Unit 4: Photosynthesis

Question 1

Why can’t plants use the ATP produced in the light dependant reaction AS THEIR ONLY SOURCE?

Answer 1

1) Photosynthesis can’t produce ATP in the DARK

2) Plant needs more ATP than can be produced in photosynthesis

Question 2

Describe how NADP is reduced in the light-dependant reaction

Answer 2

NADP + e- + H+ —-> Reduced NADP

the electrons come from the Electron Transport Chain and H+ ions come from PHOTOLYSIS OF WATER

Question 3

Describe how light energy generates ATP in the light-dependant reaction (4 MARKS)

Answer 3

CHLOROPHYLL present in plant’s leaf captures light from the sun. This [absorption of light EXCITES the electrons] causing them to be [emitted from the chlorophyll molecule] so chlorophyll molecule is oxidised. These electrons are then [carried by electron carriers down the Electron Transport Chain]. In ETC, electron PASSAGE involves REDOX REACTIONS. Each time they [move to lower energy levels, lil’ bit of energy is released]. This energy used to [synthesise ATP:
[ADP + Pi + Energy ——> ATP]

Question 4

Equation for Photosynthesis?

Answer 4

6C02 + 6H2O + Energy ——-> Glucose (C6H12O6) + 6O2

Question 5

Equation for PHOTOLYSIS of Water?

Answer 5

H2O —–> 2H+ + 1/2 02 + 2e-

Question 6

Photosystem I absorbs light at the best wavelength…

Answer 6

700 nm

Question 7

Photosystem II absorbs light at the best wavelength…

Answer 7

680 nm

Question 8

Where do the light-dependent and light-independent reactions take place?

Answer 8

light-dependent = thylakoid membrane of chloroplast
light-independent = stroma

Question 9

What is another name for the light-independent reaction?

Answer 9

CALVIN CYCLE

Question 10

What do the electrons from the photolysis of water go?

Answer 10

these electrons REPLACE the electrons LOST from the CHLOROPHYLL molecule

Question 11

Describe the Light-Independant reaction: (7 marks)

LOL good luck…

Answer 11

• RuBP and CO2 join together, forming an UNSTABLE 6 carbon compound.
• this reaction catalysed by enzyme rubisco
• the 6 C compound quickly breaks down into 2x 3 carbon compound called GP
• this converted to 2x TP
• energy for this reaction comes from ATP and H+ ions comes from Reduced NADP
• RuBP is regenerated from TP molecules
• and ATP provides energy to do this

Question 12

6 turns of the Calvin Cycle requires how many ATP and how many Reduced NADPs?

Answer 12

18 ATP and 12 Reduced NADPs

Question 13

What are the Optimum conditions for Photosynthesis? (3 marks)

Answer 13

• High light intensity
  chlorophyll a, chlorophyll b and carotene only absorb RED AND BLUE light in sunlight
• 25 degrees temperature
• Carbon dioxide = 0.4%

Question 14

Why is it bad for a plant if the temperature exceeds 25 degrees?

Answer 14

• enzymes denature e.g. rubisco and ATP synthase

- at high temp, stomato CLOSE to prevent water loss so less CO2 enters through leaf

Question 15

Explain why CO2 uptake is a measure of NET productivity

Answer 15

Shows (gross) photosynthesis

Question 16

How is NADP reduced in the light-dependent reaction of photosynthesis?

Answer 16

electrons from chlorophyll