✅11 - Photosynthesis

Question 1

Where is the site of photosynthesis?

Answer 1

The chloroplasts, within the leaf

Question 2

How are the leaves adapted for photosynthesis?

Answer 2

Large surface area to absorb light
Little overlapping of leaves
Thin, most light is absorbed in top few micrometers
Transparent cuticle/epidermis that let light through to mesophyll cells
Long, narrow upper mesophyll cells with many chloroplasts
Numerous stomata for gas exchange
Air spaces between mesophyll to allow raid diffusion

Question 3

What is the equation for photosynthesis?

Answer 3

6CO2 + 6H20 ———> C6H12O6 + 6O2

Question 4

What are the stages of photosynthesis?

Answer 4

Capturing light energy
Light dependent reaction
Light independent reaction

Question 5

What is the stroma?

Answer 5

A fluid filled matrix where the light independent reaction takes place.

Question 6

What is photoionisation?

Answer 6

When chlorophyll is struck by light and an electron is removed.

Question 7

Where do the electrons from photoionisation go?

Answer 7

They are taken up by an electron carriers

Question 8

Describe chemiosmotic theory:

Answer 8

Proton pumps pump H+ ions into the thylakoids through the cell membrane
Energy used for this process comes from electrons released by the photolysis of water
Photolysis also produces protons which increase concentration in thylakoids space
-Creates and maintains a concentration gradient across thylakoids membrane
Protons cross membrane through ATP synthase channels
As the protons pass through the cause a change of structure of enzyme which catalysts synthesis of ATP

Question 9

What is photolysis?

Answer 9

The splitting of water using light

Question 10

What is the equation for photolysis?

Answer 10

2H2O ———> 4H+ + 4e- +O2

Question 11

What happens to the protons produced by photolysis?

Answer 11

The pass out of the thylakoids through ATP synthase and are taken up by NADP,which goes to the light independent reaction

Question 12

What are the products of the light dependent reaction?

Answer 12

ATP, NADPH and Oxygen (byproduct)

Question 13

How are chloroplasts adapted to carry out the light dependent reaction?

Answer 13

• Thylakoids membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes
• A network of proteins in the Grana hold the chlorophyll in a very precise manner that allows maximum light absorption
• The Granal membranes have ATP synthase channels within them which catalyse ATP production, also selectively permeable which allows a proton gradient to form
• Chloroplasts have DNA and ribosomes so they can quickly and easily manufacture some of the proteins involved in LDR

Question 14

What are the products of the LDR use for?

Answer 14

To reduce glycerate-3-phosphate in the LIR

Question 15

Why does the LIR cease to occur without light?

Answer 15

It requires the ATP and NADH from the light dependent reaction to function

Question 16

Where does the light independent reaction take place?

Answer 16

In the stroma

Question 17

Describe the Calvin cycle:

Answer 17

• CO2 from atmosphere diffuses into leaf and dissolves in water around mesophyll cell walls, then into stroma
• CO2 reads with Ribulose Bisphosphate, catalysed by Rubisco
• This produces 2x glycerate-3-phosphate
• NADPH from LDR used to reduced it to 2x triose phosphate using ATP
• NADP reformed and goes back to LDR to be used again
• Some TP converted into organic substances
• Most used to regenerate RuBp using ATP from LDR

Question 18

How is the chloroplast adapted to the Light Independent Reaction?

Answer 18

• The stroma contains all enzymes needed
• Stroma is membrane bound which means chemical environment has high concentration of enzymes and substances
• Stoma fluid surrounds the Grana so products of LDR can readily diffuse into the stroma
• Contains DNA and Ribosomes so can quickly and easily manufacture some of proteins needed

Question 19

Where in the cell is rubisco found?

Answer 19

In the stroma of the chlorplast

Question 20

Where does the light depenedent reaction take place?

Answer 20

In the thylakoid membrane

Question 21

What absorbs light?

Answer 21

Chlorophyll

Question 22

What process is ATP made by in the light dependent reaction?

Answer 22

Photophosphorylation

Question 23

Why does the LIR occur less if the LDR occurs less?

Answer 23

Because there are less products (ATP and NADPH) of the light dependent reaction, so the LIR occurs less

Question 24

What is chemiosmosis?

Answer 24

The process of electrons flowing down the electron transport chain and creating a proton gradient across the membrane to drive ATP synthesis

Question 25

How does CO2 enter the leaf?

Answer 25

Through the stomata, and diffuses into the stroma of the chlorplast

Question 26

What is CO2 combined with?

Answer 26

Ribulose Bisphosphate, RuBP

Question 27

How many many of the Carbons in TP are used to regenerate RuBP?

Answer 27

5

Question 28

What is the leftover carbon from TP used to make?

Answer 28

Useful organic substances

Question 29

How many molecules of TP does 3 turns of the cycle create?

Answer 29

6

Question 30

How many times would the Calvin cycle have to turn to create a hexose sugar?

Answer 30

6

Question 31

What does 6 turns of the Calvin cycle require?

Answer 31

18 ATP and 12 NADPH

Question 32

At what wavelength does photosystem 1 absorb light?

Answer 32

700nm

Question 33

What is non-cyclic phosphorylation?

Answer 33

The light independent reaction

Question 34

What is cyclic phosphorylation?

Answer 34

The calvin cycle/light dependent reaction