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IB 100/101 Home
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Text Readings in Life, Lewis et al.
Chapter 6, The Energy of Life, pg. 87-101
Chapter 44, Communities and Ecosystems, pg. 873-885
Chapter 46, pg. 916-919
The "Reviewing Concepts" boxes are valuable summaries of the
main
ideas in these sections of the text.
You have open access (no log-in or password needed) to
instructional materials on the Text web site student "Online Learning Center".
Select the text chapter you want and
use the links to the e-learning modules or other available materials.
Web Crossing
You may also ask questions and see answers to your classmates'
questions in Web Crossing in the "Talk to Jim and Ed" discussion.
Objectives
The content of today's lecture will help you complete this
assignment:
After studying this material you should be able to:
-
Describe the means by which autotrophs and heterotrophs
obtain
energy and matter from their environment.
-
Describe the roles of primary producers, herbivores,
carnivores, and
decomposers in the energy flow and nutrient cycling of an
ecosystem.
-
Explain how the concepts in the table below play an
integral part in
the growth and reproduction of individuals and the energy flow and
nutrient cycling of an ecosystem.
| Photosynthesis |
Respiration |
Biosynthesis
(Anabolism) |
Net Primary
Production |
| Biomass |
Decomposition |
-
Define and explain the distinction between the terms
"energy flow"
and "nutrient cycling" in an ecosystem.
-
Apply the terms "energy flow" and "nutrient cycling" to an
explanation of the "energy pyramid" or the concept of "the rule of
tens."
-
Describe the role of each of the concepts listed in
objective #3 in
the global carbon cycle.
Web Resources
Life is made up of matter and energy
What are you made of?
Where does your energy come from?
How do you use it?
-
Anybody eat oatmeal for breakfast?
-
What about a Breakfast burrito??
-
Nutrition Facts listing on food labels indicates
nutrients that address today's health concerns.
-
Overview of Chemical Digestion. Figure: Lewis et al., Life, Fig. 38.11, pg. 751
-
METABOLISM: all the biochemical reactions within
cells that
acquire and use energy.
-
Catabolism (degradation) refers to metabolic pathways that
break
down large molecules into smaller ones, which release energy. That
energy which isn't released as heat is stored temporarily in a high
energy molecule called ATP (adenosine triphosphate) until it is
required. Figure: Lewis et al., Life, Fig. 6.9, pg. 94
-
Anabolism (biosynthesis) refers to metabolic reactions
that
use
energy to synthesize new compounds. A typical adult uses 2 billion ATP
molecules a minute! Figure: Lewis et al., Life, Fig. 6.9, pg. 94
-
Human energy and the dietary Calorie. The energy
intake of humans in the form of food is often expressed in dietary
Calories (kilocalories).
All life consists of matter (chemicals) and energy (the
ability
to do work, or the ability to change or move matter).
Reactions that provide the energy and chemical compounds for
living
organisms
Photosynthesis
| CO2 + |
H2O + |
--- |
Light
Energy |
---> |
Simple
Carbohydrates
(Organic Compounds) |
+ O2 |
(Cellular) Respiration
| O2 + |
Simple
Carbohydrates |
----> |
Heat + |
Usable
Chemical
Energy
ATP |
+ CO2 |
+ H2O |
These reactions are COUPLED to TRANSFER energy from the sun
to
chemical form. This energy transformation sustains all life.
In the process CARBON is CYCLED from the abiotic environment
to
living organisms and back to the abiotic environment.
Figure: Lewis et al., Life, Fig. 6.2, pg. 89
The chemical reactions that transfer energy are inefficient.
Only a
fraction of the energy stored in nutrients is used by cells; the rest
is
dissipated as heat.
How do organisms use energy and chemical compounds produced
by
photosynthesis and respiration?
Biosynthesis
Lewis et al. use the term anabolism; see Figure: Lewis et al., Life, Fig. 6.9, pg. 94
Simple
Organic
Compounds |
+
Minerals
+ |
Chemical
Energy
ATP
(From
Respiration) |
---> |
Complex
Organic
Compounds |
|
Simple
Carbohydrates |
|
------> |
|
Complex
Carbohydrates |
Fatty
Acids &
Glycerol |
|
------> |
|
Fats
&
Lipids |
| Amino
Acids |
|
------> |
|
Proteins |
| Nucleotides |
|
------> |
|
DNA
&
RNA |
-
Energy flow from respiration reactions to
biosynthesis
permits the structural organization seen within organisms.
-
Energy flow among organisms from photosynthesis
to
respiration results in structure seen within communities.
Energy flow: Community trophic
level relationships
Energy capture by Autotrophs ("self-feeders" or
"producers")
underpins communities by providing energy for Heterotrophs
("consumers"). Producers extract energy from the non-living
environment;
consumers obtain energy and nutrients by eating other organisms.
Decomposers are consumers that obtain nutrients from dead organisms and
organic wastes and recycle them back into the environment.
A characteristic of life is that energy is required to
maintain
organization at all biological levels. Life remains ordered and complex
because of the constant influx of energy from the sun.
The energy made available by these producer organisms to
consumer
organisms is called NET PRIMARY PRODUCTION (NPP)
Energy
"Fixed"
by Photosynthesis
(Gross Primary
Production) |
MINUS |
Energy
"Released"
by Respiration
(Heat) |
Lecture activity
1. Get together in small groups.
2. Each person PRINT and SIGN your name at the top of a
piece
of
paper.
3. What did you have for your last meal?
4. Was it an autotroph or heterotroph?
5. How many linkages are there between you and your
ultimate
energy
source?
6. What limits the number of links in a food chain?
Food webs and efficiency of energy transfer
- Figure of Food Web: Lewis et al., Life, Fig. 44.10,
pg.
876
-
Food webs describe the relationships between the
eaters
and
the
eaten in communities. They represent the pathways that nutrients and
energy follow as they move through a succession of plants, grazing
herbivores, and carnivorous predators. Producers sit at the bottom of
the food web and are in the first trophic level or link in the
food chain. Consumers (herbivores) in the second trophic level eat the
producers, and consumers in the third trophic level eat the consumers.
No organisms prey on the carnivore sitting at the highest trophic
level.
-
Most food chains only have three links (eg., grass
->
cow ->
cowboy).
-
Energy flow through an ecosystem, showing four trophic
levels. Figure: Lewis et al., Life, Fig. 44.11, pg. 877
-
Organic compounds synthesized by primary producers are
stored in the
form of biomass (the total dry weight of individual organisms,
populations, trophic levels, or entire ecosystems)
-
Moving upwards through the trophic levels, the numbers
and
biomass
of organisms decrease and the size of the organisms increase. The
larger
numbers of small organisms at the lower trophic levels collectively
have
a much larger biomass than the smaller number of organisms at the upper
levels.
-
The amount of food energy stored per unit time is
greatest
at the
first trophic level, and subsequently decreases at each successive
trophic level.
-
The Rule of Tens. Only 10% of the energy in a
trophic level
is passed on to the next trophic level. The 90% energy loss at each
trophic level goes to the metabolic needs of the organisms at
that level. These needs include the energy required for motion,
breathing, eating, growth, and reproduction. Most energy, however, is
lost as heat.
-
Energy flow through an ecosystem, showing 10% rule of
energy
transfer. Figure: Lewis et al., Life, Fig. 44.11, pg. 877
-
Energy Pyramid showing inefficiency of energy
transfer.
Decomposition and matter
cycling
-
What if portions of an organism remain uneaten, or if
a
plant or
animal dies naturally?
-
Decomposers (e.g., bacteria and fungi) break
their
tissues
down and release the energy stored within the organism's body to the
environment as heat.
-
Eventually, all stored energy is dissipated as heat.
Ecosystems
require continual energy input to function indefinitely.
-
Decomposers play a critical role in food webs because
they
break
down the organism's organic molecules to nutrients or simple molecules
such as carbon dioxide and water. They recycle the finite supply of the
essential elements of life (e.g., carbon, nitrogen, phosphorus) making
them available for primary producers to take up once more.
-
Since no significant amount of new matter comes to the
Earth from
space, this recycling of matter is vital for the continuation of life
on
the planet.
-
"We
are made of star stuff" (quote from Carl Sagan)
-
Three biogeochemical cycles:
The Greenhouse Effect: Consequences of human modification
of
the
Carbon cycle
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