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:

During photosynthesis, water undergoes the process of photolysis.

Describe what happens in the photolysis of water. 

water is split to form H⁺/hydrogen ions  AND  electrons/e^-

oxygen is formed (as a by-product)

light excites electrons  OR  light raises the energy level of electrons

The light-dependent reactions of photosynthesis synthesise ATP and reduced NADP.

These products are then used in the light-independent reaction of photosynthesis.

Describe one function of ATP in the light-independent reaction. 

provides energy to convert GP into TP

provides phosphate to produce RuBP

OR

provides energy to convert TP into RuBP

Describe one function of reduced NADP in the light-independent reaction. 

provides hydrogen/H⁺ ions to convert GP into TP  OR  reduces GP to TP

Explain how NADP is reduced in the light-dependent reaction of photosynthesis. 

electrons are transferred from chlorophyll to NADP

proton  OR  hydrogen/H⁺ ion from the photolysis of water is transferred to NADP

Products from the light-dependent reactions of photosynthesis are used to make organic substances in the light-independent reactions.

Describe how carbon dioxide is converted into organic substances during the light-independent stage of photosynthesis. 

carbon dioxide combines with RuBP

to produce 2 molecules of GP

GP is reduced to TP

using reduced NADP

using energy from ATP

TP is converted into glucose/hexose/RuBP

State the number of carbon atoms in each of the following molecules:

i) GP - 3

ii) TP - 3

iii) RuBP - 5

A decrease in temperature decreases the rate of the light-independent reaction.

Use the diagram above to explain why.

enzymes are involved

low temperatures causes enzymes to have less kinetic energy

OR

low temperatures mean there are fewer collisions between enzyme and substrate

The light-independent reaction relies on products from the light-dependent reaction.

Describe how plants use light energy during the light-dependent reaction. 

light excites electrons

OR

electrons are removed from chlorophyll

electrons move along electron carriers, releasing energy as they do

OR

electrons move down/along an electron transfer chain, releasing energy as they do

this energy is used to join ADP and P_i to form ATP

photolysis of water produces protons/H⁺, electrons, and oxygen

NADP is reduced by electrons and protons

In the light-dependent reaction of photosynthesis, light energy is used to generate ATP.

light energy excites electrons in chlorophyll

electrons pass down/along an electron transfer chain

electrons reduce carriers

OR

passage down carriers involves redox reactions

energy is released at each carrier

ATP is generated from ADP and phosphate

Explain why the increase in plant biomass is less than the mass of hexose sugars produced by the same plant. 

some hexose sugars are used in respiration

carbon dioxide is produced and released into the atmosphere

some parts of a plant are eaten

OR

some parts of a plant are destroyed by decomposers

Plants produce ATP in respiration as well as in photosynthesis.

Explain why it is important for plants to produce ATP in respiration.

in the dark no ATP can be produced via photosynthesis

some tissues cannot photosynthesise

ATP cannot be moved from cell to cell

OR

ATP cannot be stored

plants use more ATP than they produce in photosynthesis

ATP is used for active transport  OR  synthesis of a named substance (e.g. glucose)

Describe the role of chlorophyll in photosynthesis.

chlorophyll absorbs light energy

this raises the energy level of electrons OR this excites electrons

to form ATP

Explain why the concentration of GP remained constant between 0 and 800 seconds.

GP is formed from RuBP and carbon dioxide

GP is converted into TP/sugars/RuBP

allow triose phosphate for TP

GP is formed at the same rate as it is used up