Figure 1.3: Organisms in the soil
Guide questions
1. What is an ecosystem?
2. How do the living components of an ecosystem affect the nonliving components? Give example.
3. Can a fallen log be considered as an ecosystem? Explain your answer.
1.2. COMPONENTS OF AN ECOSYSTEM
In the preceding section you learned what an ecosystem is. The living component is known as the biotic
and the nonliving component is known as abiotic. The biotic component consists of plants, animals, and
bacteria. The abiotic component includes all the factors of the nonliving environment such as the
substratum, light, rainfall, nutrients, soil, and others. Both the biotic and abiotic components are equally
important in the ecosystem because without one of them the ecosystem would not function.
Insightfulness
The ecosystem consists of the biotic and abiotic components. The biotic components are the plants,
animals, and decomposers. The abiotic components are the non living factors, such as temperature,
water, and others. The abiotic affect the biotic components and vice versa.
1.2.1. Green plants
Green plants are known as the producers. They capture the energy from the sun and together with carbon
dioxide (CO
2
) in the air and water (H
2
O) convert together those into food energy. Since plants are able to
manufacture their own food, they are also known as autotrophs (or self-nourishing). These plants are able
to manufacture food though the process of photosynthesis, which will be explained in the next section.
Green plants also take substances, such as nitrogen and sulfur from the environment and convert those
into plant materials that can be used by other organisms as food. These green plants further provide
oxygen which is taken in by humans and animals in the process of respiration. For these reasons, all life,
whether in the pond, forest, or grassland, depend on green plants.
5
You might think that green plants consist only of the trees or big plants that you see around. The other
producers are invisible to your eyes. These are the microscopic drifting plants which are greater sources of
food than the big plants that you can see. We call these microscopic plants phytoplankton. When they
become too abundant, they can give a pond or a body of water a green color.
Have you ever seen a pond or a lake with green surface?
Guide questions
1. What are producers?
2. What do producers perform in an ecosystem?
3. What are phytoplanktons?
1.2.2. Animals
Animals, or the consumers, obtain their food from plants or other animals. Because of this, they are also
known as heterotrophs, which means that they feed on others and cannot manufacture their own food,
unlike the green plants.
There are three different types of consumers, namely, the herbivores, the carnivores, and the omnivores.
Figure 1.4: There are three different types of consumers
The herbivores are those that eat plants only. For example, the caterpillar that feeds on leaves is an
herbivore while the snake that eats the caterpillar is a carnivore. Omnivores eat both plants and animals. A
human being is a good example of an omnivore.
Through the process of respiration, animals combine the food they eat with oxygen to produce CO
2
and
H
2
O which are used by plants in the photosynthesis process. Animals also convert the materials of the
plant bodies into the materials that make-up their own bodies. All the energy produced and used by
animals comes from the plants.
Guide questions
1. What are consumers?
6
2. What are the three types of consumers? and give one example for each type.
1.2.3. Bacteria and fungi as agents of decay
Have you ever observed what happen to leaves that fall on the ground?
After some time, the leaves wither, break down into smaller pieces, decay, and finally become part of the
soil. What do you think is responsible for this change?
Have you heard of the word decomposer? What do you think does a decomposer do?
Decomposers make-up the third biotic component of the ecosystem. They use the bodies of dead animals
and plants for their food. The materials contained in these dead bodies are broken down by the
decomposers, thus they get the energy they need and release the minerals and other nutrients back into the
environment for use again by other organisms. Bacteria are among the most abundant decomposers while
fungi are known to be the fast-acting decomposers.
Decomposers are found everywhere. In the pond, they are abundant at the bottom where the remains of
the dead organisms (plants and animals) settle. On land, they abound on the surface of the soil where the
dead bodies of plants and animals are found.
Each of the three groups of the biotic component of the ecosystem - producers (plants), consumers
(animals), and decomposers (bacteria and fungi) - has its own specific function or task to perform.
Figure 1.5: Relationship among biotic component of the ecosystem
7
The work performed by an organism is known as its ecological niche, while the place where the organism
lives in the ecosystem is known as its ecological habitat.
Guide questions
1. What are producers?
2. Give examples of producers?
3. What do decomposers perform in the ecosystem?
1.2.4. Nonliving factors
The nonliving factors of the environment make-up abiotic component of the ecosystem. These include the
chemical and physical factors in the environment, such as light, temperature, water, pH (acidity), wind,
chemical nutrients, salinity (saltiness), soil, and others. Organisms are affected by the biotic factors
simultaneously but, of course, different species of organisms are affected differently. For example, lichens
may not survive when temperature gets very high but cactus may.
Different organisms thrive in different conditions. There are animals, like the earthworms, which favor
wet condition, while others, like ants, prefer drier conditions. Some plants, such as cactus, grow best in
sandy soil while tomatoes grow best in loamy soil.
As a whole, these environmental factors not only provide essential energy and materials but also
determine the kind of organisms that will inhabit the area. Hence, they provide the conditions necessary
for the survival of the organisms.
Guide questions
1. What are the components of an ecosystem?
2. Give examples for each component of the ecosystem.
3. In general, what are the functions of these components?
4. Can an ecosystem exists without one of its components? Justify your answer.
Vocabulary
Autotroph: Organism that is self-nourishing; one that can produce its own food.
8
Hetertrop: Organisms that feeds on others and cannot manufacture its own food.
Biological magnification: Accumulation or increase of chemical substances on organisms in succeeding
higher trophic levels.
Biomass: Amount of organic materials in plants or animals from which energy can be derived.
Energy: Capacity to do work
Energy content: The amount of energy available for doing work. For example, the amount of energy in
fuel available for powering a motor vehicle.
Food chain: Energy pathway which proceeds from the producers to the consumers.
Food web: Series of interrelated food chains in an ecosystem.
Pyramid of energy: Representation of the organic content in each trophic level.
Biosphere: Portion of the earth and its environment within which life in any of its form is manifested.
Photosynthesis: Process of manufacturing food by green plants in the presence of sunlight.
Atmosphere: Layer of air surrounding the earth.
Hydrosphere: The part of the Earth composed of water including clouds, oceans, seas, ice caps, glaciers,
lakes, rivers, underground water supplies, and atmospheric water vapor.
Lithosphere: The outer, rigid shell of the Earth, situated above the atmosphere and containing the crust,
continents and plates or the solid part of the earth’s surface
Grassland biome: Community where grass is abundant while trees are scarce and where mostly
herbivores and rodents dwell.
Carnivore: Animals that get food from killing and eating other animals.
Herbivore: Organisms that eat plants only.
Omnivore: Organisms that consume both plants and animals
Biotic factor: Living component of the ecosystem which includes plants, animals, and bacteria.
Biotic potential: Reproductive capacity of the living components of the ecosystem.
Producer (autotroph): Green plant or organism that, performs photosynthesis.
Consumer: Organism that feeds on other organisms.
9
Decomposer (also known as microconsumer): Organism which breaks down nonliving organic material;
example are bacteria and fungi.
Environment: Sum of all external forces and conditions acting on an organism or a community of
organisms.
10
CHAPTER 2
MATERIALS AND NUTRIENT CYCLES
The energy that flows into an ecosystem cannot be recycled. Once the energy is used, it is lost. But it
much be constantly repeatedly replenished if the ecosystem is to continuously function.
The important chemical nutrients, however, are used repeatedly. They are cycled between the living and
nonliving components of the ecosystem. Generally, they begin in the abiotic part of the ecosystem (water,
land, and air). Then, they enter to the bodies of plants and animals and return into the abiotic environment.
The movement of these materials and nutrients between the living and nonliving environment clearly
shows the interrelatedness of the abiotic and biotic components in an ecosystem. Among these recycled
materials and nutrients are carbon, oxygen, water, nitrogen, and phosphorus.
After studying this chapter, you should be able to
1. Identify different nutrients that can be recycled.
2. Explain the water, carbon and oxygen, nitrogen, and phosphorus cycles.
3. Discuss the importance of each of these cycles.
4. Discuss how people affect these cycles.
5. Differentiate micronutrients from macronutrients
2.1. IMPORTANCE OF THE NUTRIENT CYCLES
The energy from the sun flows to the plant goes to the herbivore that eats the plant, to the carnivore, and
to the last consumer until the energy is lost into the ecosystem. The energy does not go back to the source.
It cannot be used over and over again.
In contrast, when the bodies of dead plants and animals decompose, they are changed into nutrients
through the action of bacteria and fungi. The nutrients are stored in the abiotic environment like the soil.
The nutrients can be used again by the plants. The plants are eaten by the animals and when the animals
die, they decompose into nutrients. These nutrients can be used over and over again. In this way, a cycle
of nutrients is formed.
The cycle of nutrients is an important process that takes place in the ecosystem. Through the cycle of
nutrients, the organic compounds found in the bodies of organisms are converted into inorganic
compounds which serve as nutrients to the other organisms. In both processes of energy flow and nutrient
cycles, the plants provide the link by which the biotic and abiotic components interact with one another.
Insightfulness
Energy cannot be recycled. When using, it is lost into the ecosystem.
11
The nutrients in an ecosystem can be used over and over again. They are cycled beginning from the
nonliving environment: air, water, and soil. Then, these substances are taken in by the producers and are
passed on through several consumers. They are returned to the nonliving environment by decomposers.
Nutrients may be classified into two types, namely, the macronutrients and the micronutrients. The
macronutrients are those that are required by the organisms in large quantities. Examples are carbon,
hydrogen, oxygen, and nitrogen. Sulfur, phosphorus, and potassium are also macronutrients but are
needed by organisms in smaller quantities. The micronutrients are needed in very small amounts. They are
also essential to life. Examples are copper, zinc, iron, and boron.
The macronutrients are the major components of fats and carbohydrates. They make-up the cell structures
of plants and animals. The cell walls of plants, for example, are made up of a very rigid substance called
the cellulose. Cellulose is made up of these three elements with a ratio of 7.2 carbons, 1 hydrogen and 8
oxygen. This substance makes the cell walls very firm and rigid. It adds strength to the plant.
Nitrogen, carbon, hydrogen, and oxygen are the building blocks of proteins. Phosphorus makes up many
nucleic acids and is also essential for the transformation of energy in the cells.
The micronutrients are as important as the macronutrients. Magnesium, for example, is necessary in the
production of chlorophyll.
Guide questions
1. What happens to the energy from the sun when it enters to an ecosystem?
2. What happens to the dead bodies of plants and animals in an ecosystem?
3. Define macronutrients and micronutrients.
4. Make a listing of micronutrients and macronutrients, and give their functions?
5. What are the components of cellulose?
2.2 THE WATER CYCLE
As with any cycle, the water cycle has neither beginning nor end. However, it is useful to choose a
starting point. Let us begin with water vapor in the atmosphere.
a)
12
b)
Figure 2.1: The water cycle
When water in the atmosphere reaches saturation (the highest amount of moisture that the air can hold), it
falls as rain. This falls directly to the land and bodies of water like the oceans and seas. Some runs off the
surface of the land into rivers. The rain that falls on the land is absorbed by plants through the roots and
drank by animals. Some penetrates the soil and becomes part of the underground water, which eventually
empties into the oceans. The processes of condensation and precipitation are responsible for the return of
water from the atmosphere into the land and other bodies of water.
The water from the land and other bodies of water returns to the atmosphere through the process of
evaporation. Plants return the water by the process known as transpiration, while animals do this through
respiration. Water accumulates again in the atmosphere as clouds and falls as rain.
Guide questions
1. What is saturation?
2. What is evaporation?
13
3. What is respiration?
4. Trace the pathway of the water cycle.
2.3. THE CARBON AND OXYGEN CYCLE
Much of the carbon in the environment exists in the form of carbon dioxide. Plants absorb this gas though
the leaves and use in the process of photosynthesis. Oxygen is given off during this process. Animals and
other consumers obtain their food as well as their oxygen needs from plants. In the process of respiration,
the food is broken down into CO
2
and water which are returned into the atmosphere.
Figure 2.2: The carbon and oxygen cycles
When the animals and plants die, their bodies and waters are broken down by the decomposers. In this
process, CO
2
is produced and returned to the atmosphere. Sometimes dead organisms fail to decompose
quickly. When this happens, the dead bodies change to coal, oil, and gas which become fossil fuels after a
long time. When burned, fossil fuels release carbon dioxide into the atmosphere.
Insightfulness
Carbon dioxide is present in the atmosphere from wastes, dead bodies of organisms, and fossil fuels.
14
Không có nhận xét nào:
Đăng nhận xét