All living things are in a food chain. For example, zebras eat plants and grasses. Lions eat the zebras. Lions, zebras, and plants all belong to one food chain.

Other animals eat zebras, too. Other animals eat the same plants. They all form different food chains. Put together, these food chains are called a food web

Trophic Levels

Food chains have different levels. These are called trophic levels.

Producers

Organisms in the first trophic level are called producers. Most producers are plants. Algae and some bacteria are also producers.

Each producer makes its own food. Most producers use photosynthesis. That means they use sunlightcarbon dioxide, and water to create energy

Consumers

The next trophic levels are animals that eat producers. They are called consumers. Some consumers are herbivores while others are carnivores. They can also be omnivores, which means they eat both meat and plants.

Primary consumers are herbivores. They eat plants and other producers. Deer, mice, and elephants are herbivores. They eat grass, shrubs, and trees. In the desert, a mouse is a primary consumer. It eats seeds and fruit. In the ocean, many fish and turtles are herbivores. They eat algae and seagrass.

Secondary consumers are animals that eat herbivores. In a desert, a secondary consumer may be a snake. It eats mice. In underwater kelp forests, sea otters are secondary consumers. They hunt sea urchins. Secondary consumers are at the third trophic level.

Animals at the next level eat secondary consumers. In the desert, an owl or eagle may hunt snakes. Top predators are also called apex predators. No other animal eats an apex predator. Lions are apex predators. Great white sharks are apex predators in the ocean.

Detritivores and Decomposers

Detritivores and decomposers are at the end of food chains. Detritivores eat things that are not alive. Vultures eat dead animals, for example.

Some organisms, like fungi and bacteria, are decomposers. They turn dead plants and other organisms into soil. They let food chains start over.

For example, grass makes food through photosynthesis. A rabbit eats the grass. Then, a fox eats the rabbit. When the fox dies, worms and fungi break down its body. The animal becomes part of the soil. There, it leaves nutrients for plants to grow. This way, the cycle keeps going.

Biomass

Biomass is the energy in living creatures. It starts with the sun's energy. Plants use sunlight to create energy, or biomass, for themselves. When animals eat these plants, they also create energy, or biomass. At each step, energy gets lost, though. Animals are only able to take a part of it. 

As you go up the food chain, there is less and less biomass. There is more energy in the lower trophic levels. That is why food webs need more producers than herbivores. They can only have a few carnivores and omnivores.

Sometimes, food chains can fail. If plants are destroyed, herbivores do not have enough to eat. Their numbers go down. Humans can also destroy a food chain. People cut down forests for wood. 

Bioaccumulation

Pesticides get into the soil and water. Sometimes, an animal eats a polluted plant. The pesticides stay in the animal's fat. Then, a carnivore eats that animal. It takes in more and more pesticide. This is called bioaccumulation.

In the 1940s and 1950s, bald eagles began disappearing. DDT was a major reason. DDT stands for dichloro-diphenyl-trichloroethane. It is a pesticide. DDT was building up in soil and water. Fish ate organisms with DDT. Bald eagles ate the fish. Because of the DDT, they started laying eggs with thin shells. These shells often broke and the baby birds died.

The U.S. government decided that using DDT was against the law. Many food webs have come back. Baby eagles are now hatching again.

 

Food Web
Corals and fishes and sharks, oh my.
abundance
Noun

large amount.

accumulate
Verb

to gather or collect.

adapt
Verb

to adjust to new surroundings or a new situation.

algae
Plural Noun

(singular: alga) diverse group of aquatic organisms, the largest of which are seaweeds.

Allies
Noun

alliance of countries that opposed the Axis during World War II. The Allies were led by the U.S., the United Kingdom, and the Soviet Union.

apex predator
Noun

species at the top of the food chain, with no predators of its own. Also called an alpha predator or top predator.

aquatic
Adjective

having to do with water.

Noun

organism that can produce its own food and nutrients from chemicals in the atmosphere, usually through photosynthesis or chemosynthesis.

Plural Noun

(singular: bacterium) single-celled organisms found in every ecosystem on Earth.

Balkan
Adjective

having to do with the Balkan Peninsula in southeastern Europe.

bioaccumulation
Noun

process by which chemicals are absorbed by an organism, either from exposure to a substance with the chemical or by consumption of food containing the chemical.

biomass
Noun

living organisms, and the energy contained within them.

carbon
Noun

chemical element with the symbol C, which forms the basis of all known life.

carbon dioxide
Noun

greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

Noun

organism that eats meat.

chemosynthesis
Noun

process by which some microbes turn carbon dioxide and water into carbohydrates using energy obtained from inorganic chemical reactions.

colony
Noun

group of one species of organism living close together.

consist
Verb

to be made of.

consumer
Noun

organism on the food chain that depends on autotrophs (producers) or other consumers for food, nutrition, and energy.

dam
Noun

structure built across a river or other waterway to control the flow of water.

DDT
Noun

(dichloro-diphenyl-trichloroethane) toxic chemical used as an insecticide but illegal for most uses in the U.S. since 1972.

decay
Verb

to rot or decompose.

decline
Verb

to reduce or go down in number.

decomposer
Noun

organism that breaks down dead organic material; also sometimes referred to as detritivores

Noun

area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.

detritivore
Noun

organism that consumes dead plant material.

devastate
Verb

to destroy.

divert
Verb

to direct away from a familiar path.

Noun

period of greatly reduced precipitation.

earthquake
Noun

the sudden shaking of Earth's crust caused by the release of energy along fault lines or from volcanic activity.

Noun

community and interactions of living and nonliving things in an area.

edible
Adjective

able to be eaten and digested.

eliminate
Verb

to remove.

Noun

capacity to do work.

enormous
Adjective

very large.

farm
Noun

land cultivated for crops, livestock, or both.

fat
Noun

material found in organisms that is colorless and odorless and may be solid or liquid at room temperature.

feces
Plural Noun

waste material produced by the living body of an organism.

filter feeder
Noun

aquatic animal that strains nutrients from water.

Noun

group of organisms linked in order of the food they eat, from producers to consumers, and from prey, predators, scavengers, and decomposers.

Noun

all related food chains in an ecosystem. Also called a food cycle.

forest
Noun

ecosystem filled with trees and underbrush.

fruit
Noun

edible part of a plant that grows from a flower.

fungi
Plural Noun

(singular: fungus) organisms that survive by decomposing and absorbing nutrients in organic material such as soil or dead organisms.

glucose
Noun

"simple sugar" chemical produced by many plants during photosynthesis.

grassland
Noun

ecosystem with large, flat areas of grasses.

Noun

part of a body of water deep enough for ships to dock.

harvest
Noun

the gathering and collection of crops, including both plants and animals.

Noun

organism that eats mainly plants and other producers.

inorganic
Adjective

composed of material that is not living, and never was, such as rock.

kelp
Noun

type of seaweed.

kelp forest
Noun

underwater habitat filled with tall seaweeds known as kelp.

krill
Noun

small marine crustacean, similar to shrimp.

Noun

the fall of rocks, soil, and other materials from a mountain, hill, or slope.

larva
Noun

a new or immature insect or other type of invertebrate.

Noun

bank of a river, raised either naturally or constructed by people.

lumber
Noun

precisely cut pieces of wood such as boards or planks.

malaria
Noun

infectious disease caused by a parasite carried by mosquitoes.

marine
Adjective

having to do with the ocean.

multiple
Adjective

many.

nori
Noun

red algae that is often dried and used to wrap sushi.

Noun

substance an organism needs for energy, growth, and life.

Noun

organism that eats a variety of organisms, including plants, animals, and fungi.

organic waste
Noun

used or excess material that might be broken down to be used again. Also called biodegradable waste.

oyster
Noun

type of marine animal (mollusk).

pesticide
Noun

natural or manufactured substance used to kill organisms that threaten agriculture or are undesirable. Pesticides can be fungicides (which kill harmful fungi), insecticides (which kill harmful insects), herbicides (which kill harmful plants), or rodenticides (which kill harmful rodents.)

Noun

process by which plants turn water, sunlight, and carbon dioxide into water, oxygen, and simple sugars.

phytoplankton
Noun

microscopic organism that lives in the ocean and can convert light energy to chemical energy through photosynthesis.

plant
Noun

organism that produces its own food through photosynthesis and whose cells have walls.

plummet
Verb

to fall sharply.

pollinate
Verb

to transfer pollen from one part of a flower (the anther) to another (the stigma).

pollutant
Noun

chemical or other substance that harms a natural resource.

prey
Noun

animal that is hunted and eaten by other animals.

primary consumer
Noun

organism that eats producers; herbivores.

producer
Noun

organism on the food chain that can produce its own energy and nutrients. Also called an autotroph.

Noun

area of tall, mostly evergreen trees and a high amount of rainfall.

recycle
Verb

to clean or process in order to make suitable for reuse.

reduce
Verb

to lower or lessen.

remains
Noun

materials left from a dead or absent organism.

remarkable
Adjective

unusual and dramatic.

Noun

overflow of fluid from a farm or industrial factory.

salmon run
Noun

area or path of a river where salmon return to spawn every season.

Noun

organism that eats dead or rotting biomass, such as animal flesh or plant material.

seagrass
Noun

type of plant that grows in the ocean.

sea lettuce
Noun

seaweed with large, flat leaves.

sea urchin
Noun

marine animal (echinoderm) with a circular, spiny shell.

seaweed
Noun

marine algae. Seaweed can be composed of brown, green, or red algae, as well as "blue-green algae," which is actually bacteria.

secondary consumer
Noun

organism that eats meat.

seed
Noun

part of a plant from which a new plant grows.

shrub
Noun

type of plant, smaller than a tree but having woody branches.

stress
Verb

to strain or put pressure on.

sulfur
Noun

chemical element with the symbol S.

sunlight
Noun

visible radiation from the sun.

survive
Verb

to live.

sushi
Noun

bite-sized rolls or balls of sticky rice topped with seafood or vegetables.

terrestrial
Adjective

having to do with the Earth or dry land.

tertiary consumer
Noun

carnivore that mostly eats other carnivores.

top predator
Noun

species at the top of the food chain, with no predators of its own. Also called an alpha predator or apex predator.

toxic
Adjective

poisonous.

trophic level
Noun

one of three positions on the food chain: autotrophs (first), herbivores (second), and carnivores and omnivores (third).

tropical
Adjective

existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.

typhus
Noun

highly infectious and sometimes deadly disease with symptoms of itching sores and severe headache, caused by lice.

Noun

developed, densely populated area where most inhabitants have nonagricultural jobs.

urchin barren
Noun

site of a former kelp forest that has been destroyed by sea urchins.

vegetable
Noun

plant that is grown or harvested for food.

Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

World War II
Noun

(1939-1945) armed conflict between the Allies (represented by the United States, the United Kingdom, and the Soviet Union) and the Axis (represented by Germany, Italy, and Japan.)