Photosynthesis and Cellular respiration

Question 1

Oxygen debt

Answer 1

Lactic acid fermentation
The amount of oxygen required to allow lactate to return to oxidative pathways. It does this to protect the muscles from the acidic environment.

Question 2

Where the different parts of cellular respiration and photosynthesis occur

Answer 2

Cellular respiration
1. Glycolysis occurs within the cytoplasm
2. Pyruvate oxidation occurs within the mitochondrial matrix
3. Krebs cycle - Mitochondrial matrix
and inner membrane
4. Oxidative phosphorylation occurs within the inner-membrane space, the inner membrane, and the matrix of the mitochondria

Photosynthesis
- Light dependent reactions take place in the thylakoid membrane of chloroplasts
- Light independent reactions take place in the stroma of chloroplasts

Question 3

Products of each stage of cellular respiration

Answer 3

1. Glycolysis - Yields/products: 2 pyruvate, 4 ATP, 2 H+, 2 ADP, 2 H2O, 2 NADH
2. Pyruvate oxidation -
   Yields: 2 NADH, 2 Acetyl CoA, 2 H+, 2 CO2
3. Krebs cycle -
   Yields: 2 CoA, 4 CO2, 6 NADH, 6 H+, 2 FADH2, 2 ATP
4. Oxidative phosphorylation -
   Yields: 8 NAD+, 6 H2O, 32 ATP, 4 FAD, 24 H+
   Total energy yield of cellular respiration is 30-32 ATP

Question 4

Ethanol fermentation and lactic acid fermentation (anaerobic respiration)

Answer 4

Ethanol fermentation
1. Glycolysis occurs (Produces 2 pyruvate, 2 ATP. Uses two molecules of NAD+ in the process)
2. Each pyruvate will undergo decarboxylation to produce acetaldehyde
3. Finally, acetaldehyde is reduced by NADH to produce ethanol
This allows for the regeneration of NAD+, which can then be used in glycolysis again
The final product, ethanol, is the kind of alcohol humans consume
Lactic Acid fermentation
1. Glycolysis occurs (Produces 2 pyruvate, 2 ATP. Uses two molecules of NAD+ in the process)
2. This time the pyruvate that is produced will not decarboxylate, instead it will be directly reduced by NADH to produce lactate (Lactic acid has an extra H, but is otherwise the same)
This allows for the regeneration of NAD+, which can then be used in glycolysis again
Lactate is the conjugate base of lactic acid, and it is the production of this compound by certain fungi and bacteria that allows them to be used in the industrial production of cheese and yoghurt.
The lactic acid that is generated in muscles must be reoxidized to protect the tissues from the acidic environment.
Oxygen is needed to allow the lactate to return to oxidative pathways to be metabolised. This amount of oxygen is called the oxygen debt.
no release of carbon dioxide.

Question 5

Purpose and process of the electron transport chain

Answer 5

Its goal is to couple energy stored in electron acceptors to a proton gradient that drives ATP synthesis
Electron transport chain
Step 1: NADH (which is synthesised during the krebs cycle), becomes oxidised (gives up its
proton (H+) and electron), becomes NAD+, and its proton moves through complex 1. When this happens complex 1 becomes supercharged and is able to pump protons from the mitochondrial matrix into the intermembrane space. Now a proton gradient is beginning to form.
Step 2: The electron moves to CoQ and waits for further instructions. Meanwhile FADH2
(Produced during Krebs cycle) approaches complex 2, it gives up its electron and becomes FAD into complex 2. Complex 2 cannot become supercharge so the electron sits there before moving into CoQ (CoQ is the common electron acceptor for complex 1 & 2)
Step 3: The electrons are passed into complex 3 which becomes supercharged, moving the
protons against the concentration gradient into the intermembrane space

Step 4: Compex 3 passes its electrons to cytochromeC which then passes them to complex 4
which becomes supercharged, moving the protons against the concentration gradient into the intermembrane space
Step 5: Now complex 4 passes the electron to the final electron acceptor, oxygen, which splits
into two oxygen ions and protons are added, producing two water molecules

Question 6

Entropy and under what conditions it increases/ decreases

Answer 6

Entropy: A measure of disorder and is continually increasing.
Entropy increases when:
Solids become liquids or gases
Liquids become gases
Fewer moles of reactant become greater moles of product
Complex molecules react to form simpler molecules
Diffusion occurs

Question 7

Substrate level phosphorylation

Answer 7

At various steps in the glycolytic pathway, a phosphate group is removed from a substrate molecule and combined with an ADP molecule to form ATP (Different from ATP synthase process because substrate level phosphorylation is reliant on using the energy obtained from a coupled reaction)

Question 8

Amount of ATP created from each NADH and FADH2 molecule

Answer 8

NADH: 3 ATP
FADH2: 2 ATP

Question 9

Location of the different photosynthetic processes in the chloroplast

Answer 9

Light dependent reactions - Thylakoid membrane
Calvin cycle - Stroma

Question 10

Products and reactants of the light dependent and independent reactions

Answer 10

Light dependent reactions
Products: ATP, NADPH, O2

Light independent reactions
NADPH and ATP are required in the light independent reactions of photosynthesis (Calvin cycle)

Question 11

Cyclic and noncyclic photophosphorylation

Answer 11

Noncyclic photophosphorylation
The production of ATP by the Z scheme is often called noncyclic photophosphorylation, as the flow of electrons is unidirectional (electrons are transferred from photosystem I to NADP+ to form NADPH)
The passage of one electron pair through this system generated 1 NADPH and slightly more than 1 ATP, but this ratio is not sufficient for the light-independent reactions (need 3 ATP molecules, and 2 NADPH)
Cyclic photophosphorylation: to create more ATP
Excited electrons leave photosystem I and are passed to an electron acceptor. From the electron acceptor, they pass to the b6-f complex and back to photosystem I
ATP synthesis by chemiosmosis occurs
Because the same electron that left the P700 chlorophyll molecule in photosystem I returns to fill the hole that it left, it is cyclical
Neither NADPH nor oxygen is produced in cyclic photophosphorylation

Question 12

CAM and C4 pathways to fix carbon and how they are different from C3 plants

Answer 12

C4 and CAM Pathways: 1. Primary acceptor of CO2 is phosphoenol pyruvate, 2. First stable product is oxaloacetic acid, 3. Occurs in mesophyll and bundle-sheath cells, 4. Fast carbon fixation, photo-respiratory losses are low

C3 Pathways: 1. Primary acceptor of CO2 is RuBP, 2. First stable product is 3-phosphoglycerate, 3. Occurs in mesophyll cells, 4. Slow carbon fixation, photo-respiratory losses are high

Question 13

ATP synthase and what it does (how it works)

Answer 13

Aka, Chemiosmosis
ATP synthase takes advantage of the proton gradient in order to produce ATP. The protons want to flow down its gradient (flow from high concentration to low concentration to form an equilibrium) so protons move down ATP synthase, catalysing the reaction between ADP + Pi to form ATP
The protons that were moved through ATP synthase back into the mitochondrial matrix are now waiting for complexes 1, 3, and 4 to become supercharged again and allow the cycle to continue.

Question 14

Photorespiration- what it is and why it happens

Answer 14

Photorespiration: when oxygen reacts with ribulose-1,5-bisphosphate (RuBP) and the products are a two-carbon compound called phosphoglycolate and one three-carbon compound, 3-phosphoglycerate
As a result of photorespiration, all the energy used to regenerate the RuBP is wasted, reducing the efficiency of photosynthesis

Happens because, rubisco can use oxygen as a substrate as well as carbon dioxide and fight for each other on the same active site

Question 15

The steps of glycolysis

Answer 15

Reaction 1-3
Two molecules of ATP are used to phosphorylate substrate molecules
ATP comes from other reactions
Reaction 4
The six carbon compound, fructose 1,6-bisphosphate, is split into two different three carbon compounds: dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P)
Reaction 5
DHAP is converted into a second G3P and each of the two G3P molecules proceeds through reactions 6 to 10
Reaction 6
An inorganic phosphate group is added to G3P, and an NAD+ molecule is reduced to form NADH
This reaction proceeds twice for the two G3P molecules produced
The reaction results in two 1,3-bisphosphoglycerate (BPG)
Reaction 7
ADP is converted to ATP by using substrate level phosphorylation
The products of the reaction are two 3-phosphoglycerate
Reaction 8 and 9
The three-carbon substrate molecules are rearranged and a water molecule is removed through condensation
This results in 2 phosphoenolpyruvate
Reaction 10
A molecule of ADP is converted to ATP by substrate level phosphorylation
This process occurs twice resulting in 2 ATP
The products of the reaction are two pyruvates

Question 16

Explaining where and when the carbon from the original glucose is released as carbon dioxide in cellular respiration.

Answer 16

Pyruvate oxidation step 1 - A carboxyl group is snipped off of pyruvate and released as a molecule of carbon dioxide, leaving behind a two-carbon molecule. (Two CO2 are released as there are two pyruvates going through oxidation at the same time)

Reactions 1- 5 Krebs cycle - Acetyl-CoA reacts with oxaloacetate to produce a six-carbon molecule called citrate. Once citrate is formed, it breaks down to a four-carbon molecule called succinate. Two of these reactions are oxidation reactions that result in the release of two carbon dioxide molecules. (4 CO2 are released as there are two Acetyl-CoA reacting at the same time)

Question 17

Explaining the light dependent reaction and light independent reaction. What is needed for both, what is created and why

Answer 17

Light dependent reactions - Light is needed.
Produce ATP and NADPH. These two energy-storing molecules are then used in the light-independent reactions.
Sunlight is made into energy
Step 1: A proton is absorbed by the P680 molecule in photosystem 2 and excites an electron
This excited electron leaves and goes to the electron acceptor
Now P680 has a hole and has a powerful need to fill it with an electron, so it splits a water molecule into H+ and O
A water-splitting complex holds two water molecules in place as an enzyme strips 4 electrons from them, one at a time. P680+ accepts these electrons one at a time, and each is passed to another electron carrier.
P680+ then absorbs another photon, becomes reduced, and passes on another electron
This process occurs four times to form one oxygen molecule
The 4 H+ ions from the two water molecules remain in the thylakoid space.
The oxygen atoms from the water molecule immediately form an oxygen molecule and is released by the plant into the environment
Photosystem II can absorb photons, excite P680 and pass electrons to the electron acceptor 200 times in one second

Step 2: From the electron acceptor, the energised electrons are transferred, one by one, to the electron transport system
With each transfer of electrons along he system, a small amount of energy is released
The released energy is used by a protein complex called b6- f complex to pump hydrogen ions from the stroma, across the thylakoid membrane, and into the thylakoid space
Eventually, there are many more hydrogen ions in the thylakoid space than there are in the stroma, which creates a hydrogen ion gradient across the thylakoid membrane

Step 3: While the events of steps 1 and 2 are taking place, light energy is absorbed by photosystem I.
This energy is transferred to the reaction centre P700, where electrons become excited
Electrons are passed to a high-energy electron acceptor (Ferredoxin)
The lost electrons are replaced by those that have reached the end of the electron transport system from photosystem II

Step 4: The electrons that were received by the electron acceptor from photosystem I are used by the enzyme NADP reductase to reduce NADP+ to form NADPH
The reducing power of NADPH will be used in the light-independent reactions

Making ATP through Chemiosmosis
ATP synthesis in the light-dependent reactions occurs by the as ATP synthesis in aerobic respiration

Question 18

Calculating bond energy of a chemical reaction

Answer 18

energy in – energy out

Question 19

Exergonic and endergonic reactions

Answer 19

Exergonic - An exergonic reaction refers to a reaction where energy is released. Spontaneous

Endergonic - An endergonic reaction is one that requires free energy to proceed. Not spontaneous

Question 20

Absorbance spectrum graphs (how to read and interpret them)

Answer 20

The higher the value, the more of a particular wavelength is being absorbed. You will see that absorption peaks at a value of 217 nm. This is in the ultra-violet and so there would be no visible sign of any light being absorbed - buta-1,3-diene is colourless. You read the symbol on the graph as “lambda-max”

Question 21

Comparing anaerobic and aerobic respiration

Answer 21

Aerobic: Requires oxygen
Anaerobic: Does not require oxygen

Question 22

How the body decreases cellular respiration when less energy is required

Answer 22

2 major enzymes are controlled by feedback mechanisms
1. phosphofructokinase: glycolysis
It has an allosteric binding site for ATP. When the cell has sufficient ATP, excess ATP binds to the
site and inhibits the enzyme

2. conversion of pyruvate into acetyl-CoA and carbon dioxide Enzyme that catalyses this reaction, pyruvate dehydrogenase, is inhibited by excess NADH.
3. many other Krebs cycle enzymes are also inhibited by excess ATP, NADH, and acetyl-CoA

Question 23

Purpose of creating a hydrogen ion gradient

Answer 23

So that H+ is encouraged to push itself through ATP synthase to catalyse the ADP + Pi reaction

Question 24

Different pathways that fats and proteins can take to enter into cellular respiration

Answer 24

The proteins are broken down into amino acids, fats get broken down into glycerol and fatty acids (intermediates). Some amino acids enter Transition and Kreb Cycle. Glycerol can enter glycolysis. Fatty acids are broken down into two carbon units, acetyl CoA (beta oxidation)and enter Kreb Cycle.
If the body has excess amino acids or is starving, they are broken down for energy via cellular respiration , but must first have amino group removed. Fats work the same way, must be broken down and used as intermediates at certain stages of respiration pathways

Question 25

Comparing cellular respiration and photosynthesis (anabolic and catabolic reactions)

Answer 25

Photosynthesis converts carbon dioxide and water into oxygen and glucose (Anabolic). Glucose is used as food by the plant and oxygen is a by-product.

Cellular respiration converts oxygen and glucose into water and carbon dioxide. (Catabolic)

Question 26

Importance of creating gradients within a mitochondria and chloroplast

Answer 26

The Proton Gradient Drives ATP Synthesis

Question 27

Reactants of each stage of cellular respiration

Answer 27

Glycolysis - Glucose, 2 ATP, 2 NAD+, 4 ADP, 2 Pi

Pyruvate Oxidation - 2 Pyruvate, 2 NAD+, 2 CoA

Krebs - 2 Acetyl-CoA, 6 NAD+, 2ADP, 2 Pi, 2 FAD+, 2H2O

ETC & C.O - 8 NADH, 4 FADH2, 32 ADP, 32 Pi, 6 O2, 12 H+