Unit 3: Cell Processes
Notes set #2
Biology
Melino
Photosynthesis
Part II
What is the glucose made by photosynthesis used for in a plant?
Converted into fats and
oils for the seeds
Converted to fructose
for the fruit
Used in
respiration to
release energy
glucose
Joined together to
make cellulose for
cell walls
Combined with nitrates
from the soil to make
proteins for the new
growth
Joined together to
make starch for
storage
Plants are composed of three major parts:
1. The root system
•
•
•
Anchors the plant in place
Stores excess sugar
Absorbs water & nutrients
2. The shoot system
•
•
Supports the plant body
Provides passageway for nutrients
3. Leaves
•
Where photosynthesis occurs
• The process of photosynthesis involves the use of
light energy to convert carbon dioxide and water
into sugar, oxygen, and other organic compounds.
This process is often summarized by the following
reaction:
6 H2O + 6 CO2 + light energy --> C6H12O6 + 6 O2
• This process is an extremely complex one, occurring
in two stages
Photosynthesis occurs in two main
steps
1. The light-dependent reactions (Calvin cycle)
of photosynthesis transform light energy into
chemical energy
 The chemical energy is stored in the energy carrier
ATP (Adenosine Triphosphate)
2. The light-independent reactions of
photosynthesis produce food
 ATP from the light reactions supplies the energy
needed to combine carbon dioxide and water to make
glucose
• The light-independent reactions
can’t happen without the light
reactions.
Making ATP
• ATP is formed by ADP. The bond between
the 2nd and 3rd phosphates stores the energy.
• When the bond is broken the energy is
released
• ADP can be reused to store more energy
and released when required.
How do we get the ATP?
• Two processes occur depending on presence
of oxygen
• Aerobic respiration needs ______________
• 1 molecule of glucose can be converted to
38 ATP molecules!! Wow!
• Anaerobic respiration does not require
oxygen and makes only 2 ATP molecules.
Aerobic vs. Anaerobic
Aerobic
• Glycolysis in cytoplasm
• Mitochondria – oxygen
• Produces 38 ATP
Anaerobic
• Glycolysis in cytoplasm
• Lack of Oxygen
• 2 ATP
• Animals: Lactic Acid
• Plants: Ethanol & Carbon
Dioxide
What is the energy for?
•
•
•
•
•
•
•
Building complex molecules
Cell division and growth
Movement of organelles
Movement of whole cell
Maintaining cell organization
Active transport
Transmission of nerve impulses
The Sun – the ultimate
energy source
• The sun is the perfect energy source.
It contains all the energy you could ever need…
if only you could catch it….
• Green bacteria figured out how to do that over
2.5 billion years ago!
• Green bacteria, algae and plants use chlorophyll
to absorb light energy from the sun.
• During the light reactions of photosynthesis,
chloroplasts absorb light energy from the Sun
and transform it into the chemical energy
stored in ATP.
• When the light energy is absorbed, it splits
water molecules.
• The electrons from the water molecules help
with the energy transformation from light
energy to chemical energy in ATP.
• Plants release the oxygen from the water
molecules as waste, producing the oxygen we
breathe
• Plants use the energy in ATP to combine CO2 &
H2O molecules to create glucose during the lightindependent reactions.
• To make glucose, plants first take CO2 out of the air
through a process called carbon fixation
• Taking CO2 and attaching it to a molecule inside the cell
• Plants then use the energy from the ATP and the
electrons to convert the CO2 to sugar
• When plants make more glucose than
they need, they store their excess
matter and energy by combining
molecules into starch.
• The starch molecules can be used later
or turned into other compounds such as
proteins, nucleic acids, fats
How does the potato use starch?
• One of the most important carbohydrates in
our diet is the potato. Simple sugars bond to
form complex carbohydrates that are stored
in the fattened tubers we bake, scallop, hash
and mash. This cool-season vegetable is one
of the most widely grown staples in the
world. Although we enjoy and need it, the
potato stores starch for its own use.
Carbon fixation
• The process by which plants turn
inorganic carbon into organic
compounds
• Organisms that grow by fixing carbon
are called autotrophs
• C3 plants
• C4 plants
• CAM plants
C3 Photosynthesis : C3 plants
• Called C3 because the CO2 is first incorporated
into a 3-carbon compound.
• Stomata are open during the day.
• Photosynthesis takes place throughout the leaf.
• Adaptive Value: more efficient than C4 and
CAM plants under cool and moist conditions
and under normal light because requires less
machinery (fewer enzymes and no specialized
anatomy)..
• Most plants are C3
C4 Photosynthesis : C4 plants.
• Called C4 because the CO2 is first
incorporated into a 4-carbon compound.
• ~ 3 % of plants
• Maize (CORN), sugar cane, millet, and sorghum.
• Stomata are open during the day.
• Uses Carboxylase for the enzyme involved in
the uptake of CO2. This enzyme allows CO2
to be taken into the plant very quickly, and
then it "delivers" the CO2 directly for
photosynthesis.
C4 Plants
• Adaptive Value:
• Photosynthesize faster than C3 plants
• C4 plants have a competitive advantage over
plants possessing the more common C3
carbon fixation pathway under conditions of
drought, high temperatures, and nitrogen or
CO2 limitation
CAM Photosynthesis : CAM plants.
CAM stands for Crassulacean Acid Metabolism
• Called CAM after the plant family in which it
was first found and because the CO2 is stored in
the form of an acid before use in photosynthesis.
• Stomata open at night (when evaporation rates
are usually lower) and are usually closed during
the day. The CO2 is converted to an acid and
stored during the night. During the day, the acid
is broken down and the CO2 is released for
photosynthesis
Adaptive Value:
• Better Water Use Efficiency than C3 plants under arid conditions due
to opening stomata at night when transpiration rates are lower (no
sunlight, lower temperatures, lower wind speeds, etc.).
• May CAM-idle. When conditions are extremely arid, CAM plants
can just leave their stomata closed night and day. Oxygen given off
in photosynthesis is used for respiration and CO2 given off in
respiration is used for photosynthesis. This is a little like a perpetual
energy machine, but there are costs associated with running the
machinery for respiration and photosynthesis so the plant cannot
CAM-idle forever. But CAM-idling does allow the plant to survive
dry spells, and it allows the plant to recover very quickly when water
is available again (unlike plants that drop their leaves and twigs and
go dormant during dry spells).
CAM plants include many succulents such as
cactus, agaves & orchids
Video on C4 & CAM plants
• http://www.youtube.com/watch?v=Dq38Mp
YOb8w
Summary
• The cell’s two energy transforming organelles,
mitochondria and chloroplasts, feed on the
waste products of each other.
• CO2 given off by mitochondria is what
chloroplasts need to make the building block of
sugars and other carbohydrates.
• The oxygen released by chloroplasts is what
mitochondria need to drive the electrons -- that
pump in the hydrogen ions -- making it possible
for ATP synthesize to add that terminal phosphate
to ADP, creating ATP, the universal energy
carrier.
Comparing Cellular Respiration and
Photosynthesis
Cellular respiration
Products:
• Glucose
• Oxygen
Reactant:
• Carbon Dioxide
• Water
• Energy
Photosynthesis
Products:
• Carbon Dioxide
• Water
Reactant:
• Glucose
• Oxygen
• Water
Crash Course in Photosynthesis
• http://www.youtube.com/watch?v=sQK3Yr
4Sc_k&list=SP3EED4C1D684D3ADF&ind
ex=8
Review
• http://vcell.ndsu.nodak.edu/animations/phot
osynthesis/movie.htm
• http://www.wiley.com/legacy/college/boyer
/0470003790/animations/photosynthesis/ph
otosynthesis.htm
• Illuminating photosynthesis:
http://www.pbs.org/wgbh/nova/nature/photos
ynthesis.html