Photosynthesis

Question 1

Overview of photosynthesis

Answer 1

• chlorophyll captures light energy
• light dependent reaction (NADPH, ATP)
• light independent reaction (sugars + organic mols.)

Question 2

Photosynthesis equation

Answer 2

6CO2 + 6H2O -> C6H12O6 + 6O2

Question 3

How are thylakoids adapted for the LDR?

Answer 3

• large SA
• network of proteins in grana hold chlorophyll to maximise light absorption
• enzymes in granal membrane to generate ATP
• DNA + ribosomes make proteins

Question 4

Light dependent reaction

Answer 4

• photoionisation of 2e- excites them to higher energy level
• e’s move down e transport chain which absorbs energy at each carrier (redox) + uses it for proton pump
• chemiosmosis as protons diffuse through ATP synthase, activating it to catalyse phosphorylation of ADP -> ATP
• NADP is reduced with the addition of a proton + electron
• photolysis

Question 5

Photolysis (LDR)

Answer 5

• light energy splits water mol.
• electrons used to regenerate chlorophyll
• protons join H+ flow + used to reduce NADP
• O2 used in respiration or leaves via stomata

Question 6

How is stroma adapted for the LIR?

Answer 6

• fluid matrix contains enzymes
• surrounds grana so receives LDR products easily
• DNA + ribosomes to make proteins

Question 7

Light independent reaction

Answer 7

• CO2 + RuBP catalysed by rubisco -> 2xGP
• reduction of GP -> 2x triose phosphate (ATP donates Pi, NADPH donates H+)
• Carbon mol produced from triose phosphate
• regeneration of RuBP (ATP donates Pi)

Question 8

How are useful substances formed from the LIR?

Answer 8

6C needed to form hexosugar (glucose), cycle repeats to form components for organic mols (starch, cellulose, amino acids)

Question 9

List factors affecting photosynthesis

Answer 9

• Light intensity -> increases LDR until plateau due to another lim. factor
• CO2 conc. -> increases LIR until plateau due to another lim.factor
• Temperature -> increases LDR to optimum due to kinetic energy, then enzymes (rubisco) denature so LIR decreases

Question 10

How to enhance factors for agriculture

Answer 10

Light: artificial lighting, automatic blinds, prevent damage to chlorophyll
CO2: gas/paraffin heaters, >0.1% can damage leaves
Temp: heat glasshouse, heaters/heated floors to maintain temp