Photosynthesis

Explain why the scientists measured the rate of production of oxygen in this investigation?

• Oxygen is produced during the Light-dependent reaction

• More oxygen means faster rate of Light-dependent reaction

How does having more production of oxygen correlate to faster growth?

What are the possible limiting factors of the light independent reaction

• Temperature is a limiting factor/ below the optimum

• Light is a limiting factor

• Limited by RuBP

• Limited by enzyme (rubisco)

What is water used for in photosynthesis?

• Provides hydrogen (protons) and electrons

• For reduction by H+ ions

• Source of electrons for electron transfer chain

Describe how crop plants use light energy during the light dependent reaction:

• Excites electrons/ electrons removed from chlorophyll

• Electrons move along electron transfer chain

• Energy used to join ADP and Pi to form ATP

• Photolysis of water produces protons, electrons and oxygen

• NADP reduced by electrons and protons

After harvesting, the remains of crop plants are often ploughed into the soil. Explain how micro-organisms in the soil produce a source of nitrates from these remains:

• Protein/ amino acids/ DNA into ammonium compounds

• By saprobionts

• Ammonium/ ammonia into nitrite

• Nitrite into nitrate

• By nitrifying bacteria

What is the advantage of stomata closing when there is no light

• Water is lost through stomata

• Closure prevents/ reduces water loss

• Maintain water content of cells

Why would carbon dioxide uptake fall to zero when lights are turned off?

• No use of carbon dioxide in photosynthesis (in the dark)

• No diffusion gradient (maintained) for carbon dioxide into lead, so carbon dioxide diffuses out of leaf due to respiration

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances decribe how: