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

• large surface area (increase the number of light-dependent reactions)
• pigments arranged in photosystems (optimises the amount of light absorbed)

Question 5

Describe the process of the LDR.

Answer 5

1. Photoionisation → light absorbed by PSII, this excites two electrons to a higher energy level
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. 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
5. Chemiosmosis → ETC releases energy, allows H+ ions to be pumped into the thylakoid space, creating a proton gradient
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 6

What is the advantage of having accessory pigments.

Answer 6

Carotenoids can absorb different wavelengths of light so maximises the amount of light that can be used for photosynthesis.

Question 7

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

Answer 7

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

Question 8

Describe the process of the LIR.

Answer 8

1. Carbon fixation → carbon dioxide combines with 5C carbon called RuBP, this is catalysed by rubisco, forms unstable 6C compound that splits into 2, forms two molecules of GP
2. Reduction of GP → energy from ATP and hydrogen from reduced NADP are used to reduce GP to a phosphorylated 3C sugar known as triose phosphate (TP), 1/6 used to produce useful organic products needed for the plant (starch/sucrose/cellulose, TP (glycerol) + GP (fatty acids) to make lipids, amino acids)
3. Regeneration of RuBP → 5/6 of TP used to regenerate RuBP, this requires energy from ATP

Question 9

What are the reactions of the LIR referred to as?

Answer 9

Calvin Cycle

Question 10

What are the limiting factors for PHS.

Answer 10

• Light intensity
• CO2 concentration
• Temperature