energy transfers in and between organisms (photosynthesis) Flashcards
describe how the synthesis and breakdown of ATP meets the energy needs of a cell
-in the cell, ATP is synthesised from ADP and an inorganic phosphate using energy from an energy-releasing reaction e.g. respiration
-the energy is stored as chemical energy in the phosphate bond
- this reaction is catalysed by ATP synthase
-ATP diffuse to the part of the cell requiring the energy
-Here is it broken down into ADP and an inorganic phosphate which is catalysed by ATP hydrolase
-chemical energy is released from the phosphate bond and used by the cell
what are properties of ATP that make it useful?
-stores or releases small manageable amounts of energy at a time so no energy is wasted as heat
-it is small and soluble so it can be easily transported around the cell
-one step hydrolysis means energy can be readily released
-readily re synthesized
where does the light dependant reaction occur?
in the thylakoid membrane of the cytoplasm
describe what occurs in the light - dependent reaction
-chlorophyll molecules absorb light energy from photons of sunlight
-this excites electrons to a higher energy level which causes them to be released from the chlorophyll
-two excited electrons enter the electron transport chain (a series of carrier proteins embedded in the membrane) and are transferred down the chain through a series of redox reactions which releases energy.
-this energy is coupled to the active transport of hydrogen ions from the stroma into the thylakoid space creating an electrochemical gradient for the hydrogen ions
-in chemiosmosis the hydrogen ions move down the electrochemical gradient into the stroma via ATP synthase.
-energy is used to join ADP and an inorganic phosphate to from ATP
-the photolysis of water involves light energy splitting molecules of water into protons, electrons and oxygen
-NADP is reduced by electrons and protons
where does the light independent reaction take place?
occurs in the stroma
describe what occurs in the light-independent reaction
-a reaction occurs between carbon dioxide and ribulose bisphosphate which is catalysed by rubisco (5C + 1C)
-this reaction forms two molecules of glycerate 3-phosphate (2 x 3C)
-the two molecules of glycerate 3-phosphate is reduced by reduced NADP using energy from ATP to produce two molecules of triose phosphate.
-some triose phosphate is converted to glucose and other useful organic substances
-some triose phosphate is used to generate RuBP in the calvin cycle
define limiting factor
factors that determine the maximum rate of a reaction even if other factors change to become more favourable
what are the limiting factors that limit the rate of photosynthesis
-light intensity
-carbon dioxide levels
-temperature
-water availability
how does temperature affect the rate of photosynthesis
-calvin cycle is controlled by enzymes like rubisco
-at lower temperatures the reaction is slower as the enzyme works slowly or becomes inactive
-so levels of ribulose bisphosphate, glycerate 3 phosphate and triose phosphate will fall
-increasing temperatures increases the rate up until the optimum
-if temperatures are increased beyond the optimum, the rate is decreased as high temperatures can cause stomata to close to avoid water loss so photosynthesis slows down because less carbon dioxide enters the leaf
why is photosynthesis slow in green light?
-less absorption of light as green light is reflected
-this is because the photosynthetic pigments of chlorophyll a, chlorophyll b and carotene only absorb red and blue light in sunlight
-the light is required for light dependent reaction and photolysis
what agricultural practices overcome the limiting factors?
-carbon dioxide is added to the air by burning a small amount of propane in the carbon dioxide generator
-light can get through glass of glasshouses and lamps at night provide light
-glasshouses trap heat energy from sunlight which warms air and air circulation systems make sure the temperature is even throughout the glasshouse
what is cyclic photophosphorylation?
-only uses PSI
-electrons from chlorophyll are not passed on to NADP but passed back to PSI by electron carriers
-the electrons are recycles and repeatedly flow through PSI
-this does not produce reduced NADP or Oxygen but produces small amounts of ATP
