8.3 AND 2.9 Photosynthesis

Question 1

Whole process

Answer 1

Photosystem 2

E- transport chain

Photosystem 1

E- transport chain

Calvin cycle

Glucose formed

Question 2

Light dependent reactions

Answer 2

• Photosystem 2 and 1
• Occur in the intermembrane space of the thylakoid

Question 3

Photolysis

Answer 3

The splitting of water by enzymes to produce 2e- and 2H+ and O

Question 4

Light reactions

Answer 4

Photosystem 2:
1. Light energy from the sun is used for photolysis of H2O in the chlorophyll. O2 is waste product and released through stoma. Electrons are used for light dependent reactions.

2. Electrons released are passed through pigments in the antenna complex
3. The electron is passed to the reaction centre where it can be given to the electron acceptor at high energy.
4. The electron is picked up by the electron transport chain.

Electron transport chain:
1. Plastoquinone picks up the electron.

2. Gives it to cytochrome b6f pumping a H+ through thylakoid membrane from stroma
3. Plastocyanin takes the electron to Photosystem 1.

Photosystem 1:
1. Pigments (chlorophyll a) absorb light from sun passing an electron through antenna complex to reaction centre and electron transport chain

2. Ferredoxin picks up the excited electron
3. Passed to NADP Reductase to form NADPH from 2e- and H+, reducing them
4. A hydrogen ion gradient builds up from chemiosmosis allowing ATP synthase to produce ATP
5. ATP and NADPH is carried to Calvin cycle

Question 5

Light independent reactions

Answer 5

Calvin cycle (occurs in the stroma)
1. ATP and NADPH are received from light dependent reactions

2. 6x CO2 bind with 6x 5carbon molecules (ribulose bisphosphate) to form 6x 6carbon molecules
3. 6x 6carbon molecules split to form 12x 3carbon molecules (Glycerate-3-Phosphate)
4. 12x ATP and NADPH are oxidised to rearrange into 12x 3carbon molecule (Triose-Phosphate)
5. 2x 3carbon molecules break off to form 1 glucose
6. 10x 3carbon molecules are left
7. 6x ATP are oxidised to form 6x 5carbon molecules again (Ribulose bisphosphate)
8. Cycle occurs again in stroma

Question 6

Label the chloroplast

Answer 6

Outer membrane 
Inner membrane
Granum (whole stack of thylakoids)
Thylakoid (pancake)
Stroma (liquid)

Question 7

Stoma

Answer 7

Holes underneath leaf to allow gas exchange

Question 8

Chloroplast vs chlorophyll

Answer 8

• Chloroplast is the organelle
• Chlorophyll is the pigment in light reactions

Question 9

Explain this graph

Answer 9

Chlorophyll a and b absorb blue light and red light most. Reflecting green light giving plants their colour

Question 10

Absorption spectrum vs Action spectrum

Answer 10

Absorption = for chlorophyll. Shows absorption levels for each chlorophyll

Action = for photosynthesis. Shows relative effectiveness of photosynthesis

Question 11

Factors of photosynthesis

Answer 11

Question 12

Visible light wavelengths

Answer 12

• visible light has wavelengths between 400 and 700 nanometres
• violet has the shortest wavelength and red the longest