Photosynthesis PA

Question 1

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

Answer 1

• RUBISCO as an {enzyme / catalyst} ;
• in the Calvin cycle ;
• It is involved in {carbon fixation / bonding of CO2 to RuBP
• to form GP
• GP converted to GALP using ATP and {reduced NADP

Question 2

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

Answer 2

• stroma is the site of the light independent reaction
• there are photosynthetic pigments and chloropyll
• There is ATP synthase in the thylakoid membranes
• thylakoids provide space for the accumulation of H+ ions.
• there is a chemiosmotic gradient/ photophosphorylation.

Question 3

How is oxygen produced?

Answer 3

• made from water / H2O;
• photolysis / light splitting the water molecule
• into {O / (atom of) oxygen} (and H+ and electrons) ;
• two water molecules are needed to form
  one molecule of oxygen ;
• in chloroplast

Question 4

The photosensitive pigment involved in making this plant species produce
flowers between 12-15 hrs is likely to be what?

Answer 4

phytochrome

Question 5

Suggest how GALP, formed by reaction T, can be used to synthesise the
cellulose in plant cell walls.

Answer 5

• conversion (of GALP) to glucose
• (which is) β glucose ;
• there is a formation of glycosidic bonds ;
• 1-4 (glycosidic bonds) ;
• by condensation ;
• {straight / unbranched} (chains of glucose) ;
• cellulose is a {polysaccharide /
  polymer of glucose / eq} ;

Question 6

Where does photophosphorylation take place?

Answer 6

thylakoids

Question 7

Suggest how GP, the product of carbon fixation, can be used to
synthesise starch.

Answer 7

• conversion of GP to GALP using ATP and reduced NADP
• conversion (of GALP) to {glucose /hexose}
  4. (which is) α glucose ;
  -formation of glycosidic bonds ;
• these bonds are 1-4 and 1-6 (glycosidic bonds)
• by condensation ;
  -amylose and amylopectin ;
• amylose e.g. straight chain, 1-
  4 bonds ;
• amylopectin eg branched, 1-4
  and 1-6 bonds ;

Question 8

Explain why the light-independent stage cannot take place without the
light-dependent stage.

Answer 8

• products of light-
  dependent stage are needed
• which are reduced NADP and ATP
• reduced NADP is used as a source of H+ ions in GALP.
• Use of ATP as a source of energy.