photosynthesis

Question 1

State what is meant by the term tissue.

Answer 1

(group of) (same) cells with {same structure

Question 2

Spongy mesophyll is a site of gas exchange. The arrows on the diagram show the
direction of movement of carbon dioxide during the day.
Using the information in the diagram and your own knowledge of the properties
of gas exchange surfaces, suggest how spongy mesophyll is adapted for gas
exchange.

Answer 2

the gas exchange surface is the cell wall
so the diffusion distance is small (between air space
and cytoplasm) ;idea that the carbon dioxide can { continuously
enter the leaf /circulate around the cells } ;
3. ACCEPT carbon dioxide used {by
cells / for photosynthesis}
4. maintains a concentration gradient (between air
space and cell) ;

Question 3

Photosynthesis takes place in palisade mesophyll.

Describe what happens to the carbon dioxide that enters this tissue.

Answer 3

1. idea that carbon dioxide dissolves (in the moisture layer
2. idea that carbon dioxide { diffuses / moves / enters }
   into the { chloroplasts / stroma } ;
3. idea that carbon dioxide binds to RuBP / reference to
   carbon fixation / { reduction of carbon dioxide / eq } ;
4. ACCEPT ribulose bisphosphate
5. reference to { Calvin cycle / light-independent
   reaction } ;
6. ACCEPT glycerate (3)
   phosphate
7. to produce GP / eq ;

Question 4

Xylem transports ions and water molecules to the leaf.

Describe the roles of these ions and water molecules in photosynthesis.

Answer 4

1. water for photolysis / eq ;
   Accept any TWO from :
2. water acts
   as a solvent for {carbon dioxide /
   enzymes / eq}
3. { phosphate / Pi / PO43- } for ATP synthesis / eq ;
4. magnesium (ions) for chlorophyll ;
5. nitrate for { ATP / electron carrier protein / RUBISCO /
   ATP ase / enzymes involved in photosynthesis /
   chlorophyll / eq } ;

Question 5

Describe the roles of the thylakoid membranes in the production of ATP in the
light-dependent reaction.

Answer 5

. idea of {chlorophyll / photosystems / eq} in the
(thylakoid) membrane ;
3. for the absorption of light (energy) ;
4. so that electrons are released (from chlorophyll) / eq ;
5. idea that there are electron carriers are in the (thylakoid)
membrane ;
6. idea that electrons are {picked up by / passed down}
electron {carriers / proteins / acceptors} ;
7. resulting in {hydrogen ions / H+ / protons} being {moved
into / accumulated in} the thylakoid space / eq ;

7. NOT diffuse
8. idea that thylakoid membranes provide the (thylakoid) space ;
9. ACCEPT idea of
   compartmentalisation from stroma
10. idea of {ATPase / eq} in the (thylakoid) membrane ;
11. idea that {hydrogen ions / H+ / protons} can move (diffuse)
    through {ATPase / eq} (through the membrane / back into
    the stroma) ;
12. idea that proton movement provides the energy for the
    {formation of ATP from ADP and phosphate ions / (photo)
    phosphorylation of ADP to ATP / eq} ;
13. ACCEPT ATP {synthase /
    synthetase}

(6)

Question 6

Describe the role of RUBISCO in the production of GALP in the light-independent
reaction.

Answer 6

1. reference to RUBISCO as an {enzyme / catalyst}
2. in the Calvin cycle ;
3. involved in {carbon fixation / bonding of CO 2 to RuBP /
   reaction between CO 2 and RuBP / eq}
4. to form GP / eq ;
5. GP converted to GALP / eq ;
6. using ATP and {reduced NADP / NADPH} (CO 2 to
   GALP / GP to GALP) ;

Question 7

Describe how the membranes inside the chloroplast are involved in
photosynthesis.

Answer 7

1. idea of compartmentalisation (from stroma) ;
2. site of light-dependent reaction ;
3. credit named molecules {within / on / eq} membrane ;
4. idea of {ATPase / eq } in (thylakoid) membranes
5. e.g. photosynthetic pigments /
   chlorophyll / carotenoids /
   photosystems / electron carrier
   proteins
6. ACCEPT {ATP synthase /
   synthetase}, NADP reductase
7. idea that (thylakoid) membranes provide a space for
   accumulation of H+ ;
8. reference to photophosphorylation ;
9. ACCEPT chemiosmosis