5.1 photosynthesis

Question 1

define photosynthesis

Answer 1

the process where the energy from light is used to make glucose from water and carbon dioxide

Question 2

what are the 2 reactions in photosynthesis and which happens first

Answer 2

light dependant reaction - happen first
light independent reaction

Question 3

3 things about light LDR
1. what need?
2. where?
3. what happens?

Answer 3

1. needs light
2. takes place in the thylakoid membranes
3. light energy is converted to chemical energy

Question 4

3 things about light LIR
1. what need?
2. where?
3. what happens?

Answer 4

1. does not use light directly
2. takes place in the stroma
3. where glucose is made using the ATP for the light dependant reaction

Question 5

step 1 of light dependant reaction

Answer 5

Chlorophyll from PSII absorbs light energy.
Delocalised electrons become excited and leave via an electron transport chain in the membrane

Question 6

step 2 of light dependant reaction

Answer 6

Electrons from PSII lose energy as they pass down the ETC, this energy is used to translocate H+ ions into the thylakoid
Chemiosmosis - the H+ ions diffuse back to the strong via ATP synthase in the membrane. This catalyses the synthesis of ATM (from ADP to Pi)

Question 7

step 3 of light dependant reaction

Answer 7

Excited electrons from PSI are transferred to a carrier molecule and used to reduce NADP to become NADPH.
Photolysis of water replaces the electrons lost from PSII and oxygen is produced as a by-product

Question 8

step 1 of light independent reaction

Answer 8

CO2 enters the leaf and is combined with RuBP catalysed by the enzyme rubisco. This breaks into 2 GP molecules

Question 9

step 2 of light independent reaction

Answer 9

Each of the GP molecules are reduced trough the redox reaction when NADPH is oxidised and GP reduced. The hydrolysis of the ATP into ADP+Pi provides the energy and the ADP+Pi and NADP go back to the LDR.
The GP becomes Triosephosphate another ATP is needed for the regeneration of RuBP

Question 10

step 3 of light independent reaction

Answer 10

5 of the 6 molecules of triose phosphate are not used for the glucose/useful organic compounds but are used to regenerate RuBP. Using the last of the ATP from the LDR

Question 11

what are 4 factors affecting photosynthesis

Answer 11

1. high light intensity of certain wavelengths
2. temperature
3. carbon dioxide at 0.4%
4. without a constant supply of water

Question 12

how does high light intensity of certain wavelengths affect photosynthesis

Answer 12

light is needed to provide the energy for the LDR - the higher the intensity of the light the more energy it provides.
only certain wavelengths of light are used for photosynthesis

Question 13

how does temperature affect photosynthesis

Answer 13

photosynthesis involves enzymes, if temperature falls below 10*C these enzymes become inactive.

Question 14

how does Carbon dioxide at 0.4% affect photosynthesis

Answer 14

Carbon 0.04% dioxide makes up of the gases in the atmosphere increasing this to 0.4% gives a higher rate of photosynthesis but any higher and the stomata start to close.

Question 15

How does constant supply of water affect photosynthesis

Answer 15

Too little and photosynthesis has to stop.
Too much and the soil becomes waterlogged (reducing the uptake of minerals)