3.5.1 - Photosynthesis

Question 1

Howmany stages does photosynthesis have ?

Answer 1

2 - the light dependent reaction and light - independent reaction.

Question 2

Where does photosynthesis occur ?

Answer 2

The chloroplast of the plant cell, but in different locations.

Question 3

Where do the LDR and LIR occur?

Answer 3

LDR - on the thylakoid membraines/ grana
LIR - occurs in the stroma

Question 4

What is the LDR ?

Answer 4

The first stage of photosynthesis, requiring light.
Light energy and H2O are used to created ATP and NADPH for the LIR.

Question 5

What is photolysis?
Equation ?

Answer 5

The splitting of water by light energy
2H2O –> O2 + 4e- + 2H+

Question 6

What are the different substances in photolysis used for ?

Answer 6

H+ : picked up by NADP to form NADPH and is used in the LIR
e- : Passed along a chain of electrons by carrier proteins
O2 : respiration or diffuses out

Question 7

Process of LDR (1) - Photosystem 2

Answer 7

• Light at the red - blue/violet end of the spectrum hits the magnesium ion
• Causes electrons to become excited as the energy level increases
• Chlorphyll is oxidsied, PA will become reduced
• The high energy e- is transported down an ETC via sequential redox reactions.
• The energy is transferred to a proton pump, accumulates H+ against a con grad
• This flows through ATP synthase
• The proton motive force allows ATP synthase to synthesise ATP from ADP + Pi

Question 8

Describe the process of photosystem 1

Answer 8

• Light at the red blue/violet hits the Mg ion in the chloroplast and photoionisation takes place.
• The energy level of the e- is raised and it is lost from the chlorophyll. The chlorophyll is oxidised and the PA in the ETC is reduced.
• The e- is transported down the ETC via sequential oxidation/reduction reactions
• The electron is taken up by NADP reductase which turns NADP and a proton into NADPH

Question 9

What is the LIR also known as ?

Answer 9

The Calvin Cycle

Question 10

Where does the Calvin Cycle occur?
What does it contain ?

Answer 10

The stroma
It contains the enzyme RuBisCo which catalyses this reaction

Question 11

What are the roles of ATP and NADPH in this reaction ?

Answer 11

ATP when it is hydrolysed provides energy for the reaction, the NADPH donates the H+ to reduce the molecules of GP in the cycle.

Question 12

Process of the Calvin Cycle (LIR)

Answer 12

• CO2 reacts with RUBP to form two molecules of GP and this reaction is catalysed by Rubisco.
• GP is reduced to TP using energy from ATP and by accepting a H from NADPH.
• From the two molecules of TP produced, 1 of the C atoms is removed each time the cycle turns
• When the cycle has occured 6 times, a hexose sugar is formed.
• The left over 5 carbons are used to regenerate RUBP.

Question 13

Howmany carbons do each of these compunds have :
- RUBP
- Hexose sugars
- GP
- TP

Answer 13

• 5c
• 6c
• 3c per molecule so 6 in total
• 3c per molecule so 6 in total

Question 14

What does TP form when it leaves the cycle ?

Answer 14

Useful organic substances

Question 15

What are some useful organic (carbon containing compounds) that the hexose sugars may form ?

Answer 15

• Disaccharides - sucrose
• Polysaccharides - cellulose and starch
• Glycerol, and then it can combine with fatty acids to make lipids
• AAs for proteins and nucleic acids - DNA and RNA

Question 16

What are the limiting factors of photosynthesis ?

Answer 16

Temperature
Carbon dioxide concentration
Light intensity

Question 17

How does temperature affect the rate of photosynthesis ?

Answer 17

This affects the LIR due to it being enzyme controlled
- too cold - not enough energy
- too hot - denatured

Question 18

How does CO2 affect the rate of photosynthesis ?

Answer 18

• Has an effect on the LIR due to it being one of the reactants entering the Calvin Cycle.

Question 19

How does light intensity affect the rate of photosynthesis ?

Answer 19

• It is required for the LIR for it to hit the magnesium ion for photoionsiation to take place
• It is also needed for photolysis to take place.

Question 20

What does knowledge of limiting factors allow ?

Answer 20

Allows farmers to have the understanding of what conditions to manipulate in which they grow their plants.

Question 21

What are some ways in which farmers manipulate conditions ?

Answer 21

• Artificial lighting of the maximum intensity
• Heating the greenhouse to increase temperature
• Burning fuel (i.e, paraffin burners) to release more CO2

Question 22

What does the farmer have to consider within their agricultural practices ?

Answer 22

The profit
- To pay for lighting, heating, fuel, the farmer must consider the cost
- Whatever he is paying, is he getting more profit for it ?