2 ways organisms can be
classified by how they
obtain energy
Heterotrophs
Eat Autotrophs and
other Heterotrophs for
energy
Gain only 10% of
the energy from
the organism
they eat
Ex.: Humans, Deer, Birds
Autotrophs
make their own food
Plants, Some Bacteria, Alagae
Involves a series
of Complex
chemical reactions
in which the
product of one
reaction is
consumed in the
next reaction. This
is called a
biochemical
pathway
Generates
Energy for
Autotroph
by taking in
light, CO2,
and Water
Formula of Photosynthesis = 6 CO2 + 6 H2O + Sunlight = C6H12O6 + 6 O2
Note: Glucose isn't produced in
Photosynthesis, butt rather in the equation
to emphasize difference between
photosynthesis and cellular respiration
Energy from
Photosynthesis
is used for
Cellular
Respiration
Cellular Respiration uses
product of photosyntheses,
glucose, to produce ATP. Its
formula is the reverse of
the formula for
photosynthesis
Light Absorption in Chloroplasts
Anotações:
Note: A compound that absorbs light is called a pigment. This relates to the properties, which must be understood in order to understand how chloroplasts absorb light
Light Reactions: initial reactions of
photosynthesis. They begin with
choloplasts absorbing light.
Anotações:
While some alagae can contain one large chloroplasts, a cell in plant leaf will contain 50+.
Inside membrane surrounding chloroplast,
there is another system of membranes
arranged as flat sacs called thylakoids. They
are interconnected and layered on top of
one anotherto form stacks called grana.
Surrounding the thylakoids is a solution
called stroma.
Located in membrane of thylakoids
are variety of pigments, with most
imp. being chloropphylls. There are
several types of them, w/ most
common being chlorophylls a and b.
Slight diff. between a and b
causes them to absorb
different colors of light. But
they both allow green light to
reflect
Only chlorophyll a is directly
involved in light reactions in
photosynthesis. Chlorophyll b assists
chlorophyll a in capturing light
energy, and therefore chlorophyll b
is called an accessory pigment
Other compounds in thylakoid membrane also function as accessory pigments.
Accessory pigments enable plants to capture more of the energy in light
* During fall, many plants lose
chlorophylls and take on rich hues
of carotenoids
Electron Transport
Chlorophylls and Carotenoids
are grouped in clusters of a few
100 pigment molecules in
thylakoid membrane. Each
cluster is referred to as a
photosystem.
Two Types of Photosystems are
photosystem 1 and photosystem 2.
They both contain similiar pigment,
but have diff. roles in light reactions.
Light reactions began when
accessory pigment
molecules in both
photosystems absorb light,
which means they have
aqquired energy from light
waves. The aquired energy
is then passed to other
pigments until it reaches
specific pair of chloryhll a
molecules.
Step 1: Light Energy forces electrons to
enter higher energy level in 2
chlorophyll a molecules of
photosystem 2.
Anotações:
These energized electrons are said to be "excited"
Step 2: The Excited electrons have
enough energy and leave
chlorophyll a molecules. Because
they have lost electrons, the
chlorophyll a molecules have
undergone an oxidation reaction.
Anotações:
Each oxidation reaction must be accompanied by a refuction reaction, which means that some substance must accept the electrons that the chlorophyll a molecules have lost. The substance is known as primary electron acceptor
Step 3: The primary electron acceptor then donates the
electrons to the first of a series of molecules
located in the thylakoid membrane, which are
known as an electron transport chain (ETC) since it
transports electrons from one molecule to
another in a series. As the electrons move along
the chain, they lose energy from when they
were "excited." The energy they lost is
harnessed to mover protons into the thylakoid.
Step 4: At the same time of the last step, light is
absorbed by photosystem 1 and 2. Electrons
move from pair of chlorophyll a molecules in
photosystem 1 to another primary electron
acceptor. The electrons that are lost by these
chlorophyll a molecules are replaced by electrons
that have come from electron transport chain
from photosystem 2
Step 5: Primary electron acceptor of photosystem
1 donates electrons to diff. ETC, which
then brings electrons to side of thylakoid
membrane to face stroma. There,
electrons combine with a protein and
NADP+, and organic molecule that accepts
electrons during redox reactions.
Anotações:
A redox reaction is a reaction in which two species exchange electrons.
Also, a redox reaction causes NADP+ to be reduced down to NADPH.
If electrons from photosystem 2 are not
replaced, both electron transport chains in
both photosystems will not work, and
photosynthesis will not occur. The
replacement electrons are provided by
water molecules. An enzyme inside thlakoid
splits water molecules into protons,
electrons, and Oxygen
Anotações:
For every 2 H2O molecules split, 4 electrons become abailable to replace those lost by chlorophyll molecules in photosystem 2.
The protons produced are left in
thylakoid, but oxygen diffuses out
of plant, making it a by product.
LESSON 6.1 Review:
1. The structure of
the thylakoids is
described as a
system of
membranes stacked
as flattened sacs,
and their function is
to house
chloroplasts
2. Accessory pigments
help another
chlorophill capture
light, therefore
enabling plants to
capture more light
3. Electons lost in either
photosystem are replaced by
water molecules, which are
then broken down for use
4. Protons, Electrons, and
Oxygen is produced when
water molecules are broken
down during light reactions
5. ATP is made by ATP synthase,
which harnesses potential energy
along the proton concentration
gradient in order to make ATP
6. If there was no concentration gradient
of protons along the thlakoid
membrane, ATP won't be able to be
synthesized, and photosynthesis would
not occur.
LESSON 6.2 Review:
1. The Calvin Cycle
takes place in the
stomata of the
cloroplast.
2. The PGAL molecules
are broken down and
turned into ADP
3. It takes 3 turns of Calvin Cycle
to produce PGAL, each turn using
2 ATP and 2 NADPH molecules
4. Stomatas control
passage of water out
of plant and CO2 into a
plant.
5. C4 plants use the C4
pathway to fix carbon by
breaking into four-carbon
molecules
6. The rate of photosynthesis
increases and then reaches a
platue as the concentration of
CO2 around plant decreases
because it has reached its
furthest point
Chemiosmosis
process that synthesizes ATP
Relies on concentration gradient of protons across the thylakoid membrane
Concentration
of Protons is
higher in
thylakoid than
stroma
Concentration of Protons = potential energy, which is harnessed by protein called ATP
synthase (located in thylakoid membrane)
Anotações:
ATP synthase is a multifunctional protein. It acts as carrier protein and enzyme
ATP synthase makes ATP by adding phosphate group to ADP
ATP synthase converts potential
energy of proton concentration
gradient into chemical energy,
which is stored in ATP
Together, ATP and
NADPH provide energy
for 2nd set of reactions
in photosynthesis
The Calvin Cycle
Carbon Atoms from
CO2 are bonded into
organic compounds
Anotações:
This incorporation of CO2 into organic compounds is referred to as carbon fixation
Occurs within
stroma of
chloroplast
Has 3 Major Steps:
Step 1: CO2 diffuses into stroma. Enzyme combines CO2 with a
5-carbon carbohydate called RuBP. Product = 6-carbon molecule
that splits immediately into pair of 3-carbon molecules known as
PGA
Step 2: In 2-part process, PGA = 3-carbon
molecule, PGAL.
1st, each PGA receives phosphate group from molecule of ATP.
Resulting compound then receives a proton from NADPH and releases a phosphate group, producing
PGAL. These reactions also produce ADP, NADP+, and phosphate, which can be used again in light
reactions to synthesis enough molecules of ATP and NADPH
Step 3: Most of PGAL is converted back into RuBP in complex series of reactions. The reactions
need a phosphate group from another molecule of ATP, which is then changed into ADP. By
generating the RuBP that was consumer earlier (in Step 1), these reactions allow Calvin Cycle
to continue operating.
Anotações:
Some PGAL molecules are not converted into RuBP. Instead, they leave Calvin Cycle and can be used by plant cell to make other organic compounds
Alternative Pathways to Photosynthesis
Some species "fix" carbon using
alternative pathways, and then enter it
into calvin cycle
Generally used by plants
that live in dry and hot
climates, where they
loose a lot of water, most
of it from stomatas
Anotações:
Stomatas are also places where CO2 enters plant and O2 leaves. When stomata is closed, CO2 in plant decreases, and O2 rises due to Calvin Cycle
C4 Pathway: used by C4 plants. Even
though CO2 level is low and O2 is high,
these types of plants have an enzyme
that can fix CO2 into 4-carbon
compounds, which are then
transported to other cells, where CO2 is
released and enters Calvin Cycle
C4 plants examples: corn, sugar cane, and crabgrass
CAM Pathway: plants open their
stomata at night and close them
during the day. At night, CAM
plants take in CO2 and fix it into
a variety of organic compounds
and enter it into Calvin Cycle.
Since they have stomata open at
night when temp. is lower, they
grow slowly, but lose less water
CAM plants examples: Pineapples and cactuses
Most common pathway for photosynthesis
Plants that use it are known as C3 plants
Rate of Photosynthesis
affected by plant's envirnoment
Light Intensity
As light intensity increases, so does rate of photosynthesis
CO2 Level
Increased levels
of CO2 increase
rate of
Photosynthesis
Temperature
As temperature increases, rate of photosynthesis increases
Anotações:
Photosynthesis rate will decrease if temperature increases excessively