Energy Flow and Nutrient Systems

Transcription

OpenStax-CNX module: m41352
1
Energy Flow and Nutrient Systems
∗
Kerry Gordon
This work is produced by OpenStax-CNX and licensed under the
Creative Commons Attribution License 3.0†
Abstract
The food chain, food webs, trophic levels and how organisms are connected. The ow of energy
through living organisms, the re-cycling of nutrients - water, oxygen, carbon and nitrogen. The impact
of disrupting these systems.
1 Denitions:
Denition 1: Producer
organism that manufactures food by photosynthesis
.
Denition 2: Consumer
organism that gets it food from eating producers or other organisms
Denition 3: Herbivore
an organism that feeds on plants only.
Denition 4: Carnivore
an organism that feeds on animals only.
Denition 5: Omnivore
an organism that feeds on both plants and animals.
Denition 6: Saprotroph
an organism that feeds on dead and decaying matter. (fungi)
Denition 7: Decomposers
an organism that causes the decay of dead and dying organisms. (bacteria)
Denition 8: Food chain
a chain showing feeding relationships between organisms.
∗ Version
1.1: Oct 16, 2011 2:11 am -0500
† http://creativecommons.org/licenses/by/3.0/
http://legacy.cnx.org/content/m41352/1.1/
2
2 Energy Flow
Organisms such as plants and animals need energy to grow, move and reproduce. They get this in the form
of nutrients from the food they eat. The main source of energy for life on earth is the sun. The sun provides
energy to producers (organisms that can make their own food, such as plants) that use photosynthesis
to grow and become food for consumers (any organism that gets its food by eating producers or other
organisms). Consumers include herbivores (organisms that eat only plants), carnivores (organisms that
eats other animals) and omnivores (eat both plants and animals). Decomposers (such as bacteria, molds,
mushrooms and mildew) break down discarded plant and animal (organic) materials into simpler substances,
which returns nutrients to the soil and atmosphere for new plants to use to grow.
2.1 Food chain
Figure 1
Figure 2
3
Figure 3
A food chain is a series of nutrients and energy moving through a chain of organisms. Here is an example of
a simple food chain in a grassland:
green plant impala leopard
IMAGES sourced from: http://www.ickr.com/photos/blueridgekitties/4625665988/sizes/o/in/photostream/1
http://www.ickr.com/photos/zest-pk/924783392/sizes/m/in/photostream/2
http://www.ickr.com/photos/e3000/5922771249/sizes/l/in/photostream/3
Activity 1:
Can you trace a food chain of the vegetables, fruit, cheese, eggs or meat that you had for breakfast or
will have for dinner?
Activity 2:
1. In the food chain shown above which of the three organisms is the
a) Herbivore
b) Carnivore
c) Producer
2. Draw a food chain showing at least 4 organisms.
3. Producers use sunlight to manufacture their own food. Write a word equation as well as a balanced
equation to depict this process.
4. Draw in the decomposers in the above food chain. Ensure that the direction of the arrows is correct.
5. What animal will feed on the leopard?
2.2 Food web
A food web is made up of numerous food chains. It represents the dierent feeding relationships in an
ecosystem or a biome. It is usually more complicated than a food chain because organisms can get their
energy or food from more than one source. Here is an example of a food web in a grassland:
Diagram of food web
Activity: Human Food Web
• Divide into teams of eight students each. (Groups may be larger or smaller, if desired, but they must
be at least ve students each.)
• Have all the students stand in a circle.
• Distribute a ball of string or yarn to one member of each group. This person represents the sun and
starts each food web.
1 http://www.ickr.com/photos/blueridgekitties/4625665988/sizes/o/in/photostream/
2 http://www.ickr.com/photos/zest-pk/924783392/sizes/m/in/photostream/
3 http://www.ickr.com/photos/e3000/5922771249/sizes/l/in/photostream/
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• Have the rst student hold tightly to the end of the string and toss the ball of string to another person
in the group, across the circle.
• Have the second person name one thing in the ecosystem that uses energy from the sun. Next, have
this person clasp the string with one hand and toss the ball of string on to another student in the circle
with his/her other hand.
• Have the third student name something that eats or is eaten by the previous item named.
• Continue until all students in the circle are connected with the ball of string at least once.
• Have the student groups stop and look at the web they have created. Are some webs more complex
than others? Why? (Answer: Some species may have been named twice because they are consumers
of multiple things; some ecosystems have more variety of food sources, etc.) Point out to students how
they have modeled a food chain or food web.
(Ex http://www.oercommons.org/courses/got-energy-spinning-a-food-web/view4 )
2.3 Trophic levels and the Food Pyramid:
The trophic level of an organism is the position it holds in a food chain and depends on how much energy
it consumes or produces. The trophic level of each organism can be drawn as a pyramid with the organism
at any level having less energy than the one below it. So, the organism at the bottom gives the most energy
and needs the least and the organism at the top needs the most energy and releases the least. Energy is lost
from activities, through heat or excretion and urination, at every level which is why there is less and less
energy as you move up the pyramid.
• Plants are on the rst level, or bottom of the pyramid, because they produce their own nutrients using
energy from the sun and therefore have a lot of energy to pass on.
• Herbivores are on the second level because they feed o plants
• Carnivores that feed on herbivores directly are on the third level.
(diagram: food pyramid)
Activity 2 : Look at the food web and the diagram showing the dierent trophic levels.
1.There are some arrows that are missing in the food web. Draw them in the web.
2.Identify a food chain that has three trophic levels.
3.Identify a food chain that has four trophic levels.
4.Name 2:
4.1.Autotrophs
4.2.Primary consumers
4.3.Secondary consumers
4.4.Tertiary consumers
5.There are very few quaternary consumers compared to the primary consumers. Discuss the reasons for
this.
6. Describe the consequences of removing the impala from the food web.
http://www.learner.org/courses/envsci/interactives/ecology/5
This activity investigates how much energy is transferred to each trophic level in the energy pyramid as
it is used by organisms at each level.
The following gure shows you a diagram of an energy pyramid for a typical ecosystem.
DECOMPOSER
Tertiary consumers
Secondary consumers
Primary consumers
PRODUCERS
4 http://www.oercommons.org/courses/got-energy-spinning-a-food-web/view
5 http://www.learner.org/courses/envsci/interactives/ecology/
5
Energy content
Answer the questions that follow.
1. Write down the name of a relevant organism for each trophic level.(4)
2.Predict what percentage of the energy is transferred along the
pyramid from one trophic level to the next.
Hint: Use the size of the spaces of each trophic level to help you
make a prediction.(4)
3.Examine the data in the table below. It shows the amount of energy
(kilojoules) present at each trophic level in a real-life ecosystem.
Working from the bottom of the pyramid upwards, calculate the
energy that is transferred from one level to the next.
i.e. If the percentage energy available to primary consumers is
4 591 kj x 100
47 065 kj 1
Write the percentage for each trophic level in th4e correct space.
Producers
Primary consumers
Secondary consumers
Tertiary consumers
47 065 kj
4 591 kj
539 kj
12,1 kj
Table 1
(3)
4.Do you notice a pattern in the energy that is transferred from one trophic
level to the next? Express this as a percentage.
5.How close was your prediction in step 2 to the actual percentage?(1)
6.All organisms use energy for life processes and are consumed by
decomposers when they die. What happens to the rest of the energy?(2)
7.Assume that the producer level consists of 1 000 kg of mealies and
humans follow one of the following feeding methods:
• Method 1: Feeding at the primary consumer level.
• Method 2: Feeding at the secondary consumer level by eating
chickens that feed at the primary consumer level.
(a)How much energy is available for humans in each method?(4)
(b)Why do people in countries with high population numbers eat
mostly grain and not meat?(2)
(c)Write an essay is which you explain which feeding method
should be followed if there is a worldwide shortage of food.(18)
Unit 1 Biospheres to ecosystems\ENERGY TRANSFER(Laura RBHS).doc6
http://www.themeatrix.com/interactive7
6 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/ENERGY%20TRANSFER(Laura%20RBHS).d
7 http://www.themeatrix.com/interactive
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3 Nutrient cycles
Organisms rely on nutrients in order to survive. These include carbon, oxygen, nitrogen, water and mineral
salts. The supply of these nutrients is not endless they can be used up or become exhausted. So there must
be a process that cycles these nutrients through the ecosystem so that they can be re-used. This is called
nutrient recycling. The ow of energy you saw before from the sun to herbivores and then to carnivores is
part of this process. If the cycle stops at any point, nutrients will become locked in place and can not be
used in the next step.
The water cycle, carbon cycle and nitrogen cycle are examples of nutrient re-cycling.
3.1 Water (ex http://cnx.org/content/m16470/latest/?collection=col10548/latest)
The earth is sometimes known as the "water planet" because over 70 percent of its surface is covered by
water. All living organisms require water for their continued existence. The water cycle (hydrologic cycle) is
composed of the interconnections between water reservoirs in the environment and living organisms and the
physical processes (e.g., evaporation and condensation) involved in its transport between those reservoirs.
The oceans contain about 97 percent of the total water on the planet, which leaves about three percent as
fresh water. Most of the fresh water is locked up in glacial and cap ice or buried deep in the earth where it is
economically unfeasible to extract it. One estimate gives the amount of fresh water available for human use
to be approximately 0.003 percent of the total amount of fresh water. However, this is actually a more than
adequate supply, as long as the natural cycle of water is not severely disturbed by an outside force such as
human activity.There are several important processes that aect the transport of water in the water cycle.
Evaporation is the process by which liquid water is converted to water vapor. The source of energy for this
process is usually the sun. For example, the sun's radiation heats the surface water in a lake causing it to
evaporate. The resulting water vapor is thus added to the atmosphere where it can be transported to another
location. Two important eects of the evaporation are cooling and drying.Transpiration is a process by which
water evaporates from living plants. Water from the soil is absorbed by a plant's roots and transported to the
leaves. There, some is lost as vapor to the atmosphere through small surface openings.When water vapor in
the atmosphere cools, it can transform into tiny droplets of liquid water. This process is called condensation,
and it can occur as water vapor is transported into the cooler upper atmosphere.Dust and pollen in the
atmosphere help to initiate the process by providing condensation centers. If the droplets remain small
enough to be supported by air motions, they can group together to form a cloud. Condensation can also
occur in the air near the ground as fog or on plant leaves as dew.When condensed water droplets grow so large
that the air can no longer support them against the pull of gravity, they fall to the earth. This is the process
called precipitation. If the water droplets fall as liquid, it is called rain. If the temperature of the surrounding
air mass is cold enough to freeze the water droplets, the resultant precipitation can be called snow, sleet or
hail, depending upon its morphology.Water falling on the ground (e.g., as precipitation or irrigation), can
move downslope over the surface (e.g., surface runo) or penetrate the surface (e.g., inltration). The amount
of surface runo and inltration depends upon several factors: water infall rate, surface moisture, soil or rock
texture, type and amount of surface cover (e.g., leaves and rooted plants), and surface topography. Surface
runo is the predominate process that occurs after precipitation, with most of the water owing into streams
and lakes. On a groundslope unprotected by vegetation, runo can occur very rapidly and result in severe
erosion.Water that inltrates the surface can move slowly downward through the layers of soil or porous rock
in a process known as percolation. During this process, the water can dissolve minerals from the rock or
soil as it passes through. The water collects in the pores of rocks as groundwater when it is stopped by an
impermeable layer of rock. The upper limit of this groundwater is known as the water table and the region
of water-logged rock is know as an aquifer. The groundwater may slowly ow downhill through rock pores
until it exits the surface as a spring or seeps into a stream or lake.Water is the essence of life. There would
be no life as we know it without water. The vast oceans of water exert a powerful inuence on the weather
and climate. Water is also the agent by which the landforms are constantly reshaped. Therefore, the water
cycle plays an important role in the balance of nature.Human activity can disrupt the natural balance of
the water cycle. The buildup of salts that results from irrigating with groundwater can cause soil infertility,
7
and irrigation can also deplete underground aquifers causing land subsidence or salt water intrusion from
the ocean. The clearing of land for farming, construction, or mining can increase surface runo and erosion,
thereby decreasing inltration. Increasing human populations and their concentration in certain geographic
localities will continue to stress water systems. Careful thought is needed on local, regional and global scales
regarding the use and management of water resources for wetlands, agriculture, industry and home.
Flow diagram
http://www.planetguide.net/book/chapter_2/water_cycle.html8
3.2 Oxygen
Oxygen is one of the main gases found in the air, along with nitrogen.
Oxygen is re-cycled between the air and living organisms in the following ways:
• Organisms take in oxygen during respiration, which they use for cellular processes to break down energy
rich nutrients.
• When wood or fossil fuels burn, they release oxygen into the atmosphere through combustion.
• Plants also release oxygen into the air as a by-product of photosynthesis.
Because animals trap oxygen during respiration, the release of oxygen by plants during photosynthesis is the
main way oxygen is released into the atmosphere.
Figure: The Oxygen Cycle.
3.3 Carbon
Carbon is the basic building block of all organic materials, and therefore, of living organisms. However, the
vast majority of carbon resides as inorganic minerals in crustal rocks. Other reservoirs of carbon include
the oceans and atmosphere. Several physical processes aect carbon as it moves from one reservoir to
another. The inter-relationships of carbon and the biosphere, atmosphere, oceans and crustal earth and the
processes aecting it are described by the carbon cycle.The carbon cycle is actually comprised of several
inter-connected cycles. The overall eect is that carbon is constantly recycled in the dynamic processes
taking place in the atmosphere, at the surface and in the crust of the earth. For example, the combustion of
wood transfers carbon dioxide to the atmosphere. The carbon dioxide is taken in by plants and converted
to nutrients for growth and sustenance. Animals eat the plants for food and exhale carbon dioxide into
the atmosphere when they breathe. Atmospheric carbon dioxide dissolves in the ocean where it eventually
precipitates as carbonate in sediments. The ocean sediments are subducted by the actions of plate tectonics,
melted and then returned to the surface during volcanic activity. Carbon dioxide gas is released into the
atmosphere during volcanic eruptions. Some of the carbon atoms in your body today may long ago have
resided in a dinosaur's body, or perhaps were once buried deep in the earth's crust as carbonate rock
minerals.The main carbon cycling processes involving living organisms are photosynthesis and respiration.
These processes are actually reciprocal to one another with regard to the cycling of carbon: photosynthesis
removes carbon dioxide from the atmosphere and respiration returns it. A signicant disruption of one
process can therefore aect the amount of carbon dioxide in the atmosphere.Plants absorb carbon dioxide
from the atmosphere through their leaves and absorb water from the soil through their roots.
During a process called photosynthesis, raw materials are used to manufacture sugar. Photosynthesis
occurs in the presence of chlorophyll, a green plant pigment that helps the plant utilize the energy from
sunlight to drive the process. Although the overall process involves a series of reactions, the net reaction can
be represented by the following:
The sugar provides a source of energy for other plant processes and is also used for synthesizing materials
necessary for plant growth and maintenance. The net eect with regard to carbon is that it is removed from
the atmosphere and incorporated into the plant as organic materials.
8 http://www.planetguide.net/book/chapter_2/water_cycle.html
8
The reciprocal process of photosynthesis is called respiration. The net result of this process is that sugar
is broken down by oxygen into carbon dioxide and water. The net reaction is:
This process occurs not only in plants, but also in humans and animals. Unlike photosynthesis, respiration
can occur during both the day and night. During respiration, carbon is removed from organic materials and
expelled into the atmosphere as carbon dioxide. Another process by which organic material is recycled is the
decomposition of dead plants and animals. During this process, bacteria break down the complex organic
compounds.Carbon is released into the soil or water as inorganic material or into the atmosphere as gases.
Decomposed plant material is sometimes buried and compressed between layers of sediments. After millions
of years fossil fuels such coal and oil are formed. When fossil fuels are burned, the carbon is returned to
the atmosphere as carbon dioxide.The carbon cycle is very important to the existence of life on earth. The
daily maintenance of living organisms depends on the ready availability of dierent forms of carbon. Fossil
fuels provide an important source of energy for humans, as well as the raw materials used for manufaturing
plastics and other industrially important organic compounds. The component processes of the carbon cycle
have provided living things with the necessary sources of carbon for hundreds of millions of years. If not
for the recycling processes, carbon might long ago have become completely sequestered in crustal rocks and
sediments, and life would no longer exist.Human activity threatens to disrupt the natural cycle of carbon.
Two important ways by which humans have aected the carbon cycle, especially in recent history, are: 1) the
release of carbon dioxide into the atmosphere during the burning of fossil fuels, and 2) the clearing of trees
and other plants (deforestation) that absorb carbon dioxide from the atmosphere during photosynthesis. The
net eect of these actions is to increase the concentration of carbon dioxide in the atmosphere. It is estimated
that global atmospheric carbon dioxide is increasing by about 0.4% annually. Carbon dioxide is a greenhouse
gas (i.e., it prevents infrared radiation from the earth's surface from escaping into space). The heat is instead
absorbed by the atmosphere. Many scientists believe that the increased carbon dioxide concentration in the
atmosphere is resulting in global warming.This global warming may in turn cause signicant changes in global
weather, which could negatively aect all life on earth. However, increased photosynthesis (resulting from
the increase in the concentration of carbon dioxide) may somewhat counteract the eects. Unfortunately, the
issues of fossil fuel burning, deforestation and global warming are intertwined with economic and political
considerations. Furthermore, though much studied, the processes are still not well-understood and their
ramications cannot be predicted with condence.
Flow diagram
Carbon Cycle Questions
Name 4 things that have carbon in them.
Which gas in the air contains Carbon?
How does carbon get into plants?
How does Carbon get into animals?
How does Carbon get into microbes?
Name the process that releases Carbon Dioxide into the atmosphere.
Name three types of living things that carry out respiration.
What do we call the movement of carbon round living things.
Do forests increase or decrease Carbon Dioxide in the air?
Does burning fossil fuels increase or decrease Carbon Dioxide in the air?
How does carbon get into microbes?
9
How does carbon get into microbes?
Draw a clearly labelled diagram to show the Carbon Cycle.
To gain full marks you must include stages and processes.
12 marks
Describe 2 main ways in which human activity is aecting the Carbon cycle and explain their eects.
6 marks
List three things that intensive farmers do to increase yield. For each explain how it works.
6 marks
What would you advise a Developing village to farm? Cattle or crops?
Draw a food chain to explain your answer.
6 marks
Write the word equation for Photosynthesis and for Respiration
10 marks
Unit 1 Biospheres to ecosystems\The Carbon Cycle (Hassiena).pptx9
Unit 1 Biospheres to ecosystems\Carbon Cycle Diagram.doc10
Unit 1 Biospheres to ecosystems\Carbon Cycle Questions.doc11
Unit 1 Biospheres to ecosystems\Carbon Cycle Test.doc12
Unit 1 Biospheres to ecosystems\Carbon Cycle TF.doc13
3.4 Nitrogen
Description
Flow diagram
The Nitrogen cycle
The element Nitrogen is important to living organisms and is used in the production of amino acids,
proteins and nucleic acids (DNA, RNA). Molecular nitrogen (N2) is the most abundant gas in the atmosphere.
However, only a few single-cell organisms are able to utilize this nitrogen form directly. These include the
bacteria species Rhizobium, which lives on the root nodules of legumes, and cyanobacteria (sometimes called
blue-green algae), which are ubiquitous to water and soil environments. In order for multi-cellular organisms
to use nitrogen, its molecular form (N2) must be converted to other compounds, e.g., nitrates or ammonia.
This process is known as nitrogen xation. Microbial organisms such as cyanobacteria carry out most of
the earth's nitrogen xation. The industrial manufacture of fertilizers, emissions from combustion engines,
and nitrogen burning in lightning account for a smaller fraction.The nitrogen cycle is largely dependent
on microbrial processes. Bacteria x nitrogen from the atmosphere in the form of ammonia (NH3) and
9 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/The%20Carbon%20Cycle%20(Hassiena).pptx
10 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/Carbon%20Cycle%20Diagram.doc
11 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/Carbon%20Cycle%20Questions.doc
12 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/Carbon%20Cycle%20Test.doc
13 http://legacy.cnx.org/content/m41352/latest/../Unit%201%20Biospheres%20to%20ecosystems/Carbon%20Cycle%20TF.doc
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convert the ammonia to nitrate (NO3-).Ammonia and nitrate are absorbed by plants through their roots.
Humans and animals get their nitrogen supplies by eating plants or plant-eating animals. The nitrogen is
returned to the cycle when bacteria decompose the waste or dead bodies of these higher organisms, and
in the process, convert organic nitrogen into ammonia. In a process called denitrication, other bacteria
convert ammonia and nitrate into molecular nitrogen and nitrous oxide (N2O). Molecular nitrogen is thus
returned to the atmosphere to start the cycle over again.Humans have disturbed the nitrogen cycle in recent
history by activities involving increased xation of nitrogen. Most of this increased nitrogen xation results
from the commercial production of fertilizers and the increased burning of fuels (which converts molecular
nitrogen to nitric oxide, NO). The use of commercial fertilizers on agricultural lands increases the runo
of nitrates into aquatic environments.This increased nitrogen runo stimulates the rapid growth of algae.
When the algae die, the water becomes depleted in oxygen and other organisms die. This process is known
as eutrophication. The excessive use of fertilizers also stimulates the microbial denitrication of nitrate to
nitrous oxide. Increased atmospheric levels of nitrous oxide are thought to contribute to global warming.
Nitric oxide added to the atmosphere combines with water to form nitric acid (HNO3), and when nitric acid
dissolves in water droplets, it forms acid rain. Acid rain damages healthy trees, destroys aquatic systems
and erodes building materials such as marble and limestone.
When a plant photosynthesises it uses carbon dioxide from the atmosphere and water from the soil to
manufacture carbohydrates which are made up of 3 elements which are carbon, hydrogen and oxygen. The
equation is shown below.
CO2 + H2O → C6H12O6 + O2
Proteins are made up of 4 elements namely carbon, hydrogen, oxygen and nitrogen. These elements are
used to make amino acids which are the building blocks of proteins.
Plants need to absorb nitrogen in some way. Even though the earth's atmosphere is made up of approximately 78% nitrogen, the plant is unable to absorb this directly from the atmosphere. They need to have
a dierent way to absorb this nitrogen. It can only absorb this nitrogen as ammonium (NH4) , ammonia
(NH3) or nitrates (NO3).
Unit 1 Biospheres to ecosystems\The Nitrogen cycle (Hassiena).docx14
3.5 Environmental concerns and Nutrient Re-cycling
Activity: debate
3.6 Summary
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Energy Flow and Nutrient Systems

Transcription

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