Outline
I. Photosynthesis
A. Introduction
B. Reactions
II. Cellular Respiration
A. Introduction
B. Reactions
Photosynthesis
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Converts sun energy into chemical energy
usable by cells
Autotrophs: self-feeders, organisms can make
their own food
– 
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Photoautotrophs: use sun energy (e.g.
photosynthesis-makes glucose
Chemoautotrophs: use chemical energy (e.g.
bacteria that use methane: CH4)
Photosynthesis
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Photosynthesis takes place in plant cell
organelles called chloroplasts
– 
Light absorbing pigment molecules (e.g. chlorophyll)
Overall Reaction
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6CO2 + 6 H2O + light energy → C6H12O6 + 6O2
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Carbohydrate made is glucose.
Water is split as a source of electrons from H atoms
releasing O2 as a byproduct (used later?).
Electrons increase potential energy when moved from
water, so energy is required (from where?).
Remember: atoms are made of protons (identity),
neutrons (radioactivity) and electrons (energy).
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Basic model of an atom
Light-dependent Reactions
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Overview: light energy is absorbed by
chlorophyll, “exciting” electrons in H atoms and
boosts them to higher energy levels (increased
potential).
These electrons then “fall back” to a lower energy
state, releasing energy held in ATP
Light-dependent Reactions
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Electrons in chlorophyll must be replaced so cycle may
continue-these come from water! Oxygen is “made”
from left over oxygen atoms.
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Light reactions yield ATP and NADPH to fuel reactions of
Calvin cycle (aka: “dark reactions”, do not need light)
Energy Shuttling
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Recall ATP: molecule with 3 phosphate groups
bonded to it, when removing the third phosphate,
lots of energy freed= superb molecule for
shuttling energy around cells (ADP + P3).
Other energy shuttles: NADP + H
Calvin Cycle (“dark” reactions)
 
ATP and NADPH made in light reactions fuel the
dark reactions.
 
Called carbon fixation: taking carbon from an
atmospheric CO2 and making glucose
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Simplified version of how carbon and energy
enter the food chain
Harvesting Chemical Energy
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Now autotrophs (like plants) can “harvest”
chemical energy to fuel their bodies.
Heterotrophs must eat glucose for fuel.
Heterotrophs: must take in energy from outside
sources, cannot make their own (e.g. animals)
When we take in glucose (or other carbs),
proteins, and fats-these foods don’t come to
us the way our cells can use them
Cellular Respiration Overview
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Transfer of chemical energy in food into chemical
energy cells can use: ATP!
Both plants and animals (cellular respiration).
Overall Reaction:
1 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
Its 3 reactions
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1. Glycolysis
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Breaks 6-carbon glucose molecule into 2 molecules
called pyruvate
Process is an ancient: all organisms from simple
bacteria to humans perform it the same way!!
Yields 2 ATP molecules for every one glucose
molecule broken down
Yields 2 NADH per glucose molecule
Anaerobic Cellular Respiration
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Some organisms thrive in places with little or no oxygen.
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Marshes, bogs, gut of animals, sewage treatment ponds
No oxygen used= ‘an’aerobic
Results in no more ATP!!
End products such as ethanol and CO2 (single cell fungi
(yeast) in beer/bread) or lactic acid (muscle cells)
Aerobic Cellular Respiration
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Oxygen required=aerobic
2 more reactions occur in an organelle in the cell
called the mitochondria
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1. Kreb’s Cycle
2. Electron Transport Chain
2. Kreb’s Cycle
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Completes breakdown of glucose
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Takes pyruvate and breaks it down: carbon and
oxygen atoms end up in CO2 and H2O!
Hydrogens and electrons are stripped and loaded onto
NADH and other carriers.
Production of only 2 more ATP but loads up
with H+ and electrons which move to the 3rd
stage
3. Electron Transport Chain
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“Excited” electrons from Kreb’s cycle move to
chain-like series of molecules.
As electrons move they are less excited and
energy released & stored in 32 ATP!
Oxygen waits at end, picks up electrons and H
atoms and in doing so becomes water!
Energy Tally
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34 ATP for aerobic vs. 2 ATP for anaerobic
– 
Glycolysis
2 ATP
– 
Kreb’s
2 ATP
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Electron Transport
32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but
are important for global recycling of carbon!