Photosynthesis

Question 1

In what organelle does photosynthesis occur?

Answer 1

Chloroplast

Question 2

Where does the light dependent reaction take place?

Answer 2

Thylakoid Membrane

Question 3

Where does the light independent reaction take place?

Answer 3

Stroma

Question 4

Describe the structure of the thylakoid.

Answer 4

• loads of folds so large surface area (increase the number of light-dependent reactions) and more photosynthetic proteins and electron carrier proteins, speeding up the rate if light independent reaction

Question 5

describe the process of photoionisation

Answer 5

1. light energy is absorbed in the chlorophyll
2. results in electrons becoming excited and raising up an energy level
3. causes them to break through the chlorophyll electrons are lost
   - electrons used to make ATP and reduced NADP in chemiosmosis

Question 6

describe the process of photolysis of water

Answer 6

1. light energy is absorbed by chlorophyll and splits water into: oxygen, proton, and an electron
   - oxygen is produced to be used in respiration
   - proton is picked up by NADP to form NADPH

Question 7

Describe the process of chemiosmosis and production of ATP and NADPH

Answer 7

1. electrons that gained energy and left the chlorophyll move along electron transport proteins
2. as they move down the ETC they release energy
3. energy is sued to pump H+ across the thylakoid membrane
4. creates an electrochemical gradient which enables H+ to pass through ATP synthase, this releases energy needed to synthesis ATP from ADP and Pi.
5. reduced NADP is formed from protons from photolysis of water and electron from photoionisation of chlorophyll

Question 8

Describe the process of the LDR.

Answer 8

1. Photoionisation → light energy is absorbed by the chlorophyll, resulting in electrons becoming excited and raising up an energy level to leave chlorophyll
2. Electron Transport Chain → excited electrons move down ETC
3. Photolysis of Water → the splitting of water by light into H+, e- and oxygen, the excited electrons that pass down ETC are replaced by e- from the photolysis of water
4. Chemiosmosis → ETC releases energy, allows H+ ions to be pumped through the thylakoid membrane, creating a proton gradient
5. Reduction of NADP → electron in ETC combine with H+ from photolysis of water and NADP carrier molecule to make NADPH which is passed onto the light independent reaction
6. Photophosphorylation → protons that were pumped into the thylakoid lumen return to the stroma down the proton gradient by facilitated diffusion, releases energy needed to synthesis ATP from ADP and Pi, ATP is also passed onto the LIR

Question 9

what are the 4 key stages of the light dependent reaction

Answer 9

1. photoionization of chlorophyll
2. Photolysis
3. Chemiosmosis
4. production of ATP and NADP

Question 10

what is needed for the LDR and what is formed

Answer 10

• light energy + water is needed
• ATP and reduced NADP is formed
• O2 is produced

Question 11

What is the advantage of having accessory pigments.

Answer 11

a wider range of wavelengths are absorbed therefore more light absorbed for the light dependent reaction

Question 12

Why is most of the light falling on plants not used in PHS.

Answer 12

• light is reflected
• light is the wrong wavelength
• light does not hit the chlorophyll
• co2 concentration of temperature is a limiting factor

Question 13

Describe the process of the Light Independent Reaction

Answer 13

1. CO2 reacts with ribulose biphosphate (RuBP) to form two molecules of GP (2, 3C molecules), this is catalysed by RuBisCo)
2. GP is reduced to TP using energy from ATP and Hydrogen from reduced NADP
3. 1 one of the carbon atoms is removed from cycle→ this occurs six times to form a hexose sugar
4. ATP is used to regenerate RuBP into a 6 carbon molecule from a 5C molecule

Question 14

The light independent reaction is temperature sensitive because..

Answer 14

it involves enzymes

Question 15

What are the reactions of the LIR referred to as?

Answer 15

Calvin Cycle

Question 16

What are the limiting factors for PHS.

Answer 16

• Light intensity
• CO2 concentration
• Temperature

Question 17

Describe the effect of light intensity photosynthesis

Answer 17

1. rate of photosynthesis increases as light intensity increases
2. more light= more energy supplied to plant = faster the LDR can occur = producing more ATP and reduced NADP for the Calvin cycle in LIR
   - graph levels off, rate becomes constant

Question 18

Describe the effect of CO2 concentration of photosynthesis

Answer 18

1. the rate of photosynthesis increases as CO2 concentration increases
2. higher CO2 conc= faster CO2 combines with RuBP by enzyme RuBisCo.
   - graph levels off rate becomes constant

Question 19

Describe the effect of temperature

Answer 19

1. As temperature increases the rate of photosynthesis increases up until optimum temp whereby enzymes in LIR denature and rate of photosynthesis decreases
2. Increasing temp causes stomata to close= CO2 cant enter the leaves= low rate if photosynthesis

Question 20

what is chlorophyll

Answer 20

pigment that catches energy from the sun, which the plant then uses for photosynthesis
- each pigment absorbs a different wavelength of light