photosynthesis

Question 1

Photosynthesis

Answer 1

6O2 + 6H2O -> C6H12O6 + 6O2

Question 2

Respiration + photosynthesis

Answer 2

• interdependent relationship

- products of photosynthesis are reactants of respiration

Question 3

Compensation point

Answer 3

• point at which the rate of respiration and the rate of photosynthesis is the same and there is no loss or gain of carbohydrate

Question 4

Light dependant stage

Answer 4

• occurs in thylakoid membrane in grana

- thylakoid membrane provides a large surface area for the distribution of photosystems and ATP enzymes

Question 5

Light-independent stage

Answer 5

• occurs in the stroma

Question 6

Photosystems

Answer 6

• contain photosynthetic pigments which absorb different wavelengths of light

Question 7

Chlorophylls

Answer 7

PRIMARY
chlorophyll a = absorb red and some blue light

SECONDARY
chlorophyll b = only absorbs red light
carotenoids
xanothophylls

accessory pigments = absorb other wavelengths in order to maximize photons absorbed

Question 8

Light-dependant stage

Answer 8

1. photosystem 2 accepts photons
2. photons excite a photolytic enzyme which splits up a water molecule into H+, electrons, and oxygen (photolysis)
   2H2O -> 4H+ + 4e- + O2
3. other electrons are excited by photons to a higher energy level and accepted by an electron carrier
4. energy released by electron transfer pumps H+ from the stroma into the thylakoid
5. H+ moves back into stroma through protein channels associated with ATP synthase
6. ATP is produced
7. H+ in stroma combine with NADP (reduce it) forming NADPH

at the same time…

1. electrons excited when light hits photosystem 1
2. little ATP is produced because no photolysis occurs

Question 9

Cyclic vs non-cyclic

Answer 9

cyclic

1. PSI
2. little ATP
3. no NADPH
4. no oxygen

non-cyclic

1. PSII and PSI
2. lots of ATP
3. NADPH
4. oxygen

Question 10

Light independent stage

Answer 10

• used products from light dependant stage (NADPH and ATP)

Carbon dioxide (source of carbon for all organic molecules) is fixated during the Calvin cycle

Carbon dioxide enters leaf by diffusing through stomata
Diffuses through airspaces into spongey mesophyll
and through palisade mesophyll layer
Diffuses through the cell wall, membrane, and cytoplasm and reaches chloroplasts
Diffuses through chloroplast membrane into the stroma

1. CO2 combines with RuBP - reaction catalyzed by enzyme Rubisco forming a 6 carbon unstable intermediate
2. this intermediate immediately breaks down into 2 molecules of GP (glycerate phosphate)
3. GP is reduced by NADPH using energy from ATP to produce 2 TP molecules (triose phosphate)
4. some TP is stored/ put aside to form glucose, fatty acids, amino acids, the rest is used to regenerate RuBP using ATP

6 turns of the Calvin cycle produce 1 hexose sugar. 12 TP molecules, 2 used for hexose sugar, 10 used to regenerate RuBP.

Question 11

Light intensity

Answer 11

• more light = more photosynthesis

- more photons, more photolysis, light-dependent stage happens at a faster rate so glucose is produced faster

Question 12

Temperature

Answer 12

• too high = enzymes such as Rubisco and photolytic enzyme becomes denatured

Question 13

Carbon dioxide concentration

Answer 13

• high = more photosynthesis, more carbon is fixed

- low = less photosynthesis, it’s a reactant

Question 14

Limiting factor

Answer 14

factors in short supply that prevents photosynthesis from occurring at its maximum rate