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Photosynthesis Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Heterotrophs

A

must get energy from the food they
eat,

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2
Q

autotrophs

A

can make their own food.
Photoautotrophs take light energy and convert it to chemical energy using photosynthesis.

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3
Q

Photosynthesis

A

reduces atmospheric carbon
dioxide, releases oxygen, and creates chemical energy that can be transferred through food chains. Photons (light energy) are used to synthesize sugars (glucose) in photosynthesis.

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4
Q

Carbon fixation

A

is the process by which inorganic
carbon (CO2) is converted into an organic molecule (glucose). Photosynthesis takes electrons released from photolysis (the process of splitting water molecules) and excites them using solar energy. These excited electrons are then used to power carbon fixation.

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5
Q

Photosynthesis vs Cellular Respiration

A

Photosynthesis and cellular respiration are reverse processes in terms of their overall reactions:

6CO2+6H2O<=(photosynth forward, cellular resp going reverse)=====>C6H12O6 + 6O2

Photosynthesis is non-spontaneous and
endergonic, producing glucose after an input of
solar energy.

Cellular respiration is spontaneous and exergonic, breaking down glucose to generate energy in the form of ATP.

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6
Q

Epidermis

A
  • an outer layer of cells that provides
    protection and prevents water loss.
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7
Q

Palisade mesophyll cells

A
  • located right below the
    upper epidermis, has many chloroplasts; this is
    where most photosynthesis occurs.
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8
Q

Spongy mesophyll cells

A
  • found at the bottom of the leaf where there is space for gas exchange, allowing these cells to facilitate movement of gases within the leaf; has some chloroplasts for moderate amounts of photosynthesis.
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9
Q

Stomata

A
  • pores on underside of leaf where gas
    can enter and exit.
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10
Q

Guard cells

A
  • surround stomata and control their
    opening/closing.
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11
Q

Chloroplasts

A

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).

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12
Q

Chloroplast Structure includes:

A

1) Outer membrane
2) intermembrane
3) inner membrane
4) stroma
5) thylakoids
6) thylakoid lumen

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13
Q

Outer membrane

A

Outer plasma membrane made of
phospholipid bilayer.

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14
Q

Intermembrane space

A

Space between the outer and inner
membranes

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15
Q

Inner membrane

A

Inner plasma membrane made of
phospholipid bilayer.

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16
Q

Stroma

A

The fluid material fills the area inside the inner membrane. The Calvin cycle occurs here.

17
Q

Thylakoids

A

A phospholipid bilayer structures
organelle suspended within the
stroma, and where the light
dependent reactions occur. The
individual membrane layers are
thylakoids, while an entire stack is
called granum. A junction between
grana is called lamella.

18
Q

Thylakoid lumen

A

Interior of the thylakoid and H+
ions accumulate here, making it acidic.

19
Q

light dependent reactions

A

occur in the thylakoid membrane and harness light energy to produce ATP and NADPH (an electron carrier) for later use in the Calvin cycle (ATP generated here is not used to power the cell - it is consumed in the
Calvin cycle).

20
Q

Photosystems

A

contain special pigments, such as
chlorophyll and carotenoids, that absorb photons.

21
Q

reaction center

A

is a special pair of chlorophyll molecules in the center of these proteins.

Chlorophyll has a porphyrin ring
structure with a magnesium atom bound in its
center. Photosystem II (P680) and Photosystem I(P700) are used in photosynthesis.

22
Q

Non-cyclic photophosphorylation

A

is carried out by the light-dependent reactions.

23
Q

Steps of Non-cyclic photophosphorylation

A
  1. Water is split (photolysis), passing electrons
    to photosystem II and releasing protons into the thylakoid lumen.
  2. Photons excite electrons in the reaction
    center of photosystem II, passing the
    electrons to a primary electron acceptor.
  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.
  4. Photons excite pigments in photosystem I,
    energizing the electrons in the reaction center
    to be passed to another primary electron
    acceptor.
  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.
  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.
24
Q

Cyclic photophosphorylation

A

happens 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.

25
Q

The Calvin cycle

A
  • made up of reactions known as
    light-independent reactions because they do not directly use light energy, but can only occur if the light-dependent reactions are providing ATP and NADPH.
  • takes place in the chloroplast
    stroma of plant mesophyll cells. It fixes carbon
    dioxide that enters stomata.

6 CO2 + 18 ATP + 12 NADPH + H+ →
18 ADP + 18 Pi +12 NADP+ + 1 glucose

26
Q

Steps in Carbon Cycle:

A

1) Carbon Fixation
2) Reduction
3) Regeneration
4) Carb synthesis

27
Q

Carbon fixation (Calvin Cycle)

A
  • 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.
28
Q

Reduction (Calvin Cycle)

A
  • PGA is phosphorylated by ATP and
    subsequently reduced by NADPH to form
    glyceraldehyde-3-phosphate (G3P).
29
Q

Regeneration (Calvin Cycle)

A
  • Most of the G3P is converted
    back to RuBP.
30
Q

Carbohydrate synthesis(Calvin Cycle)

A
  • some of the G3P is
    used to make glucose.
31
Q

RuBisCo

A

in addition to fixing carbon dioxide into
RuBP, can also cause oxygen to bind to RuBP in a process called photorespiration.

32
Q

Photorespiration

A
  • occurs in the stroma, producing a two-carbon molecule phosphoglycolate that is shuttled to
    peroxisomes and mitochondria for conversion
    into PGA. However, fixed carbon is lost as carbon dioxide in the process. Overall, there is a net loss of fixed carbon atoms and no new glucose is made.
  • Also called C2 photosynthesis, since two-carbon phosphoglycolate is produced.
33
Q

What happens to stomata during hot and dry weathers/seasons:

A
  • stomata are closed to minimize
    water loss, oxygen accumulates inside the leaf
    while carbon dioxide is used up. RuBisCo binds oxygen and photorespiration occurs.
34
Q

C3 photosynthesis

A
  • normal photosynthesis,
    where three-carbon PGA is produced.
35
Q

C4 photosynthesis

A
  • produces four-carbon oxaloacetate; occurs in plants living in hot environments. Carbon dioxide is spatially isolated to prevent photorespiration.
36
Q

Steps of C4 Photosynthesis

A
  1. PEP carboxylase fixes CO2 into a three carbon PEP molecule, producing oxaloacetate, which is converted into malate in the mesophyll cell.
  2. Malate is transferred to bundle sheath cells,
    which have lower concentrations of oxygen.
  3. 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.
  4. Pyruvate is converted back into PEP.
37
Q

Crassulacean acid metabolism (CAM)
photosynthesis

A

uses temporal isolation of
carbon dioxide to prevent photorespiration in hot environments.

38
Q

Steps to Crassulacean acid metabolism (CAM) photosynthesis

A
  1. During the day, stomata are closed to prevent transpiration (evaporation of water from plants).
  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.
  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.

Biology (15 decks)

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