Topic 8 - Photosynthesis and respiration and their role in plant metabolism

Question 1

Absorption of light energy

Answer 1

By photosynthetic pigments in the thylakoid membrane

Question 2

Process of photosynthesis

Answer 2

2n H20 + n CO2 → n (CH2O) + n H2O + n O2

Absorption of light energy (light reactions)
↓
CO2-fixation and reduction (dark reactions)
↓
Triose-phosphate → starch, sucrose, synthesis

Question 3

Light reactions of photosynthesis

Answer 3

Photosystem II
Photon → 2e- → Electron acceptor → Plastoquinone → Cytochrome complex → plastocyanin → Photosystem I

Photosystem I
Photon → 2e- → Electron acceptor → Ferredoxin → NADH reductace → NADPH

Question 4

Calvin-Benson-Cycle

Answer 4

C3-pathway

Energy demand:
2 NADPH + 3 ATP/CO2

NET production:
1 triose-phosphate/ 3 CO2

Question 5

Starch synthesis

Answer 5

Triose phosphate (from calvin cycle) → starch formation or transported to cytosol in exchange for inorganic translocator in the inner chloroplast membrane

Triose phosphate → ADPG → Starch → Storage

Question 6

Sucrose synthesis

Answer 6

In cytosol

Triose phosphate → Fructose-1,6-bisphosphate → Fructose-6-phosphate → Sucrose phosphate → sucrose → transport or storage

Question 7

Starch

Answer 7

The most important stored carbohydrate form in the plants

But, certain plants accumulate FRUCTANS as stored carbohydrate

Question 8

Respiratory pathway

Answer 8

Glycolysis and pentose phosphate pathway in cytosol → convert sugars to organic acids, via hexose and triode phosphates → NADH or NADPH, and ATP

Organic acids → oxidised in mitochondrial citric acid cycle → NADH and FADH2 → Energy for ATP synthesis (oxidative phosphorylation)

Question 9

Major linking points at Glycolysis

Answer 9

Glucose – 6 – phosphate (G-6-P) →Pentose-phosphate-pathway

3 – phospho-glycerinacid (3-PGA) → Serin amino acid family

Phospho-enol-pyruvate (PEP) → Shikimic acid pathway

Pyruvate (PYR) → Citric acid cycle (presence of O2)
Fermentation (absent of O2)
ALANIN amino family

Question 10

Major linking points at Citric acid pathway

Answer 10

Acetyl-CoA → Lipid synthesis, izoprenoids (carotenoid, gibberellin etc.) synthesis

𝛼-keto-glutar acid → Glutamin acid

Oxalic acid (OA) → Asparagin Acid

Succinate-CoA → Profirin skeleton synthesis (e.g. chlorophylls)

Question 11

Major linking points at pentose phosphate pathway

Answer 11

Ribulose-5-phosphate → Polynucleotides synthesis

Eryhtrose-4-phosphate → Shikimic acid pathway

At G-6-P joint to glycolysis

Question 12

Major linking points at shikimic acid pathway

Answer 12

Aromatic amino acids, amino acid family, lignin etc.