Biology 2201
Unit 1: Matter & Energy for Life
Chapter 3
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One of the basic characteristics of life is the
need for energy.
Organisms require energy to do work, and no
matter what kind of organism, they all do
work.
There are two main classifications of
organisms based upon their method of
obtaining energy.
1. Autotrophs
◦ able to make their own food.
 Plants – use the process of photosynthesis to
make their own food (sugars, starches) and carry
out cellular respiration to “burn” the food they
make for energy.
2. Heterotrophs
◦ not able to make their own food.
 Animals – must get their food from their
environment and carry out respiration.
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All energy ultimately comes from the sun.
The energy of the sun can only be utilized by
the chemical reaction called photosynthesis.
Photosynthesis allows inorganic compounds,
such as carbon dioxide and water, to be
converted into organic, energy rich
substances such as sugars which cells can
then use as an energy source.
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Photosynthesis is the base of all
food chains - it is the source of all
life on earth.
Photosynthesis is the process of
converting carbon dioxide, CO2 (g)
and water, H20 (l) into simple sugar
by using the sun’s energy. Oxygen,
O2 (g) is given off as a waste
product.
6CO2 (g) + 6H2O (l)  C6H12O6 (s) + 6O2 (g)
Carbon dioxide
+
water
+
light energy
& chlorophyll
See pg. 73 ~Figure 3.4
=
glucose
+
oxygen
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Plants use carbon, in the form of
CO (g) during photosynthesis to
make carbohydrates.
2
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This takes carbon from its inorganic
state and transforms it into organic
compounds.
This carbon then gets passed up the
food chain through consumers.
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
Carbon is returned to its inorganic
state when organisms break down
carbohydrates to get energy.
They use carbohydrates in a cell
reaction process called cellular
respiration.
Cellular respiration requires oxygen.


This reaction releases energy to the
body and gives off inorganic carbon
dioxide and water vapor to the air.
Decomposer organisms also release
carbon dioxide to the air.
C6H12O6 (s) + 6O2 (g)  6CO2 (g) + 6H2O (g) + ENERGY
Glucose
+ oxygen
= Carbon dioxide
+ water
+
ATP
(energy storage molecule)
In fact, photosynthesis and cellular
respiration are complementary reactions;
they are the opposite of each other in terms
of reactants and products:
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
Photosynthesis is the base of all food
chains.
It also produces the oxygen necessary
for the process of cellular respiration.
Comparing Photosynthesis and Cellular Respiration
(A chloroplast is
about 4x larger than
a mitochondrion)
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Photosynthesis is the route by which
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Cellular respiration recycles carbon
inorganic molecules , carbon dioxide
and water, are converted into organic
molecules such as glucose which is
useable in organisms for their
metabolism.
back into inorganic form by releasing
carbon dioxide. This allows the
oxygen and carbon cycles to continue.
There are two types of cellular respiration:
Aerobic Respiration: a process that requires
oxygen. (It will release 38 ATP molecules in
bacterial cells and 36 ATP molecules in cells
with mitochondria). See figure 3.14 pg. 82.
Anaerobic Respiration: a process that will occur
in the absence of oxygen. Some microorganisms are capable of metabolizing without
the presence of oxygen. (An example would be
glycolysis which can occur in muscle cells. It
will only release 2 ATP molecules from the
breakdown of one glucose molecule).
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Global Implications
(Pages 86-90)
The earth is a closed system; little or no matter comes in from the
outside. The processes of photosynthesis and aerobic respiration
have great importance to our world:
1. to sustain life:
to sustain life, nutrients are moved through a series of cycles, the
carbon cycle being one of them.
Photosynthesis and respiration are the two ‘halves’ of the living
component of the carbon cycle :
(i) on land —> photosynthesis takes carbon from CO2 and forms organic
molecules, (carbohydrates), for use in life processes and respiration
breaks them down releasing energy and returning CO2 to the
atmosphere once again.
(ii) in oceanic water —> CO2 dissolves in oceanic water to form carbonic acid which
breaks down to form bicarbonate ions = the source of
carbon for aquatic plants to carry out photosynthesis.
2. In industry
Photosynthesis is the biological basis for the primary industries of
the world.
(a) agriculture and (b) forestry
These involve the harvesting of plants / plant materials for food,
construction, paper, fabrics, cosmetics, medicines, personal care
products.
(c) fisheries
The fisheries depend on aquatic autotrophs as the basis of
the aquatic food chain to feed the species they wish to catch
(herring, turbot, lobster)
(d) mining
The mining of fossil fuels has its beginnings when the petroleum
and coal of today were the oceanic beds and ancient forests millions
of years ago. Petrochemicals are the source of fuels (95%) and
plastics, cosmetics, detergents, drugs, synthetic fibers like nylon,
and synthetic rubber.
3. on the environment
The carbon cycle is different today than it was in the past:
1850 - 28 ppm or 0.028 % by volume
Today - 350 ppm or 0.035%
The increase in CO2 levels is an important factor in global
warming and is due to:
-society’s dependence on fossil fuels as an energy source
and
- the removal and burning of vast stands of trees that
otherwise would absorb CO2 in photosynthesis.
Discussion Question:
How have human activities affected the
processes of photosynthesis and respiration
through:
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chemicals ?
pollution ?
selective breeding ?
genetic engineering ?
other ?