Topic 5

Question 1

What are the four stages of aerobic respiration

Answer 1

Glycolysis
Link reaction
Krebs Cycle
Oxidative phosphorylation. (Electron transport chain & chemiosmosis)

Question 2

Explain the process of glycolysis

Answer 2

occurs in the cytoplasm of the cell. net production of 2ATP.

Glucose is phosphorylated to phosphorylated 6C sugar, due to the addition of phosphate from 2 ATP molecules (turn to ADP)

Lysis of the 6C sugar occur as it is unstable => 2 X glycerine 3 phosphate (GP).

Oxidation of GP occurs to form 2 x pyruvate molecules. Due to 2 NAD+ -> 2 NADH + H and 4 ADP -> 4 ATP.

Question 3

Explain the link reaction.

Answer 3

Occurs in the mitochondrial matrix.

2x Pyruvate -> acetyl coenzyme A due to the addition of NAD -> NADH and the removal of CO2.

Question 4

Explain the Krebs Cycle

Answer 4

Occurs in the mitochondrial matrix.

Acetyl Conenzyme A -> Citrate 6C.

Citrate 6C -> 5C acid. Due to removal of CO2 and NAD -> NADH.

5C acid -> 4C aid. Due to removal of CO2. ADP-> ATP. 2NAD -> 2NADH. FAD -> FADH.

4C acid -> acetyl coenzyme A.

Question 5

Explain oxidative phosphorylation

Answer 5

Oxidative Phosphorylation is made up of the electron transport chain and chemiosmosis.
The electron transport chain takes place in the inner mitochondrial membrane.

1. Electrons removed from glucose by NAD during glycolysis and the Krebs Cycle are transferred from NADH to the first carrier protein (cytochrome.) Cytochrome oxidase is required to receive electrons.
2. The carrier protein is oxidised and donates its electrons to the next carrier protein.
3. The energy provided is used to transport H+, by active transport, into the inter membrane space.
4. Redox reactions pass electrons down energy level. The carries proteins are all receiving and donating electrons.
5. The final electron acceptor is oxygen. When oxygen is reduced it combines with H+ to from H20.
6. The active transport of H+ causes the concentration in the membrane space to be higher than in the matrix. This creates an electrochemical gradient. The H+ wants to move down the concentration gradient back into the matrix.
7. The only place the H+ can do this is by passing through the protein complex ATP synthase. As they pass through, ATP synthase uses the energy from the H+ gradient to synthesise ADP to ATP.

Question 6

Why is it called oxidative phosphorylation?

Answer 6

It is called Oxidative phosphorylation because the carrier proteins are OXIDISED. And ADP is transformed to ATP by phosphorylation.

Question 7

Anaerobic equations

Answer 7

In mammals:
glucose -> lactic acid (+ ATP)
C6H12O6 -> 2C3H603 (+ ATP)

In plants and fungi:
glucose -> ethanol + carbon dioxide (+ ATP)
C6H12O6 -> 2C2H5OH + 2CO2 (+ATP)

Question 8

What is anaerobic respiration? How does it occur?

Answer 8

Anaerobic respiration is the partial breakdown of hexoses to produce a limited yield of ATP, in the absence of oxygen.
At the end of glycolysis, if the oxygen levels are low, the pyruvate remains in the cytoplasm.
The net yield of ATP in anaerobic respiration is 2 ATP. Whereas in aerobic respiration the final net yield is 38 molecules. ( 2 form glycolysis, 2 from Krebs and 34 form oxidative phosphorylation)
aerobic respiration is the partial breakdown of glucose to produce limited yield of ATP in the absence of oxygen.
Lactic acid dissociates to form lactate and H+ ions. The movement of lactate and H+ ions into the blood form the muscles lowers the PH of the blood which affects the CNS.
Oxygen debt is the amount of oxygen needed after anaerobic respiration to oxidise the lactate.
Training allows long distance athletes to get more oxygen to their muscles faster as a better blood supply develops and to tolerate higher levels of lactate before muscles fatigue.

Question 9

Define absorption spectra

Answer 9

Absorption Spectra: the absorbance of light by a photosynthetic pigment at different wavelengths.

Question 10

Define action spectra

Answer 10

Action Spectra: the rate of photosynthesis by the plant at different wavelengths.

Question 11

What are photosynthetic pigments?

Answer 11

Photosynthetic pigments: 
Chlorophyll a - Most Abundant
Chlorophyll b
Carotenoid: b-carotene, xanthophyll
Most plants have a variety of photosynthetic pigments so that they can absorb most of the spectra of light, as they contain more than one pigment. 

Photosynthetic pigments carry out the absorption of light in two distinct chlorophyll complexes called photosystems. PSI absorbs light wavelength 700nm and is involved in cyclic and non-cyclic phosphorylation. PSII absorbs 680nm and is only involved in non-cyclic phosphorylation.

Question 12

Describe the structure of a chloroplast

Answer 12

Chloroplasts are large organelles found in the cells of the green parts of plants.

Envelope: outer and inner membrane. This is permeable to let CO2 and H2O in.
Thylakoids: stacks of membrane disks where the chlorophyll is found.
Grana: The stacks of thylakoids. Gives a large surface area to absorb light energy.
Stroma: matrix surrounding the grana, containing enzymes needed for the light independent stage.

Question 13

Explain how the light dependent stage of photosynthesis occurs.

Answer 13

A photon hits chlorophyll in PSII, exciting an electron. Light energy splits water into H+, electrons, and O2.
The excited electron is passed along the electron transport chain and gains energy from light.
Energy is used to pump H+ into the thylakoid lumen.
H+ and electrons from PSI combine with NADP to form NADPH.
The electrochemical gradient drives the reaction ADP + Pi -> ATP, catalysed by ATP synthase in photophosphorylation.

Question 14

What are the difference between cyclic photophosphorylation and non-cyclic photophospohylation?

Answer 14

Photosystems involved: CP = PS1. NCP = PS1 & PS11.

Takes place in: CP = thylakoid membrane. NCP = Thylakoid membrane.

Requires Water? CP = no. NCP = yes.

Enzymes involved: CP = ATP synthase. NCP = ATP synthase and NADP reductase.

Involves chemiosmosis to produce ATP? CP = yes. NCP = yes.

OXygen produced? CP = no. NCP = yes.

NADPH produced? CP = no. NCP = yes.

Question 15

Explain how the light independent stage of photosynthesis occurs.

Answer 15

In carbon fixation; CO2 is fixed with RuBP to form 2x GP using enzyme RUBISCO.
In reduction; GP is reduced by NADPH and activated by ATP to synthesise 2x GALP.
In regeneration; five out of 6 GALP molecules are used to regenerate RuBP.
In glycogenesis; two GALP molecules are combined to form a glucose molecule from which many organic compounds are synthesised.

Question 16

Factors that limit photosynthesis.

Answer 16

Light:
Light energy is needed in the LDS. It excites electrons and splits H2O in photolysis.
Electrons gain energy from light as they are passed along the electron transport chain. NADPH and ATP are made.

Carbon Dioxide:
CO2 is the substrate in carbon fixation reaction in LIS. Hence more CO2 = more GP so calvin cycle can turn faster.

Temperature:
Increase in kinetic energy as temperature increases, hence RUBISCO changes RuBP to GP faster as more successful collisions. Does no effect LDS.
Denaturing of enzymes as active site changes shape due to breaking of bonds, hence less enzyme substrate complexes.