Photosynthesis

Question 1

light dependent reaction

Answer 1

occurs in thylakoid membrane
chlorophyll a absorbs light energy, electrons excited and leave chlorophyll- photoionisation
high energy electrons move down ETC and H+ are actively pumped across TM and electrochemical gradient is formed in thylakoid space
H+ diffuse down gradient, through ATP synthase, losing energy used to resynthesise ADP +Pi to ATP - chemiosmosis
photolysis- splitting of water in the presence of light energy (energy also from ETC)
water to 2H+, 2e- and 1/2 o2
e- replaces e lost in chlorophyll a
chlorophyll b absorbs light, e are excited and leave chl b
electrons from chl b and h+ from photolysis reduce NADP to NADPH
e- from ETC replace e lost in chlorophyll b

Question 2

products

Answer 2

oxygen
reduced NADP (NADPH)- LDR
ATP- LDR

Question 3

light independent reaction

Answer 3

occurs in stroma
CO2 (1C) combines with ribulose bisphosphate (5C)
carbon fixation by rubisco enzyme
produces 2 x glycerate 3 phosphate (2x 3C)
this is reduced to 2x triose phosphate (2x 3C) using NADPH and ATP (from LDR)
some triose phosphate is used to regenerate RuBP using ATP (H+ atom from NADPH added to become triose)
triose phosphate is converted to glucose (6C) which is used to make carbohydrates, lipids and proteins

Question 4

light

Answer 4

light is not required for the LIR but it is reliant on the products of the LDR - reduced NADP and ATP- so the LIR cannot occur without light

Question 5

limiting factor

Answer 5

factors that, when in short supply, decrease the rate of P/S
if you increase the LF, you increase the rate of P/S
on graph- as graph levels off, another LF is affecting P/S

light- depends on wavelength of light, light duration- day length, light intensity
CO2- fixed (RuBP)/ converted into organic compounds
temp- reactants have more kinetic energy, more successful collisions but once optimum temp is passed, enzymes may denature
chlorophyll- rate of P/S increases if more is present

Question 6

pigments

Answer 6

substances that absorb visible light
chlorophyll- absorbs red and blue violet, reflect green
caretenoids- absorb blue violet, reflect orange + yellow
different pigments absorb light of different wavelength
the more pigments there are absorbing light, the more efficient P/S will be

plants under canopy- smaller range of wavelengths pass through and reach plants, little light passes through, plants may be adapted to survive and have more caretenoids, some plants wont be adapted so won’t photosynthesise enough for growth

Question 7

light compensation point

Answer 7

photosynthesis requires Co2 + produces glucose
respiration produces Co2 + requires glucose
rate of P/S = rate of resp - no growth as glucose is used up in respiration
rate of P/S> rate of resp- growth occurs as there is glucose available to make complex molecules, forming biomass/tissues
(graph = resp co2 flat line and photo co2 curved line)

Question 8

more o2 in PS

Answer 8

faster production of ATP and reduced NADP
faster / more light-independent reaction
produce more sugars that can be used in respiration
have more energy for growth
have faster / more synthesis of new organic materials