5A Photosynthesis

Question 1

explain relationship between STRUCTURE and FUNCTION of granum in photosynthesis

Answer 1

1. thylakoid membrane -> big s.a so absorbs as much light energy as possible
2. thylakoid membrane -> contains lots of ATPsynthase = PRODUCES ATP in light DEP. reaction
3. thylakoid membrane -> contain photosynthetic pigments
   eg. CHLOROPHYLL (attached to proteins) to absorb light

x2 membrane chloroplasts also keeps reactants for p/s close to react

Question 2

describe how starch is formed FROM PRODUCTS of light indep. stage

Answer 2

1. 2 GALP molecules make GLUCOSE
2. glucose joined together by GLYCOSIDIC BONDS -> make AMYLOSE and AMYLOPECTIN by CONDENSATION REACTIONS
3. amylose + amylopectin = STARCH

Question 3

where does light DEPENDENT stage take place?

Answer 3

thylakoids of chloroplasts

Question 4

where does light INDEPENDENT stage take place?

Answer 4

stroma of chloroplasts

Question 5

how does light DEP. reaction generate ATP?

Answer 5

1. light energy excites e- in chlorophyll -> as they leave PS1 they are replaced by e- from PHOTOLYSIS OF H₂O
2. e- pass down electron transfer chain of e- carriers
   -> lose energy down E.T.C …
3. … allows chemiosmosis to occur
4. H⁺ ions actively pumped from a low conc. in
   stroma-> high conc. in the thylakoid = conc. grad. across thylakoid membrane
5. ATPsynthase allows H⁺ ions thylakoid->stroma
6. movement of H⁺ causes ATPsynthase to generate ATP

Question 6

in light INDEP. stage

Answer 6

• 3 ADP + Pi made from ATP
• 2 NADP made from NADPH

Question 7

ADP -> ATP

Answer 7

phosphorylation

Question 8

ATP -> ADP

Answer 8

hydrolysis

Question 9

ATP

Answer 9

adenosine triphosphate

phosphorolated nucleotide

Question 10

metabolism

Answer 10

chemical processes that occur within a living organism in order to maintain life

Question 11

outline the overall reaction of photosynthesis

IMPORTANT!!!

Answer 11

1. in light dependent stage -> light energy breaks strong covalent bonds in H₂O
2. O₂ released into atm
3. in light indep stage (Calvin cycle) fixation with CO₂ enables H₂ to be stored as glucose a respiratory fuel

Question 12

describe the light dependent stage of photosynthesis

non-cyclic phosphorylation

Answer 12

1. light energy absorbed by PSII and excites e- in chlorophyll
2. e- move along E.T.C
3. photolysis of water
   H₂O -> 2H⁺ + 2e⁻ + ½ O₂
4. e- made replace those lost in PSI
5. energy lost by e- down E.T.C used to make ATP
6. e- transferred to NADP + H⁺(from stroma) -> ↓ NADP

Question 13

how do excited e- generate ATP?

Answer 13

1. excited e- lose energy down E.T.C
2. this energy is used to transport H⁺ into thylakoids
3. so thylakoid has higher conc of H⁺ than stroma
4. forms H⁺ gradient across membrane
5. H⁺ move down conc grad into stroma via ATPsynthase
6. (chemiosmosis) - energy from this movement causes
   ADP + Pi -> ATP

Question 14

chemiosmosis

Answer 14

process where movement of H⁺ ions across a membrane generates ATP

Question 15

how is energy stored in ATP?

Answer 15

stored as chemical energy in the phosphate bond

Question 16

what enzyme catalyses the phosphorylation of ADP?

Answer 16

ATPsynthase

Question 17

how does ATP supply energy?

IMPORTANT!!!

Answer 17

• diffuses to part of cell that needs energy …
• … where it is broken down via hydrolysis into ADP and inorganic Pi …
• … causing chemical energy release from Pi bond and used by cell
• ATPase catalyses this reaction

Question 18

what enzyme catalyses hydrolysis / the breakdown of ATP to ADP?

Answer 18

ATPase

Question 19

what happens after ATP is broken down into ADP and inorganic phosphate?

Answer 19

they are RECYCLED and process starts again

Question 20

coenzyme

Answer 20

molecule that aids function of enzyme

Question 21

how do coenzymes work?

Answer 21

transfer chemical group from one molecule to another

Question 22

what is the coenzyme used in photosynthesis?

Answer 22

NADP -> tranfers H₂ from one molecule to another
-> so can red. (give H₂) or ox. (take H₂) a molecule

Question 23

what is the function of the double membrane in chloroplasts?

Answer 23

keeps reactants for p/s close to reaction sites

Question 24

what are photosynthetic pigments?

Answer 24

coloured substances that absorb light energy needed for photosynthesis

Question 25

at what wavelength does **PSI** absorb light best?

Answer 25

700nm

Question 26

at what wavelength does **PSII** absorb light best?

Answer 26

680nm

Question 27

structure and function of **stroma**

Answer 27

- contains all **enzymes, sugars and organic acids** - required for light **independent** reaction of p/s - contains **oil droplets** -> **store non-carbohydrate organic material**

Question 28

what happens at the **thylakoid membranes** in the light dependent reaction of p/s?

Answer 28

- **light** energy **absorbed** by photosynthetic pigments (eg. **chlorophyll**) in photosystems ... - ... and converted to **chemical energy**

Question 29

what does NADPH transfer to light **in**dependent reaction?

Answer 29

H₂

Question 30

what happens to H₂O in light dependent reaction?

Answer 30

ox. to O₂

Question 31

what does the calvin cycle rely on?

Answer 31

products of light dependent reaction

Question 32

what is **ATP** and **NADPH** from the light dependent reaction **used for** in the Calvin cycle?

Answer 32

3ATP used **supply energy** to catalyse GP->GALP and GALP->RuBP (regeneration of RuBP) 2NADPH used to catalyse GP->GP

Question 33

cyclic phosphorylation ## Footnote understand this

Answer 33

- **only uses PSI** - **e-** from chlorophyll are **NOT** passed onto **NADP** -> are **passed back to PSI** via e- carriers - e- are **recycled** and repeatedly flow through PSI - only produces **small amount of ATP**

Question 34

what is stage 1 of the Calvin cycle called?

Answer 34

carbon fixation

Question 35

describe the process of carbon fixation in the Calvin cycle

Answer 35

1. **CO₂ enters leaf** through **stomata** and **diffuses into stroma** of chloroplast 2. here it is **combined with RuBP** , catalysed by **RUBISCO** 3. this gives an unstable 6C compound which immediately splits into 2 3C compunds called **GP**

Question 36

what is stage 2 of the Calvin cycle called?

Answer 36

reduction of GP

Question 37

describe the process of reduction of GP in the Calvin cycle

Answer 37

1. hydrolysis of ATP from light dep. reaction provides energy to turn GP -> GALP (3C) 2. this reaction requires H⁺ (come from NADPH from light dep.) NADPH is recycled to NADP 3. 1/6 GALP is converted into useful organic compounds rest continues in Calvin cycle to regenerate RuBP ## Footnote check if its 1/6

Question 38

what is stage 3 of the Calvin cycle called?

Answer 38

regeneration of RuBP

Question 39

describe the process of regeneration of RuBP in the Calvin cycle

Answer 39

1. 2 GALP molecules used to make hexose sugar BUT 5/6 GALP used to regenerate RuBP 2. regenerating RuBP uses rest of ATP from light dep. reaction

Question 40

what organic substances can be made from products of the Calvin cycle? ## Footnote products being GP and GALP

Answer 40

- CARBS -> simple sugars eg. glucose -> polysaccharides eg. starch and cellulose (join hexose sugars) - LIPIDS made using ... -> glycerol made from GALP -> fatty acids made from GP - A.A -> some made from GP - NUCLEIC ACIDS -> **sugar in RNA (ribose) made using GALP** ## Footnote go into more detail for how lipids and nucleic acids made in diff flashcards -> for 3 marks

Question 41

why is the production of simple sugars eg. glucose from products of the Calvin cycle essential for an organism?

Answer 41

- glucose is **used in respiration** ... - ... which **provides energy** needed for **biological processes**

Question 42

what is the role of e- in PS1?

Answer 42

- generate **ATP** in **chemiosmosis** -> movement of **H⁺** down **conc grad** via **ATPsynthase** - **reduce NADP** in **photophosphorylation** - produce **O₂** in **photolysis of H₂O**

Question 43

design an experiment to **investigate photosynthesis using isolated chloroplasts**

Answer 43

(Hill reaction) 1. using pestle + mortar, **grind 5g chopped spinach leaves** with **10cm³ cold** (0.5M) **sucrose sol** 2. **strain** this liquid (funnel + muslin cloth) into cool centrifuge tube + **centrifuge for 10 mins high speed** 3. pipette **liquid** from top of centrifuge and **discard** -> now have **pellet** 4. add **2cm³ cold sucrose** sol + **20cm³ cold pH 7 phosphate buffer** sol + mix 5. add **5cm³ chloroplast / buffer sol** to 2 **test tubes (A + B)** 6. add **10cm³ DCPIP each** -> leave A under bench lamp (**well lit**) -> wrap B in tin foil (**no light**) 7. observe A until **DCPIP decolourises** -> pop A + B sols in **cuvettes** + use **colorimeter** to ***compare*** % absorbance NOTE: control = test tube only containing DCPIP + cilled isolation sol (**NO CHLOROPLASTS**) -> proves **DCPIP colour doesn't just deteriorate over time**!!!

Question 44

explain how DCPIP can be used to investigate p/s

Answer 44

hill reaction depends on **e- released** in light-**dep** stage being **picked up by DCPIP** (e- acceptor) - so **DCPIP takes the place of NADP** so allows **photolysis** to continue even when all NADP used up - DCPIP **decolourises when it has accepted e-** (been **reduced**) -> so can see that light-dep stage happened!!!

Question 45

suggest why sucrose sol is used in hill reaction

Answer 45

to **prevent H₂O** being **drawn from chloroplasts** by **osmosis**

Question 46

describe how **triglycerides** are made using products of the Calvin cycle (3 marks)

Answer 46

- **GALP** used to produce **glycerol**... - which is used for **building lipid molecules** eg. phospholipids, triglycerides - **GP** used to produce **fatty acids** -> triglyceride = 1 **glycerol** + 3 **fatty acids** joined by **condensation** reactions