Photosynthesis

Question 1

Heterotrophs

Answer 1

must get energy from the food they
eat,

Question 2

autotrophs

Answer 2

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

Question 3

Photosynthesis

Answer 3

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.

Question 4

Carbon fixation

Answer 4

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.

Question 5

Photosynthesis vs Cellular Respiration

Answer 5

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.

Question 6

Epidermis

Answer 6

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

Question 7

Palisade mesophyll cells

Answer 7

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

Question 8

Spongy mesophyll cells

Answer 8

• 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.

Question 9

Stomata

Answer 9

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

Question 10

Guard cells

Answer 10

• surround stomata and control their
  opening/closing.

Question 11

Chloroplasts

Answer 11

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).

Question 12

Chloroplast Structure includes:

Answer 12

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

Question 13

Outer membrane

Answer 13

Outer plasma membrane made of
phospholipid bilayer.

Question 14

Intermembrane space

Answer 14

Space between the outer and inner
membranes

Question 15

Inner membrane

Answer 15

Inner plasma membrane made of
phospholipid bilayer.

Question 16

Stroma

Answer 16

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

Question 17

Thylakoids

Answer 17

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.

Question 18

Thylakoid lumen

Answer 18

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

Question 19

light dependent reactions

Answer 19

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).

Question 20

Photosystems

Answer 20

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

Question 21

reaction center

Answer 21

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.

Question 22

Non-cyclic photophosphorylation

Answer 22

is carried out by the light-dependent reactions.

Question 23

Steps of Non-cyclic photophosphorylation

Answer 23

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.

Question 24

Cyclic photophosphorylation

Answer 24

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.

Question 25

The Calvin cycle

Answer 25

- 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

Question 26

Steps in Carbon Cycle:

Answer 26

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

Question 27

Carbon fixation (Calvin Cycle)

Answer 27

- 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.

Question 28

Reduction (Calvin Cycle)

Answer 28

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

Question 29

Regeneration (Calvin Cycle)

Answer 29

- Most of the G3P is converted back to RuBP.

Question 30

Carbohydrate synthesis(Calvin Cycle)

Answer 30

- some of the G3P is used to make glucose.

Question 31

RuBisCo

Answer 31

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

Question 32

Photorespiration

Answer 32

- 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.

Question 33

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

Answer 33

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

Question 34

C3 photosynthesis

Answer 34

- normal photosynthesis, where three-carbon PGA is produced.

Question 35

C4 photosynthesis

Answer 35

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

Question 36

Steps of C4 Photosynthesis

Answer 36

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.

Question 37

Crassulacean acid metabolism (CAM) photosynthesis

Answer 37

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

Question 38

Steps to Crassulacean acid metabolism (CAM) photosynthesis

Answer 38

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.