Photosynthesis

Cards (55)

  • Photosynthesis is the most vital function on earth, thought to have begun 3.4 billion years ago.
  • Photosynthesis works by combining carbon dioxide, water, and light energy to produce glucose, oxygen, and water.
  • The equation for photosynthesis is: 6 CO2 + 12 H2O + lightC6H12O6 + 6 O2 + 6 H2O.
  • Gases in Earth’s Atmosphere: CO2 levels are rising due to human activities such as burning of fossil fuels and deforestation.
  • The increase in CO2 acts like a greenhouse, trapping the sun’s solar radiation and contributing to global warming.
  • Effects of CO2 increase on plant growth include reduction in crop yields due to drought caused by climate change.
  • An increase in CO2 may lead to an increase in photosynthesis for plant life, but for animal life, a rise in carbon dioxide could have serious consequences.
  • Crassulacean Acid Metabolism (CAM) is a photosynthesis process found in orchids, bromeliads, cacti, and many succulents.
  • CAM is similar to the C4 system, producing 4 carbon compounds.
  • In very hot climates, stomata are closed during the day.
  • At night, stomata open to allow CO2 in and it diffuses into mesophyll cells.
  • The carbon dioxide is then stored as 4-carbon malic acid in the vacuoles at night.
  • During the day, the pre-collected CO2 is transported to the chloroplast and converted back to carbon dioxide as required.
  • Pre-collected CO2 is concentrated around enzyme RuBisCo to increase efficiency.
  • The law of limiting factors and photosynthesis states that the rate of a physiological process will be limited by the factor which is in shortest supply.
  • Any change in the level of a limiting factor will affect the rate of reaction.
  • Up to 50% of atmospheric oxygen originates from algae in lakes and oceans.
  • Pollution can have a drastic effect on these organisms.
  • Photosynthesis takes place in chlorenchyma tissue, mostly found in leaves.
  • The two layers of chlorenchyma tissue are the Upper palisade mesophyll, which contains 80% of the chloroplasts, and the Lower spongy mesophyll, which are loosely arranged cells containing abundant air spaces.
  • Stomata regulate the input and output of water and carbon dioxide.
  • Less than 1% of water absorbed by plants is used in photosynthesis, and a water shortage may indirectly limit photosynthesis because stomata close and this reduces the carbon dioxide supply.
  • The two photosystems create ATP and NADPH, which is used to drive the next phase of photosynthesis.
  • The light reactions and chemiosmosis are the two main parts of photosynthesis.
  • The organisation of the thylakoid membrane is crucial in photosynthesis.
  • The Calvin cycle, also known as the Calvin-Benson cycle, takes place in the Stroma and was called the dark reaction as light is not directly used.
  • The Calvin cycle or Calvin-Benson cycle takes atmospheric carbon dioxide and combines it with 5 carbon sugars, resulting in a net gain of glyceraldehyde 3-phosphate (G3P).
  • C3 photosynthesis is named due to the combining of the 1 carbon from CO2 with 5 Carbon compound Ribulose, resulting in a 6 carbon compound that is unstable and rapidly splits into a 3 Carbon compound.
  • Glyceraldehyde-3-phosphate (G3P) is the end product of the Calvin cycle and is an energy-rich 3-carbon sugar.
  • Ribulose-1,5-bisphosphate carboxylase (Rubisco) is an enzyme in the Calvin cycle that catalyzes the first step of carbon fixation but is easily confused and sometimes picks up oxygen instead, resulting in a series of reactions that result in a loss of carbon and energy.
  • C4 photosynthesis is a system evolved by plants to increase their photosynthesis rates in hot weather.
  • C4 plants use an enzyme called PEP carboxylase to first capture the CO2 which is then stored in the bundle sheath cells that surround leaf veins.
  • Over 7,000 angiosperm species use C4 carbon fixation, with classic ones being some of the grass species (sugar cane, maize, millet).
  • Other species belonging to the Asteraceae, Euphorbiacea & Brassicaceae families also use C4.
  • Under hot climate conditions, C4 photosynthesis is much faster than C3.
  • CO2 enters the leaf via stomata, H2O enters via roots and stem xylem carrying mineral salts, and O2 and excess water vapour diffuse out of the leaf via intercellular air spaces and stomata.
  • The products of photosynthesis are moved via phloem.
  • The sun’s energy reaches the earth in the form of electromagnetic radiation which consists of waves and particles.
  • Particles known as photons are the smallest divisible units of light and carry a certain amount of energy which determines how much the photon vibrates.
  • Electromagnetic radiation spans a wide spectrum of wavelengths, from gamma rays with short wavelengths of less than 10 pm to radio waves with long wavelengths of 1mm - 100 km.