Unit C: Photosynthesis** and Cellular Respiration

Question 1

Photosynthesis *Definition –> the process, who performs it?

Answer 1

• Performed by plants
• the process of trapping radiant energy from the sun, converting it into chemical energy, and storing it as glucose
  ● energy conversion process
  occurs in chloroplasts
  ● an anabolic pathway

Question 2

Cellular Respiration *Definition –> the process, who performs it?

Answer 2

performed by animals AND plants
● the process of trapping & breaking down chemical
energy stored in the bonds of glucose into ATP
(usable energy)
● energy conversion process occurs in mitochondria
● a catabolic pathway

Question 3

Catabolic Pathway

Answer 3

Catabolic pathways break down larger molecules into smaller
ones; they release energy in the process (“exothermic”)
○ Cellular respiration is catabolic because it breaks down glucose into ATP

Question 4

Anabolic Pathway

Answer 4

● Anabolic pathways synthesize larger molecules from smaller
ones; they require energy to do so (“endothermic”)
○ Photosynthesis is anabolic because it constructs glucose from other
particles derived from the sun’s energy

Question 5

Chloroplasts (what are they, where are the found, what are in them, parts)

Answer 5

● The site of photosynthesis ● Bound by an inner and outer membrane
● Flattened, interconnected sacs called thylakoids contain chlorophyll, a green-coloured molecule responsible for trapping solar energy
● Thylakoids are stacked in structures called grana, which are connected by lamellae
● The inner fluid of the chloroplast, known as the stroma, contains a concentrated mixture of proteins
and other chemicals used in the synthesis of glucose

Question 6

thylakoids (in chloroplasts)

Answer 6

Flattened, interconnected sacs that contain chlorophyll, a green-coloured molecule responsible for trapping solar energy

Question 7

chlorophyll (in chloroplasts)

Answer 7

a green-coloured molecule responsible for trapping solar energy

Question 8

Grana (in chloroplasts)

Answer 8

the stacks of thylakoids

Question 9

lamellae (in chloroplasts)

Answer 9

provide a platform for the light-dependent reactions of photosynthesis
- flat membranous tubules that connect the grana

Question 10

Stroma (in chloroplasts)

Answer 10

The inner fluid of the chloroplast that contains a concentrated mixture of proteins and other chemicals used in the synthesis of glucose

Question 11

Mitochondria (structure, what is it, parts)

Answer 11

● The site of cellular respiration ● Bound by an inner and outer
membrane
● The fluid-filled space of the inner membrane is called the matrix. It contains proteins and other chemicals needed to break down glucose into ATP
● The folds of the inner membrane, referred to as
cristae, increase the surface area for the production of ATP

Question 12

matrix

Answer 12

the fluid-filled space of the inner membrane containing proteins and other chemicals needed to break down glucose into ATP

Question 13

Cristae

Answer 13

folds of the inner membrane that increase the surface area for the production of ATP

Question 14

Oxidation vs Reduction

Answer 14

LEO the lion says GER
- Loses Electrons = Oxidation
- Gains Electrons = Reduction
- When a reactant loses electrons during a reaction, it is called oxidation. When a reactant accumulates electrons during a reaction, it is called reduction.

Question 15

Photosynthesis (where it takes place and 2 reactions)

Answer 15

• takes place in the chloroplasts of plants. This process
  combines carbon dioxide, water, and energy from the sun to synthesize glucose. Oxygen is a by-product of photosynthesis, which involves two separate sets of reactions:

1. Light Independent Reactions
2. Light Dependent Reactions

Question 16

Light-Dependent: Requirements and Products of reaction

Answer 16

Requirements: H2O, Sunlight
Products: ATP, NADPH, O2

Question 17

What happens in the Light Dependent Reaction?

Answer 17

In the light-dependent reactions, solar energy is trapped by chlorophyll molecules and used to generate two high-energy compounds, ATP and NADPH.
- The first step of photosynthesis is the light dependent reactions. As their name suggests, these reactions require energy from the sun to take place.
- The main purpose of the light-dependent reactions is to synthesize ATP and NADPH in the stroma of the chloroplast; these reactions also release oxygen as a by-product. The energy from ATP & NADPH is then used to synthesize glucose via the light-independent reactions.

Question 18

Chemiosmosis

Answer 18

The process where the hydrogen building up in the thylakoid is pushed into the stroma by the energy that was released by the ETC.

Question 19

Photosystem 2 Explanation (Light-Dependent)

Answer 19

1. Light energy from sun –> chlorophyll molecule in photosystem II (PSII), causing electron in the reaction centre of PSII to become excited.
   2) The excited electron leaves PSII –> passed down a series of other molecules (electron transport chain aka ETC). With each transfer of the
   electron, a small amount of energy is released into the thylakoid.
   3) Meanwhile, water molecules are split through a series of chemical reactions inside the thylakoid.
   Hydrogen ions build up in thylakoid –> oxygen = released, electron generated by
   reactions replace the electron that left PSII.
   4) The hydrogen building up in the thylakoid is pushed into the stroma by the energy that was
   released by the ETC in step 2. This process is referred to as chemiosmosis.
   5) Hydrogen ions enter the stroma through a molecule known as ATP synthase. As it enters the stroma,
   H+ is used to reduce ADP to ATP. ATP is one of the main products of the light-dependent reactions; it
   will later be used for the light-independent reactions.

Question 20

Photosystem 1 Explanation (Light-Dependent following Photosystem 2)

Answer 20

PHOTOSYSTEM I
6) While the events in PSII are taking place, light energy also excites an electron in Photosystem I, leading to a similar series of events. The excited electron leaves PSI and is passed down a second ETC, releasing energy along the way. The electron that leaves PSI is replaced by the original electron that left PSII during the first two steps.
7) The electron from PSI is then received by an electron carrier in the stroma which is then releases hydrogen which reduces NADP+ to NADPH. NADPH is another main product of the light-dependent reactions; it will later be used for light-independent reactions.

* End result of the light-dependent reactions = production of ATP and NADPH*

Question 21

What is the end result of light-dependent reactions? **

Answer 21

* End result of the light-dependent reactions = production of ATP and NADPH*

Question 22

What happens in the Light-Independent Reaction?

Answer 22

In the light-independent reactions, the energy of ATP and the reducing power of NADPH are used to reduce carbon dioxide and make glucose.

Once there is a sufficient amount of ATP and NADPH in the stroma of the chloroplast
(6 of each molecule), the energy from these molecules can be used to synthesize
glucose. This process, also known as the Calvin Cycle, may occur in the absence of light
because it does not rely on the excitation of electrons to initiate any reactions. However, it does usually take place during the daytime.

Question 23

Light-Independent: Requirements and Products of reaction

Answer 23

Requirements: NADPH, ATP, RuBP, CO2
Products: G3P

Question 24

The light-independent reactions involve three essential steps: (just naming)

Answer 24

1) Carbon dioxide fixation
2) Activation & Reduction
3) Replacement of RuBP

Question 25

what happens in Carbon Dioxide Fixation? (step 1)

Answer 25

3 CO2 molecules are required to initiate the cycle. The carbon atom in each molecule of CO2 binds to a molecule of ribulose bisphosphate (RuBP) in the stroma via an enzyme called rubisco. The resulting compound is very unstable and immediately breaks down into two identical 3-carbon compounds known as 3-PGA, thereby resulting in 6 of these 3-carbon compounds in total.

Question 26

What happens in the reduction process (step 2) **(gaining electrons by bonding with H+)

Answer 26

The six low-energy 3-carbon compounds (3-PGA) are then activated by the ATP generated by the light-dependent reactions. The activated complex is then reduced by NADPH, resulting in the generation of one molecule of glyceraldehyde- 3- phosphate (G3P) from each initial 3-carbon compound (so 6 G3P total). Some of these G3P molecules are used to make glucose; however, most are required for the third stage of the cycle.

Question 27

What happens in the replacement of RuBP process (step 3)

Answer 27

Of the 6 G3P molecules produced in step two of the cycle, 5 are used to regenerate RuBP. The Calvin Cycle must be completed twice in order to synthesize one molecule of glucose, as each G3P contains 3 carbons and a glucose molecule needs 6 C’s.

Question 28

How many times must the Light-Independent Cycle repeat to create 1 glucose?

Answer 28

CYCLE MUST REPEAT TWICE TO PRODUCE ONE MOLECULE OF GLUCOSE!!!

Question 29

How much ATP, NADPH, CO2 and RuBP does it take for the Calvin Cycle to produce 1/2 of Glucose?

Answer 29

1/2 Glucose = (half of what it takes to produce 1 full glucose) ● 9 ATP ● 6 NADPH ● 3 CO2 ● 3 RuBP

Question 30

How much ATP, NADPH, CO2 and RuBP does it take for the Calvin Cycle to produce 1 Glucose?

Answer 30

1 Glucose = (must cycle twice to produce this amount) ● 18 ATP ● 12 NADPH ● 6 CO2 ● 6 RuBP

Question 31

RuBP

Answer 31

molecule used to "fix" carbon dioxide

Question 32

The Calvin Cycle takes takes place in this part of the chloroplast

Answer 32

Stroma

Question 33

G3P is the main product

Answer 33

Calvin Cycle

Question 34

the most important by-product of photosynthesis

Answer 34

oxygen

Question 35

the movement of hydrogen ions down a gradient

Answer 35

chemiosmosis

Question 36

the protein through which hydrogen ions are passed as they enter the stroma

Answer 36

ATP synthase

Question 37

used to make glucose

Answer 37

G3P

Question 38

electron transport chain

Answer 38

a series of membrane-embedded proteins through which high energy electrons are transferred.

Question 39

photosynthesis is considered to be this type of reaction because it requires energy from the sun to occur

Answer 39

endothermic

Question 40

what causes the electron to leave the PS2?

Answer 40

A photon of light from the sun hit PS2 and that causes the electrons to leave the PS2 and move through the ETC.

Question 41

What happens to the hydrogen ions that are released as the electron from PS2 is passed down the ETC? (use chemiosmosis and ATP synthase in your explanation)

Answer 41

As the electrons move through the ETC, the energy is used to move H+ against their concentration gradient in the thylakoid lumen. Because the concentration is greater in the thylakoid, the H+ will move via chemiosmosis through the ATP synthase to create ATP.

Question 42

Why is water required for PS2 of the light-dependent reactions but not PS1?

Answer 42

- PS2: H2O is required --> split of the H2O releases the electrons required to replace those bumped out of the PS2 by photons of light. - PS1 doesn't require H2O since replacement electrons come from electrons from ETC from PS2. (doesn't require split)

Question 43

What role does RuBP play in the light-independent reactions?

Answer 43

RuBP allows for carbon fixation of CO2. - can be cycled back to be used repetitively when G3P is removed at the end of the Calvin cycle to create glucose.

Question 44

Is RuBP considered to be a highly efficient protein in terms of the generation of glucose?

Answer 44

not entirely. 3RuBP molecules are required with 3 molecules of CO2 to produce 1 G3P molecule. The cycle needs to be repeated twice for 1 molecule of glucose. Calvin cycle requires 18ATP and 6NADPH x2 to get 1 glucose.

Question 45

Rubisco catalyses the carbon fixation reaction between carbon dioxide and a 5 carbon compound. Name the 5C compound.

Answer 45

Ribulose biphosphate (RuBP)

Question 46

Suggest why the 6C compound produced during carbon fixation has not been discovered yet

Answer 46

It is unstable and splits to dorm 2x3 carbon composition.

Question 47

Explain how the products of the light-dependent reaction are important in stage 2 (reduction)?

Answer 47

NADP (red) donates electrons and the ATP provides energy

Question 48

The 2C compound GALP/G3P does not accumulate in the chloroplast after reduction. Explain what happens to this compound.

Answer 48

R GALP combine to form glucose and the rest are recycled to reform RuBP (step 3).

Question 49

RuBP needs to be regenerated. How many RuBP and sugar molecules are produced for every 2 turns of the cycle?

Answer 49

6 RuBp 2 G3P = 1 Glucose