AP Environmental Science
NDHS
Name: _______________________
Per: __________ Date: __________
Ch 3: Ecosystems and Energy
Ecology: the study of one’s house –
- composed of biotic and abiotic components
Biotic: living components of the system
Abiotic: non-living components of the system – space, temperature,
sunlight, soil, wind, precipitiation
- incorporates all the sciences and many other areas of study
- focus can be limited or large based on the purpose of the study – usually focuses
on a specific level of interaction
Biological Hierarchy
Atom – molecule – organelle – cell – tissue – organ – organ system –
organism – population (part of a species) – community – ecosystem (includes the
abiotic) – biome (landscape) – biosphere (atmosphere, hydrosphere, lithosphere)–
universe – infinity and beyond
- all levels can come under study of ecology, although most studies are done at the
organism and higher level
Tying Ecology Together – movement of energy
Energy – ability to do work
Types: Chemical
Electromagnetic (radiant)
Thermal
Nuclear
Mechanical
Electrical
Potential
Kinetic
Study of Energy = Thermodynamics
First Law of Thermodynamics:
- the amount of energy in the universe is constant
- an organism cannot create energy but must capture the energy
from outside itself and then convert it into usable forms
Second Law of Thermodynamics:
- the amount of energy available to do work decreases over time
- ordered systems of energy become disordered by becoming
heat
- the amount of disorder is measured as Entropy
- theoretically all the energy in the universe will eventually be
evenly distributed as heat and no work will be done (Heat Death of the Universe)
- thus no transformation of energy is 100% efficient
Ex: Car engine 20 – 30% efficient at converting chemical
energy in the bonds of gasoline into mechanical energy – rest is lost as heat
Human metabolism – 40 % efficient
Energy Exchange in the Ecosystem
Photosynthesis and Cellular Respiration
Photosynthesis: process of capturing photons (light energy) and using them to excite
electrons to a higher energy state in order to generate a chemical gradient of hydrogen
ions in order to manufacture ATP in order to fix carbon dioxide into simple sugars
6 CO2 + 6 H2O  C6H12O6 + 6 O2
Photon capture is done by a system of proteins called pigments that absorb light
energy - main pigment is chlorophyll, which appears green because it reflects green
light and best absorbs red and blue light
- chlorophyll is found in the chloroplast of plant cells
Organisms: Plants, algae, some protests, cyanobacteria (blue-green algae)
Process: CO2 is fixed to several organic molecules in order to form it into glucose, uses
the ATP for energy
Glucose is used for energy for growth and reproduction – extra glucose is
stored as starch
By products are Oxygen
Cellular Respiration: process of breaking down organic molecules into CO2 and
energy –
- reverse of photosynthesis –
C6H12O6 + 6 O2  6 CO2 + 6 H2O
Glucose is broken down through a series of steps to ensure the slow release of the
energy – slow release makes the process more energy efficient – carried out mainly by
the mitochondria
Process:
Organisms: All eukaryotes (Plants, animals, fungus, most protests)
In the end - CO2 that was fixed by the photosynthesis is released by the
cellular respiration, which also consumes the O2 that was generated
- together they form the base process for the carbon cycle
However, the energy that is captured by the phototrophs is not transferred to
the heterotrophs completely. Much of it lost as heat and through biological
processes.
Energy Flow Through Ecosytems
Terms:
Producers/Autotrophs (self-feeders) – initial organisms that capture and store
energy
Types: Photoautotrophs – capture solar energy and convert it to
chemical energy
Ex: plants and algae- some bacteria and protists
Chemoautotrophs – use the energy in other chemicals to build
biological molecules Ex: deep sea vent bacteria
Consumers/Heterotrophs (other feeders): must consume biological molecules
for a source of energy – cannot make their own food
Types: Carnivores: meat eaters - cats
Herbivores: plant eaters - cows
Omnivores: any eaters – bears
Decomposers/Saprotrophes (rotten eaters):
Detrivores/Saprobes: break down dead things – fungus and
bacteria
Trophic Levels
Primary Consumers – herbivores
Secondary Consumers – carnivores – herbivore eaters
Tertiary Consumers – carnivores – eaters of other carnivores
Keystone Predator – top of the food chain – presence helps
regulate the populations of the lower trophic levels Ex: lions, wolves
- removal of the keystone predator often causes a large disruption in the
lower trophic levels – removal of wolves from the United States causes a large upsurge of
deer populations which in turn ate more and more plants making them less available for
the other species
Detrivores – complete the cycle of nutrients - break things down
which make nutrients available for the producers
Together these make up a food chain (page 54) (consumer to decomposer) which
more accurately portrayed as a food web (page 55).
Ecological Pyramids: Biomass and Energy Transfer Between Trophic Levels
Producers: Trap and convert energy into usable forms
Producers use this energy for life functions (growth, repair,
reproduction) which decreases the amount of energy that is available to the next level
Same is true for each consumer level
Result: As you move up in levels, the number of organisms, the overall
biomass and the amount of energy decreases.
Types of Pyramids:
1. Pyramid of Numbers: Figure 3.11
- typically, the organisms at the base of the food chain are most abundant
2. Pyramids of Biomass: Figure 3.12
- Biomass: amount of biological material – indicates the amount of
fixed energy in an organism or system
- Average is about 90% decrease
3. Pyramid of Energy: Figure 3.13
- expressed as kilocalories per square meter
- since the producers are most abundant they will contain the most energy
per square meter, but not per organism
Ecological Pyramids allow us to look at an ecosystem and determine its
productivity.
Ecosystem Productivity:
Gross Primary Productivity (GPP) is the rate at which energy is
captured during photosynthesis
Net Primary Productivity (NPP) is the amount of energy left over after
the producers have used the amount they need for life functions
- measured by the kilocalories per square meter per year or the grams of
biomass (dry weight of CO2) incorporated per square meter per year
Consumers eat the producers and the NPP becomes available for use (not
all – depends on the efficiency of the consumers digestive system)
Consumer uses the energy for basic life functions (movement, tissue
repair) and the remaining energy (Secondary Productivity) can be used for growth and
reproduction