photosynthesis

Question 1

what is the equation for photosynthesis

Answer 1

carbon dioxide + water = oxygen + glucose

Question 2

what is the definition of photosynthesis

Answer 2

the process by which the light energy is used in the synthesis of organic molecules
-so is a reduction reaction
-endothermic reaction

Question 3

why is ATP a useful molecule

Answer 3

-readily releases a small, manageable amount of energy
-simple, single-step reaction
-reversible reaction
-small water soluble molecule
-can be used to add a phosphate group which lowers the Ea and makes it more reactive
eg active transport and synthesis of macromolecules

Question 4

why are chloroplasts involved in photosynthesis

Answer 4

-Chloroplasts are the organelles in plant cells where photosynthesis occurs
Each chloroplast is surrounded by a double-membrane envelope
Each of the envelope membranes is a phospholipid bilayer
-The membranes of the grana create a large surface area to increase the number of light-dependent reactions that can occur

Question 5

where does the light dependent stage occur

Answer 5

thylakoid membranes of the chloroplasts

Question 6

give a general overview of the light dependent stage of photosynthesis

Answer 6

Light energy is used to breakdown water in a reaction known as photolysis; this produces hydrogen ions, electrons, and oxygen in the thylakoid lumen
A proton gradient is formed as the photolysis of water results in a high concentration of hydrogen ions in the thylakoid lumen
Electrons travel through an electron transport chain of proteins within the membrane
Reduced NADP (NADPH) is produced when hydrogen ions in the stroma and electrons from the electron transport chain combine with the carrier molecule NADP
ATP is produced during a process known as photophosphorylation (ADP + Pi → ATP) using the proton gradient between the thylakoid lumen and stroma to drive the enzyme ATP synthase

Question 7

describe the process of the light-dependent stage

Answer 7

-occurs on the thylakoid membranes in a chloroplasts
-photons of red/blue light energy hit the chlorophyll causing photoionisation
-excited electrons are emitted from the chlorophyll
-electrons pass down a series of carrier molecules at successfully lower energy level -ETC
-redox reaction release energy
-some of the energy is used for photophosphorylation
ADP + P = ATP
-some of the energy is used for photolysis
H2O = 2H+ + 2e- + 1/2 O2
-H+/e- are used to reduce NADP to form NADPH2

Question 8

what is the NADPH2 and ATP used for

Answer 8

the light independent stage
and are used to reduce GP to TP in turn glucose - acts as a chemical potential store of energy

Question 9

what is the light independent stage also known as

Answer 9

the Calvin cycle

Question 10

how is the calvin cycle a cyclical process

Answer 10

-the RuBP is used and regenerated in a cycle

Question 11

what is the first ‘stage’ of the calvin cycle

Answer 11

-RuBP molecule combines with CO2 and incorportates it into its orgainc structure
-the carbon is said to be fixed
-this is done under the influnece of the enzyme RuBISCO - the most common enzyme on the planet
-this forms an unstable 6-carbon compound
-this spilts up into 3 carbon GP molecule - but have 12

Question 12

what is the second stage of the calvin cycle

Answer 12

reduce 3C acid is reduced to a 3C carb
-this requires NADPH2 and ATP
-this produces TP which is also 3 carbon moleucle
-the NADPH2 is returned back to the chlorophyll and is oxidised to NADP
-the ATP is formed to ADP and Pi
-for every 6 CO2 12 TP are produced - two moleucles are then used to convert into glucose or another carb

Question 13

how many molecules of TP are used to regenerate the RuBP molecule

Answer 13

10 TP

Question 14

what was the lollipop experiment

Answer 14

His experiment involved providing radioactive CO2 to algae
contained within a structure resembling the shape of a lollipop,hence the name of the experiment. Light sources were provided on either side, with heat screens to prevent overheating.
He tracked the radioactive carbon in the cycle. In this way he
was able to see what the different stages were. He would drop a section of algae into hot methanol to stop all chemical reactions instantly. This process was repeated at regular intervals to identify the different compounds present at different times, thus the stages of the cycle.

Question 15

why did Melvin Calvin use radioactive 14CO2

Answer 15

-allows to trace the C atoms
-identify the intermediates containing them

Question 16

why use a thin glass structure- loliipop

Answer 16

short light path for the light to pass through

Question 17

what is the role of the ethanol in the loliipop

Answer 17

kills plant cells at very specific times due to rapid tap

Question 18

explain why the RuBP levels fall in the graph- in the dark

Answer 18

-in the light the level is costant as it is being used and regenerated at the same rate
-in the dark RuBP continues ot be combined with CO2 to produce GP
-no ATP and NADP is avliable so GP cannot be reduced to TP
-no TP to regenrate RuBP
-RuBP levels fall

Question 19

explain why the GP levels rise then level out in the graph

Answer 19

-in the light GP is formed and used at a constant rate
-in the dark RuBP + CO2 = GP , so the levls rise, GP levels cannot be reduced to TP
-GP levels rise untill all RuBP is used up

Question 20

what are the limiting factors of the rate of photosynthesis

Answer 20

A supply of carbon dioxide
A supply of water
Light energy
temperature

Question 21

describe and explain the shape of the light intensity graph

Answer 21

D- as light intnesity increase, the rate increases directly proportionally until a max rate is reached and increasing the light further has no effect on the rate

E- more light = more photoionisation = more excited electrons going into the ETC leading to more photophosphorolyation = more ATP and more photolysis = more NADPH2
more ATP/NADPH2 = more reduction og GP to TP = more glucose
At some point, if light intensity continues to increase, the relationship above will no longer apply and the rate of photosynthesis will reach a plateau/levels off
At this point, light intensity is no longer a limiting factor of photosynthesis – another factor is limiting the rate of photosynthesis

Question 22

describe and explain the graph of temperature

Answer 22

D- at low intensity - temp has no effect on rate until 35 degrees where rate falls rapily
high intensity - as temp increases from 0-35 rate increases- after 35 rate falls rapidly

E- low intensity - light is the limting factor- above 35 any functional enzymes of the calvin cycle denature
high intensity - enzymes of clavin cycle gain more KE = more ES complexes as more collisions = ore prodcut
after 35 rate is max
avove 35 - dentaure as bond holding the teritay structure in place break - AS no longer comp so enzyme non-functional

Question 23

describe and explain the graph for carbon dioxide

Answer 23

D- as CO2 increases the rate increases directly proportionally until max rate is reached and increasing the CO2 further has no effect

E- more CO2 reacts with RuBP forming more CP which can then be reduced to more TP and thus forms more glucose
levels off as another factor is limiting
added extra
thus more respiration and more cellular syntehsis

Question 24

how are limiting factors used to increase crop yield in greenhouses

Answer 24

-In the most sophisticated glasshouses, for example, sensors can be used to monitor the light intensity, the humidity of the atmosphere and the carbon dioxide concentration around the crops
-This means that plants could continue to grow through the night if they are kept lit with artificial lighting
-Plants can be grown out of their natural season and habitat because the temperature can be kept constant all year round
-Water can be supplied by irrigation systems throughout the glasshouse or fields which sometimes contain added fertilisers or growth nutrients such as nitrates to aid plant growth
-Natural pests that may spread disease or eat the crops can be controlled within agricultural settings by pesticides or by separating the plants from unfiltered outside air
-This maximises the yield of the crop
-Farmers have to find a balance between crop yield and the cost of maintaining 24 hour lighting and year-round heating as well as the environmental implications this has

Question 25

required practicle 7

Answer 25

-Use of chromatography to investigate the pigments isolated from leaves of different plants
-use chromotography
-1. Set up boiling tubes at the start of the investigation. Add 7cm^3 of running solvent to each of the two boiling tubes. Put a bung on top of each tube and stand them upright in a rack. Label the tubes A and B. 2. Take a piece of chromatography paper that fits the boiling tube. Rule the pencil line 2cm from the bottom of the filter paper. This line is called the origin. Write leaf A at the top of the chromatography paper in pencil.
3. Cut a disc from leaf A with a cork borer. Avoid the veins and midrib of the leaf when you do this.
4.Place the lead disc on the chromatography paper at the center of the line marking the origin. Crush the disc into the paper with the end of a glass rod. The crushed leaf should leave a stain on the chromatography paper.
5.Pin the chromatography paper to the bung with a drawing pin, and then put the chromatography paper into the labelled A. Make sure the end of the chromatography paper is in the solvent and that the solvent doesn’t come above the origin. Put the tube carefully back into the rack and don’t move again.
6. Let the solvent run up the chromatography paper until it almost reaches the top of the paper. Remove the chromatography paper from the tube and immediately draw a pencil line to show how far the solvent moved up the paper. This line marks the solvent front.
7. Replace the bung in the tube.
8. The filter paper with its coloured spots called chromatograph. Let the chromatograph dry.Using a pencil, draw around each coloured spot on the chromatogram. Repeat two with the second piece of paper but write B at the top of the chromatography paper.
9. Repeat steps 3-8 with leaf B.
10. Calculate the Rf value of the pigment spots on each chromatograph
11. deduce which pigement is which usiing the Rf and databook

Question 26

conclusion of required practicle 7

Answer 26

● Rf values should be compared to the Rf known values in a database to identify
pigment. When looking at the databases, ensure that they are for paper
chromatography and use the same solvent as these variables will make
results differ.
Factors that affect the rate of mobility
1. Affinity- pigments have different affinities to the chromatography paper; those with
lower affinities will travel further up the paper.
2. Solubility- pigments that are more soluble travel faster up the paper and will end up
closer to the top at the solvent front.
Pigments that travel further up the paper will have a higher Rf value.

Question 27

what is the Rf value

Answer 27

distance travelled by pigment / distance travelled by the solvent from the origin