Food Webs and Energy Transfer

Grade 5 · Science · Study Guide

Learn how energy flows through ecosystems from the sun to producers, consumers, and decomposers.

All living things need energy to survive, and in ecosystems that energy comes originally from the sun. A food chain shows a simple, linear path of energy transfer from one organism to another. A food web is a more realistic model that shows the many overlapping food chains in an ecosystem.

Producers (also called autotrophs) are organisms like plants, algae, and phytoplankton that make their own food through photosynthesis. They capture sunlight and convert it into chemical energy stored in glucose.

Consumers (heterotrophs) must eat other organisms to get energy. Primary consumers (herbivores) eat producers. Secondary consumers eat primary consumers, and tertiary consumers eat secondary consumers. Predators hunt other animals; prey are the animals that get eaten.

Decomposers like bacteria and fungi break down dead organisms and return nutrients to the soil, which producers then use again. This closes the nutrient cycle.

A critical rule: energy is lost at each step in a food chain. Only about 10% of the energy from one level passes to the next — the rest is lost as heat. This means ecosystems can support far more producers than top predators, which is why there are always more mice than hawks in any field.

Key terms

Producer: An organism that makes its own food through photosynthesis; the base of every food chain.
Consumer: An organism that gets energy by eating other organisms; cannot make its own food.
Decomposer: An organism (bacteria, fungi) that breaks down dead matter and recycles nutrients back into the ecosystem.
Food Web: A diagram showing the many interconnected feeding relationships in an ecosystem.
10% Rule: Only about 10% of energy stored at one trophic level is passed to the next level; the rest is lost as heat.
Trophic Level: A step in a food chain representing the position of an organism based on what it eats.

Flashcards

Food Chain: A linear sequence showing how energy flows from one organism to the next: Producer → Primary Consumer → Secondary Consumer.
Food Web: Multiple intersecting food chains showing the complex feeding relationships in an ecosystem.
Herbivore: An animal that eats only plants; a primary consumer in the food chain.
Carnivore: An animal that eats other animals; can be a secondary or tertiary consumer.
Omnivore: An animal that eats both plants and animals (e.g., bears, humans).
Energy Pyramid: A diagram showing decreasing energy at each higher trophic level; widest at the bottom (producers).

Questions

Which organism is always found at the BASE of a food chain or food web?
1. A top predator like a hawk
2. A decomposer like a mushroom
3. A producer like a plant
4. A secondary consumer like a fox
Show answer
Answer: A producer like a plant
Producers (plants, algae) are at the base of all food chains because they convert sunlight into chemical energy, providing the foundation that all other organisms depend on.
In a food web, all of the energy from one trophic level is transferred to the next level.
Show answer
Answer: False
Only about 10% of the energy at one trophic level passes to the next. About 90% is lost as heat through metabolism, movement, and body heat.
Organisms like bacteria and fungi that break down dead matter are called ________.
Show answer
Answer: decomposers
Decomposers break down the organic matter in dead organisms and waste, releasing nutrients back into the soil and air for producers to use again.
Why can ecosystems support far more producers (plants) than top predators (hawks)?
1. Plants grow faster than animals
2. Energy is lost at each trophic level so less energy is available higher up
3. Top predators eat too many organisms
4. Producers do not need energy to survive
Show answer
Answer: Energy is lost at each trophic level so less energy is available higher up
Because ~90% of energy is lost at each transfer, far less energy is available at higher trophic levels. An ecosystem can support many plants but only a few top predators.
A food web is a more complete model of energy flow than a single food chain.
Show answer
Answer: True
A food web shows all the overlapping food chains in an ecosystem, giving a more realistic and complete picture of how energy and nutrients flow between organisms.

Get a personalized course on Food Webs and Energy Transfer built around your child.