Photosynthesis

Question 1

What is a photoautotroph?

Answer 1

Organism that uses light to produce organic molecules from inorganic

Question 2

How are granum and intergranal lamella adapted for photosynthesis

Answer 2

• large SA for light absorption
• photosynthetic pigments
• have ATPsynthase
• have electron carriers

Question 3

which part of a chloroplast does the light dependant stage happen?

Answer 3

granum and intergranal lamella

Question 4

where does the light independent stage happen?

Answer 4

stroma

Question 5

describe a photosystem

Answer 5

antennae complex
funnel shaped
accessory pigments surround a primary pigment (chlorophyll A)

Question 6

what are the two types of chlorophyll A found in photosystems

Answer 6

P700 photosystem 1 (intergranal lamella)
P680 photosystem 2 (granum)

Question 7

name some accessory pigments

Answer 7

chlorophyll B
carotenoids
xanthophylls

Question 8

describe the process of light absorption at a photosystem

Answer 8

1. light hits accessory pigments
2. electrons excited but return to same pigment
3. energy passed on to next accessory
4. process repeats until energy reaches primary pigment chlorophyll A
5. electrons lost from chlorophyll A to electron carriers

Question 9

chlorophyll A and B both contain an important chemical group, what is it?

Answer 9

porphyrin group with Mg at its centre

Question 10

what is the importance of accessory pigments?

Answer 10

to absorb wavelengths of light that chlorophyll cannot

Question 11

LDR non cyclic photophosphorylation

Answer 11

1. Photon strikes PSII, excites 2 electrons which leaves chlorophyll A and passes down electron carriers (associated with Fe)
2. The electrons release energy that pumps H+ into the thylakoid space
3. PSII has a enzyme that in light performs PHOTOLYSIS of water forming 2H+, 2e- and 1/2O2 . The 2e- reduce the oxidised chlorophyll is PSII that had originally lost electrons
4. Light hits PSI and excites 2 electrons which leave the chlorophyll and pass down the electron carriers. They are accepted by NADP. The electrons from PSII replace those lost from PSI
5. H+ flow down the proton gradient (chemiosmosis) through ATP synthase and this potential energy creates ATP
6. The protons along with the 2e- from PSI join with NADP to form reduced NADP

Question 12

LDR cyclic photophosphorylation

Answer 12

1. Light hits PSI and excites 2 electrons which leave the chlorophyll and pass down electron carriers
2. They then move back through the carriers and create ATP

NO PHOTOLYSIS AND NO REDUCED NADP

Question 13

LIR calvin cycle

Answer 13

1. occurs in stroma
2. CO2 fixed by RuBP (rubisco adds CO2 to RuBP)
3. makes unstable 6C molecule
4. this breaks into 2 3C GP molecules (used to make fatty acids and amino acids)
5. converted to TP (using ATP (energy) NADPH (provides H to make TP) from light dependant reaction)
6. 5/6 TP converted to RuP
7. phosphate from ATP given to make RuBP
8. 1/6 TP used to make glucose fructose sucrose starch cellulose glycerol and amino acids

Question 14

3 limiting factors of photosynthesis

Answer 14

Temperature
Light intensity
CO2 concentration

Question 15

how does temperature affect photosynthesis?

Answer 15

high temp creates more KE so more collisions with enzymes
more enzyme substrate complex formed per second
enzymes can be denatured by too high temps so less photosynthesis
above 25C rubisco fixes more O2 and less CO2

Question 16

what is the compensation point?

Answer 16

point at which there is no net exchange of CO2 into or out of the plant
photosynthesis rate= respiration rate

Question 17

what is a photosynthometer and how is it used

Answer 17

use to measure rate of photosynthesis
plant placed in light with sodium hydrogen carbonate solution as CO2 source
temp controlled and volume measured using 1pir^2

Question 18

limitations of photosynthometer set up

Answer 18

bubbles might contain air from air spaces
bubble might be CO2 from sodium hydrogen carbonate solution
some O2 might be used by plant in respiration
some O2 might dissolve in solution

Question 19

list control variables to get valid results using a photosynthometer

Answer 19

water bath control temp
no ambient light
check its air tight
use a gas syringe to collect oxygen
repeat

Question 20

which indicator can be used to show if CO2 concentration is high or low and what colour it goes?

Answer 20

hydrogen carbonate indicator
red = normal CO2
yellow = high CO2
purple = low CO2

Question 21

what happens to the amounts of RuBP, GP and TP in calvin cycle if CO2 drops

Answer 21

GP decreases = Rubisco cant fix CO2
TP decrease = less GP made so less TP
RuBP increases = cant be converted to GP so builds up

Question 22

what happens to the amounts of RuBP, GP and TP in calvin cycle if light levels drops

Answer 22

GP increases = Rubisco can fix CO2 without light
TP decrease = GP cant be converted to TP without ATP and reduced NADP from LDR
RuBP decreases = can be converted to GP and not remade from TP as it requires ATP from LDR

Question 23

how can rate of photosynthesis be maximised in commercial greenhouse

Answer 23

heater keeps temp at optimum
lights of correct wavelength in dark
CO2 levels high from burning fuel
automatic irrigation
pesticides used

Question 24

what does photophosphorylation mean

Answer 24

making ATP in the presence of light