Chapter 6
Photosynthesis
Photosynthesis
• Organisms need to have food to live. The way
organisms get food differs depending on what
kind of organism they are.
• Animals get food from the things that they eat.
(plants, animals etc.)
*Animals that only eat plants are herbivores.
*Animals that eat only meat are carnivores.
*Animals that eat both plant and animal
materials are omnivores.
What goes in and exchanges, then what comes out!
• Where does this take place in the plant?
• Where in the cell?
Light Capturing (continued)
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Organism Types
• Autotrophs: these organisms make their
own food. They use the energy from the
light (sun) to make their food.
• Heterotrophs: these organisms can not
make their own food they must get food
from what they consume.
Autotrophs
• These organisms make their food by
converting sun light energy to usable
energy (ATP) In most autotrophs this is
done by photosynthesis. These
organisms use light to make their food.
• Photosynthesis: process that converts
light energy into chemical energy in the
form of organic compounds.
(carbohydrates)
Photosynthesis Unbalanced
Equation
• YOU MUST KNOW THIS!!
CO2 + H2O
C6H12O6 + O2
light
Balancing the equations
• When writing a chemical equation, what
ever you put in must balance at the other
end just like it does in a math problem.
• Six carbons in must equal 6 carbons out.
Balance the Photosynthesis
Equation from before
6CO2 + 6H2O
C6H12O6 + 6O2
light
Reactions
• Light reaction: Light energy is
converted to chemical energy which is
stored in ATP and the energy carrier
molecule NADPH.
• Calvin Cycle: Organic compounds are
formed using CO2 and the chemical
energy stored in ATP and NADPH.
Light Capturing
• Happens in the chloroplasts of the plant
cell(s).
• Thylakoids are membranes in the inner
part of the chloroplast. These look like
small coins. They are really flattened
sacs.
• Grana (Granum) are where the stacks of
coins are connected from one stack to
another
• Stroma: The fluid area around the grana
Pigments
• Pigments are colors that absorb light
energy
• In Plants there are many pigments that
play a role in light absorption
• Different pigments absorb light at different
wave lengths
• Different wave lengths have different
energy
• Pigments
Chlorophyll – green color absorbs with
the broadest pigments (color) range.
Xanthophyll-Carotenoid – orange, red
and brown is a weak pigment much less
broad light absorption than chlorophyll
Pigmentation
• Photosystem is a cluster of pigments and
the proteins that the pigments are
attached to. There are two types of
photosystems.
• Photosystem I and Photosystem II they
play an important role in photosynthesis
but in different ways.
Light reaction
• Step 1
Light energy forces electrons to enter the
high energy level in the chlorophyll a
molecules in photosystem II.
These electrons are now excited and
have lots of energy.
The electrons now leave chlorophyll and
this reaction is called an oxidation
reaction.
Light reaction
• Step 2:
When ever an electron is lost one must
be moved to be added. The acceptor for
the molecule electrons of chlorophyll a is
the thylakoid membrane (sac) coin.
This is called the Primary Electron
Acceptor
Light reaction
• Step 3
The primary electron acceptor donates an
electron to the electron transport chain.
As electrons chain the energy is lost and
put into H+. The hydrogen atoms now
have lots of energy in the thylakoid.
Light reaction
• Step 4
The light is absorbed by photosystem I.
This is taking place while photosystem II
is already at work. Electrons here are
also moved into an excited stage and
then move to another primary electron
receptor. These electrons then again
chain to make hydrogen atoms with
energy.
Light reaction
• Step 5
All the excited H+ atoms join with the
NADP to make NADPH which holds the
energy until the cell needs it.
While the electrons are moving water is
being split into usable parts.
2H2O
4H+ + 4e- + O2
Note that we have 4 electrons and 4 hydrogen atoms made here!
Oxygen is also made here as a result of water splitting.
Light reaction
• How is ATP made????
• Chemiosmosis is the making of ATP
which is vital for the plant cell to work.
ATP is the energy for the cell to do it’s
work and for the bike to run. When
NADPH is moving around the thylakoid
the N and H are used and an additional P
is added as ADP passes through the ion
channel in the thylakoid membrane and
ATP is made.
The Calvin Cycle
• This should really be called carbon
fixation cycle. This cycle uses ATP and
NADPH to move and combine carbon
molecules into a 6 carbon molecule
(sugar) CO2 is added to a carbon
molecule that has four carbons becomes
a 6 carbon molecule.
Quiz 6
Photosynthesis
Quiz 6 Photosynthesis
• 1. What is photosynthesis?
• 2. Where does it take place?
• 3. Why do we need photosynthesis?
Quiz 6
• 4. Write the balanced equation for
photosynthesis.
• 5. Why are animals dependent on
plants?
• 6. What is a pigment?
Quiz 6
• 7. What is the molecule that carries the
energy on the chloroplast?
• 8. What is a stoma?
• 9. Describe/draw a chloroplast and its
internal structures.
Quiz 6
• 10. What are two of the pigments in
photosynthesis?
• 11. Explain;
Why plants are so important to humans.
Use what you know about the
photosynthesis process, the plant cell,
organelles, and the products and
reactants of the equation for
photosynthesis to best answer the
question.