.2.

Big idea: Most organisms eat more than one kind of food and are eaten by more than one kind of organism. A food web joins many chains together.

Learning goals: Explain why one chain is not the whole story

Describe what a food web shows

Find the chains inside a web

One chain leaves things out

A fox does not eat only rabbits. It eats squirrels, insects and fallen fruit too.

A rabbit is not eaten only by foxes. Hawks eat rabbits as well.

So a single chain is only one path. Real ecosystems have many paths crossing each other.

A web is chains joined together

A food web is a drawing of many food chains at once. The same organism can appear in several chains.

Every arrow in a web still means the same thing. Energy moves from the food to the eater.

A web looks busier than a chain, but you read it the same way, one arrow at a time.

Worked examples

Question: In a woodland, grass is eaten by rabbits and by deer. Rabbits are eaten by foxes and by hawks. How many food chains can you find here, and why is a web a better drawing than a chain?

Steps: List the paths. Grass → rabbit → fox. Grass → rabbit → hawk. Grass → deer.

That is three chains sharing the same grass and the same rabbits.

A web draws all three at once, so nothing is left out.

Answer: Three chains. A web shows them all together, so you can see that the grass feeds two kinds of animals and the rabbit is food for two kinds of animals.

Common mistakes

Most animals eat more than one thing

A food chain shows one food for each animal, so it can seem like a fox eats only rabbits.

Real animals usually eat several kinds of food. That is exactly why food webs exist. A chain is one path picked out of the web.

Check your thinking: If a question says an animal has only one food, look at the web again. Count the arrows pointing into that animal.

Remember

A web is a bundle of chains

To find a chain inside a web, start at a producer and follow one arrow at a time until you reach an organism with no arrow leaving it. That is one chain. Start again for the next.

Practice tip

Remember: Count the arrows, not the animals.

Tip: When Ohio asks how many foods an organism has, count the arrows pointing into it. When it asks how many things eat it, count the arrows leaving it.

Written practice

A classmate says a fox eats only rabbits because that is what the food chain on the poster showed. Explain why the poster does not prove that.

Sample response: A food chain shows only one path through an ecosystem. It picks one food for each animal and leaves the rest out. A fox eats squirrels, insects and fruit as well as rabbits. A food web would show all of those arrows.

Scoring guide: 1 point: explains that a chain shows only one path and leaves other foods out.

1 point: states that most animals eat several kinds of food, or names another food a fox eats.

Ohio lists 'organisms only eat one kind of food' as a misconception it builds wrong answers from.