photosynthesis and respiration

Question 1

What is a photosystem?

Answer 1

Protein and pigment in chloroplasts. Used by plants to capture light energy

Question 2

What is a co-enzyme?

Answer 2

A molecule that aids the function of an enzyme, in photosynthesis it is NADP

Question 3

What are the two stages of photosynthesis?

Answer 3

Light dependent reaction- takes place in the thylakoids

Light independent reaction- takes place in the stroma

Question 4

What are the four stages of the light dependent reaction?

Answer 4

Photoionisation of chlorophyll, photolysis, production of ATP and NADPH, and chemiosmosis

Question 5

Describe photolysis:

Answer 5

Light energy is absorbed by chloroplast and splits water into oxygen, H+ and e-

Question 6

Describe the photoionisation of chlorophyll:

Answer 6

Light energy is absorbed by chlorophyll and results in electrons becoming excited and raising up an energy level to leave the chlorophyll (chlorophyll has been ionised by light). Some of the energy released from the e- is used to make ATP and reduced NADP in chemiosmosis

Question 7

Describe chemiosmosis:

Answer 7

e- from photoionisation move along the electron transport chain. As the e- move along, they release energy and some of this is used to pump protons (from photolysis) across the membrane. An electrochemical gradient is created (as higher conc. of H+ in thylakoid lumen than in stroma). H+ pass through ATP synthase (facilitated diffusion) which results in the production of ATP from ADP+Pi. The H+ combines with e- to form hydrogen which combines with NADP to form NADPH

Question 8

What is the electron transport chain?

Answer 8

Series of proteins embedded within the thylakoid membrane

Question 9

Describe the light independent reaction (Calvin Cycle):

Answer 9

Carbon dioxide reacts with RuBP to form two molecules of glycerate 3-phosphate (5C). GP reduced to triose phosphate using energy from ATP and by accepting a H from reduced NADP. Some carbon from triose phoshate leaves the cycle each turn to be converted to useful organic substances. The rest of the molecule is used to regenerate RuBP, with the energy from ATP.

Question 10

What can the product of the LIR be used for?

Answer 10

Glucose can join to form disaccharides and polysaccharides, and can be converted into glycerol

Question 11

What factor affects the light dependent reaction?

Answer 11

Light intensity. Higher light intensity increases the rate of photosynthesis as more photolysis and photoionisation can occur

Question 12

What factors affect the LIR?

Answer 12

CO2 concentration. Calvin cycle occurs at a faster rate if theres a higher CO2 availability

Temperature. LIR is an enzyme controlled reaction so the enzymes can become denatured at too high a temp, or not have enough kinetic energy at low temperatures.

Question 13

What are the respiration coenzymes?

Answer 13

NAD, FAD - both transfer hydrogen

Coenzyme A - transfers acetate

Question 14

What are the four stages of aerobic respiration?

Answer 14

Glycolysis, link reaction, Krebs cycle and oxidative phosphorylation

Question 15

Describe glycolysis:

Answer 15

Glucose phosphorylated by two ATP molecules to form hexose bisphospate
Hexose bisphosphate splits into triose phosphate. Each triose phosphate is oxidised to pyruvate, forming 2xATP and reduced NAD

Question 16

What are the products of glycolysis and where do each of them go?

Answer 16

2x reduced NAD: goes to oxidative phosphorylation
2x pyruvate: actively transported into the matrix for use in the link reaction
2x ATP: used for energy

Question 17

Describe the link reaction:

Answer 17

Pyruvate is decarboxylated (1C removed in the form of CO2)
Pyruvate is also oxidised to form acetate, which is then combined with coenzyme A to form acetyl coenzyme A
No ATP is produced

Question 18

What are the products of the link reaction and where do each of them go?

Answer 18

2 acetyl coenzyme A: to the Krebs cycle
2 carbon dioxide: released as a waste product
2 reduced NAD: to oxidative phosphorylation

Question 19

Describe the Krebs Cycle:

Answer 19

Acetyl coenzyme combines with 4 carbon acceptor (oxaloacetate) to form a 6C compound (citrate). Citrate decarboxylated to a 5 C compound and 3x NADH formed. 5C is also decarboxylated and oxaloacetate is regenerated. Substrate level phosphorylation occurs and FAD froms reduced FAD

Question 20

What are the products of the Krebs Cycle and where do each of them go?

Answer 20

Coenzyme A: reused in next link reaction
Oxaloacetate: regenerated for use in next Krebs cycle
2 CO2: released as a waste product
ATP: used for energy
3 NADH: oxidative phosphorylation
1 FAD: oxidative phosphorylation

Question 21

What is substrate level phosphorylation?

Answer 21

When a phosphate group is directly transferred from one molecule to another

Question 22

Describe oxidative phosphorylation:

Answer 22

Hydrogen released from reduced NAD and reduced FAD as they’re oxidised (split into H+ and e-)
e- move down electron transport chain, losing energy at each carrier
Energy used to pump H+ into intermembrane space
H+ diffuse down electrochemical gradient across membrane via ATP synthase, producing ATP from ADP and Pi
H+, e- and oxygen (final electron carrier) form H2O.

Question 23

How many ATP molecules are made from reduced NAD and reduced FAD, and so how many molecules of ATP are made from aerobic respiration?

Answer 23

2.5 from reduced NAD
1.5 from reduced FAD
32 ATP made in total

Question 24

How can lipids be used as an alternative respiratory substance?

Answer 24

Glycerol is phosphorylated into triose phosphate (link reaction and Krebs can occur). Fatty acids are broken down into 2 carbon fragments and converted into acetyl coenzyme A. Extra hydrogen is used in oxidative phosphorylation

Question 25

How can proteins be used as an alternative respiratory substance?

Answer 25

Deaminated (amino group removed). If 3C then become pyruvate, 4 and 5 C become intermediates of Krebs Cycle

Question 26

What is the additional step for glycolysis in anaerobic respiration, and why is it necessary?

Answer 26

Pyruvate converted into lactate (animals) or carbon dioxide and ethanol. This regenerates NAD from reduced NAD, and allows glycolysis to continue