MODULE 1.3 PHOTOSYNTHESIS

Question 1

define autotroph

Answer 1

an organism that makes complex organic molecules using light or chemical energy and inorganic molecules

Question 2

define heterotroph

Answer 2

an organism that ingests and digests organic molecules releasing the chemical potential energy stored in them

Question 3

give some examples of photoautotrophs

Answer 3

plants, some bacteria and algae

Question 4

define photosynthetic pigment

Answer 4

a pigment that absorbs light energy

each pigments absorbs at different wavelengths and has a distinct absorption peak and reflect other wavelengths

Question 5

describe the structure of a chloroplast

Answer 5

• 2-10 micrometre wide
• envelope membrane
• outer mem permeable to small ions inner mem has transport proteins
• inner mem folded in =to lamellae; stack = granum intergranal lamalla between grana

Question 6

what are the 2 distinct regions inside the chloroplast and their structure/functions

Answer 6

stroma- fluid filled matrix which contains DNA. prokaryote ribosomes, oil droplets + starch grains; light independant stage of ps happens here grana- flattened membrane compartments called thykaloids; sites of light absoption and ATPsynthesis

Question 7

give an example of a chemoautotroph

Answer 7

nitrifying bacteria that obtain energy by oxidising ammonia to nitrite or nitrite to nitrate

Question 8

how are chloroplasts adapted for their role (inner membrane, grana, stroma, photosynthetic pigments

Answer 8

• inner membrane has transport proteins controls entry and exit of substances
• many grana contain many thykaloids maximum surface area for light absorption in light dependant
• photosynthetic pigment arranged in photosystems which allow maximum absorption of light energy
• grana surrounded by stroma so it can gain whats needed from light dependant reaction for light independant

Question 9

what is chlorophyll made out of

Answer 9

mixture of pigments each made of porphyrin group and hydrocarbon chain
porphyrin group like haem group but with mg instead of fe

Question 10

how does a chlorophyll pigment work

Answer 10

-light hits it exciting electrons associated with mg
-2 forms chlorophyll a- p680 and p700 both appear yellow green
-each absorb red light at slightly diff wavelength
-p680 is photosystem 2 at 680nm
-p700 photosystem 1 at 700nm
both found in primary pigment reaction centre
chlorophyll a also absorbs blue light at 480nm and c b absorbs 500nm and 640nm = blue green

Question 11

what are the accessory pigments

Answer 11

carotenoids which dont contain porphyrin group and reflect orange/yellow light and absorb blue light
absorb light wavelengths not abosrbed well by chlorophyll and take energy to chlorophyll a
carotene and xanthophyll

Question 12

what is the limiting factor for a metabolic process

Answer 12

the factor present with the lowest or least favourable value

Question 13

define photophosphorylation

Answer 13

making atp from adp and p in the presence of light

Question 14

where does light dependant stage of photosynthesis take place

Answer 14

thylakoids membrane; ps1 takes place mainly on intergranal lamellae and ps2 takes place exclusively on granal lamallae

Question 15

what is the role of water in the light dependant stage of photosynthesis

Answer 15

can be split into o2, electrons and h+ ions (photolysis)
some 02 used for plants aerobic respiration but most given into atmosphere
h+ ions used in chemiosmosis to create atp
accepted by coenzyme nadp to make reduced nadp used in in light independent stage to reduce carbon dioxide and produce organic molecules

Question 16

what is the overall gist of the light dependant stage

Answer 16

-photon hits chlorophyll molecule and excites electrons
-captured by electron acceptors and passed along electron carriers
-energy passed along causes protons to be pumped across thylakoid membrane into space where they accumulate
-proton gradient formed and they flow down gradients through channels associated with atp synthase enzymes
causes force that joins adp and ip to make atp

Question 17

what is cyclic p

Answer 17

electrons excited pass to electron acceptor and then back to chlorophyll they originally came from only producing atp (only using ps1at 700nm)
atp can be used in light independant reaction or to be used in guard cells to bring in pottasium ions to lower water potential so water flows in via osmosis

Question 18

what is non cyclic p

Answer 18

photoloysis of water
electrons from ps2 pass along carriers releasing energy used to make atp
light has also hit ps1 causing it 2 lose electrons which along with protons combine with NADP to make reduced NADP
electrons from ps2 replace ps1
electrons from photolysis of water replace ps2