Section 2Energy Flow in Ecosystems

Grade 10 BiologySpring 2011

A robin, snake, hawk, frog, grasshopper, mouse, and rabbit can all be found in an open field.

Draw arrows to show what eats what in this field ecosystem.

Distinguish between producers and consumers

Compare food webs with food chains Describe why food chains are rarely

longer than three or four links

Primary Productivity: the rate at which organic material is produced by photosynthetic organisms in an ecosystem

Producers: organisms that first capture energy Plants, some bacteria, algae Make energy storing molecules

Consumers: organisms that consume plants or other organisms to obtain energy necessary to build their molecules

Trophic Level: an energy level that is used to study how energy is moved through an ecosystem Organisms are assigned

to trophic levels Energy moves from one

trophic level to another SUN PRODUCE

RCONSUMER

CONSUMER

Food Chain: path of energy through the trophic levels of an ecosystem

First Level: occupied by producers Plants, algae, bacteria Producers use energy of

the sun to build energy-rich carbohydrates

Many also incorporate key nutrients (nitrogen) from the environment into their biological molecules

Second Level: herbivores eat the primary producers from the first trophic level Primary consumers

Herbivores: animals that eat plants or other primary producers

Third Level: carnivores eat the primary consumers (herbivores) from the second trophic level

Carnivore: animals that eat other animals

Omnivore: both herbivores and carnivores

Detritivores: consumer, obtain their energy from the organic wastes and dead bodies that are produced at all trophic levels Bacteria, fungi, worms

Decomposers: cause decay Bacteria, fungi

This releases nutrients back into the environment

Fourth Level: carnivores that consume other carnivores Tertiary consumers, top carnivores

Food web: complicated, interconnected group of food chains In most ecosystems, energy does not

follow simple straight paths Individual animals often fed at several

trophic levels

Energy transfer: during every transfer of energy within an ecosystem, energy is lost as heat Amount of useful energy

available to do work decreases as energy passes through an ecosystem

Loss of energy limits number of trophic levels

Energy Pyramid: diagram in which each trophic level is represented by a block, and the blocks are stacked on top of each other, with the lowest trophic level on the bottom Pyramid shaped because each level represents the amount of energy stored in the organisms at that level

At each trophic level, the energy stored by the organisms in a level is about one-tenth of that stored by the organisms in the level below

First Trophic Level: 1,000J energy

Second Trophic Level: 100J energy

Third Trophic Level: 10J energy

Fourth Trophic Level: 1J energy

Most ecosystems involve three or four levels

Too much energy is lost at each level to allow more

Why can’t a large human population survive from eating lions?

HUMANS EATING BREAD: HUMANS EATING BEEF:

it takes a certain amount of grain……

To produce enough bread……

To provide one person with a certain amount of energy.

It takes 10 times more grain…….

To feed one cow……

To make enough beef…..

To provide one person with the same amount of energy.

Biomass: dry weight of tissue and other organic matter found in a specific ecosystem

Each higher level on the pyramid contains only 10% of biomass found in the trophic level below it Used to determine the amount of energy present

in trophic levels Used because the number of individuals in a trophic level may not be an accurate indicator of the amount of energy in that level

Due to size of organisms

1. How much energy is lost as you move up a trophic level?

2. List the reasons why food chains do not tend to exceed four links?

3. How are producers different from consumers.

1. 90% of energy is lost at each trophic level2. Food chains do not tend to exceed four

links because so much energy is lost at each trophic level.

3. Producers use energy (usually from the sun) to assemble food molecules, hence “producing food”. Consumers must take in (or consume) these food molecules to obtain their energy.