Photosynthesis

Question 1

Label the structure of chloroplast

Answer 1

See notes include
- granum
- lamella
- ribosomes
- stoma
- outer membrane
-inner membrane
- starch grain
- thylakoid
- lipid droplet

Question 2

What photosynthetic pigments do plants contain

Answer 2

Chlorophyll ( a & b)
Carotenoid (b-carotene & xanthophyll)

Question 3

explain why plant benefits from having pigments that absorb different wavelengths
E,g what does chlorophyll absorb

Answer 3

Each pigment absorbs slightly different wavelengths so having different pigments plants maximise the wavelengths of light they can absorb energy from
E.g chlorophyll absorbs blue and red wavelengths of visible light

Question 4

Absorption spectrum shows…

Answer 4

% light of different wavelengths absorbed by isolated pigments

Question 5

What type of light does chlorophyll absorb

Answer 5

Blue and red wavelengths

Question 6

Action spectrum shows..

Answer 6

Rate of photosynthesis of plants exposed to different wavelengths of light

E.g. highest rates of photosynthesis stimulated by blue and red wavelengths of light

Question 7

Def of photosystem

Answer 7

Light- harvesting cluster of pigment molecules in the thylakoid membrane

Question 8

What is photosystem I and photosystem II?

Answer 8

Photosystem I
Reaction centre (cluster of pigment molecules) = chlorophyll A with peak absorption 700nm

Photosystem II
Reaction centre (cluster of pigment molecules) = chlorophyll A with peak absorption 680nm

Question 9

Role of accessory pigments in photosystem
(Examples of pigments)

Answer 9

Accessory pigments (Chlorophyll A & B and carotenoids) pass energy from light to the chlorophyll A at the reaction centre for start of photosynthesis

Question 10

Def of Photophosphorylation

Answer 10

The synthesis of ATP using energy harvested from light

Question 11

The process of cyclic photophosphorylation (photosystem I)
(5 steps)

Answer 11

1) light energy excites electron from chlorophyll A in photosystem I
2) electron passes down electron transport chain (ETC) in the thylakoid membrane
3) energy lost from electron used to pump protons across membrane into thylakoid lumen
4) protons diffuse through ATP synthase & energy is used to synthesis ATP
5) electron returns to chlorophyll molecule

Question 12

Compare photophosphorylation & oxidative phosphorylation
1) organelle
2) location of ETC
3) Location of high [H+]
4) source of high energy electrons

Answer 12

organelle
Photo) Chloroplast
OP) mitochondrion

location of electron transport chain
Photo) thylakoid membrane
OP) inner mitochondrion membrane

location of high H+ concentration
Photo) thylakoid lumen
OP) inter mitochondrion membrane

source of high energy electrons
Photo) chlorophyll A
OP) glucose

Question 13

What does the light- dependent reaction of photosynthesis (non-cyclic phototphosphorylation) involve?

Answer 13

-both photo systems 1 & 2
- synthesis of ATP and reduced NADP
- the splitting of water (photolysis)

Question 14

Process of photolysis

Answer 14

1) energy from light used to split water into
H2O —> 2H+. + 2e- + 1/2 O2

2) electrons from water replace electrons lost from chlorophyll a and PS2

Question 15

Explain the differences between cyclic and non-cyclic photophosphorylation

Answer 15

Cyclic
- only photosystem 1 used
- exited electrons return to photosystem 1 to go through cycle again
- no photolysis
- only ATP produced
- produces steady supply of ATP in presence of sunlight

Non-cyclic
- photosystems 1 & 2 used
- exited electrons enter photosystem 1 to be picked up by NADP —> reduced NADP
- photolysis of water replenishes electrons lost to photosystem 1
- produces both NADPH and ATP
- allows for synthesis’s of organic molecules for long term energy

Question 16

Summaries non-cyclic photophosphorylation into a diagram

Answer 16

• light absorbed by photosystem 2, exited electron enters into an electron transport chain to produce ATP
• photoactivation of photosystem 1 results in the release of electron which reduce NADP+ ( to from reduced NADP)
• the photolysis of water releases electrons which replace those lost by photosystem 2

Question 17

Step by step of non-cyclic photophosphorylation

Answer 17

1. Photons are absorbed by PSII
2. An e- is exited and reduces and e- accpetor
3. The e- passed onto ETC
4. At the of ETC from PSII an electron replaces that lost at PSI
5. ETC drives H+ into thylakoid lumen
6. Protons pass through ATP synthase due to the concentration gradient (chemiosmosis) generating ATP from ADP + Pi
7. Protons diffused through ATP synthase are available to reduce NADP
8. Photons also absorbed y PSI
9. E- exited and reduces e- acceptor
10. The ETC (in PSI) transfers e- to NADP forming reduced NADP
11. Photolysis of water provides e- to replace those lost from PSII, proton contributes to chemiosmosis, O2 is waste

Question 18

Where does Calvin cycle take place

Answer 18

The stroma of the chloroplast

Question 19

What is required for the Calvin cycle to occur

Answer 19

CO2
ATP
Reduced NADP
RUBISCO enzyme

Question 20

Steps of the Calvin cycle

Answer 20

1. Enzyme RUBISCO catalyses the reaction combining CO2 and RuBP
   This forms 2x GP (3 carbon glycerate 3- phosphate)
2. The hydrolysis of ATP provides energy to reduce 2x GP to 2x TP (3 carbon triose Phosphate)
   This reaction requires H+ ion from reduced NADP which recycles back to NADP
3. Some of the TP is then converted into useful organic compounds like glucose and some continues in the. Calvin cycle to regenerate RuBP
4. 5/6 molecules of TP produced in the cycle are used to regenerate RuBP (5x carbon)
   Regenerating RuBP uses energy released from ATP

Question 21

4 main stages in Calvin cycle

Answer 21

1. Carbon fixation
2. Reduction of GP
3. Formation of glucose
4. Regeneration of RuBP

Question 22

How is CO2 used in the Calvin cycle

Answer 22

CO2 is used as a reactant that combines with RuBP. This reaction is catalysed by RUBISCO. To from 2 molecules of 3 carbon GP

Question 23

Where is ATP used in the Calvin cycle

Answer 23

ATP is used in 2 places in the Calvin cycle

1) ATP is used to redcue GP into TP
2) ATP is used in the reaction to regenerate RuBP from TP

Question 24

If the light dependent reactions were inhibited why would this also stoop the light-independent reaction

Answer 24

The light dependent reactions (non-cyclic) produces ATP molecules and reduced NADP which are both used in the Calvin cycle to allow it to occur.
ATP is hydrolysed to provide energy for GP to be reduced by reduced NADP into TP
Without these this stage could not occur preventing the Calvin cycle continuing
ATP is also used in the regeneration of RuBP
Without RuBP not GP can be produced again preventing the Calvin cycle continuing

Question 25

How are hexose sugars like glucose formed during the Calvin cycle

Answer 25

The Calvin cycle needs 6 x turns to make 1 hexose sugar *this is due to 2 molecules of TP are produced from every 1 CO2 used. 5/6 of the TP molecules are used to regenerate RuBP. This means that for 3 cycle turns only 1 TP used to make Glucose and TP is a 3 carbon so 2 are needed*

Question 26

What is needed in the calvin cycle (how many of each molecule) to allow 1 glucose to be formed

Answer 26

18 ATP 12 reduced NADP 6 Carbon dioxide

Question 27

How are other organic molecules like lipids and proteins formed from molecules produced in the Calvin cycle

Answer 27

**lipids** - made using glycerol, synthesised from Triose phosphate (TP) , and fatty acids, synthesised from glycerate 3- phosphate (GP) **amino acids** - some amino acids are made from glycerate 3-phosphate (GP)

Question 28

What are limiting factors of photosynthesis?

Answer 28

- light intensity - carbon dioxide concnetration - temperature (Water)

Question 29

Why is light intensity a limiting factor of photosynthesis

Answer 29

Pigments absorb light to produce high energy electrons which are needed to synthesise ATP and reduced NADP, both of which are required to use CO2 in Calvin cycle to produce sugar. So in low light intensities rate of photosynthesis is low, an increase in light intensity causes an increase in photosynthesis.

Question 30

Why is carbon dioxide concentration a limiting factor for photosynthesis

Answer 30

CO2 is reactant which sugars are made from in the Calvin cycle, lower CO2 concentrations means lower rate of reaction

Question 31

Why is temperature a limiting factor to photosynthesis

Answer 31

The reaction of Calvin cycle are catalysed by enzyme. Enzyme activity is dependent on temperature, reading the temperature means reduced rate of reaction. Increase temperature too high, proteins denature so rate of reaction decreases.

Question 32

Explain what the most ideal conditions for plants in the UK

Answer 32

High light intensity of a certain wavelength - different pigments absorb different wavelengths so more wavelengths absorbed by chloroplast A & B and carotene the more photosynthesis Temperature around 25oC - if below 10oC photosynthesis enzymes can become inactive, but more than 45oC they denature. Also increased temperature too high = water loss so plants close stomata decrease availability of CO2 CO2 at 0.4% - rate of photosynthesis is at maximum rate here, any higher concentration stomata dose so rate decreases

Question 33

How can farmers manage limiting factors of photosynthesis

Answer 33

Light intensity - farmers use glasshouses to prevent this being limited as light can get through the glass, lamps can also provide light at night time Temperature - glasshouses trap heat energy from the sun which warms the air. Heaters and cooling systems can also be used to keep a constant optimum temperature Carbon dioxide concentration - Carbon dioxide is added to the air, e.g. by burning a small amount of propane in a CO2 generator