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Chapter 9Ecosystem Energy

ALABAMA 7TH GRADE SCIENCE STANDARDS COVERED IN THIS CHAPTER INCLUDE:

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7 Describe biotic and abiotic factors in the environment.

BioTic AND ABI0TIc FACTORS.

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You might remember — ecosystems are the interactions

INKS between plants, animals and their environment. They are.q;wwLrrzL1 systems that demonstrate how organisms interact with each

ABCO35 other and their physical environment. Living things inecosystems are called biotic factors. Some examples ofbiotic

factors include plants, animals, fungi bacteria and protists. Non-living things are

called abiotic factors. Things like rocks, soil, air, sunlight, shade, chemicals or

temperature are all abiotic factors. So, to put it all together, an ecosystem is roughly

defined as the interaction between the abiotic and biotic factors in an area.

Remember, it is not defined by its size; it can be as large as a desert or as small as a

puddle. It is a system!

Activity

Fill in the table below with biotic or abiotic.

Type of Factor Example

grass in a field

nitrogen in the air

salt content of seawater

bacteria in the soil

granite bedrock

beavers building a dam

dam built by beavers

humidity level

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Chapter 9

INTERACTION AND INTERDEPENDENCEMatter within an ecosystem is constantly recycled over and over again. Elements,chemical compounds and other sources ofmafter pass from one state to another throughthe ecosystem. This is called an energy cycle. As a deer eats grass, the nutrientscontained in the grass are broken down into their chemical parts and then rearranged tobecome living deer tissue. Waste products (feces) are produced in the deer’s digestivesystem and pass from the deer’s body back into the ecosystem. Organisms break downthis waste into simpler chemical components. The grass growing close by is able to takeup those components and utilize them; they become a part of the grass. Then the cyclebegins again.

Figure 9.1 Energy Cycle

FooD CHAINS AND FOOD WEBSThe producers,consumers anddecomposers of eachecosystem make up afood chain. Energy flowthrough an ecosystem

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The Energy Cycle

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figure 9.2 A Food Chain

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Ecosystem Energy

The producers of an ecosystem use abiotic (not living) factors to obtain and store. energy for themselves or the consumers that eat them. In a forest ecosystem, th&\producers are: trees, bushes, shrubs, herbs, grass, vines and moss. Producers aresometimes called autotrophs.

Consumers, also called heterotrophs, are members of the ecosystem that depend onother members for food. Each time a plant or animal consumes another organism,energy transfers to the consumer. Deer, foxes, rabbits, raccoons, owls, hawks, snakes,mice, spiders and insects are examples of consumers in a forest ecosystem. There arethree types of consumers: herbivores, carnivores and omnivores. Table 9. 1 listscharacteristics ofthe three different types of consumers.

Table 9. 1 What Different Consumers Eat

Consumer Food Supply

Herbivore animals that eat only plants

Omnivore animals that eat both plants and other animals

Carnivore animals that eat only other animals

Saprophyte organisms that obtain food from dead organisms or from thewaste products of living organisms

The decomposers are members of the ecosystem that use dead or decaying organismsas a source of energy. As they feed on this organic matter, they further reduce it to itssimplest chemical components. Decomposers include fungi and bacteria. They are also

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Activity :Draw a food chain using organisms found in your ecosystem. 1

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Chapter 9

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The interaction of many food chains is a food web. Mostproducers and consumers interact with many others, forming acomplex food web out of several simple food chains. The imagebelow shows more complex food web.

When you think of a predator, do you think of a lion? Or a shark? How about a big,scary. . . grasshopper? Well, a predator is any organism that feeds on other living things.The organism it feeds on is its prey. So, grasshoppers qualify as predators; their prey isthe grass they consume.

Predator and prey together help maintain an ecological balance within their ecosystem.This balance benefits the community as a whole, but can be either helpful or harmful tothe individuals that make up the community, depending upon whether they are thepredator or the prey.

Research a particular ecosystem or biome (i.e. desert, rainforest orgrassland). List all the organisms found in this environment. Arrange a food

i web on poster board using all the organisms. Use magazines, drawings or

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figure 9.3 Food Web

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Ecosystem Energy

IROPHIC LEVELSWhen one organism is consumed by another, its energy transfers as a part of thedigestive process. Take a look at the energy pyramid in Figure 9.4. Energy pyramidsare a graphical way to show the flow of energy within an ecosystem.

Notice that the amount of available energy decreases as organisms go up the food chain.For this reason, food chains rarely have more than five links. A trophic level is theposition occupied by an organism in a food chain. Organisms that share a trophic levelget their energy from the same sources. Let’s put our producers, consumers anddecomposers into the energy pyramid, as in Figure 9.4.

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figure 9.4 Energy PyramidF.-

Plants are found at the base of the energy pyramid and comprise the first trophic levelof the food chain. They are called producers. Why? They “produce” their own energyby making their own food (natural sugars). The energy that drives the food makingprocess (remember, photosynthesis?) comes from the Sun. Above producers are theprimary consumers — they make up the second trophic level. These are the organismsthat eat plants, usually, herbivores like deer and grasshoppers. Above primaryconsumers are secondary consumers, which occupy the third trophic level. These areorganisms that eat primary consumers. Finally, there are top consumers also called .

tertiary consumers. They make up thejourth trophic level.

The Sun has been, and still is, the most influential force on Earth. At! ofthe energy usedby living systems comes from the Sun. Think about it: every blade of grass, everysquirrel, every fish and every human alive gets the energy needed to live from the Sun.

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Chapter 9

Nuclear reactions in the Sun release energy that travels through space to Earth. Some ofthe Sun’s energy is reflected back into space by clouds and the atmosphere, and some isabsorbed by the Earth’s oceans and land surfaces. Some solar energy is trapped by livingsystems (around 10%). Plants like trees and grasses trap solar energy and convert it tochemical energy (glucose) for living systems. The plant then uses some chemical energyto survive (i.e., grow and reproduce) and some of the energy is stored in the plant’stissues (as starches and sugars).

When a plant is eaten by a grasshopper, the energy contained in the grass (again around10%) transfers to the grasshopper. Does the grasshopper store all the energy it receivesfrom the plant? NO ! Some is used to move, grow and reproduce. So, in effect someenergy is “lost” during this energy transfer. Is the energy gone or destroyed? Absolutelynot! Energy is never destroyed. It simply changes form. It changes from grass tograsshopper. The energy changes from stored chemical energy (glucose) to kineticenergy (organism movement). The plant’s energy gives the grasshopper the ability togrow, repair injury, maintain homeostasis, move and reproduce. Essentially, the plant’senergy is used to drive life’s physical processes of the grasshopper and is dispersed asheat. The usage of energy in each trophic level means there is less available energy forthe next tropic level, because each uses some for survival.

This is a very important concept. You may have wondered how a huge animal like anelephant or a blue whale can grow to such a huge size by eating plant matter. It isbecause plant matter is a concentrated nutritional powerhouse. It contains the greatestamount of biologically available energy. Now, think about just how far that fast foodlunch is from nutritious. Think hard. Seriously, go get an apple instead.

. . .

Activity .

Examine the list of organisms below. Describe each organism s food source. Thenclassify the organisms as autotrophic or heterotrophic.

Horse-

Blueberry bush-

Timothy grass-g Wheat-

: Corn-

Human-

‘ Cat-

. Bear-

. Maple tree-

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Ecosystem Energy

CHAPTER 9 REVIEW

1. Animals that eat both plants and other animals are

A herbivores.B carnivores.C omnivores.B decomposers.

2 The interactions between many food chains is a(n)

A food web. C abiotic factor.B trophic level. B ecological balance.

3. In a deciduous forest, hundreds of dead leaves fall to the forest floor eachautumn. Which group of organisms breaks down this tissue for food?

A herbivore B omnivore C carnivore B saprophyte

4. What two organisms would be found in the third trophic level?

A hawk and humanB robin and snakeC dogwood and foxB grasshopper and deer

5. The bottom of the energy pyramid is made up of which kind of organisms?

A producers a

B primary consumersC secondary consumersB top consumers

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