3.2 Photosynthesis Uses Light Energy To Synthesise Organic Molecules Flashcards
Equation for photosynthesis is
6CO2 + 6H2O –> C6H12O6 + 6O2
Some leaf adaptations include
• large surface area to capture light
• have stomata so gases can diffuse
• has airspaces between cells so CO2 can diffuse to the photosynthesising cells
• most chlorophyll is found in the palisade mesophyll
• palisade cells are arranged vertically which allows more light to be absorbed
Adaptations of the chloroplast for photosynthesis
• large surface area to maximise light absorption
• can move within the palisade cells to maximise light absorption
Chloroplasts contain pigments such as
Chlorophylls - a and b
Carotenoids - xanthophylls, B-carotene
Which pigments are accessory pigments
Carotenoids
Function of a pigment
Absorb light energy
Why are several pigments used
Allow the plants to absorb a wider range of wavelengths of light
Chloroplasts are transducers which means
They change energy from light energy to chemical energy
what did the Engelmann experiment discover
The site of photosynthesis
What happened in the Englemann experiment?
• A light was shone through a prism to separate the different wavelengths of light
• this light was exposed to a suspension of algae with evenly distributed, motile, aerobic bacteria
• after time the bacteria had congregated around the algae exposed to the blue and red regions because this algae photosynthesised more and so produced more oxygen with would attract more bacteria
What does Rf stand for and what it the equation
• the movement of the pigment/solute relative to the solvent
• must be equal or less than 1
• Rf= distance moved by solute/distance moved by solvent
In chromatography what kind of molecules travel further?
Smaller
What is the absorption spectrum?
a graph that shows how much light energy is absorbed at different wavelengths.
What is the action spectrum
a graph that shows the rate of photosynthesis at different wavelengths.
What is an antenna complex
an array of protein and pigment molecules in the thylakoid membranes with chlorophyll a at the reaction centre. It transfers energy from light of a range of wavelengths to chlorophyll a.
What does the reaction centre contain
2 chlorophyll a molecules
Where does the light dependent stage occur
Thylakoid membrane
Describe what happens in the light dependent stage
Non-cyclic photophosphorylation
- Photons of light energy are absorbed by chlorophyll a in PSII and each has one electron boosted to an excited state
- Electrons are accepted by an electron carrier in the thylakoid membrane
- The oxidised chlorophyll removes electrons from water which produces protons and oxygen through photolysis which occurs in the thylakoid space
- As electrons pass from carrier to carrier the electron energy is lost which pumps protons from the stroma into the thylakoid space. As protons flow back through the stalked particle 2ATP are made
- Electrons enter PSI where light excites them which boosts them to an even higher energy level
- Electrons enter a final electron acceptor and the electrons and protons reduce NADP to NADPH which pass to the Calvin cycle with the 2ATP made
Describe what happens in the light dependent stage
cyclic photophosphorylation
Excited electrons from PSI can pass from the electron acceptor to the electron carriers and back through the proton pump to PSI
No PSII, oxygen, NADPH
1 ATP is made
Where does the light independent stage occur
Stroma
Describe what happens in the Calvin cycle
- CO2 diffuses into the leaf through the stomata and dissolves in the water surrounding the palisade mesophyll cells before diffusing into the cells
- Carbon fixation - CO2 combines with ribulose biphosphate using the enzyme RuBisCO to form an unstable 6C compound
- The unstable 6C compound immediately breaks down into 2 molecules of glycerate 3-phosphate
- using 1 ATP molecule and 1 NADPH from the light dependent stage, GP is reduced to triose phosphate
- Through a complex series of reaction most of the triose phosphate is converted into ribulose-5-phosphate
- RuBp is regenerated from ribulose-5-phosphate using ATP as a source of phosphate
- From TP glucose, lipids, nucleic acids and amino acids can be manufactured
How was the sequence in the Calvin cycle discovered
Using Calvin’s lolipop
• used radioactive 14C in hydrogen carbonate
• at regular intervals the sample was removed into hot methanol (kill algae and stop all reactions)
• then chromatography was used to identify the products by exposing it to X-ray film and detect the products containing 14C and the order they were produced
How can carbohydrates be synthesised from the Calvin cycle
2 Triose phosphate can from fructose phosphate which can be converted to glucose
How can lipids be synthesised from the Calvin cycle
Glycerate 3-phosphate can form fatty acids
Triose phosphate can form glycerol
How can proteins be synthesised from the Calvin cycle
Glycerate 3-phosphate can form the amino acids
ALSO will need a nitrogen from nitrate ions
Effect of CO2 on photosynthesis
Low - limiting factor
High - plateau (another limiting factor)
Higher - stomata close
Effect of light intensity on photosynthesis
Low - limiting factor
High - plateau
Higher - decrease in rate as it bleaches the pigments
Effect of temperature on photosynthesis
Low - limiting factor, low kinetic energy
High - up to optimum, no plateau
Higher - low, denatured enzyme
What is the compensation point
When CO2 uptake is 0
The plant uses all the CO2 produced in respiration in photosynthesis
When does the compensation point happen
Night and dawn
Inorganic nutrients plants need
Nitrogen
Magnesium
Mineral ions of nitrogen
Nitrates
Ammonium ions
Use of nitrogen in plants
Synthesis of proteins, nucleic acids and chlorphyll
Effect of a deficiency of nitrogen
Stunted growth
Chlorosis
Magnesium mineral ions
Mg2+
How is magnesium used by plants
Used as a component of chlorophyll and is an enzyme cofactor
Effect of deficiency of magnesium on a planet
Chlorosis
