PHOTOSYNTHESIS

Question 1

what is the photosynthesis purpose?

Answer 1

convert light into chemical energy to synthesise large organic molecules

Question 2

what are plants known as for being able to produce their own nutrients using light?

Answer 2

photoautotrophs

Question 3

whats a photon?

Answer 3

particle of light

Question 4

what is carbon fixation?

Answer 4

process by which co2 is converted into useful substances such as glucose in the Calvin Cycle (when Co2 binds with RuBP)

Question 5

what is a compensation point?

Answer 5

when respiration and photosynthesis occur at the same rate

Question 6

what are the main part of a chlorplast involved in photsynthesis?

Answer 6

thylakoid membrane and stroma

Question 7

what is the LIGHT DEPENDENT STAGE?

Answer 7

stage of photosynthesis that requires light to produce its products used later in the light independent stage

Question 8

what are the thing involved in the LDS

Answer 8

occurs in the thylakoid membrane
photosystems 2 and 1 (P680 and P700)
an electron transport chain
NADP
ATP synthase
Pigments CHLORPHYLL A and CHLORPHYLL B and CAROTENOIDS
reaction centre

Question 9

what does a photosystem have ?

Answer 9

accessory pigment (carotene and chlorophyll b ) which absorb light

primary pigment (chlorophyll a ) in the reaction centre that gains energy to then excite electrons

Question 10

describe the light dependent stage

Answer 10

1. light is absorbed by leaves and end up in the chloroplast , thylakoid membrane
2. accessory pigments in the P680 have the function to absorb light energy and transfer it to the primary pigment found in the reaction centre
3. light is absorbed directly or indirectly by the reaction centre
4. as light energy is absorbed, energy is gained which means that electrons in the reaction centre are excited
5. excited electrons leave the reaction centre and move along an electron transport energy form high energy to low energy each time loosing energy, which is used to pump H+ in the thylakoid lumen against concentration gradient, so an electrochemical gradient is formed
6. when the electron reaches the P700, the electron is excited again as P700 absorb light energy and gains energy in the same way as the P680.
7. the re-excited electrons are passed along the electron transport chain , and eventually electrons are accepted by FERRODOXIN which then reduces NADP into NADPH, released into the stroma
8. electrons in the P680 are replaced by the process of photolysis of water (splitting water into protons and electrons and oxygen )
9. H+ in the thylakoid lumen pass through the ATP synthase to produce ATP, H+ pass through down concentration gradient

Question 11

what are the products of LDS?

Answer 11

ATP
NADPH
O2

Question 12

what is the cyclic phosphorylation?

Answer 12

it involves only P700
electron are not passed to NADP bu repeatedly cycle through P700
ATP produced but no NADPH

Question 13

what is the next the LDS?

Answer 13

light independent stage

Question 14

where does LIS occur and what does it use?

Answer 14

stroma, product of the LDS (ATP , NADPH) and CO2

Question 15

what is the role of CO2 in LIS?

Answer 15

being converted into organic molecules in Calvin cycle

Question 16

what is the Calvin cycle and when does it occur?

Answer 16

is the cycle in which Co2 IS CONVERTED INTO ORGANIC MOLECULE and it occurs only at daylight

Question 17

describe the Calvin Cycle

Answer 17

1. Co2 is absorbed from the environment
2. passes into the stroma
3. reacts with RuBP

4.this step is catalysed by the enzyme RuBisCO

5. co2+RuBP = 2 x GP
6. 2x GP uses ATP and is being
   reduced (accepting H+ from NADPH) to make 2 x TP (6 molecules)
7. 1 TP MOLECULE IS REMOVED, resulting in a 5 compound molecule (RuBP), this is how RuBP is recycled each time to be re-used in the cycle
8. this cycle has to be repeated 6 times in order to produce a hexose molecule (as at each cycle 1 TP molecule is removed)

Question 18

why does the Calvin cycle runs only during daylight?

Answer 18

as LDS pumps H+ into the thylakoid lumen, H+ concentration decrease in the stroma raising the pH to 8, which is optimum for RuBisCo so calvin cycle can run.
Also, Magnesium concentration increases during daylight, which binds to the active site if rubisco acting as a cofactor, activating the enzyme.

Question 19

what are the factors that affect photosynthesis rate?

Answer 19

light intensity
temperature
CO2 concentration
H2O
chlorophyll availability
turgidity of cell

Question 20

explain how light intensity can be a limiting factor

Answer 20

if not enough light is present, not enough stomata are open, not enough transpiration occurs, so not enough water uptake to deliver it to the leaves so not enough electrons to the photosystems
so as light intensity increases, photosynthesis increases, since more light is absorbed by chlorophyll and more excitation of the primary pigment reaction centre.

Question 21

explain how CO2 can be a limiting factor

Answer 21

low CO2 - low amount available of Co2 in the Calvin Cycle leads to less RuBP converted to GP, which leads to RuBP accumulation, slows down the rate so less TP produced

high CO2 - can cause stomata to close , which means less uptake of CO2 so less photosynthesis can occur

Question 22

explain how water can be a limiting factor

Answer 22

low amount of H2O - less photolysis can occur during LDS, so less ATP and NADPH produced needed in the Calvin cycle

Question 23

explain how temperature is a limiting factor

Answer 23

low temperature - enzyme action slowed down, not enough kinetic energy in the chloroplast, therefore less collision rate , which means less photosynthesis rate

high temperature - enzyme action slowed down as enzyme get denatured, stomata close at really high temp to avoid water loss, which also means less co2 uptake, reduced Calvin Cycle rate

Question 24

what is a characteristic of the chloroplast membranes?

Answer 24

phospholipid bilayer within chloroplast are impermeable to protons

Question 25

TP can be synthesised to make?

Answer 25

carbohydrates,starch,lipids,amino acids, cellulose

Question 26

primary pigment

Answer 26

chlorophyll a

Question 27

accessory pigment

Answer 27

carotenoids and chlorophyll b

Question 28

first stable product of carbon fixation

Answer 28

GP