photosynthesis

Question 1

where does the light dependant reaction take place ?

Answer 1

in the thylakoid membrane/ grana

Question 2

what are the stages of the LDR ?

Answer 2

• photoionisation of chlorophyll
• photolysis
• production of ATP and reduced NADP
• chemiosmosis

Question 3

describe photolysis

Answer 3

its the splitting of water molecules with light energy.
H2O > 1/2 O + 2e- + 2H+

the H+ is being picked up by NADP to form NADPH (which will be used in the LIR)
the e- are passed along a chain of electron carrier proteins
the oxygen is either used for respiration or it diffused out of the leaf

Question 4

what happens in the photoionisation stage of the LDR?

Answer 4

light energy is being absorbed by the chlorophyll molecule which excites the electrons causing them to raise up in energy level and leave the chloroplast.

the chloroplast has therefore been ionised

the energy being released is used to make ATP and NADP in chemiosmosis

Question 5

what happens in chemiosmosis?

Answer 5

the electrons that were gained from the photoionisation if chlorophyll are picked up by proteins that are embedded in the thylakoid membrane. those electrons pass along an electron transfer chain. as they do so, they release energy which is used to actively pump protons along the membrane into the the thylakoid lumen/ intermembrane space. there are also H+ ions that come from the photolysis of water. this creates an electrochemical gradient and so facilitated diffusion occurs where the H+ ions diffuse though ATP synthase and causing it to change shape.
this change in shape is what provides enough energy for ADP to bing to Pi and form an ATP molecule.
the electrons that were used in the electron transfer chain, as well as the protons that have diffused through ATP synthase are picked up by the NADP to form reduced NADP.

Question 6

what are the products of the LDR?

Answer 6

ATP and reduced NADP

Question 7

outline the key stages of LDR

Answer 7

• chlorophyll is ionised and loses electrons ( this is called photoionisation)
• water molecules are split by light energy to form oxygen, electrons and hydrogen ions,
• reduced NADP get oxidised and release H+ ions and e-
• the electrons are passed along electron carriers to provide energy for proton pumps
• H+ ions are actively pumped from the stroma to the intermembrane space
• H+ diffuses through ATP synthase and provide energy for ATP to be made
• once the H+ have diffused, they get picked up (along with electrons from the electron carriers) by NADP to form reduced NADP.

Question 8

what happens to the electrons that are formed on photolysis?

Answer 8

they either join the electron transfer chain or they replace the electrons lost from the chlorophyll molecule

Question 9

where does the light independent reaction take place ?

Answer 9

occurs in the stroma

Question 10

what is the other name for the LIR?

Answer 10

celvin cycle

Question 11

what is the enzyme that catalyses the LIR?

Answer 11

rubisco

Question 12

what does RuBP stand for and how any carbon atoms is it ?

Answer 12

ribulose bisphosphate

5 carbon

Question 13

what does GP stand for and how many carbon atoms is it ?

Answer 13

glycerate 3- phosphate

3 carbon molecule

Question 14

what does TP stand for and how many carbon atoms is it?

Answer 14

triose phosphate

3 carbon molecule

Question 15

why does temperature effect the rate of reaction of the calvin cycle ?

Answer 15

because its an enzyme catalysed reaction

Question 16

what things are needed for the calvin cycle to happen (ie. reactants)

Answer 16

CO2

ATP and reduced NADP from LDR

Question 17

what are the products of the LIR?

Answer 17

a hexose sugar

Question 18

give a detailed description of the calvin cycle

Answer 18

a carbon dioxide molecule enters the cycle - by diffusing from the atmosphere through the stomata - reacts with RuBP. The enzyme rubisco catalyses that reaction and 2 molecules of GP are produced.

ATP is hydrolysed which releases energy to convert GP to TP, and the hydrogen from the reduced NADP is being picked up by GP - therefore reducing it which helps with the conversion. this is a reduction stage.

one of the carbon molecules from the 2 TP molecules, leaves the cycle making a 5 carbon sugar as well as a single carbon molecule. once the cycle has happened 6 times, a hexose sugar can be made/ (useful organic substances).

now RuBP has to be regenerated - a process that requires energy from ATP - so that the cycle can continue over and over again.

Question 19

why does AQA use the term ‘organic substances’ rather than ‘glucose/ hexose sugar’ in the calvin cycle?

Answer 19

because the carbon molecules can form a large range of compounds eg. the monosaccharide sucrose, or disaccharides such as starch and cellulose. it can also be converted into glycerol or lipids

Question 20

why does AQA use the term ‘organic substances’ rather than ‘glucose/ hexose sugar’ in the calvin cycle?

Answer 20

because the carbon molecules can form a large range of compounds eg. the monosaccharide sucrose, or disaccharides such as starch and cellulose. it can also be converted into glycerol or lipids

Question 21

what are limiting factors?

Answer 21

any factors that reduce the rate of photosynthesis

Question 22

what are the 3 limiting factors or photosynthesis?

Answer 22

light intensity, CO2 levels and temperature

Question 23

why are the ideas of limiting factors important ?

Answer 23

due to agricultural practices,
farmers can manipulate the conditions under which they grow their plants ~ artificial lighting, hearing and burn fuels to produce CO2

the farmer has to also make sure that its cost effective, meaning that whatever they need to make enough profit from those plants to pay for the light, heat and fuel they are using for the plants