C1.3 Photosynthesis

photosynthesis

energy conversion process converting light energy into chemical energy in carbon compounds (carbohydrates, proteins, lipids, nucleic acids), supplies chemical energy needed for life processes in ecosystems

• 6CO₂ (carbon dioxide) + 6H₂O (water) -(light)→ C₆H₁₂O₆ (glucose) + 6O₂

• done by plants (mainly leaves), algae, cyanobacteria; creates carbohydrates

photolysis

reaction that splits molecules of water

• 2H₂O → 4e + 4H⁺ + O₂

• a part of the photosynthesis process that occurs in the chloroplast

• only happens when light is available to provide energy

• produces hydrogen needed for reduction reaction in photosynthesis that converts carbon dioxide into glucose

• increases concentration of oxygen inside of chloroplasts, oxygen diffuses out of chloroplasts, out of leaf cells to air spaces inside the leaf

• oxygen diffuses through stomata to air outside leaf

absorption of light

• pigments - chemical substances that absorb light

• white/transparent substances are not pigments

  • white - reflect all wavelengths of visible light

  • transparent - allow all wavelengths to pass through

• black - pigment that absorb all wavelengths of light

• other pigments absorb some wavelengths of visible light, not others

photon

particle/unit of light, discrete quantity of energy

• energy related to wavelength

• absorbed by pigment molecule if energy held by photon causes an electron in an atom of the pigment molecule to jump into higher energy level (excitation) - requires specific amount of energy supplied by certain wavelengths of light

chloroplasts

organelles in plants where photosynthesis occurs

chlorophylls

main photosynthetic pigments, absorbs red and blue most effectively, reflects green to avoid light fluctuation and regulate light taken in

• appears green - photons in red and blue parts of the spectrum can excite an electron in chlorophyll, wavelengths in green part of the spectrum cannot, most green light is reflected

absorption spectrum

graph showing percentage of light absorbed at each wavelength of light by pigment(s)

• x-axis: wavelength of light, 400 nm (violet) to 700 nm (red)

• y-axis: absorption of light, can show multiple pigments on the same graph

action spectrum

graph showing rate of photosynthesis at each wavelength of light

• x-axis: wavelength of light, 400 nm (violet) to 700 nm (red)

• y-axis: relative amount of photosynthesis, percentage of maximum rate

comparing action and absorption spectrums

• similarities between curves - photosynthesis can only occur in wavelengths of light absorbed by chlorophyll or other photosynthetic pigments

• differences between curves - action spectrum is less dramatic, includes photosynthesis rate considering all pigments within a plant, absorption spectrum only focuses on 1 pigment (mainly chlorophyll)

FACE experiments (free-air carbon dioxide enrichment experiments)

experiments conducted on the effect of increasing CO₂ concentration on plant growth in free air because factors in experiments in labs or greenhouses differ from open conditions; circles of CO₂-releasing towers and control towers

1. Does increased atmospheric carbon dioxide increase carbon storage within a mature woodland ecosystem?

2. Do mineral nutrients, especially nitrogen or phosphorus, become limiting factors on uptake of carbon?

3. What aspects of biodiversity, ecosystem structure, and function are altered when the ecosystem is exposed to elevated carbon dioxide levels?

4. How can FACE experiments be generalized to other woodlands and forests?

explain the process of photosynthesis

• autotrophs perform photosynthesis

• reactants CO₂ and H₂O required for photosynthesis

• light splits water molecules/causes photolysis

• releases O₂ as a waste product

• light energy converted to chemical energy

• produces organic compounds/glucose/carbohydrates

• occurs in chloroplasts

• chlorophyll - photosynthetic pigment that absorbs light

• different pigments absorb different wavelengths of light

• chlorophyll absorbs red and blue light/ends of the spectrum

• limiting factors - CO₂ concentration, temperature, light intensity