Photosynthesis

Question 1

How are photosynthesis and respiration related

Answer 1

Carbon dioxide and water are raw materials for photosynthesis and products of respiration
O2 and glucose are the raw materials for photosynthesis and the products of respiration

Question 2

Describe the structure of a chloroplast

Answer 2

Usually disc shaped
Double membrane
Thylakoids- flattened discs stack to form grana
Intergranal LAMELLAE - tubular extensions attach thylakoids in adjacent grana
Stroma fluid filled matrix with high enzyme and substrate concentration of own loop of DNA

Question 3

How are chloroplast adapted to photosynthesis

Answer 3

Strong- gel like fluid contains enzymes that catalyse the reactions of the light independent stage
Grana - granal stack creates a large SA for the prescient of many photosystems
DNA- chloroplast DNA contains genes that code for some protein and enzymes used in photosynthesis

Question 4

How many stages does photosynthesis occur

Answer 4

Light dependent stage, takes place in the thylakoids

Light independent stage- takes place in the stroma

Question 5

What occurs during the light dependent stage

Answer 5

Light energy breakdown water to produce hydrogen ions,electrons and oxygen in the thylakoid lumen
Proton gradient is formed

Question 6

Define photosynthetic pigment

Answer 6

Coloured substances that absorb the light energy needed for photosynthesis
E.g chlorophyll a,chlorophyll b
Found in the thylakoid membranes

Question 7

What are photosystem

Answer 7

Pigments attached to proteins
Contains two types - primary and accessory
Primary - reaction centres, electrons are excited
Accessory - light harvesting systems, transfer light energy,

Question 8

What are the two photosystem that are used to capture light energy

Answer 8

Photosystem 1 - absorb light wavelength of 700nm

Photosystem 2- absorb light best at 680nm

Question 9

Name the processes in the light dependent reaction

Answer 9

Photoionsation 
Electron transfer chain 
Chemiosmosis
Non cyclic 
Reduction of NADP
photolysis of water

Question 10

Define photoionisation

Answer 10

Excites electrons

Question 11

Explain the role of light in photoionisation

Answer 11

Chlorophyll molecules absorb energy from photons of light

Excites 2 electrons(raises them to a higher energy level) causing them to be released from the chlorophyll

Question 12

What happens in the electron transfer chain

Answer 12

Electrons releases from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions, releases energy

Question 13

How does chemiosmosis produce ATP in the light dependent stage

Answer 13

Some energy releases from the ETC is couples in active transport of H+ ions from the stroma into thylakoid space
H+ moves down concentration gradient from thylakoid space into stroma via transmembrane protein ATP synthase
ATP synthase catalyse ADP+ pi -> ATP

Question 14

Describe non cyclic photophosphorylation

Answer 14

Uses PS1 and 2
Excites electrons enter ETC to produce ATP
NADP acts as final electron acceptor and is reduced
Water is photolysed to release electrons to replace those lost from PS 2
Produce ATP and reduced NADP

Question 15

Describe cyclic photophosphorlyation (adding phosphate using light)

Answer 15

Uses PS1
Excited electrons enter ETC to produce ATP the return directly to phosystem
Purpose- produce additional ATP

Question 16

What happens to the products of the photolysis of water

Answer 16

H+ ions move out of thylakoid spaces via ATP synthase and are used to reduce the co enzyme NADP
E- replace electrons lost from chlorophyll
O2 used for respiration or diffuses out of leaf as waste product

Question 17

How and where is reduced NADP produced in the light dependent reaction

Answer 17

NADP+2H+(from photolysis of water) + 2e- (from acting as final electron acceptor in ETC)- reduced NADP
Catalysed by dehydrogenase enzymes
Stroma of chloroplast

Question 18

Name the 3 main stages in light dependent reaction

Answer 18

Carbon fixation
Reduction
Regeneration

Question 19

Explain how ribulose bisphosphate (RuBP) is regenerated in the Calvin cycle

Answer 19

Regenerated from triose phosphate

ATP provides the energy to do this

Question 20

Name the products of the light dependent stage of photosynthesis

Answer 20

Reduced NADP
ATP
Oxygen

Question 21

Explain why it is incorrect to say energy is produced

Answer 21

Energy cannot be created or destroyed instead energy is transferred and ATP is produced

Question 22

Explain why ATP is not a good energy storage molecule but why organic molecules, like lipids and carbohydrates are

Answer 22

ATP is not very stable, easy to remove phosphate group, organic molecules are more stable and OM such as glycogen are more energy dense

Question 23

Explain the interrelationship between respiration and photosynthesis in organisms

Answer 23

Photosynthesis: light energy is converted into chemical energy, inorganic molecules are converted into organic molecules, water and CO2 are converted to glucose and oxygen
Respiration: uses o2 prod. in photosynthesis, organic molecules broken down into inorganic molecules, energy released to synthesis ATP

Question 24

Explain the importance of ATP to living organisms

Answer 24

Universal energy currency, energy transfer is quick, ATP can be re synthesised

Question 25

Describe the properties of cell membrane necessary for the formation of a proton gradient

Answer 25

Contains embedded protein such as ATP synthase which is responsible for the synthesis of ATP

Question 26

Name the type of diffusion which enables protons to move through ATP synthase and explain the role of ATP synthase in the production of ATP

Answer 26

Facilitated diffusion, ATP synthase provides hydrophilic channel for diffusion of protons, catalyses the synthesis of ATP, lowers activation energyb

Question 27

ATPase and ATP synthase are the same enzyme,explain how this is possible

Answer 27

Reversible reaction, the products formed from reaction in one direction are the substrates of reaction in reverse direction
Active site is complementary to both substrates and products

Question 28

Explain the meaning of the term photophosphorylation

Answer 28

Syntheiss of ATP/addition of phosphate group to ADP by using energy from light

Question 29

Explain why photoysntheis stops when plants are exposed to green light

Answer 29

Green is reflected and not absorbed. No energy for light dependent stage, no ATP and reduced NADP for light independent stage

Question 30

Explain what is meant by the term fixation

Answer 30

Inorganic carbon added to organic molecule

Question 31

Explain why the alternate name of the Calvin cycle, the light independent stage, is also not completley accurate

Answer 31

Calvin cycle requires ATP and reduced NADP, supplied from light dependent stage

Question 32

Suggets the possible benefits of cyclic photophosphoryation

Answer 32

ATP produced and reduced NADP not produced, electrons not required from PS2, less ATP used in calvin cycle

Question 33

Describe how RuBP is regenerated from TP in the Calvin cycle

Answer 33

One glucose molecule to be produced = 6 CO2 enter calvin cycle
Result in 12 TP, two will be removed to make glucose molecule
10 x three carbon TP =30