Biology 2201
Unit 1: Matter & Energy for Life
Chapter 3
 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.
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.



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.
CO2 (g) + H2O (l)  C6H12O6 (s) + O2 (g)



Plants use carbon, in the form of
CO2 (g) during photosynthesis to
make carbohydrates.
This takes carbon from its inorganic
state and transforms it into organic
compounds.
This carbon then gets passed up the
food chain through consumers.



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) + O2 (g)  CO2 (g) + H2O (g)
In fact, photosynthesis and cellular
respiration are complementary reactions;
they are the opposite of each other in terms
of reactants and products:


Photosynthesis is the base of all food
chains.
It also produces the oxygen necessary
for the process of cellular respiration.

Photosynthesis is the route by which

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).