Cell Process Photosynthesis€¦ · Cell Process Photosynthesis. Cell Process - Photosynthesis....
Transcript of Cell Process Photosynthesis€¦ · Cell Process Photosynthesis. Cell Process - Photosynthesis....
CO 7
Cell Process
Photosynthesis
Cell Process - Photosynthesis
Photosynthesis is used to
build carbohydrates (the
main energy source of all
life.)
- - Producers (like plants)
use carbon dioxide and
water to make
carbohydrates; oxygen gas
is released as waste
- - Occurs in the
chloroplasts
- - {Write Equation}
Chloroplast Structure
- Stroma is the space between the grana
which are stacks of tylakoid membranes
which are full of pigments (quick pic)
Figure 7.2
Photosynthetic Pigments – chemicals such as chlorophyll that absorb
various portions of visible light. (Anything green denotes chlorophyll
and is photosynthetic. Chlorophyll is great at absorbing all colors
except green. Green is reflected, which is why it looks green to our
eyes.)
1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.
2. Both chlorophylls absorb violet, blue, and red wavelengths best.
3. Most green is reflected back; this is why leaves appear green.
Accessory pigments help
absorb the light colors that
chlorophyll can’t.
- Carotenoids are yellow-
orange pigments which
absorb violet, blue, and
green regions.
- Phycobilins are red-purple
pigments
- When chlorophyll breaks
down and is reabsorbed in
fall, it is pulled out of the
leaves first. This allows the
accessory pigments in
leaves show through.
Absorption Spectrum - spectrophotometer measures the
amount of light that passes through a sample of pigments (like
crushed green leaves)
Action Spectrum - measures the rate of photosynthesis
at different wavelengths of light; measured by the rate
oxygen is produced
In one sentence summarize what this graph says about wavelengths,
color of light, absorption and photosynthesis.
Checkpoint
1. What is the relationship between the absorption spectrum and the
action spectrum?
2. How can we measure the rate of photosynthesis?
3. How is the wavelength of light related to the rate of
photosynthesis?
4. A radish plant is grown
using lights of different
colors. Explain the chart.
Photosynthetic Reaction
1. In 1930 C. B. van Niel showed that O2 given off by
photosynthesis comes from water and not from CO2.
2. The net equation reads:
Two Sets of Reactions in Photosynthesis (general detail)
1. Light reactions only happen with light. They are the
energy-capturing reactions that take place in the
thylakoids.
a. Water is split into
oxygen, two H+, and
two free e-
b. The electrons and
hydrogens are sent
to the electron
transport chain
where they are used
to make ATP and
NADPH to power the
Calvin Cycle
c. Oxygen is
released
2. Calvin Cycle Reactions
(aka dark reactions)
a. take place in the stroma
in either the light or dark.
b. The NADPH and ATP
from light rxns provide
energy to combine 6CO2
molecules into a six
carbon sugar carb.
What you should know by now..
1. The equation for photosynthesis. Write it!
2. The structure of a chloroplast. Sketch it!
3. The two reactions of photosynthesis.
Same Photosynthesis Reactions (in more detail)
- The Light Reactions occur in two systems: Photosystem I
and Photosystem II. These photosystems create the cyclic
and the non-cyclic electron transport chains. The ETC’s are
able to create ATP (c and n-c) and NADPH (n-c only) through
membrane compartments and gradients – (Obviously the
creation of ATP is a complicated process/ I told you
compartmentalization was important! Your HW should help.)
Non-cyclic ETC – electrons are removed from the water molecule using light energy
at PSII; they are passed down a chain of enzymes where their energy is used to pull
H+ molecules from the stroma into the thylakoid, creating the concentration gradient
needed to drive ATP Synthetase; electrons are then re-charged at PSI and attached
to an NADP+ to make NADPH and sent to power the Calvin cycle.
- Summary- IN: Water and Light. OUT: equal amounts of ATP and NADPH. GEN
DIRECTION: PSII (energy used to pull in H+) PSI recharge NADPH
Calvin Cycle
Cyclic ETC – extra ATP molecules are needed for the Calvin Cycle. The Cy ETC just
creates more ATP. Electrons are charged by PSI, then passed down the ETC where
their energy is used to pull more H+ into the thylakoid to keep the concentration
gradient going and driving ATP. They are then returned to PSI, recharged, and used
the same way all over again. IN: Electrons. OUT: ATP only. GEN DIRECTION: PSI
energy used to pull in H+ PSI again! (cycles!)
ATP Synthetase – this enzyme uses the energy from moving H+ molecules to
recharge ADP to ATP in both ETCs. The ETCs cram the H+ inside the thylakoid
creating an area of a high concentration. The H+ want out and away from that high
concentration. The only way out is through ATP Synthetase. As they move through
ATP Synthetase, the enzyme spins and generates power to recharge ATP. It’s
remarkably like a hydroelectric power plant! Note, membranes and
compartmentalization are HUGE here! It wouldn’t work without them!
Are you still confused? Check out the videos on my website to see it in action.
Now for the dark reactions…
Summary Statements:
What is the purpose of the Calvin Cycle?
To make sugar from carbon dioxide
Where does the cell get its energy to perform these reactions? From the ATP and
NADPH charged in the light reactions
What is the final product? Glucose (and ADP/NADP+ to be sent back to light rxn)
Why is carbon dioxide necessary? The 6 carbons from 6CO2 molecules become the
6 carbons in one molecule of C6H12O6; process called carbon fixation
Enzyme to know: Rubisco – used to bind the CO2 in carbon fixation; can bind to O2
accidentally if there’s too much around which leads to photorespiration (which is bad)
FORTUNATELY, AP Biology no longer
requires the memorization of every step of
the Calvin Cycle, but you should
understand the beginning and the end and
the purpose.
Photorespiration- Problem caused when Rubisco bonds to O2 in the Calvin Cycle
instead of CO2 (and you can’t make sugar without carbon); happens
when too much O2 builds up in the leaf; a concern of hot weather
plants who have to keep their stomata (holes to allow gas exchange)
closed to prevent excess transpiration (water evaporation)
- Adaptations to Avoid…
- CAM photosynthesis: temporal (timing) separation of
photosynthesis reactions; close stomata during the day and just do light
reactions, open at night to release O2 build up and bring in CO2 for calvin
cycle; store CO2 and preliminary sugar molecules as an acid overnight,
use the carbon acid during the day to make sugar when energy is
available
- C4 photosynthesis: spatial separation of photosynthesis
reactions; first convert CO2 into a carbon chemical called malate and
move it to cells in darker regions of the leaf for the Calvin cycle; the cells
in the lighter areas do the light reactions while the cells in the darker
regions do the Calvin Cycle
Factors the Affect Photosynthesis
1. Light Quality (color)- white is best, followed by blue; green is
worst due to pigment absorption
2. Light Intensity (typically, brighter = better)
3. Light Period (longer time in light = better)
4. Carbon Dioxide Availability – more is better
5. Water Availability – more is better
Note: Rate of Photosynthesis can be measured by the amount
of oxygen released OR the amount of CO2 absorbed. More O2
released or CO2 absorbed = more photosynthesis
Quick Practice
Quick Practice
thylakoid
O2
stroma
grana
Pg 129b
Light & H2O
O2
CO2
glucose
ATP
NADPH
ADP
NADP
A = photosystem II
B = photosystem I
C = H20
D = Electron Transport Chain
E = ATP Synthase
AB = ATP
AC = phospholipids
AD = light (energy)