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Ch7. Photosynthesis
7.10 – 7.12
How the ETC helps create
ATP & NADPH
Calvin cycle:
Converting CO2 to Sugar
• Where does the Calvin
cycle happen?
• The stroma
• What is needed to start
the Calvin cycle?
• ATP = usable energy
• NADPH = High energy
electrons
• CO2 = used to make
sugar
• Where did this chemical
energy come from?
• The Light Reaction
Four steps, Step 1
• What happens in step 1,
carbon fixation?
• The enzyme rubisco
combines 3 molecules
CO2 with 3 molecules
RuBP (ribulose
bisphosphate) Making 6
molecules of 3 PGA a
3carbon organic-acid,(3phosphoglyceric acid)
Step 2
• What are the two
chemical reactions in
Step 2?
• 1. Energy consumption of
6 ATP’s
• 2. Oxidation of 6 NADPH
• What does this step
yield?
• 6 molecules of 3PGA are
reduced producing 6
G3P’s. G3P’s have the
high energy electrons
from NADPH.
Step 3
• How many CO2 or carbon
molecules does the Calvin
cycle use at once?
• It uses only one carbon at a
time
• Where do the other 5 G3P’s
go?
• They are recycled in the cycle.
• How many cycles does it take
to produce glucose?
• Since the cycle uses only one
carbon at a time, Six full turns
are needed to make 2 G3P
molecules (3 carbons each)
that make up 1 Glucose
molecule (6 carbons each)
Step 4
• What happens to start
the cycle over?
• ATP supplies the
energy to make 3
RuBP from 5 G3P
which start the cycle
over again.
Summary of Photosynthesis
• Where does the Light reaction
take place?
• Occurs in the thylakoids, the
photosystems capture solar
energy & use it to energize
electrons.
• What is Oxidized?
• Water is Oxidized to O2
• How is chemical energy
made?
• PS1 & PS2 transfer electrons
to ETC. ATP & NADPH
contain energy from the
excited electrons.
Summary of Photosynthesis
• What happens to all the food
made by plants?
• They stock up extra sugar as
starch, storing it in
chloroplasts, roots, tubers and
fruits. They can also use it to
make proteins, fats & nucleic
acids.
• How is even a carne asada
burrito or hamburger the
product of photosynthesis?
• The cow ate grass which
contained the carbs, proteins,
fats and nucleic acids ALL built
as a result of photosynthesis.
3 Adaptations to fix carbon & save water
• What is photorespiration? (Left picture) (C3 plants like rice, wheat,
soybeans & oats)
• C3 (3 carbon) plants close stomata due when it is hot to reduce water
loss. This prevents CO2 from entering or O2 from leaving. Rubisco
binds O2 and can’t do Calvin cycle. Decreasing photosynthesis
• What do C4 plants do differently? (corn & sugarcane)
• Store CO2 in 4 carbon sugar so that there is always enough CO2
even when stomata are closed.
• How have CAM plants adapted? (cactus, pineapple, & succulents)
• Close stoma during the day when hot, but store CO2 (at night) like C4
plants so they can prevent photorespiration.