Bioenergetics:
Photosynthesis
and Cellular
Respiration
PHOTOSYNTHESIS:
Capturing and
Converting Energy
ENERGY
Energy is the ability to do work.
 All living things depend on energy.
 Energy comes in the form of light, heat, electricity, or
sound.
 Energy can be stored in chemical compounds.
ATP- Adenosine Triphosphate
 ATP
is the cell’s energy currency.
 Energy is stored in the chemical bonds of ATP.
 ATP
is made up of 3 parts: adenine base, ribose
sugar, 3 phosphate groups
ATP
 Energy
is released when the chemical bonds in
ATP are broken.
 ATP can be broken down by breaking bonds
with the phosphate molecules into ADP, and
AMP.


ADP- Adenosine Diphosphate (2 phosphate groups)
AMP- Adenosine monophosphate (1 phosphate group)
 The
energy released by breaking down ATP can
be used for processes such as:
 Active
Transport (ex: the sodium/potassium pump)
 Muscle contractions
Autotrophs and Heterotrophs
 Autotrophs
own food.
are organisms that make their
 Use
light energy from the sun to produce food
 Ex: Plants
 Heterotrophs
obtain energy from the food
they consume.
 Unable
 Must
to directly use the sun’s energy.
consume other organisms either by ingesting
(eating) them or decomposing them.
 Ex: Animals
The Photosynthesis Equation



Photosynthesis is the process whereby plants use the
energy of sunlight to convert water and carbon
dioxide into oxygen and high-energy
carbohydrates.
Carbon dioxide +water  sugar and oxygen
In addition to water and carbon dioxide,
photosynthesis requires light and chlorophyll, a
molecule in chloroplasts.
The Photosynthesis Equation
3 Requirements for Photosynthesis:
1. Sunlight
2. Pigments
3. Energy storing compounds
1. LIGHT

Light travels to the Earth in the form of
sunlight

We perceive sunlight as white light


Made of a mixture of many different
wavelengths of light
Wavelengths of light that are visible to us
are known as the visible light spectrum
2. PIGMENTS
 Pigments
are light absorbing molecules
that help plants gather the sun’s energy

The main pigment found in plants is
chlorophyll
 Chlorophyll
absorbs red and blue
wavelengths of light, but it reflects green
making the plant appear green
 When the pigments absorb light they are also
absorbing the energy in that light, producing
more energy for the cell
INSIDE A CHLOROPLAST
 Photosynthesis
takes place in chloroplasts.
 Chloroplasts contain saclike photosynthetic
membranes called thylakoids.


Thylakoids contain clusters of chlorophyll and
other pigments and proteins known as
photosystems that are able to capture sunlight.
The light reaction takes place in thylakoids
 Grana-
stacks of thylakoids
 Stroma- the region outside the thylakoid
membrane

The dark reaction takes place in the stroma
3. Energy Storing Compounds


Used to trap high energy electrons into chemical bonds.
Occurs in 2 ways:
 1. Electron carrier NADP+ accepts a pair of high
energy electrons and gets converted to NADPH.
 2. AMP is converted to ADP which is then converted
to ATP. This requires light!
Adenosine Triphosphate (ATP)- a molecule that provides
energy for cellular reactions and processes.

ATP releases energy when one of its high-energy bonds is
broken to release a phosphate group.


-the cell’s energy currency
NOTE: The energy stored in these molecules is released
by breaking chemical bonds to generate things the cell
needs, like glucose!
Light Rxns - SUMMARY

Take place in thylakoids

The light reactions USE:


water, light energy, chlorophyll pigments
The light reactions PRODUCE:



oxygen, NADPH, ATP
Occurs by converting ADP and NADP+ into ATP and
NADPH.
These reactions REQUIRE light.
Dark Reactions/ Light
Independent Reactions/ Calvin
Cycle - SUMMARY


Takes place in the stroma
Calvin Cycle USES:


NADPH, ATP ,CO2
Calvin cycle PRODUCES:

glucose (C6H12O6)

Glucose is more stable and can store up to 100 times more
energy than NADPH and ATP.
These reactions do not require light.
Organisms that eat plants indirectly use the energy from
glucose.


Biology in a Minute:
Photosynthesis
 http://www.youtube.com/watch?v=BeU
mj8d6Mag
Photosynthesis Summary Chart
CELLULAR RESPIRATION
Photosynthesis vs. Respiration
- almost opposite processes
-equations are opposites
Photosynthesis- deposits energy
-occurs only in plants, algae, and some bacteria
Respiration withdraws energy
-takes place in all eukaryotes and some
prokaryotes
Chemical Energy In Food
Purpose of food:



Source of raw materials used to make new
molecules
Source of energy
calorie – the amount of energy needed to raise
the temperature of one gram of water one
degree Celsius.


Cells gradually release the energy from glucose.
Cellular Respiration Overview
Cellular Respiration – the process that releases energy
by breaking down food molecules in the presence of
oxygen.

Contains 3 Pathways:



Glycolysis
Krebs cycle
Electron transport
Cellular Respiration overview
The equation for cellular respiration is:
6O2 + C6H12O6  6CO2 + 6H2O + ATP (energy)


If cellular respiration took place in one step, all
the energy would be released at once and most
would be lost as heat.

SOLUTION: Each of the three stages of cellular
respiration captures some of the chemical energy
available in food molecules and uses it to
produce ATP or energy.
Step 1: Glycolysis
-process in which 1 molecule of glucose is broken in half,
producing 2 molecules of pyruvic acid
-does NOT require oxygen
location: cytoplasm
Uses: 2 stored ATP, 1 molecule of glucose
Produces: 4 ATP molecules, 2 molecules of pyruvic acid
NET GAIN: 2 ATP (2% of the total chemical energy in glucose),
2 molecules pyruvic acid
OXIDATIVE (AEROBIC)
RESPIRATION



Respiration - process that involves oxygen
and breaks down food molecules to release
energy.
To get the rest of the energy from the food
molecules, the cell uses oxygen.
Aerobic – requires oxygen.

the reason we need to breathe, to respire.
Step 2: Krebs Cycle
location: mitochondria
Uses: the carbon from pyruvic acid (made in
broken down
glycolysis)
Produces:
CO2 (waste product, released when you exhale)
NADH
FADH2
is
Step 3: Electron Transport
location: mitochondria
Uses: NADH and FADH2 (from the Krebs Cycle)
- passed from one carrier protein to the next
- uses the high energy electrons
Produces: converts ADP  ATP, H20
ENERGY AND EXERCISE

Aerobic cellular respiration produces 36 total ATP molecules from each
glucose molecule (37% efficient).

Remainder of energy from glucose is released as heat (body feels warm after exercise).

Eating food:
 Complex carbs are broken down into simple sugars that are converted to
glucose.
 Lipids and proteins broken down into molecules that enter glycolysis or
Krebs cycle.

Breathing and respiration:



Oxygen is needed to produce ATP in mitochondria
Without oxygen, the body tries to make ATP by glycolysis alone (not sufficient for most
cells).
Relationship between photosynthesis and cellular respiration:


Photosynthesis produces glucose and oxygen
Cellular Respiration breaks down glucose using oxygen, to produce ATP
Fermentation
anaerobic- does not require oxygen
fermentation
-process of breaking down glucose in the absence of oxygen
-cells perform glycolysis followed by fermentation
(this means Krebs cycle and electron transport DO NOT occur)
Uses: 1 glucose molecule
Produces: CO2, NAD+
2 main types:
1. Alcoholic Fermentation
2. Lactic Acid Fermentation
Alcoholic Fermentation
Pyruvic Acid + NADH  ethyl alcohol + CO2 + NAD+
-used by yeast
-(facultative anaerobes- will use aerobic respiration when oxygen is
present, but if not they will use fermentation)
Products: ethyl alcohol, CO2, and NAD+
-CO2 production causes bread dough to rise, bubbles in beer, etc.
Lactic acid fermentation
Pyruvic Acid + NADH  lactic acid + NAD+
-occurs during rapid exercise
- not enough oxygen to continue oxidative respiration (through Krebs Cycle and
Electron Transport Chain)
-lactic acid buildup causes the painful, burning sensation in muscles
after intense activity
- bacteria use this process to make foods like sour cream, yogurt,
buttermilk, and sauerkraut
Why is fermentation useful?
-produces NAD+ that is used in glycolysis so that it can continue to
make small amounts of ATP

A Guide to Cellular Respiration:
http://www.youtube.com/watch?v=13qlVd34J
kM&feature=youtu.be