Lesson 1: Understanding Science
Section 1: Energy Flow in Ecosystems
Objectives:
❑ Describe how energy is transferred from the sun to producers and then to consumers.
❑ Describe one way in which consumers depend on producers.
❑ List two types of consumers.
❑ Explain how energy transfer in a food web is more complex than energy transfer in a food chain.
❑ Explain why an energy pyramid is a representation of trophic levels.
A. Definitions
1. Photosynthesis: the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to produce carbohydrates and oxygen
2. Producer: an organism that can make organic molecules from inorganic molecules; a photosynthetic or chemosynthetic autotroph that serves a s the basic food source in an ecosystem
3. Consumer: an organism that eats other organisms or organic matter instead of producing its own nutrients or obtaining nutrients from inorganic sources
4. Decomposer: an organism that feeds by breaking down organic matter from dead organisms; examples include bacteria and fungi
5. Cellular respiration: the process by which cells produce energy from carbohydrates; atmospheric oxygen combines with glucose to form water and carbon dioxide
6. Food chain: the pathway of energy transfer through various stages as a result of the feeding patterns of a series of organisms
7. Food web: a diagram that shows the feeding relationships between organisms in an ecosystem
8. Trophic level: one of the steps in a food chain or food pyramid; examples include producers and primary, secondary, and tertiary consumers
B. Life Depends on the Sun
1. The ultimate source of energy for almost all organisms is the Sun.
2. Energy from the sun enters an ecosystem when a plant uses sunlight to make sugar molecules by photosynthesis.
3. During photosynthesis, plants, algae, and some bacteria capture solar energy.
4. The solar energy is absorbed by chlorophyll in the chloroplasts of a plant cell. During photosynthesis, carbon dioxide from the atmosphere and water from the ground along with the solar energy is converted into carbohydrates (glucose) and oxygen.
5. Carbohydrates are energy-rich molecules, which organisms use to carry out daily activities.
C. From Producers to Consumers
6. Plants and algae are producers, which means that they make their own food. They are also called autotrophs, meaning self-feeders.
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solar energy producer primary consumer secondary consumer
7. Consumers get their energy by eating other organisms. They are also called heterotrophs, meaning other-feeders.
8. Some producers get energy directly from the sun by absorbing it through their leaves. Consumers get energy indirectly from the sun by eating producers and other consumers.
D. An Exception to the Rule: Deep-Ocean Ecosystems
1. In 1977, scientist discovered large communities of worms, clams, crabs, mussels and barnacles living near thermal vents in the ocean floor where sunlight did not reach. These communities exist in total darkness where photosynthesis cannot occur. Where did the energy come from?
2. The tubeworms depend on bacteria that live inside them to survive. The bacteria use energy from hydrogen sulfide to make their own food. The hydrogen sulfide escapes for the cracks in the ocean floor.
E. What Eats What
1. Consumers that only eat producers are called herbivores. Ex: rabbits, cows, sheep, deer, grasshoppers, etc.
2. Consumers that eat other consumers are called carnivores. Ex: lions, hawks, etc.
3. Consumers that eat both plants and animals are called omnivores, or eaters of all. Ex: humans, beard, pigs, cockroaches, etc.
4. Consumers that get their food by breaking down dead organisms are called decomposers. The decomposers allow the nutrients in the rotting material to return to the soil, water, and air.
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F. Cellular Respiration: Burning the Fuel
1. Animals consume food and breathe in oxygen, which is produced by plants and other producers.
2. During cellular respiration, cells absorb oxygen and use it to release energy.
3. In cellular respiration, sugar and oxygen combine to yield carbon dioxide, water, and most importantly, energy (ATP).
G. Food Chains and Food Webs
1. Energy flow in an ecosystem is much more complicated than energy flow in a simle food chain.
2. Ecosystems contain more species than a single food chain contains and most organisms eat more than one kind of food.
3. Food chains are just one strand of a food web.
Food Chain Food Web
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H. Trophic Levels
1. Each step in the transfer of energy through a food chain or food web in an ecosystem is known as a trophic level.
2. Each time energy is transferred from one organism to another, some of the energy is lost as heat and less energy is available to organism at the next trophic level.
3. Some of the energy is lost during cellular respiration. Organisms use much of the remaining energy to carry out the functions of living, such as producing new cells, regulating body temperature and moving around.
4. Ninety percent of energy is used to carry out the functions of living. Only 10% of the energy is stored and available to the next trophic level when one organism consumes another organism.
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I. Energy Pyramid
1. One way to visualize the loss of energy from one trophic level to the next trophic level is to draw an energy pyramid. (see above)
2. Each layer in the energy pyramid represents one trophic level. Producers are on the bottom and contain the most energy. Herbivores eat the producers. Carnivores eat the herbivores and other carnivores.
3. A pyramid is a good way to illustrate trophic levels because the pyramid becomes smaller toward the top, where less energy is available.
J. How Energy Loss Affects an Ecosystem
1. The decreased amount of energy at each trophic level affects the organization of an ecosystem.
a. There are fewer organisms at the higher trophic levels because so much energy is lost at each level.
b. The loss of energy from trophic level to trophic level limits the number of trophic levels in an ecosystem. There are rarely more than four or five trophic levels because ecosystems don’t have enough energy left to support higher levels.
c. The organisms that do feed on higher trophic level organisms are usually small, such as parasitic worms and fleas that require a very small amount of energy.
Section 2: The Cycling of Materials
Objectives:
❑ Describe the short-term and long-term process of the carbon cycle.
❑ Identify one way that humans are affecting the carbon cycle.
❑ List three stages of the nitrogen cycle.
❑ Describe the role that nitrogen-fixing bacteria play in the nitrogen cycle.
❑ Explain how the excess use of fertilizer can affect the nitrogen and phosphorus cycles.
1. Definitions:
a. Carbon cycle: the movement of carbon from the nonliving environment into living things and back
b. Nitrogen-fixing bacteria: bacteria that convert atmospheric nitrogen into ammonia
c. Nitrogen cycle: the process in which nitrogen circulates among the air, soil, water, plants, and animals in an ecosystem
d. Phosphorus cycle: the cyclic movement of phosphorus in different chemical forms from the environment to organisms and then back to the environment
2. The Carbon Cycle
a. Carbon is an essential component of proteins, fats, and carbohydrates, which make up all organisms.
b. The carbon cycle is a process by which carbon is cycled between the atmosphere, land, water, and organisms.
• Short-term cycle:
1. Carbon enters when producers, such as plants, convert CO2 in the atmosphere into carbohydrates during photosynthesis.
2. Carbon is returned to the atmosphere as CO2 when consumers eat producers obtaining carbon from the carbohydrates and breaking them down during cellular respiration.
• Long-term cycle:
1. Carbon is converted into carbonates (the hard parts of bones and shells). Over million of years, the carbonate deposits produce limestone rocks, which is one of the largest carbon sinks, or carbon reservoirs, on Earth.
2. Carbohydrates in organisms that are converted into fats, oils, and other molecules that store energy are released into the soil after the organisms die. This forms deposits of coal, oil, and natural gas known as fossil fuels. Fossil fuels are essentially stored carbon left over from bodies of pants and animals that died millions of years ago.
THE CARBON CYCLE
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c. How humans affect the carbon cycle:
• We burn fossil fuels releasing carbon into the atmosphere as CO2.
• One-third of all carbon dioxide emitted by the U.S. comes from vehicle emissions.
• Other two-thirds of carbon dioxide emission is from natural burning of wood or forest fires.
• Increased levels for CO2 may contribute to global warming.
• CO2 not absorbed by the atmosphere, dissolves into the ocean and forms carbon sinks.
3. The Nitrogen Cycle
a. Nitrogen is needed by all organisms to build proteins, which are used to build new cells.
b. Nitrogen makes up 78% of the gases in the atmosphere, but most organisms cannot use atmospheric nitrogen.
c. Nitrogen must be altered, or fixed, before organisms can use it. Nitrogen-fixing bacteria are the only organisms that can fix atmospheric nitrogen into useable chemical compounds and live within nodules on the roots of legumes (beans, peas, and clover).
d. Steps of the Nitrogen Cycle:
• Step 1- Nitrogen Fixation- Special bacteria convert the nitrogen gas (N2) to ammonia (NH3), which the plants can use.
• Step 2- Nitrification- Nitrification is the process, which converts the ammonia into nitrite ions, which the plants can take in as nutrients.
• Step 3- Ammonification- After all of the living organisms have used the nitrogen, decomposer bacteria convert the nitrogen-rich waste compounds into simpler ones.
• Step 4- Denitrification- Denitrification is the final step in which other bacteria convert the simple nitrogen compounds back into nitrogen gas (N2), which is then released back into the atmosphere to begin the cycle again.
THE NITROGEN CYCLE
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e. How humans affect the carbon cycle:
• Nitric Oxide (NO) is released into the atmosphere when any type of fuel is burned, including coal, wood, oil or using internal combustion engines.
• NO combines with oxygen to form Nitric Acid (NO2), which contributes to acid precipitation.
• Nitrous Oxide (N2O) is released into the atmosphere through bacteria in livestock waste and commercial fertilizers applied to the soil.
• Removing nitrogen from the Earth’s crust and soil when we mine nitrogen-rich mineral deposits.
• Discharge of municipal sewage adds nitrogen compounds to aquatic ecosystems, which disrupts the ecosystem and kills fish.
4. The Phosphorus Cycle
a. Phosphorus is an element that is a part of many molecules that make up the cells of living organisms (found in bones and teeth in animals).
b. The phosphorus cycle is slow and does not normally occur in the atmosphere because phosphorus rarely occurs as a gas.
c. Phosphorus enters soil and water in a few ways:
• Rocks erode and small amounts of phosphate dissolve in the soil and water.
• Plants absorb phosphates through their roots.
• Excess phosphorus excreted in waste from organisms and the decomposition of dead organisms adds phosphorus to the soil and water.
• Some phosphorus washes off the land and eventually ends up in the ocean.
• Phosphate salts don’t dissolve in water and accumulate as sediment at the bottom of the ocean.
THE PHOSPHORUS CYCLE
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d. How humans affect the phosphorus and nitrogen cycle:
• Fertilizers contain both nitrogen and phosphorus.
• Excess nitrogen and phosphorus in an aquatic ecosystem or nearby waterway can cause rapid and overabundant growth of algae.
• Algal blooms can deplete the oxygen in an aquatic ecosystem resulting in fish death.
Section 3: How Ecosystems Change
Objectives:
❑ List two examples of ecological succession.
❑ Explain how a pioneer species contributes to ecological succession.
❑ Explain what happens during old-field succession.
❑ Describe how lichens contribute to primary succession.
1. Definitions:
a. Ecological succession: a gradual process of change and replacement of the types of species in a community
b. Primary succession:: succession that begins in an area that previously did not support life
c. Secondary succession: the process by which one community replaces another community that has been partially or totally destroyed
d. Pioneer species: a species that colonizes an uninhabited area and that starts an ecological cycle in which many other species become established
e. Climax community: a final, stable community in equilibrium with the environment
2. Ecosystems are constantly changing.
Examples:
a. A forest could have been a shallow lake a thousand years ago.
b. Mosses, shrubs, and small trees cover the concrete of a demolished building.
3. Ecological Succession
a. In nature, ecological succession may take hundreds or thousands of years.
b. Newer communities make it harder for the older ones to survive.
Example:
Taller beech trees compete with shorter, young beech trees for sun and make it hard for the younger trees to survive. However, a shade loving tree may replace the smaller birch trees.
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c. Primary succession
1. It occurs where no ecosystem existed before.
2. It may occur on rocks, cliffs, and sand dunes.
3. Primary succession is very slow.
4. Begins where there is no soil.
5. Takes several hundred years to produce fertile soil naturally.
6. First species to colonize bare rock would be bacteria and lichens.
d. Lichens
1. Do not require soil.
2. Colorful, flaky patches.
3. Composed of two species, a fungus and an alga.
4. The algae photosynthesize and the fungus absorbs nutrients from rocks and holds water.
5. Over time, they break down the rock.
6. As the rocks break apart, water freezes and thaws on the cracks, which breaks up the rocks further.
7. When the lichens die, they accumulate in the cracks.
8. Then mosses begin to grow and die, leading to the creation of fertile soil.
9. Fertile soil is made up of the broken rocks, decayed organisms, water and air.
e. Mosses on rocks
1. Primary succession can be seen happening on the sidewalks.
2. If left alone, even NYC would return to a cement-filled woodland.
f. Secondary succession
1. It occurs on a surface where an ecosystem has previously existed.
2. It occurs in ecosystems that have been disturbed or disrupted by humans, animals, or by natural processes such as storms, floods, earthquakes, and volcanoes.
3. Mount St. Helens is now in secondary succession after the volcanic eruption in 1980.
• 44,460 acres were burned and flattened.
• The first plants to colonize the volcanic debris were called pioneer species.
• Over time, the pioneer species make the area habitable for other species.
• Plants, flowers, new trees and shrubs have started to grow.
• If this continues, over time they will form a climax community.
• Climax community will continue to change in small ways, but left undisturbed, it will remain the same through time.
g. Fire and Secondary Succession
1. Natural fires caused by lightening are a necessary part of secondary succession.
2. Some species of trees (ex: Jack pine) can only release their seeds (germinate) after they have been exposed to the intense heat of a fire.
3. Minor forest fires remove brush and deadwood.
4. Some animals depend on fires because they feed on the newly sprouted vegetation.
5. Foresters allow natural fires to burn unless they are a threat to human life or property.
h. Old-field Succession
1. Occurs in farmland that has been abandoned.
2. Grasses and weeds grow quickly, and produce many seeds that cover large areas.
3. Over time, taller plants grow in the area, shading the light and keeping the pioneer species from receiving any light.
4. The longer roots of the taller plants deprive the pioneer species from water.
5. The pioneer species die.
6. Taller trees begin to grow and deprive the taller plants of water and light.
7. Followed by slow growing trees (oaks, maples, hardwoods) take over the area.
8. After about a century, the land returns to a climax community.
SECONDARY SUCCESSION: OLD-FIELD SUCCESSION
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D
O
C
H
C
P
Cellular Respiration: C6H12O6 + 6O2 [pic] 6CO2 + 6H2O + ATP (energy)
Photosynthesis: 6CO2 + 6H2O + solar energy (sunlight) [pic] C6H12O6 + 6O2
C6H12O6 = glucose (sugar)
O2 = oxygen
CO2 = carbon dioxide
H2O = water
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