Photosynthesis

• photosynthesis


  the conversion of light energy to chemical energy that's stored in sugars or other organic compounds; occurs in plants, algae, & certain prokaryotes
• autotroph


  an organism that obtains organic food molecules without eating other organisms or substances derived from other organisms (producer)
• heterotroph


  an organism that obtains organic food molecules by eating other organisms or substances derived from them (consumer)
• chlorophyll


  green pigment located w/i the chloroplasts of plants & algae & in the membranes of certain prokaryotes
• mesophyll


  ground tissue of a leaf, sandwiched between the upper & lower epidermis & specialized for photosynthesis
• Most chloroplasts are found in the cells of the mesophyll
• Oxygen enters the leaf & carbon dioxide enters through pores called stomata
• stoma (stomata)


  a microscopic pore surrounded by guard cells in the epidermis of leaves & stems that allows gas exchange between the environment & the interior of the plant
• stroma


  dense fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide & water
• thylakoid


  a flattened membraneous sac inside a chloroplast
• thylakoid space


  interior of the thylakoid
• Chlorophyll is found in the membrane of the thylakoid
• The O2 given off by plants comes from splitting water molecules
• When water is split, the electrons are transferred w/ hydrogen ions from water to carbon dioxide. This reduces it to sugar
• Electrons increase in potential energy as they move from water to sugar
• Photosynthesis is endergonic
• light reactions


  the first of two major stages in photosynthesis; these reactions occur in the thylakoid membranes of the chloroplast & convert solar energy to chemical energy of ATP & NADPH, releasing oxygen in the process
• Calvin Cycle


  the second of two major stages in photosynthesis, involving fixation of atmospheric CO2 & reduction of the fixed carbon into carbohydrate
• NADP+


  nicotinamide adenine dinucleotide phosphate, an electron acceptor that, as NADPH, temporarily stores energized electrons produced during the light reactions
• photophosphorylation


  process of generating ATP from ADP & phosphate by means of a proton-motive force generated across the thylakoid membrane of the chloroplast during the light reactions of photosynthesis
• carbon fixation


  the initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism
• The Calvin cycle reduces the fixed carbon to carbohydrate by adding electrons
• Light reactions happen in the thylakoids
• Calvin cycle happens in the stroma
• wavelength


  distance between crests of waves, such as those of the electromagnetic spectrum
• electromagnetic spectrum


  the entire spectrum of electromagnetic radiation ranging in wavelength from less than a nanometer to more than a kilometer
• visible light


  the portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from 380nm to 750nm (most important to life)
• photon


  a quantum, or discrete quantity, of light energy that behaves as if it were a particle
• Shorter wavelength = greater energy of each photon
• spectrophotometer


  an instrument that measures the proportions of light in different wavelengths absorbed & transmitted by a pigment solution
• absorption spectrum


  the range of a pigment's ability to absorb various wavelengths of light; also a graph of such a range
• chlorophyll a


  a photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy
• chlorophyll b


  an accessory pigment that transfers energy to chlorophyll a
• carotenoids


  accessory pigments, either yellow or orange, in the chloroplasts of plants that increase the spectrum of light that can be absorbed
• The spectrum of chlorophyll a suggest that violet-blue & red light work best for photosynthesis. Green is the least effective.
• Carotenoids provide photoprotection: they absorb & dissipate excessive light energy that could damage chlorophyll or interact w/ oxygen to form dangerous compounds
• When pigments absorb light, one of the molecule's electrons is elevated to an orbital where it has more potential energy. This is called an excited state. It cannot stay like this for long and generally the electron will drop back down & the excess energy is released as heat.
• photosystem


  a light-capturing unit located in the thylakoid membrane of the chloroplast, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes
• reaction-center complex

  a complex of proteins associated w/ a special pair of chlorophyll a molecules & a primary electron acceptor

  • centrally located w/i a photosystem
  • excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor which passes an electron to an electron transport chain
• light-harvesting complex


  a complex of proteins associated w/ pigment molecules that captures light energy & transfers it to reaction-center pigments in a photosystem

  • when a pigment absorbs a photon, the energy is transferred from pigment to pigment w/i a light-harvesting complex