DAT bio Chapter 4. Photosynthesis Flashcards
epidermis
outer layer of cells that provides
protection and prevents water loss.
Palisade mesophyll cells
- located right below
upper epidermis, has many chloroplasts; this is
where most photosynthesis occurs.
Spongy mesophyll cells -
- found at the bottom of
the leaf, where the leaf has a lot of spaces for gas
movement; has some chloroplasts for moderate
amounts of photosynthesis.
stomata
- pores on underside of leaf where gas
can enter and exit.
guard cells
- surround stomata and control their
opening/closing.
chloroplasts
are organelles found in plants and
photosynthetic algae, but not in cyanobacteria.
They are similar to mitochondria and contain the
structures listed below (outermost to innermost).
can you find cholorplast in cyanobacteria?
no
where does the light dependent reaction take place?
thylakoid membrane
What is the function of light dependent reaction?
harness light energy to produce ATP and NADPH
ATP generated in the light dependent reaction is not used to power the cell, it is consumed in the Calvin cycle T/F
True
What special pigments does photosystems contain?
chlorophyll and carotenoids, that absorb photons.
What is the reaction center?
special pair of chlorophyll
molecules in the center of these proteins (photosystems)
2 types of photosystems
Photosystem 2 (P680) and photosystem 1 (P700)
The first of photosynthesis
Non-cyclic photophosphorylation. carried out by the light dependent reactions.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 1
Water is split (photolysis), passing electrons
to photosystem II and releasing protons into the
thylakoid lumen.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 2
Photons excite electrons in the reaction
center of photosystem II, passing the
electrons to a primary electron acceptor.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 3
The primary electron acceptor sends the
excited electrons to the electron transport
chain (ETC). During the redox reactions within
the ETC, protons are pumped from the stroma
to the thylakoid lumen. The electrons are
then deposited into photosystem I.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 4
Photons excite pigments in photosystem I,
energizing the electrons in the reaction center
to be passed to another primary electron
acceptor.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 5
The electrons are sent to a short electron
transport chain that terminates with NADP+
reductase, an enzyme then reduces NADP+
into NADPH using electrons and protons.
Non-cyclic photophosphorylation (carried out light dependent reaction
STEP 6
The accumulation of protons in the thylakoid
lumen generates an electrochemical gradient
that is used to produce ATP using an ATP
synthase, as H+ moves from the thylakoid
lumen back into the stroma.
when does Cyclic photophosphorylation happen
when
photosystem I passes its electrons back to the
first ETC instead of the second ETC. This causes
more proton pumping and more ATP production,
while no NADPH is generated.
Calvin cycle is also known as
light-independent reaction since they do not directly use light energy. But they do rely on light dependent reactions because they need ATP and NADPH made from it/
Where does the calvin cycle take place
chloroplast stroma of plant mesophyll cells.
What does calvin cycle do?
turns inorganic CO2 (carbon dioxide into organic glucose
First step of Calvin cycle
(CARBON FIXATION)
carbon dioxide combines
with five-carbon ribulose-1,5-bisphosphate
(RuBP) to form six-carbon molecules, which
quickly break down into three-carbon
phosphoglycerates (PGA). This reaction is
catalyzed by RuBisCo.
What catalyzes the first step of the calvin cycle
catalyzed by RuBisCo.
second step of Calvin cycle
(REDUCTION)
- PGA is phosphorylated by ATP and
subsequently reduced by NADPH to form
glyceraldehyde-3-phosphate (G3P).
Third step of Calvin cycle
REGENERATION)
- Most of the G3P is converted
back to RuBP.
fourth step of Calvin cycle
Carbohydrate synthesis)
some of the G3P is used to make glucose
Another process where RuBisCo causes oxygen to binds to RuBP
photorespiration
location of Photorespiration
stroma
what does Photorespiration produce?
2 carbon molecule know as phosphoglycerate that is shuttled to peroxisomes and mitochondria for conversion into PGA.
Is glucose made in photorespiration
no
Another way to think of Photorespiration
wasteful pathway that occurs when the Calvin cycle enzyme rubisco acts on oxygen rather than carbon dioxide. By interfering with photosynthesis in this way, photorespiration may significantly limit the growth rate of some plants.
another name for photorespiration
C2 photosynthesis, since two-carbon
phosphoglycolate is produced.
What conditions are needed for photorespiration to occur?
hot and dry conditions that closes stomata to minimize water loss. oxygen needs to escape but it cannot so it starts to build up while carbon dioxide is used up. RuBisCo binds
oxygen and photorespiration occurs.
what is C3 photosynthesis
normal photosynthesis,
where three-carbon PGA is produced.
What is C4 photosynthesis
produces four-carbon
oxaloacetate; occurs in plants living in hot
environments. Carbon dioxide is spatially isolated
to prevent photorespiration.
Step 1 of C4 photosynthesis
PEP carboxylase fixes CO2 into a three carbon
PEP molecule, producing oxaloacetate, which
is converted into malate in the mesophyll cell
Step 2 of C4 photosynthesis
Malate is transferred to bundle sheath cells,
which have lower concentrations of oxygen.
Step 3 of C4 photosynthesis
Malate is decarboxylated to release CO2 ,
spatially isolating where CO2 is fixed by
RuBisCo. The only drawback is that pyruvate
is also produced and needs to be shuttled back
to mesophyll cells using ATP energy.
Step 4 of C4 photosynthesis
Pyruvate is converted back into PEP.
What is CAM photosynthesis?
- uses temporal isolation
of carbon dioxide to prevent photorespiration in
hot environments.
CAM photosynthesis Step 1
During the day, stomata are closed to prevent
transpiration (evaporation of water from
plants).
CAM photosynthesis Step 2
During the night, stomata are open to let
carbon dioxide in. Just like in C4
photosynthesis, PEP carboxylase fixes CO2
into PEP, producing oxaloacetate and
afterwards malate. However, malate is stored
in vacuoles instead of being shuttled to
bundle sheath cells.
CAM photosynthesis Step 3
During the next day, the stomata are closed
again and malate is converted back into
oxaloacetate, which releases CO2 and PEP.
Thus, CO2 accumulates in the leaf for use in the
Calvin cycle through temporal isolation.
