photosynthesis

Question 1

What happens during photoionisation

Answer 1

Light is absorbed by chlorophyll
This excites electrons to move into chlorophyll
Electrons enter electron transport chain
chlorophyll becomes positively charged

Question 2

What are the thylakoid membranes?

Answer 2

Folded membranes which contain photosynthetic proteins (chlorophyll) and electron carrier proteins embedded within these membranes which are both involved in LDR

Question 3

What are the stroma?

Answer 3

Fluid centre which contains enzymes involved in the LIR

Question 4

What are the stroma?

Answer 4

Fluid centre which contains enzymes involved in the LIR

Question 5

What are the roles of the inner and outer membrane in chloroplast

Answer 5

Control what Can enter and leave the organelle

Question 6

Where does the LIR occur

Answer 6

Stroma

Question 7

Where does the LDR occur

Answer 7

Thylakoid membranes/ grana

Question 8

State the 4 stages of light dependent reaction

Answer 8

1) Photolysis
2) photoionisation of chlorophyll
3) chemiosmosis
4) production of ATP and reduced NADP

Question 9

What happens in the Photolysis of water and what stage is it

Answer 9

1st stage
Light energy is absorbed by chlorophyll and splits water into O2, protons (hydrogen ions) and electrons
Protons picked up by NADP = NADPH (used in LIR)
Electrons are passed along chain of electron carrier proteins
Oxygen either used for respiration or diffuses out of stomata

Question 10

What happens in Photoionisation of chlorophyll?

Answer 10

Light energy is absorbed by chlorophyll and the energy results in electrons becoming excited and raising up an energy level to leave chlorophyll
=chlorophyll has been ionised by light

Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis

Question 11

What happens during chemiosmosis?

Answer 11

Electrons that gained energy and left the chlorophyll move along a series of proteins embedded within the thylakoid membrane

As move along proteins they release energy, some of energy used to pump protons from stroma across chloroplast membrane (proteins) into thylakoid lumen

= electrochemical gradient built up
= protons move by facilitated diffusion back down CON GRAD to stroma ( by ATP SYNTHASE)
= enables atp synthase (enzyme) to phosphorylate ADP to ATP

Protons back in stroma
NADP enzyme picks up electrons from end of electron transport chain + protons after passing through ATP synthase
= reduces NADP

Question 12

Why is the LIR temperature sensitive?

Answer 12

The stroma contains enzyme Rubisco Which catalysed the reaction.

Question 13

What compounds does the Calvin Cycle use and why?

Answer 13

CO2, reduces NADP, ATP

ATP is hydrolysed to provide energy for reaction
Rescued NADP donated the hydrogen to reduce molecules GP

Question 14

What happens in the Calvin Cycle (LIR)

Answer 14

CO2 reacts with ribulose bisphosphate (RuBP) = 2molecules of glycerine 3phosphate (GP) - a 3 carbon compound
That reaction is catalysed by enzyme RUBISCO

GP is then rescued to TP using energy from ATP and by accepting a hydrogen from reduced NADP = NADP

Some of the carbon from TP leaves the cycle each turn to be converted into useful organic substances
The rest of the molecule is used to REGENERATE RuBP (energy from ATP)

Whilst glucose is the product - Calvin cycle needs to happen 6 times to produced glucose(or any hexose sugar) - monosaccharide Can join to from disaccharides (sucrose / polysaccharides like cellulose and starch).
Can convert into glycerol - combine with fatty acids = lipids for plants

Question 15

Why can CO2 be classified as a limiting factor for photosynthesis?

Answer 15

Because CO2 is a reactant in the Calvin cycle

Question 16

What is light intensity classified as a limiting factor?

Answer 16

Light energy is needed in LDR for photolysis and photoionisation

Question 17

The monitoring of limiting factors

Answer 17

Agricultural practises for maximum photosynthesis
Artificial lighting - max light intensity
Heating a greenhouse - increase temperature
Burning fuel - release more CO2

Each technique needs to be consider in terms of profit
If extra growth from photosynthesis is minimal, it won’t be COST EFFECTIVE to pay for

Question 18

What is the sim of the Calvin’s experiment

Answer 18

To measure the incorporation of carbon 14 isotope into carbohydrate molecules
Trace movement of carbon through Calvin cycle
Visualise the distribution of radioactivity in plant material

Question 19

Equipment used in Calvin experiment and it’s Role

Answer 19

Funnel - add algae
Syringe - inject radioactive carbon isotope (CO2)
Hot methanol - denature enzymes and stop reaction
Rapid action tap - get samples at precise time and rapidly in quick succession (into hot methanol)
Analyse quantity of radioactive carbon in all different molecules (how much carbon isotope in each molecule)

Flat Lollipop - flat on both sides gives larger SA = more of algae exposed to light = rate of LDR faster

Question 20

Explain why each stage of Calvin experiment is done

Answer 20

Isolation of chloroplasts - homogenise sample of cells + centrifuge to isolate
Incorporation carbon 14 - carbon injected into apparatus, leave for set of time under conditions = allow co2 fully incorporated into all carbon containing compounds

Perfusion of chloroplasts - simulstsneuodly continue to inject carbon14 isotope as co2 through rapid action tap = multiple sample at precise times and measure exact quantity of carbon isotope in all carbon containing compounds

Measurement of radiosctvity - using radiography, mesure quantity of radioactive substances in carbon containing compound

Question 21

Why is there a high amount of radioactive substance in GP in the light than RuBP?

Answer 21

GP is 3 carbon compound but have 2 GP molecules within Calvin cycle
Only have one RuBP (5 carbon compound
= ALWAYS gonna have higher amount of radioactivity in GP than RuBP because it contains more carbons (carbon is radioactive)

Question 22

Why does the amount of glucose decrease and amount of GP increase in the dark?

Answer 22

Un every tune of the Calvin cycle one of the carbons from TP goes towards making hexose sugar (glucose)

Dark - LDR stop = no NADPH or ATP
These r required in Calvin cycle to reduce GP into TP
= increase in GP and decrease in TP
= glucose decreases (since it is a hexose sugar made by joining 2 TP molecules)

Question 23

Why does RuBP levels decrease in the dark?

Answer 23

RuBP is still able to combine with CO2 (using rubisco) = GP
GP isn’t converting into TP
= no TP available to regenerate RuBP

ALSO no ATP available to regenerate TP into RuBP