20.1 Photosynthesis

Question 1

what is the function of the chloroplast envelope?

Answer 1

selective permeability

inner membrane - has embedded transport proteins + is less permeable than outer

Question 2

why do chloroplasts contain their own circular DNA and 70Svedberg ribosomes?

Answer 2

{cpDNA}

for producing their own photosynthetic proteins

Question 3

what is the function of a starch grain in a chloroplast?

Answer 3

storage of photosynthetic products

Question 4

what is the function of a photosynthetic pigment?

Answer 4

the absorption of specific wavelengths of light and converting it to CPE

Question 5

how is the observed colour of a plant determined?

Answer 5

the wavelength of light that is reflected by the photosynthetic pigments

Question 6

what is the advantage of having multiple photosynthetic pigments?

Answer 6

move wavelengths can be absorbed

∴ more light is absorbed

more light-dependent reactions (LDRs) can occur

∴ more CPE

Question 7

which mineral ion is required for chlorophyll?

Answer 7

Mg2+

Question 8

what are the features of photosystem II?

Answer 8

P680

absorbs 450nm (blue)

peak absorption at 680nm

granal lamellae

Question 9

what are the features of photosystem I?

Answer 9

P700

absorbs 450nm (blue)

peak absorption at 700nm

intergranal lamellae

Question 10

where are photosystems located?

Answer 10

in the thylakoid membranes of lamellae and grana

Question 11

what is the structure of a photosystem?

Answer 11

funnel shaped structures

held in place by extrinsic proteins embedded in PPL bilayer

Question 12

where does photolysis occur?

Answer 12

photosystem II in granal lamellae

Question 13

what are the products of photolysis? what is their fate?

Answer 13

4 H+ ions - used in chemiosmosis to produce ATP + to reduce NADP

4 e- - oxidises the Mg in the chlorophyll to Mg2+

O(2) - used for aerobic respiration + excreted as a waste gas

Question 14

what are other uses of water?

Answer 14

maintaining turgidity

translocation of sucrose

opening/closing stomata via turgidity of guard cells

transpiration

Question 15

outline the process of photophosphorylation

Answer 15

photon of light hits a chlorophyll molecule in PSII

E from photon transferred to 2 e-

e- can leave Mg atom –> Mg2+

e- accepted by e- acceptor

e- passed along series of e- carriers embedded in thylakoid membrane to PSI (e- transport change)

e- received by NADP+ reductase

e- lost from chlorophyll replaced from a water molecule

2H+ from water molecule combine with e- to reduce NADP+ to red. NADP

Question 16

outline the process of chemiosmosis

Answer 16

E released from e- transport chain used to pump H+ against concentration gradient across thylakoid membrane into thylakoid space

H+ concentration increases inside thylakoid –> proton electrochemical gradient generated

H+ diffuse back down gradient through ATP synthase

ATP produce from ADP and P(i)

Question 17

why can’t plants use ATP from the LDR as their only source of ATP?

Answer 17

PHS only occurs in the light

rate of production is insufficient for needs

some plant cells (e.g. root hair) have no chloroplasts ∴ cannot generate ATP

Question 18

where does the Calvin cycle/light-independent reaction take place?

Answer 18

the stroma of the chloroplast

Question 19

outline the process of the Calvin cycle

Answer 19

CO(2) diffuses into the leaf into the stroma of the chloroplast

CO(2) fixed to RuBP in the presence of RuBisCO to form a 6C intermediate

6C breaks down into 2x glycerate-3-phosphate

ATP and red. NADP used to convert G3P into triose phosphate

1 TP exits the cycle; 6 TP regenerated to RuBP

Question 20

what happens to G3P?

Answer 20

reduced to RuBP

converted to aCoA –> fatty acids and a.a. synthesis

Question 21

what happens to TP?

Answer 21

5/6 recycled to allow continuation of Calvin cycle

2x TP can be converted to hexoses

glucose can be isomerased into fructose –> G + F can be condensed to sucrose

can be polymerised into other polysaccharides

can be converted to glycerol and combined with fatty acids to form trigylcerides

Question 22

outline some specialisations of a palisade mesophyll cell

Answer 22

closely packed and arranged vertically - max light absorption

large vacuole - pushes chloroplasts to the edge of the cell

cylindrical with air spaces - circulation of gases

large SA - increased gas diffusion

thin cell walls - increased light penetration/gas diffusion

Question 23

outline the features of RuBisCO

Answer 23

globular protein –> enzyme

has 4 prosthetic groups (∴ quaternary structure)

optimum pH = 8

has 8 active sites

Question 24

what is the action of RuBisCO in the presence of high concentrations of O(2)?

Answer 24

O(2) binds with active site instead of CO(2)

different chemical reactions –> fully oxygenated product

produces toxic H(2)O(2)

increased temperature –> increased oxygenase activity

Question 25

what is the light compensation point (LCP)?

Answer 25

the amount of light intensity on the light curve where the rate of photosynthesis exactly matches the rate of respiration

Question 26

when is the LCP achieved normally?

Answer 26

at dawn and dusk

Question 27

how can limiting CO(2) be corrected?

Answer 27

paraffin burners (although also increases gas exchanges –> increase transpiration)

Question 28

what is the effect of light on controlling the rate of photosynthesis?

Answer 28

causes stomata to open

photolysis of water

excitation of e- in chlorophyll molecule

Question 29

how does temperature affect the rate of photosynthesis?

Answer 29

above 25.C, RuBisCO increases oxygenase activity –> photorespiration > photosynthesis

if too high, increased H(2)O loss ∴ stomata close ∴ CO(2) available decreases

Question 30

what are the variables that affect the rate of transpiration?

Answer 30

light intensity

temperature

CO(2) availability

Question 31

how can the rate of photosynthesis be measured?

Answer 31

uptake rate of CO(2)

rate of increase of dry mass of plants

rate of O(2) production

Question 32

how is light intensity calculated?

Answer 32

1 / (distance from light source)^2