Lab 7 Identifying Limiting Nutrient - Sayre School

Lab 7: The Ecosystem Drawing
Introduction:
Food chains and food webs show the flow of energy through an ecosystem. Food chains are
linear depictions of energy flow, while food webs show the multiple interactions among the
different organisms. Food webs are generally more realistic since most organisms eat more
than one type of food and can be eaten by more than one type of predator.
The energy source for most ecosystems is the sun. Autotrophs (plants, algae, etc) capture the
sun’s energy and use it to make sugar through photosynthesis. Autotrophs are also called
primary producers because they start all food webs on earth. Each level of a food web is
called a trophic level, and the organisms are classified as either producers, decomposers,
or consumers. Consumers are heterotrophs since they eat the organic material made by the
autotrophs. Heterotrophs cannot make their own food and are dependent on the autotrophs.
Try this activity: making a food chain. Then try this activity: making a food web. Place
the organisms in their correct places on the food chain or food web. Remember that the arrows
indicate the direction of energy flow.
What would you hypothesize might happen to the other organisms in the web, if killer whales
went extinct What might happen if we exhausted the fishery (through over fishing), and
fish were no longer a component of our food web What might happen if we removed the
algae from the food web What does this tell you about the importance of the base of the
food web Now that you understand food chains and webs, complete the prelab.
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glossary 7.1

Lab 7: The Ecosystem Drawing
The water cycle is driven by the sun’s energy. The sun heats the water and some of it evaporates
into the air. Ice and snow can sublimate directly into water vapor. Rising air currents take the
vapor up into the atmosphere, along with water from transpiration, which is water transpired
from plants. The vapor rises into the air where cooler temperatures cause it to condense into
clouds. Air currents move clouds around the globe, cloud particles collide, grow, and fall out
of the sky as precipitation. Some precipitation falls as snow and can accumulate as ice caps
and glaciers, which can store frozen water for thousands of years.
Nutrients cycle through the environment, but energy has a one way
flow and is lost as heat.
Most precipitation falls back into the oceans or onto land, where, due to gravity, the precipitation
flows over the ground as surface runoff. A portion of runoff enters rivers which move
water towards the oceans. Runoff, and ground-water seepage, accumulate and are stored as
freshwater in lakes. Not all runoff flows into rivers, though. Much of it soaks into the ground
as infiltration. Some water infiltrates deep into the ground and replenishes aquifers (saturated
subsurface rock), which store huge amounts of freshwater for long periods of time.
Over 96% of the world’s total water supply is salt water. Of the total freshwater, 68% is
locked up in ice and glaciers. Another 30% of freshwater is in the ground. Fresh surface-water
sources, such as rivers and lakes, only constitute about 1/150 of one percent of total water.
Yet, rivers and lakes are the sources of most of the water people use everyday.
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glossary 7.2

Lab 7: The Ecosystem Drawing
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glossary 7.3

Lab 7: The Ecosystem Drawing
Carbon enters the living world through the action of autotrophs (plants and algae) that use
the sun’s energy to convert carbon dioxide (CO 2
) into organic sugar. Animals eat plants to
get the energy rich sugar, and perform cellular respiration to convert the sugar into usuable
energy. Carbon returns to the atmosphere by respiration, burning fossil fuels, and decay.
The uptake and return of CO 2
are not currently in balance. The carbon
dioxide content of the atmosphere is gradually and steadily increasing.
The graph shows the CO 2
concentration at a summit in Hawaii from 1958
through 1999. The seasonal fluctuation is caused by the increased uptake
of CO 2
by plants in the summer. Samples of air trapped over the centuries
in the glacial ice of Greenland show no change in CO 2
content until 300
years ago.
• Since 1958 concentrations have risen over 20%. This increase is caused by human activities:
burning fossil fuels (coal, oil, natural gas) which returns to the atmosphere carbon that has
been locked within the earth for millions of years.
• clearing and burning of forests, especially in the tropics. In recent decades, large areas of
the Amazon rain forest have been cleared for agriculture and cattle grazing.
Despite CO 2
sinks (ocean, desert sand, plants), the concentration of atmospheric CO 2
continues
to rise. Carbon dioxide is transparent to light but rather opaque to heat rays. Therefore, CO 2
in
the atmosphere retards the radiation of heat from the earth back into space - the “greenhouse
effect”. This greenhouse effect is causing a change in the world’s climate.
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glossary 7.4

Lab 7: The Ecosystem Drawing
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glossary 7.5

Lab 7: The Ecosystem Drawing
Phosphorus is an important element for making DNA and RNA, and is also a component of
ATP which serves as an energy source. The phosphorus cycle differs from the other major
cycles because it does not include a gas phase.
When it rains, phosphates are removed from the rocks (via weathering) and are distributed
throughout both soils and water. Plants take up the phosphate from the soil. The phosphates
then move from plants to animals when herbivores eat plants and carnivores herbivores.
The phosphates in the animal tissue eventually return to the soil through excretion, and
decomposition of plants and animals. The same process occurs in aquatic ecosystem.
algae bloom off
coast of Florida
While obviously beneficial for many biological processes, an excessive amount of phosphorus
is considered a pollutant in water. Phosphate stimulates the growth of plankton and plants.
When there are no longer enough nutrients, the plants die. Excess growth of decomposers
tends to consume large amounts of dissolved oxygen, potentially suffocating fish and other
marine animals. While the excess dead plants block available sunlight to bottom dwelling
species. This is known as eutrophication.
Humans can alter the phosphorus cycle in many ways, including deforesting the tropical rain
forests and the using agricultural fertilizers. As the forest is cut, heavy rains quickly wash away
nutrients originally stored in plants. Agricultural runoff provides much of the phosphate
found in waterways. Crops often cannot absorb all of the fertilizer in the soils, causing excess
fertilizer runoff and increasing phosphate levels in rivers and other bodies of water.
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glossary 7.6

Lab 7: The Ecosystem Drawing
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glossary 7.7

Lab 7: The Ecosystem Drawing
Nitrogen is used to produce proteins and DNA. Despite its abundance in the atmosphere,
nitrogen is often the limiting nutrient for plant growth. This occurs because most plants can
only use nitrogen in two solid forms: ammonium and nitrate. Animals receive the nitrogen they
need for metabolism, growth, and reproduction by eating living or dead organic material.
In the process of nitrification, ammonium is chemically altered by bacteria to form nitrate.
Nitrate is very soluble and it is easily lost from the soil system by leaching. Some of this leached
nitrate flows through the water system where it is returned to the atmosphere by denitrification.
Denitrification is also common in soils and is carried out by heterotrophic bacteria.
Nitrifying Bacteria
Almost all of the nitrogen found in any terrestrial ecosystem originally came from the
atmosphere. Significant amounts enter the soil in rainfall or through the effects of lightning.
The majority, however, is fixed within the soil by bacteria. Members of the bean family form
symbiotic relationships with nitrogen fixing bacteria. In exchange for some nitrogen, the
bacteria receive carbohydrates and a moist environment from the plants.
Humans have altered the nitrogen cycle by:
• The over-use of nitrogen fertilizers has caused nitrate to leach into water. The additional
nitrogen flows into streams, rivers, lakes, and estuaries which can lead to eutrophication.
• The farming of livestock which release large amounts of ammonia into the environment
from their wastes.
• Sewage waste and septic tank leaching.
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glossary 7.8

Lab 7: The Ecosystem Drawing
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glossary 7.9

Lab 7: The Ecosystem Drawing
Procedure:
Your teacher will assign you and your partner a biome. The inspiration file linked next to the
biome name has a background photograph for you to use in your drawing:
• Desert
• Tropical Rain Forest
• Tundra
• Alpine
• Chaparral
• Savanna
• Grasslands
• Taiga
From the information that you have learned in class you will create an Ecosystem Drawing of
your assigned Biome. Your drawing should include the four major nutrient cycles: phosphorus,
carbon, nitrogen, and water. This drawing will illustrate the interaction between biotic and
abiotic factors, how energy flows through the ecosystem, and how inorganic materials are
recycled back into the ecosystem.
Be sure to look at the scoring guide to understand what material should be on your drawing
and how you will be graded. If your partner is absent for an extended time period, you
need to discuss with your teacher how to proceed. You will also need to properly cite the
source of your pictures.
You will use Inspiration to make your Drawing. Be sure to go to the Link menu and uncheck
“draw links under symbols”. This will allow you to make food chains over the background
picture.
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glossary 7.10

Lab 7: The Ecosystem Drawing
The following items should be ILLUSTRATED in your ecosystem:
1. On your Ecosystem drawing you need four producers, correctly labeled with organism
common name, scientific name and correctly labeled with trophic level.
2. On your Ecosystem drawing you need at least 9 consumers (including herbivores, carnivores,
omnivores), correctly labeled with organism common name, scientific name, and correctly
labeled with trophic level.
3. On your Ecosystem drawing you need two decomposers correctly labeled with trophic level.
You may use generic decomposers like fungi and bacteria to make the nutrients cycle in your
biome.
4. On your Ecosystem drawing, you need four different Food Chains, each color-coded to
identify them clearly. Arrows should be drawn in correct direction. Each chain will be used
for one of the nutrient cycles. Make sure the organisms in your food chains actually live in the
same area of the Earth.
5. On your Ecosystem drawing you need the Abiotic Factors listed in lower left corner.
6. On your Ecosystem drawing you need a Primary Energy Source properly labeled and attached
to one plant. Color code that arrow yellow to show how sunlight energy is moving into your
Ecosystem.
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Lab 7: The Ecosystem Drawing
7. The Water Cycle on your Ecosystem drawing should include transpiration, precipitation,
condensation, evaporation, percolation, runoff, root uptake, and groundwater. The arrows
should be color-coded blue.
8. The Carbon Cycle on your Ecosystem drawing should include the processes of respiration,
eating, photosynthesis, decomposition, and combustion. The arrows should be color-coded
grey.
9. The Phosphorus Cycle on your Ecosystem drawing should include a cycle on land and a
cycle in water. Be sure to label weathering, uplifting and sediments. The arrows should be
color-coded orange.
10. The Nitrogen Cycle on your Ecosystem drawing should include nitrogen fixation,
assimilation, ammonification, nitrification, and denitrification. The arrows should be colorcoded
green.
11. Be sure to include a man-made disturbance that exists in your biome. Think about tying
the disturbance to burning of fossil fuels.
12. You will be awarded points for neatness and creativity. Points will be deducted if you don’t
have a bibliography or if you use animals that don’t live in the same area of the Earth.
13. Don’t forget to do you homework. It is a review of all the information we have discussed
on Ecosystems and a review for your quiz.
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glossary 7.12

Lab 7: The Ecosystem Drawing
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glossary 7.13

Lab 7: The Ecosystem Drawing
References:
Biology Sciences Curriculum Study. Biology: A Human Approach. Kendall/ Hunt Publishing:
Iowa. 1997.
deCharon, Annette. Toxic and Harmful Algal Blooms Educational Activities. Bigelow Laboratory
for Ocean Sciences. www.bigelow.org/edhab/fitting_algae.html. 29 September 2008.
Holsinger, Rachel and Debbie Wheeler. “Lab 7: The Ecosystem Drawing” Sayre School:
Lexington, KY. September 2014.
Kimball, John. The Carbon Cycle. Kimball’s Biology Pages. September 2008 http://users.rcn.
com/jkimball.ma.ultranet/BiologyPages/C/CarbonCycle.html. 29 September 2008.
Pidwirny, Michael. Chapter 9: Introduction to the Biosphere. Physical Geographyhttp://www.
physicalgeography.net/fundamentals/9s.html. 29 September 2008.
Water Cycle. Envrionmental Literacy Council. 26 June 2008. http://www.enviroliteracy.org/
article.php/704.php. 29 September 2008.
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glossary 7.14