Photosynthesis

Question 1

Photosynthesis

Answer 1

The use of photons (light energy) to make sugars (glucose)

Question 2

Carbon fixation

Answer 2

Inorganic carbon (CO₂) is incorporated into an organic molecule (like a sugar molecule)

Question 3

Photolysis

Answer 3

The term used to describe the splitting of water molecules by photosynthetic organisms, which releases electrons that can be excited/powered-up by solar energy

The energy from the excited electrons are then used to fix carbon dioxide into an organic glucose molecule

Question 4

What type of reaction is photosynthesis?

Answer 4

Non-spontaneous, endergonic reaction (positive Gibbs free energy)
solar energy is absorbed

Question 5

Stomata

Answer 5

Pores found in the bottom of the leaves and are the site of atmospheric gas exchange, which includes carbon dioxide and oxygen

Question 6

Outer membrane of chloroplast

Answer 6

Outer plasma membrane
Composed of a phospholipid bilayer

Question 7

Intermembranous space of chloroplast

Answer 7

The space between the outer and inner membranes

Question 8

inner membrane of chloroplast

Answer 8

The inner plasma membrane
Composed of a phospholipid bilayer

Question 9

Stroma

Answer 9

Fluid that fills the area inside the inner membrane
Where the calvin cycle occurs

Question 10

Thylakoids

Answer 10

• membrane is a phospholipid bilayer structured organelle
• Suspended within the stroma
• Where light dependent reactions (non-cyclic) occur
• Individual membrane layers = thylakoids, an entire stack = granum
• A junction between two grana is called a lamella
• contains photosystems I and II, cytochromes and electron carriers

Question 11

Thylakoid lumen

Answer 11

The interior of the thylakoid
Where H+ ions accumulate due to ETC

Question 12

What is the goal of light dependent reactions?

Answer 12

Use light to make chemical energy/storage molecule (ATP) and a reduced electron carrier (NADPH)

Question 13

What is the ATP for light dependent reactions used for?

Answer 13

It is not used to power the cell
It is consumed to power the Calvin cycle which makes glucose

The glucose then undergoes cellular respiration to produce ATP that does power the cell

Question 14

Photosystems

Answer 14

large proteins embedded in the thylakoid membrane that contain special pigments (like chlorophyll and carotenoids) that are directly responsible for absorbing photons

Question 15

What is another name for photosystmes I and II?

Answer 15

Photosystem I: P700
Photosystem II: P680

Named due to the wavelength in which they are able to absorb

Question 16

Why does photorespiration occur?

Answer 16

Occurs when RuBisCo (which normally helps plants used carbon dioxide for energy) binds oxygen instead of carbon dioxide, producing a two-carbon molecule called phosphoglycolate which cannot be directly used in plants —> in order to fix this problem, plants undergo photorespiration

Question 17

What is the result of photorespiration

Answer 17

Causes the cell to undergo oxygen fixation which derails the Calvin cycle, reduces the cell’s supply of fixed carbon, and wastes energy

Question 18

What source of energy do C4 plants use to shuttle pyruvate back to the mesophyll cells?

Answer 18

Energy from the hydrolysis of ATP to AMP (equal to 2 ATP)

Question 19

How many times does the Calvin cycle repeat to produce one molecule of glucose?

Answer 19

6 times

Question 20

Where is malate stored in CAM plants?

Answer 20

Stored in the vacuole of the mesophyll cell for later use

it is not shuttles to a different cell (bundle-sheath cells) like C4 photosynthesis

Question 21

When malate is decarboxylated in the bundle-sheath cells, what molecules are released?

Answer 21

Inorganic carbon dioxide —> which can now undergo the Calvin cycle with RuBisCo in an environment where oxygen is not prevalent (RuBisCo will have a lower risk of photorespiration)
Three-carbon pyruvate

Question 22

What is required to convert 12 PGA to 12 G3P?

Answer 22

ATP and NADPH

Question 23

Spatial isolation

Answer 23

Ensures carbon dioxide is sent to a location where oxygen will not compete for RuBisCo. Utilized in C4 photosynthesis

Question 24

Temporal isolation

Answer 24

Ensures carbon dioxide is fixed at a different time so that oxygen will not compete for RuBisCo. Utilized by CAM photosynthesis

Question 25

cyclic photophosphorylation

Answer 25

• only involves photosystem I and the first electron transport chain
• no electrons will reduce NADP⁺ to NADPH and therefore no NADPH is generated (extra ATP is made when cyclic photophosphorylation occurs)

The cell recycles electron from Photosystem I back to the first ETC (instead of the second ETC) which cause more pumping of protons into the thylakoid lumen to synthesize more ATP

Question 26

What are the products of the light-dependent reactions in photosynthesis?

Answer 26

O₂: comes from photolysis of H₂O; emitted into the atmosphere
ATP and NADPH: needed to power the calvin cycle

Question 27

General process of photorespiration:

Answer 27

Two-carbon molecule phosphoglycolate is shuttled to peroxisomes and mitochondria for conversion into a useful molecule called PGA (phosphoglycerate) which can enter the Calvin cycle
Fixed carbon is lost as carbon dioxide leading to an overall net loss of fixed carbon atoms and no new glucose is made

(Also called C₂ photosynthesis since 2 carbon molecule produced)

Question 28

What are the 4 steps of the Calvin cycle:

Answer 28

1) carbon fixation
2) reduction of 3-carbon intermediate
3) regeneration of RuBP
4) Carbohydrate synthesis

Question 29

Step 1 of the Calvin cycle:

Answer 29

1) Carbon fixation: 6 CO₂ + 6 RuBP —> 12 PGA (catalyzed by RuBisCo)

Carbon dioxide (1-C) combines with RuBP (5-C) to form a 6 carbon molecule which quickly breaks down into 2 PGA molecules (3-C/molecule)

Reaction is catalyzed by RuBisCo

Question 30

What is the difference between cyclic photophosphorylation and non-cyclic photophosphorylation?

Answer 30

Non-cyclic photophosphorylation produces ATP and NADPH while cyclic photophosphorylation produces more ATP and no NADPH

Question 31

what is the equation for photosynthesis?

Answer 31

6 CO₂ + 6 H₂O –> C₆H₁₂O₆ + 6O₂

Question 32

where does cyclic photophosphorylation occur?

Answer 32

stroma lamellae

Question 33

where does photolysis occur?

Answer 33

thylakoid lumen and then passes electrons to the thylakoid membrane for non-cyclic photophosphorylation

Question 34

what are examples of crops that use C3 photosynthesis?

Answer 34

wheat, potato, rice and tomato

Question 35

what are examples of crops that use C4 photosynthesis?

Answer 35

corn and sugarcane - avoid photorespiration in warm climates

Question 36

where does chemiosmosis occur?

Answer 36

• across the thylakoid membrane

Question 37

step 2 of the calvin cycle:

Answer 37

• reduction: 12 ATP + 12 NADPH convert 12 PGA –> 12 G3P
• PGA is phosphorylated by ATP and NADPH is reduced to form G3P
• energy is incoperated
• by products: NADP+ and ADP go into non-cyclic photophosphorylation

Question 38

step 3 of calvin cycle:

Answer 38

• ** regeneration**: 6 ATP convert 10 G3P –> 6 RuBP
• most G3P is converted back to RuBP which allows the calvin cycle to repeat

Question 39

step 4 of calvin cycle:

Answer 39

• carbohydrate synthesis
• the two remaning G3P are used to make glucose

Question 40

overall reaction of the calvin cycle:

Answer 40

6CO₂ + 18 ATP + 12 NADPH –> 18 ADP + 18 P_i + 12 NADP⁺ + 1 glucose (or 2 G3P)