Download The Study of Life (Chapter 1)

The Biosphere
What is Ecology?
Ecology is the scientific study of interactions among organisms and between organisms and their environment.
There are different levels of organization in the study of ecology, listed below in order from smallest to largest:
1. Individual Species – a group of organisms so similar that they can breed and produce fertile offspring.
Example: a white-tail deer
2. Populations – groups of individuals that belong to the same species and live in the same area. Example:
A herd of white-tail deer.
3. Community – groups of different populations that live together in a defined area. Example: owls,
white-tail deer, skunks, rabbits, and beavers that all live in a grassy meadow.
4. Ecosystem – a collection of all the organisms that live in a particular place, together with their nonliving
environment. Example: a forest community of animals and plants.
5. Biome – a group of ecosystems that have the same climate and dominant communities. Example: the
temperate forest biome, which covers a lot of different forests.
6. Biosphere – the combined portions of the planet in which all life exists, including land, water and air.
Energy Flow
The flow of energy through an ecosystem is one of the most important factors that determines the system’s
capability to sustain life. There are different levels in the energy flow:
1. Producers – Sunlight is the main source of energy for life on earth. However, some other organisms
obtain energy from energy stored in inorganic chemical compounds. A producer is an organism that
can make its own food from one of the above sources, also called an autotroph. They do that through
one of two processes:
a. Photosynthesis – when light energy is used to power chemical reactions that convert carbon
dioxide and water into oxygen and sugars. Example: plants
b. Chemosynthesis – when organisms use chemical energy to produce carbohydrates. Example:
bacteria found in volcanic vents on the deep-ocean floor and hot springs.
2. Consumers – Many organisms cannot harness energy directly like producers do. The only way they
can acquire energy is from eating other organisms. These organisms are called heterotrophs. There are
different types of heterotrophs:
a.
b.
c.
d.
e.
Herbivores – organisms that eat only plants
Carnivores – organisms that eat only animals
Omnivores – organisms that eat plants and animals
Detritivores – organisms that feed only on dead matter
Decomposers – organisms that break down organic matter
Feeding Relationships
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Energy flows through an ecosystem in one direction, from the sun or inorganic compounds to autotrophs
(producers) and then to various heterotrophs (consumers). The relationships between producers and consumers
connect organisms into feeding networks based on who eats whom.
 Food Chains – a series of steps in which organisms transfer energy by eating and being eaten.
See
picture below for sample food chain:
 Food Webs – a network of complex interactions in an ecosystem, which links all the food chains in an
ecosystem together. Notice in a food web that arrows point from what is being eaten, to what eats it.
See picture below for sample food web:
 Trophic Levels – each step in a food chain or food web is called a trophic level.
Producers make up the
first trophic level, etc.
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Ecological Pyramids
An ecological pyramid is a diagram that shows the relative amounts of energy or matter contained within each
trophic level in a food chain or food web. See picture below:
Only about 10% of the energy available within one trophic level is transferred to organisms at the next
trophic level. This is called the ten percent rule.
In each given trophic level above, the total amount of living tissue is referred to as biomass.
Cycles of Matter
Organisms need more than just energy to survive in an ecosystem. They also need oxygen, carbon, hydrogen,
and nitrogen, water, minerals, etc. Unlike the one-way flow of energy in an ecosystem, matter is recycled
within and between ecosystems. This happens through biogeochemical cycles, which are cycles that connect
biological, geological, and chemical aspects of the biosphere. These chemicals move in a circular motion,
recycling the same atoms over and over again. Organisms must have these nutrients to survive.
 The Water Cycle – Water moves between the ocean, atmosphere, and land.
Water molecules enter the
atmosphere as water vapor when they evaporate from bodies of water. This is called evaporation.
Water can also enter the atmosphere by evaporating from the leaves of plants in the process of
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
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transpiration. Eventually, the water vapor condenses into tiny droplets that form clouds. When these
droplets become large, water returns to Earth through process of precipitation, or rain. The cycle
begins again. See picture on page 75 of your textbook.
The Carbon Cycle – Carbon is the key ingredient in all living organisms. In the atmosphere, carbon is
present as CO2 gas. It is released into the atmosphere by volcanic activity, respiration, burning of fossil
fuels, and by decomposition of organic matter. Plants take in CO2 and use the carbon to make sugars for
energy. Animals eat the plants. Eventually these organisms die and decompose, which makes more
fossil fuels, fuels more volcanoes, etc. See picture on page 77 of your textbook.
The Nitrogen Cycle – Organisms require nitrogen to make amino acids, which in turn make our DNA.
There are many forms of nitrogen in the biosphere: N2 is nitrogen gas found in atmosphere, NH3
(ammonia), NO3- (nitrate), and NO2- (nitrite) are found in the wastes produced by many organisms and
in dead and decaying organic matter. Bacteria in the soil convert nitrogen gas into ammonia in a process
known as nitrogen fixation. Other bacteria convert ammonia into nitrates and nitrites, which allow
producers to use them to make proteins. Consumers eat the producers, and then die and return the
nitrogen to the ground.
The Phosphorus Cycle – Phosphorus is important to organisms because it also forms DNA and RNA.
Phosphorus is found only on land in rocks and soil minerals and in ocean sediments. Phosphate is
released as rocks wear down, goes into the oceans where marine animals use it, and some stays on land
where plants absorb it, consumers eat plants, die, decay, etc.
Nutrient Limitation
If a nutrient is in short supply, it will limit an organism’s growth. This is called a limiting nutrient. Thus the
reason we need to add fertilizers to plants occasionally.
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