Photosynthesis

Question 1

How is the plant leaf is adapted to carry photosynthesis?

Answer 1

-Plant cells have chloroplasts
-Chlorophyll (in thylakoid membrane) absorbs light energy for the photoionisation of chlorophyll.
-Thylakoid membranes contain photosystems
-Stroma, contained in the inner membrane of chloroplast contains enzymes, sugars and organic acids, and stores carbohydrates produced by photosynthesis as starch grains.

Question 2

What is the main stages of Photosynthesis?

Answer 2

1. Light-dependent reaction uses light energy and water to produce ATP, NADPH, and oxygen.
2. The Calvin cycle uses ATP, NADPH, and carbon dioxide to create sugar.

Question 3

What are the stages of the Light-Dependent Reaction?

Answer 3

Takes place in the Thylakoid Membrane of the chloroplast?
1. Light energy excites electrons in chlorophyll
- Light Energy absorbed by PSII
- Energy excites electrons in chlorophyll and moves to a higher energy level
- High energy electrons released from chlorophyll. moves down the ETC to PSI
2. Photolysis of H2O products
-(photolysis) Light energy splits water into protons (H+), e-, and oxygen.
-H2O to 2H+ and 1/2O2
3. Energy from excited e- makes ATP.
-Excited electrons lose energy down the ETC
-energy transports H+ into thylakoid, thylakoid has a higher proton concentration than stroma. Proton gradient formed across the thylakoid membrane.
-Protons move down conc. gradient, into the stroma. via enzyme ATP synthase, embedded in the thylakoid membrane.
-Energy from this drives the formation of ATP, combining ADP and Pi.
4. Reduced NADP
-light energy absorbed by PSI, excites electrons to even higher energy levels. Electrons transferred to NADP and proton H+ ion from stroma to produce NADPH.

Question 4

Describe the stages of the Light Independent Reaction (Calvin Cycle).

Answer 4

1. CO2 combines with RuBP to from 2x GP
   -CO2 enters the leaf through stomata, and diffuses into the stroma of chloroplast.
   -CO2 combines with RuBP (5C), catalysed by rubisco
   -Creates 6 C compound, breaks down into 2x 3C compound called glycerate 3-phosphate
2. ATP and NADPH required to reduce GP to TP
   -hydrolysis of ATP (from LDR) provides energy to convert GP to TP.
   -requires H+ ions from NADPH (from LDR), recycled to NADP
   -TP converts into useful organic compounds e.g glucose, and some continue in the cycle to regenerate RuBP.
3. RuBP is regenerated
   -5/6 TP molecules used to regenerate RuBP, uses the rest of the ATP produced by LDR.

Question 5

How many times does the Calvin Cycle needs to turn to make one hexose sugar and why?

Answer 5

-6
-Three turns in the cycle produce 6 molecules of TP as 2 TP made for every CO2 mol used
-5/6 TP molecules used to regenerate RuBP
-3 turns, one TP produced used to make hexose sugar.
-hexose sugar has 6C, two TP molecules needed to form 1 hexose sugar.
-cycle turns six times to produce 2 TP molecules, used to make 1 hexose sugar
-6 turns of cycle need 18ATP and 12 NADPH from the LDR

Question 6

In photosynthesis what is oxidised and what is reduced?

Answer 6

In photosynthesis water is oxidised and CO2 is reduced to carbohydrates

Question 7

Photolysis in LDR

Answer 7

Photolysis of H2O,
light energy splits water into protons (H+ions), electrons and oxygen.

Question 8

Role of ATP in LIR

Answer 8

hydrolysis of ATP (from LDR) provides energy to convert GP to TP

Question 9

Role of NADPH

Answer 9

requires H+ ions from NADPH (from LDR), recycled to NADP

Question 10

How is CO2 incorporated into organic molecules?

Answer 10

CO2 combines with RuBP (5C), catalysed by rubisco

Question 11

What are the optimum conditions for photosynthesis?

Answer 11

1. High Light Intensity to provide energy for LDR, the higher the light intensity, the more energy it provides.
2. Temperature (25)
   -enzymes (ATP and Rubisco). below 10 enzymes inactive, over 45 enzymes denature
   -high temp stomata close to avoid water loss. slows photosynthesis rate, less CO2 can enter
3. CO2 at 0.4% increases the rate of photosynthesis, any higher stomata close.

Question 12

How do farmers overcome limiting factors?

Answer 12

CO2 conc- added to the air, by burning propane
Light- Glass so light can get through, lamps at night time
Temperature- Glasshouses trap heat energy from sunlight, and warm the air. Heaters and cooling systems for optimum temperature and air circulations to ensure even temp in a glass house.

Question 13

How reducing factors limit photosynthesis?

Answer 13

-factors too low or high, limit photosynthesis, even if just one is too low and the others are too stable