C1.3 Photosynthesis Flashcards
What is photosynthesis?
- the conversion of light energy to chemical energy -> pigments (coloured substances e.g chlorophyll)
- Carbon compounds produced contain chemical energy previously light. (glucose)
Equation for photosynthesis?
Carbon dioxide + water (+light) -> glucose + oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2
What are light dependent reactions?
reactions that require light in order to occur.
occur on the thylakoid membranes
- photolysis of water
- photophosphorylation
What are light independent reactions?
reactions that do not req light, occur in stroma
- e.g carboxylation (carbon fixation)
- calvin cycle
- synthesis of carbohydrates
How is hydrogen and oxygen obtained?
- splitting water molecules into hydrogen and oxygen (byproduct)-> when light is available -> energy req
- twelve molecules split for 1 glucose molecule
organisms carrying out photosynthesis?
- plants
- algae
- cyanobacteria
bubbles underwater produced (o2) rise to surface
terrestrial organisms diffuse o2 to atmosphere
Outline an experiment for chromatography
1) tear leaf to small pieces
2) grind leaf -> with sharp sand + propanone -> extract pigments
3) sample -> watch glass
4) evaporate to dryness -> hot air (blow dryer)
5) drops of propanone -> dissolve pigments
6) place a concentrated amount 10mm away from end of chroma paper
7) suspend strip -> tube -> base dips into solvent
8) remove -> when solvent nearly reached top -> pencil line, shows how far solvent moved (draw)
9) pigment identified by:
- colour
- Rf value
what does the rf value show?
- pigments travel -> different rates -> whether pigment is more attracted to the hydrophobic solvent -> or hydrophilic chromatography strip
rf value
Distance moved by spot/distance moved by solvent
general rule between wavelength and energy?
- shorter WL, higher energy a photon of light has
What happens when a photosynthetic pigment uses energy obtained from absorption of light?
- electron in molecule -> higher energy level jump
- conversion of energies
- “excited” electron -> can be passed on to other molecules
- energy carried by electrons -> ends up in glucose/other compounds
- specific wavelengths required -> have the amount of energy needed -> other wavelengths are reflected
What wavelengths does chlorophyll absorb effectively?
- red, blue
- green is mostly reflected, making it appear green
other pigments used in photosynthesis?
-xanthophyll, carotene
What is an absorption spectra?
- graph -> shows the absorbance of light by photosynthetic pigments (here chlorophyll) for all the wavelengths of light
action spectra
Action spectrum is a graph curve depicting the relative rates of photosynthesis for all wavelengths of light as a % maximum rate
What is a limiting factor?
- factor limiting rate at a particular time -> nearest to its minimum
temperature as a limiting factor
increases -> rate increases steeply until optimum temp -> past, and rate falls steeply
light intensity as a limiting factor
at low/medium, rate is directly proportional to intensity
at high, intensities -> rate plateaus
co2 concentration as a limiting factor
no photosynthesis -> low conc
low - high -> positive correlated (conc and rate)
very high -> plateaus
Design an investigation to deduce rate of photosynthesis…
- 1 limitant investigated (IV)
- suitable range should be chosen (lowest to where no longer limits)
- accurate method chosen for rate (DV) -> measure of o2 production per unit time
- all other factors are constant (CV)
How to measure temperature
- place pondweed -> thermostatically controlled water bath
- 5 - 45C (in 5/10 intervals)
- Controlling factor: set thermo at 25 and keep it there throughout experiment
How to measure light intensity
- move light source -> different distances -> measure intensity -> lux metre -> intensity = 1/distance^2
- range: 4,5,7,10,14 cm, + no light
- Controlling factor: keep light source at constant distance (5cm)
How to measure co2
- use pondweed, place in beaker
- start with boiling, cooled water -> add NaHCO3 -> increase co2 concentration
- range = 0-50 mmol dm^-3 -> in 10 mmol dm^-3 intervals
- Controlling: add enough -> give high concentration (50 mmol dm^-3)
What are carbon dioxide enrichment experiments?
- experiments to predict future rates of photosynthesis and plant growth
- co2 artificially increased - e.g greenhouses + free air carbon dioxide enrichment (FACE) experiments.