Photosynthesis

Question 1

Name and briefly describe the components of the chloroplast

Answer 1

DNA
Starch grains - energy storage
Ribosomes - protein synthesis
Thylakoid - site for light dependent stage, a membrane
Granum/grana - stack of thylakoids
Intergranal lamella - connect grana
Stroma - fluid that fills the space, site for light independent stage (calvin stage)

Question 2

Where are the primary and accessory pigments found and what pigments do they contain, and what is the difference between these pigments?

Answer 2

Primary pigment - reaction centre - chlorophyll a
Accessory pigment - antenna complex - chlorophyll b/carotenoids
They absorb different wavelengths of light, different combinations of pigments are why different leaves have different shades and colours

Question 3

Explain the process of photolysis in the light dependent stage

Answer 3

• Water is absorbed from root, travels up to leaf and enters thylakoid membrane and PSII
• Light from the sun hits PSII, and the energy breaks the water molecule down
• Broken down into 1/2 O2 which is released, into 2 hydrogen ions, and 2 electrons which go into PSII and get excited because of the light energy

Question 4

Explain what happens after photolysis after electrons are excited in the light dependent stage

Answer 4

• Electrons are transferred into electron carriers to an ETC
• Electrons lose/release energy as they travel along the ETC by forming ATP from ADP+Pi, and arrive at PS1
• PS1 absorbs light energy from the sun, and electrons are excited again
• Electrons can either go through the same process through the ETC via an electron carrier again (cyclic photophosphorylation), or arrive at enzyme NADP reductase via an electron carrier (non cyclic photophosphorylation)
• NADP receives electrons and protons (H+) previously released, to form reduce NADP
• Protons also go through ATP synthase on the way to NADP reductase to release ATP

Question 5

What are the products from the light dependent stage that enter the light independent stage (Calvin cycle), and the product that doesn’t enter the calvin cycle?
What also enters the calvin cycle that isn’t a product of the light dependent stage?

Answer 5

Reduced NADP
ATP

Oxygen

Carbon dioxide

Question 6

Explain the process of the Calvin cycle

Answer 6

• Carbon dioxide enters and combines with ribulose bisphosphate (5C) to make glycerate phosphate (6C)
• Catalysed by enzyme ribulose bisphosphate carboxylase
• Glycerate phosphate is then converted into triose phosphate (6C) by ATP being converted into ADP+Pi, which provides energy for molecular rearrangement, and reduced NADP to NADP, donates the proton to GP, reducing it to become TP
• TP is converted back into eibulose bisphosphate by ATP to ADP + Pi

Question 7

Explain how the biological molecules required for plants to function are made from the Calvin cycle

Answer 7

• Glycerate phosphate can combine with a nitrogen from the soil to make amino acids, and fatty acids
• Triose phosphate can make glycerol, which can combine with the fatty acids to form lipids
• Glucose can also be made from triose phosphate, to then go onto form structures like starch and cellulose