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Chapter 8
Cellular energy
Energy
!  The ability to do work
Quick Review:
!  Autotroph – makes its own food from
the energy from the sun
!  Heterotroph – must consume food to
get energy
Different types of autotrophs:
!  Photoautotrophs – convert light into
energy
!  Chemoautotrophs- use inorganic
substances for energy (hydrogen
sulfide)
Metabolism
!  All of the chemical reactions in a cell
Catabolic pathways
!  Release energy by breaking down larger
molecules into smaller molecules
Anabolic metabolic pathways
!  Builds larger molecules
!  Ex: photosynthesis
ATP
!  Adenosine triphosphate
!  Molecule that provides chemical energy
!  When ATP is broken down (removal of
a phosphate group), energy is released
Chloroplasts
!  Contain chlorophyll – allow plants to
undergo photosynthesis
!  They capture light energy from the sun
to produce energy for plants
!  Leaves have large surfaces that act as
light collectors for plants
Parts of the chloroplast
!  Thylakoids - Flattened saclike
membranes that are arranged in stacks
!  Grana – stacks of thylakoids
!  Stroma – fluid-filled space outside the
grana
Diagram of chloroplast
Photosynthesis
!  The anabolic pathway in which light
energy from the Sun is converted to
chemical energy to use by the cell
During photosynthesis:
!  According to the second law of
thermodynamics, heat is released in this
process
Leaves of Trees
!  Yellow, red, and orange pigments also
exist in leaves of trees
!  Chlorophyll (green) is most abundant,
that’s why leaves are green
!  In autumn, chlorophyll breaks down,
making the rest of the pigments visible
Photosynthesis energy
!  Energy for photosynthesis is used to
make glucose
!  Glucose is made outside of the
chloroplasts
Photosynthesis
!   Made of 2 reactions
1.  Light reactions – require light to take
place
2.  Calvin cycle – does not require light
! 
Generally does not occur at night because
it depends on the products of light
reactions
Cellular respiration
!  Living organisms obtain energy by
breaking down organic molecules during
cellular respiration
Aerobic
!  Requires oxygen
anaerobic
!  Does not require oxygen
Fermentation
!   Occurs without oxygen
!   2 types
1.  Lactic acid
! 
Causes muscles to feel sore
2.  Alcoholic
! 
Occurs in some yeast and bacteria
How are photosynthesis and
cellular respiration related?
!  The products of photosynthesis are
used in cellular respiration
!  The product of photosynthesis is
glucose
!  Glucose is then the substrate used in
photosynthesis