Photosynthesis - 13 Flashcards Preview

Biology > Photosynthesis - 13 > Flashcards

Flashcards in Photosynthesis - 13 Deck (20):

Basic equation for photosynthesis?

CO2 + H20 --> C6H12O6 + O2


Where does the light dependent reaction occur?



Where does the light independent reaction occur?



Basic equation for light dependent reaction?

Water --- Light energy ---- O2 released ---- ADP +Pi to ATP ---> H


Basic equation for Light independent reaction?

H ---- CO2 added --- ATP to ADP +Pi ----> Glucose


Light-dependent reaction

Comes first
Photolysis: Light energy splits water into H+ (protons) + e-s + O2
Light energy absorbed by photosystems
Light energy excites electrons in the chlorophyll
Chlorophyl has been photoionised
Energy released from electrons used to form ATP when travelling down the ETC and reduce NADP to NADP using e-s + H
ATP transfers energy and reduced NADP transfers hydrogen to the light-independent reaction
H20 is oxidised to O2 which is released into the atmosphere


Use of energy from photoionisation

Making ATP from ADP and inorganic phosphate - photophosphorylation
Making NADPH from NADP


Non-cyclic photophosphorylation

Photosystems are linked by electron carriers
Producing ATP from the ETC
Light energy is absorbed by PSII
Light energy excites electrons in chlorophyll
Electrons move to a higher energy level
High energy electrons released from the chlorophyl and move down the electron transport chain to PSI
As the excited electrons leaves the chlorophyl photolysis occurs
Energy used to transport protons into the thylakoid, causing a higher concentration and therefore producing a proton gradient
Protons move down the their concentration gradient via the enzyme ATP synthase
Forms ATP from ADP and inorganic phosphate
Light energy absorbed by PSI, exciting the electrons further, electrons transferred to NADP along with proton (H+) from the stroma to produce NAPH


Light Independent reaction

Calvin cycle
5C RuBP is carboxylated by CO2 under the addition of the enzyme rubisco
6C molecule is formed which immediately is broken down to 2x3C molecules (GP)
GP is converted to TP using a phosphate from the breakdown the breakdown of ATP-->ADP and H from NADPH --> NADP
TP continues to make 5C RuBP
1C sugar released
Every 3 turns of the Calvin Cycle one molecule of TP is regenerated
6 turns makes 1 molecule of 6C Glucose (Hexose sugar)


Names of all molecules in Calvin Cycle

RuBP = Ribulox Biphosphate
GP = Glycerate phosphate
TP = Triose Phosphate


Why is ATP a good energy source?

Releases a small, manageable amount of energy at time so no energy is wasted as heat
Small, soluble so is easily transported
Easily broken down
ATP can't pass out of cell so the cell always has an immediate source of energy


Photosynthesis-limiting factors: light intensity?

Light intensity measured in LUX
Increase in light intensity increases rate of photosynthesis when light intensity is limiting factor
Will level off when temp or CO2 becomes a limiting factor - saturation point


Chlorophyl absorbing light?

Energy needed for light independent reaction
Only certain wavelengths can be absorbed - red and blue light in the sunlight
Green light is reflected - why plants look green


Temperature affecting plants

Photosyntehsis involves enzymes (ATP synthase, Rubisco) - falls below 10 degrees become inactive - more than 45 degrees denatures
High temperatures stomata close - photosynthesis slows down due to less CO2 intakes


Photosynthesis-limiting factors: Temperature?

As temp increases molecules have more kinetic energy
Enzyme and substrate collide more frequently
Increased the rate of photosynthetic reactions
Above optimum temp the enzyme becomes denatured


Photosynthesis-limiting factors: CO2 Conc?

CO2 required in the light independent reaction to carboxylate RuBP to 2xGP
CO2 is limiting factor until increasing conc no longer increases RuBP carboxylation


Investigating different pigments using chromatography - theory

Plants contain several different photosynthetic pigments in their leaves
Can use thin layer chromatography (TLC) to determine what pigments are present
Possible to identify a certain pigment by calculating its Rf value - the distance a substance has moved through the gel in relation to the solvent - each pigment has a specific Rf value


Investigating different pigments using chromatography - Method

Grind up several leaves with some anhydrous sodium sulfate - add a few drops of propanone
Transfer the liquid to a test tube, add some petroleum ether and gently shake
Two layers will form - top with pigments
Transfer some of the top layer into a second tube with anhydrous sodium sulphate
Draw a pencil line near the bottom of a TLC plate
Build up a concentrated spot of the liquid - origin point
Put the plate into a small glass of solvent (cyclohexane) - point of origin above the the solvent
Pigments move up
Mark the solvent front with a pencil
Measure how far the separated pigments moved
Calculate Rf values = Distance travelled by spot/ distance travelled by solvent


Investigating the activity of dehydrogenase in Chloroplasts: theory?

In light-dependent reaction - NADP acts as an electron acceptor and is reduced - catalysed by dehydrogenase enzyme
Activity of enzyme can be investigated by a redox indicator dye to extract chloroplasts
Is an electron acceptor and is reduced causing a colour change - DCPIP changes from blue to colourless
Can use a calorimeter to measure the rate at which DCPIP loses its blue colour


Investigating the activity of dehydrogenase in Chloroplasts: method?

Cut a few leaves into pieces
Grind up using pestle and mortar with some chilled isolation solution (sucrose, potassium chloride and phosphate buffer at pH 7)
Filter the liquid into a beaker through a funnel and filter paper
Transfer the liquid to centrifuge tubes and centrifuge them at high speed for 10 minutes
Chloroplasts gather at bottom of each tube in a pellet
Filter out liquid leaving just pellet
Re-suspend the pellets in fresh, chilled isolation
Set up calorimeter with a red filter and zero it using a cuvette containing the chloroplast extract and distilled water
Set up test tube rack at a set distance from a bench lamp
Add set volume of chloroplast extract and DCPIP in test tube and mix
Immediately take sample and place in clean cuvette
Then place the cuvette in your colorimeter and record the absorbance. Do this every 2 minutes for the next 10.
Repeat for the distances.